JP2024160692A - Electrolyte composition, electrolyte and secondary battery - Google Patents

Abstract

To provide an electrolyte composition or the like which can suppress an increase in resistance during high-temperature storage.SOLUTION: The electrolyte composition contains a fluorine-containing ether compound (1) represented by the following formula (1) and a fluorine-containing ether compound (2) represented by the following formula (2). The content of the fluorine-containing ether compound (2) is 0.001-5 vol.% based on the fluorine-containing ether compound (1). Formula (1): HCF2-CF2-O-Rf1 (where Rf1 represents a C1-5 alkyl group which may be fluorinated). Formula (2): CF3-CHF-CF2-O-Rf2 (where Rf2 represents a C1-5 alkyl group which may be fluorinated).SELECTED DRAWING: None

Description

This disclosure relates to an electrolyte composition, an electrolyte, and a secondary battery.

In recent years, with the trend towards lighter and smaller electrical products, the development of electrochemical devices with high energy density, such as lithium-ion secondary batteries, is progressing. In addition, as the fields of application of electrochemical devices such as lithium-ion secondary batteries expand, there is a demand for improved characteristics. In particular, when lithium-ion secondary batteries are used in vehicles in the future, improving battery characteristics will become increasingly important.

Patent Document 1 describes an electrolyte for a secondary battery that contains two specific fluorine-containing ether compounds and at least one selected from a specific fluorine-containing phosphate compound and a specific sulfone compound in specific contents. Patent Document 2 describes a secondary battery that includes a negative electrode and an electrolyte, in which the negative electrode includes a negative electrode active material that includes a silicon-containing compound, and the electrolyte includes a specific fluorine-containing ether compound, a specific fluorine-containing phosphate compound, a specific sulfone compound, and a cyclic carbonate compound in specific contents. Patent Document 3 describes a non-aqueous electrolyte that includes a solvent for dissolving electrolyte salt that includes a fluorine-containing solvent, at least one compound selected from the group consisting of a specific cyclic siloxane compound, a specific fluorosilane compound, and a specific compound, and an electrolyte salt.

International Publication No. 2014/181877 International Publication No. 2016/063902 JP 2009-163939 A

The present disclosure aims to provide an electrolyte composition that can suppress an increase in resistance during high-temperature storage, as well as an electrolyte and a secondary battery that use the electrolyte composition.

The present disclosure (1) relates to a composition for an electrolyte solution comprising a fluorinated ether compound (1) represented by the following formula (1) and a fluorinated ether compound (2) represented by the following formula (2), in which the content of the fluorinated ether compound (2) is 0.001 to 5% by volume relative to the fluorinated ether compound (1):
Formula (1): HCF ₂ -CF ₂ -O-Rf ¹
(In the formula, Rf ¹ is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.)
Formula (2): CF ₃ -CHF-CF ₂ -O-Rf ²
(In the formula, ^Rf2 is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.)

The present disclosure (2) is the composition for an electrolyte solution according to the present disclosure (1), wherein Rf ¹ in the above formula (1) is a fluorinated alkyl group having 1 to 3 carbon atoms, and Rf ² in the above formula (2) is a fluorinated alkyl group having 1 to 3 carbon atoms.

_The present disclosure (3) relates to a composition _for an electrolyte solution according to the present disclosure (1 ₎ or (2), in which the fluorine _- containing ether compound (1) is at least one selected from the group consisting of HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H and CH ₃ CH ₂ CH ₂ OCF ₂ CF ₂ H, and the fluorine-containing ether compound (2) is at least one selected from the group consisting of CF ₃ CHFCF 2 OCH 2 CF 2 CF 2 H and CH ₃ CH ₂ CH ₂ OCF ₂ CHFCF ₃ .

The present disclosure (4) is a composition for an electrolyte solution in any combination with any of the present disclosures (1) to ( ₃ ) in which the fluorine-containing ether compound (1) is HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H and the fluorine-containing ether compound (2) is CF ₃ CHFCF ₂ OCH ₂ CF ₂ CF 2 H.

The present disclosure (5) is an electrolyte solution containing an electrolyte solution composition in any combination with any of the present disclosures (1) to (4).

The present disclosure (6) is an electrolyte solution according to the present disclosure (5), in which the total content of the fluorinated ether compounds (1) and (2) is 5 to 90 volume % relative to the electrolyte solution.

The present disclosure (7) is an electrolyte solution according to the present disclosure (5) or (6), in which the content of the fluorinated ether compound (1) is 1 to 90% by volume relative to the electrolyte solution, and the content of the fluorinated ether compound (2) is 0.00001 to 4.5% by volume relative to the electrolyte solution.

The present disclosure (8) is an electrolyte solution in any combination with any of the present disclosures (5) to (7), in which the content of the fluorinated ether compound (1) is 8 to 80% by volume relative to the electrolyte solution, and the content of the fluorinated ether compound (2) is 0.00008 to 4% by volume relative to the electrolyte solution.

The present disclosure (9) is an electrolyte solution of any combination of at least one solvent selected from the group consisting of carbonates and carboxylates and any of the present disclosures (5) to (8) containing a lithium salt.

The present disclosure (10) is a secondary battery having an electrolyte in any combination with any of the present disclosures (5) to (9).

The present disclosure provides an electrolyte composition that can suppress an increase in resistance during high-temperature storage, as well as an electrolyte and a secondary battery that use the electrolyte composition.

This disclosure is explained in detail below.

The present disclosure relates to a composition for an electrolyte solution comprising a fluorinated ether compound (1) represented by the following formula (1) and a fluorinated ether compound (2) represented by the following formula (2), in which the content of the fluorinated ether compound (2) is 0.001 to 5% by volume relative to the fluorinated ether compound (1):
Formula (1): HCF ₂ -CF ₂ -O-Rf ¹
(In the formula, Rf ¹ is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.)
Formula (2): CF ₃ -CHF-CF ₂ -O-Rf ²
(In the formula, ^Rf2 is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.)

The composition of the present disclosure contains two specific fluorine-containing ether compounds in a specific ratio, which makes it possible to suppress an increase in resistance during high-temperature storage in secondary batteries such as lithium-ion secondary batteries.

In formula (1), ^Rf1 is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.
The alkyl group represented by ^Rf1 preferably has 1 to 4 carbon atoms, and more preferably has 1 to 3 carbon atoms. The alkyl group represented by ^Rf1 may be linear or branched. ^Rf1 may be a fluorinated alkyl group or a non-fluorinated alkyl group, but is preferably a fluorinated alkyl group.
Among these, Rf ¹ is preferably a methyl group, an ethyl group, an n-propyl group, an n-butyl group, -CH(CH ₃ ) ₂ , -CH ₂ CH(CH ₃ ) ₂ , -CF ₃ , -CF ₂ H, -CF ₂ CF ₃ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CH ₂ CH _{2 CF 3} , -CH ₂ CF ₂ CF ₃ , -CH ₂ CF ₂ CF ₂ H, -CH ₂ CF ₂ CFH ₂ , and -CH ₂ CF ₂ CF ₂ CF ₂ CF ₂ H, with -CH ₂ CF ₂ CF ₂ H being particularly preferred from the viewpoint of suppressing an increase in resistance during high temperature storage.

Examples of the fluorine-containing ether compound (1) include HCF ₂ CF ₂ OCH ₃ , HCF ₂ CF ₂ OCH ₂ CH ₃ , HCF ₂ CF ₂ OCF ₃ , HCF ₂ CF ₂ OCF ₂ H, HCF ₂ CF ₂ OCF _{2 CF3 , HCF2CF2OCH2CF3 , HCF2CF2OCH2CF2H , HCF2CF2OCH2CFH2 , HCF2CF2OCH2CH2CF3 , HCF2CF2OCH2 CF 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ CF3 , HCF2CF2OCH 2CF2CF2H , HCF2CF2OCH2CF2CFH2 , HCF2CF2OCH2CH2CH3 , HCF2CF2OCH2CH2CH2CH3 , HCF2CF2OCH ( CH3 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​} ) ₂ , HCF ₂ CF ₂ OCH ₂ CH(CH ₃ ) ₂ , and HCF ₂ CF ₂ OCH ₂ CF ₂ CF 2 CF ₂ CF ₂ H are preferred, and HCF ₂ CF ₂ OCH ₂ is particularly preferred from the viewpoint of suppressing an increase in resistance during storage at high temperatures _{. CF2CF2H} is _particularly preferred.

The fluorine-containing ether compound (1) may be used alone or in combination of two or more kinds.

The fluorine-containing ether compound (1) preferably has a fluorine content of 40 to 75 mass %. When the fluorine content is in this range, the balance between non-flammability and compatibility is particularly excellent. In addition, it is also preferable in terms of good oxidation resistance and safety.
The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass, and the upper limit is more preferably 70% by mass, and further preferably 66% by mass.
The fluorine content of the fluorine-containing ether compound (1) is a value calculated based on the structural formula of the fluorine-containing ether compound (1) by the formula {(number of fluorine atoms×19)/molecular weight of the fluorine-containing ether compound (1)}×100(%).

In formula (2), ^Rf2 is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.
The alkyl group represented by ^Rf2 preferably has 1 to 4 carbon atoms, and more preferably has 1 to 3 carbon atoms. The alkyl group represented by ^Rf2 may be linear or branched. ^Rf2 may be a fluorinated alkyl group or a non-fluorinated alkyl group, but is preferably a fluorinated alkyl group.
Among these, Rf ² is preferably a methyl group, an ethyl group, an n-propyl group, an n-butyl group, -CH(CH ₃ ) ₂ , -CH ₂ CH(CH ₃ ) ₂ , -CF ₃ , -CF ₂ H, -CF ₂ CF ₃ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CH ₂ CH _{2 CF 3} , -CH ₂ CF ₂ CF ₃ , -CH ₂ CF ₂ CF ₂ H, -CH ₂ CF ₂ CFH ₂ , and -CH ₂ CF ₂ CF ₂ CF ₂ H, with -CH ₂ CF ₂ CF ₂ H being particularly preferred from the viewpoint of suppressing an _increase in resistance during high temperature storage.

_{Examples of the fluorine - containing ether compound ( 2 ) include , among others , CF3CHFCF2OCH3 , CF3CHFCF2OCH2CH3 , CF3CHFCF2OCF3 , CF3CHFCF2OCF2H , CF3CHFCF2OCF2CF3 , CF3CHFCF2OCH2CF3 , CF3CHFCF2OCH2CF3 , CF3CHFCF2OCH2CF2H , CF3CHFCF2OCH2CFH2 , CF3CHFCF2OCH2CH2CF3 , CF3CHFCF2OCH2CF2CF3 , CF3 ​ CHFCF2OCH2CF2CF2H , CF3CHFCF2OCH2CF2CFH2 , CF3CHFCF2OCH2CH2CH3 , CF3CHFCF2OCH2CH2CH2CH3 , CF3CHFCF2OCH ( CH3} ) _{2 , CF3CHFCF2OCH2CH ( CH3} ) _{2 , and CF3CHFCF2OCH2CF2CF2CF2CF2CF2H are preferred , with CF3CHFCF2OCH2CF2CF2H being particularly preferred from the viewpoint of suppressing} an _{increase in resistance during high temperature storage .}

The fluorine-containing ether compound (2) may be used alone or in combination of two or more kinds.

The combination of the fluorine-containing ether compounds (1) and (2) is not particularly limited, and the above-mentioned combinations can be used as appropriate. Among these, from the viewpoint of suppressing an increase in resistance during high-temperature storage, it is preferred that the fluorine-containing ether compound (1) is at least one selected from the group consisting of HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H and CH ₃ CH ₂ CH ₂ OCF ₂ CF ₂ H, and the fluorine-containing ether compound (2) is at least one selected from the group consisting of CF ₃ CHFCF ₂ OCH ₂ CF ₂ CF ₂ H and CH ₃ CH ₂ CH ₂ OCF ₂ CHFCF _3, and it is more preferred that the fluorine-containing ether compound (1) is HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H, and the fluorine-containing ether compound (2) is CF ₃ CHFCF ₂ OCH ₂ CF ₂ CF ₂ H.

In the composition of the present disclosure, the content of fluorine-containing ether compound (2) is 0.001 to 5 volume % relative to fluorine-containing ether compound (1). In terms of further suppressing an increase in resistance during high-temperature storage, the content of fluorine-containing ether compound (2) is more preferably 0.01 volume % or more relative to fluorine-containing ether compound (1), even more preferably 0.05 volume % or more, more preferably 3 volume % or less, even more preferably 1 volume % or less, even more preferably 0.5 volume % or less, and particularly preferably 0.3 volume % or less.

The composition disclosed herein is used in an electrolyte solution and can be suitably used as a component of the electrolyte solution (solvent, additive, etc.).

The present disclosure also relates to an electrolyte comprising the composition of the present disclosure.
The electrolyte solution of the present disclosure contains the composition of the present disclosure, and thus can suppress an increase in resistance during high-temperature storage in a secondary battery such as a lithium-ion secondary battery.

The electrolyte solution of the present disclosure may have a total content of fluorine-containing ether compounds (1) and (2) of 1 to 95% by volume, preferably 5 to 90% by volume, relative to the electrolyte solution. In order to further suppress the increase in resistance during high-temperature storage, the total content of fluorine-containing ether compounds (1) and (2) is preferably 10% by volume or more, more preferably 15% by volume or more, even more preferably 20% by volume or more, even more preferably 25% by volume or more, and preferably 85% by volume or less, more preferably 70% by volume or less, even more preferably 60% by volume or less, even more preferably 55% by volume or less, especially preferably 45% by volume or less, especially more preferably 40% by volume or less, and especially preferably 35% by volume or less.

In the electrolyte solution of the present disclosure, the content of the fluorine-containing ether compound (1) may be 1% by volume or more and 90% by volume or less, and is preferably 1% by volume or more and less than 90% by volume, relative to the electrolyte solution. In order to further suppress the increase in resistance during high-temperature storage, the content of the fluorine-containing ether compound (1) is preferably 5% by volume or more, more preferably 8% by volume or more, even more preferably 10% by volume or more, even more preferably 15% by volume or more, especially preferably 20% by volume or more, and particularly preferably 25% by volume or more, and is preferably 85% by volume or less, more preferably 80% by volume or less, even more preferably 70% by volume or less, even more preferably 60% by volume or less, especially preferably 55% by volume or less, especially more preferably 45% by volume or less, especially preferably 40% by volume or less, and especially particularly preferably 35% by volume or less.

In the electrolyte solution of the present disclosure, the content of the fluorine-containing ether compound (2) may be 0.00001 volume% or more and 4.5 volume% or less, and is preferably 0.00001 volume% or more and less than 4.5 volume% relative to the electrolyte solution. In order to further suppress the increase in resistance during high-temperature storage, the content of the fluorine-containing ether compound (2) is more preferably 0.00008 volume% or more relative to the electrolyte solution, even more preferably 0.0001 volume% or more, even more preferably 0.001 volume% or more, and especially preferably 0.01 volume% or more, and is preferably 4 volume% or less, more preferably 3 volume% or less, even more preferably 2 volume% or less, even more preferably 1 volume% or less, particularly preferably 0.1 volume% or less, and especially more preferably 0.05 volume% or less.

The electrolyte solution of the present disclosure preferably contains a solvent. The fluorine-containing ether compounds (1) and (2) can be used as the solvent, but the electrolyte solution may further contain a solvent other than the fluorine-containing ether compounds (1) and (2).

The solvent preferably contains at least one selected from the group consisting of carbonates and carboxylic acid esters.

The carbonate may be a cyclic carbonate or a chain carbonate.

The cyclic carbonate may be a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.

The non-fluorinated cyclic carbonate may be a non-fluorinated saturated cyclic carbonate, preferably a non-fluorinated saturated alkylene carbonate having an alkylene group with 2 to 6 carbon atoms, more preferably a non-fluorinated saturated alkylene carbonate having an alkylene group with 2 to 4 carbon atoms.

Among these, the non-fluorinated saturated cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate, because of its high dielectric constant and suitable viscosity.

The non-fluorinated saturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

When the non-fluorinated saturated cyclic carbonate is included, the content of the non-fluorinated saturated cyclic carbonate is preferably 5 to 90% by volume relative to the solvent, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume.

The fluorinated cyclic carbonate is a cyclic carbonate having a fluorine atom. The solvent containing the fluorinated cyclic carbonate can be suitably used even under high voltage.
In this specification, the term "high voltage" refers to a voltage of 4.2 V or higher. The upper limit of the "high voltage" is preferably 5.5 V, and more preferably 5.4 V.

The above fluorinated cyclic carbonate may be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.

The above-mentioned fluorinated saturated cyclic carbonate is a saturated cyclic carbonate having a fluorine atom, specifically, represented by the following general formula (A):

（式中、Ｘ^１～Ｘ^４は同じか又は異なり、それぞれ－Ｈ、－ＣＨ_３、－Ｃ_２Ｈ_５、－Ｆ、エーテル結合を有してもよいフッ素化アルキル基、又は、エーテル結合を有してもよいフッ素化アルコキシ基を表す。ただし、Ｘ^１～Ｘ^４の少なくとも１つは、－Ｆ、エーテル結合を有してもよいフッ素化アルキル基、又は、エーテル結合を有してもよいフッ素化アルコキシ基である。）で示される化合物が挙げられる。上記フッ素化アルキル基とは、－ＣＦ_３、－ＣＦ_２Ｈ、－ＣＨ_２Ｆ等である。

(wherein X ¹ to X ⁴ are the same or different and each represents -H, -CH ₃ , -C ₂ H ₅ , -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond, provided that at least one of X ¹ to X ⁴ is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond). The fluorinated alkyl group includes -CF ₃ , -CF ₂ H, -CH ₂ F, etc.

When the electrolyte solution of the present disclosure contains the above-mentioned fluorinated saturated cyclic carbonate, the oxidation resistance of the electrolyte solution is improved and stable and excellent charge/discharge characteristics are obtained when the electrolyte solution is applied to a high-voltage lithium ion secondary battery or the like.
In this specification, an "ether bond" is a bond represented by --O--.

From the standpoint of good dielectric constant and oxidation resistance, it is preferred that one or two of X ¹ to X ⁴ are -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond.

Since a decrease in viscosity at low temperatures, an increase in flash point, and an improvement in the solubility of the electrolyte salt can be expected, it is preferable that X ¹ to X ⁴ are -H, -F, a fluorinated alkyl group (a), a fluorinated alkyl group having an ether bond (b), or a fluorinated alkoxy group (c).

The fluorinated alkyl group (a) is an alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom. The fluorinated alkyl group (a) preferably has 1 to 20 carbon atoms, more preferably 1 to 17 carbon atoms, further preferably 1 to 7 carbon atoms, and particularly preferably 1 to 5 carbon atoms.
If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and even an increase in viscosity.

Among the above fluorinated alkyl groups (a), those having a carbon number of 1 include CFH ₂ --, CF ₂ H-- and CF ₃ --. In particular, CF ₂ H-- or CF ₃ -- is preferred in terms of high-temperature storage properties, and CF ₃ -- is most preferred.

Among the above-mentioned fluorinated alkyl groups (a), those having 2 or more carbon atoms include those represented by the following general formula (a-1):
R ^a1 - ^{R a2} - (a-1)
(wherein R ^a1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom; R ^a2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that at least one of R ^a1 and R ^a2 has a fluorine atom) is a preferred example from the viewpoint of good solubility of the electrolyte salt.
Incidentally, R ^a1 and R ^a2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

R ^a1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. R ^a1 is preferably a linear or branched alkyl group having 1 to 16 carbon atoms. The number of carbon atoms in R ^a1 is more preferably 1 to 6, and further preferably 1 to 3.

Specific examples of R ^a1 include a linear or branched alkyl group such as CH ₃ --, CH ₃ CH ₂ --, CH ₃ CH ₂ CH ₂ --, CH ₃ CH ₂ CH ₂ CH ₂ --,

These include:

When R ^a1 is a linear alkyl group having a fluorine atom, the following are usable: CF ₃ --, CF ₃ CH ₂ --, CF ₃ CF ₂ --, CF ₃ CH ₂ CH ₂ --, CF ₃ CF ₂ CH ₂ --, CF ₃ CF ₂ CF ₂ --, CF ₃ CH ₂ CF ₂ --, CF 3 CF ₂ CH ₂ CH ₂ --, CF 3 CF 2 CF _{2 CH 2} --, CF ₃ CF 2 CF ₂ CH ₂ -- _, CF ₃ CF ₂ CF 2 CH ₂ --, CF ₃ CF 2 CF ₂ CH ₂ --, CF 3 CF ₂ CF 2 CH 2 --, CF ₃ CF 2 CH ₂ CF ₂ --, CF ₃ CF ₂ CH ₂ CF ₂ --, CF ₃ CH ₂ CH ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ -, CF ₃ CH ₂ CF _{2 CH 2} CH ₂ -, CF ₃ CF ₂ CF ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ - ₃ CF ₂ CH ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ - ₂ -, HCF ₂ CH ₂ -, HCF ₂ CF ₂ -, HCF ₂ CH ₂ CH ₂ -, HCF ₂ CF ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ -, HCF ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ -, HCF ₂ CF ₂ CH ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ -, FCH ₂ -, FCH ₂ CH ₂ -, FCH ₂ CF ₂ -, FCH ₂ CF ₂ CH ₂ -, FCH ₂ CF ₂ CF ₂ -, CH ₃ CF ₂ CH ₂ -, CH ₃ CF ₂ CF ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ -, CH ₃ CF ₂ CF ₂ CF ₂ -, CH ₃ CH ₂ CF ₂ CF ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ CF ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ CF ₂ CH ₂ CH ₂ -, CH ₃ CH ₂ CF ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, HCFClCF ₂ CH ₂ -, HCF ₂ CFClCH ₂ -, HCF ₂ CFClCF ₂ CFClCH ₂ -, HCFClC Examples include F ₂ CFClCF ₂ CH ₂ -.

When R ^a1 is a branched alkyl group having a fluorine atom,

However, since the presence of branches such as CH ₃ — or CF ₃ — tends to increase the viscosity, it is more preferable that the number of branches is small (one) or zero.

R ^a2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom. R ^a2 may be linear or branched. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below. R ^a2 is composed of these alone or in combination.

(i) A linear minimum structural unit:
-CH ₂ -, -CHF-, -CF ₂ -, -CHCl-, -CFCl-, -CCl ₂ -

(ii) Smallest branched structural unit:

Among the above examples, it is preferable to use structural units that do not contain Cl, since they are more stable and do not undergo a base-induced HCl removal reaction.

When R ^a2 is linear, it is composed only of the above-mentioned linear minimum structural unit, and among them, -CH ₂ -, -CH ₂ CH ₂ - or -CF ₂ - is preferable. -CH ₂ - or -CH ₂ CH ₂ - is more preferable from the viewpoint of further improving the solubility of the electrolyte salt.

When R ^a2 is branched, it contains at least one of the above-mentioned branched minimum structural units, and a preferred example is one represented by the general formula -(CX ^a X ^b )- (X ^a is H, F, CH ₃ or CF ₃ ; X ^b is CH ₃ or CF ₃ , provided that when X ^b is CF ₃ , X ^a is H or CH ₃ ). These can particularly further improve the solubility of the electrolyte salt.

Preferred fluorinated alkyl groups (a) include, for example, CF ₃ CF ₂ -, HCF ₂ CF ₂ -, H ₂ CFCF ₂ -, CH ₃ CF ₂ -, CF ₃ CHF-, CH ₃ CF ₂ -, CF ₃ CF ₂ CF ₂ -, HCF ₂ CF ₂ CF ₂ -, H ₂ CFCF ₂ CF ₂ -, CH ₃ CF ₂ CF ₂ -,

These include:

The fluorinated alkyl group (b) having an ether bond is an alkyl group having an ether bond in which at least one hydrogen atom has been replaced with a fluorine atom. The fluorinated alkyl group (b) having an ether bond preferably has 2 to 17 carbon atoms. If the number of carbon atoms is too large, the viscosity of the fluorinated saturated cyclic carbonate increases, and the number of fluorine-containing groups increases, which may result in a decrease in the solubility of the electrolyte salt due to a decrease in the dielectric constant, or a decrease in compatibility with other solvents. From this perspective, the number of carbon atoms in the fluorinated alkyl group (b) having an ether bond is more preferably 2 to 10, and even more preferably 2 to 7.

The alkylene group constituting the ether portion of the fluorinated alkyl group (b) having an ether bond may be a linear or branched alkylene group. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below.

(i) A linear minimum structural unit:
-CH ₂ -, -CHF-, -CF ₂ -, -CHCl-, -CFCl-, -CCl ₂ -

(ii) Smallest branched structural unit:

The alkylene group may be composed of these minimum structural units alone, or may be composed of a combination of linear (i) units, a combination of branched (ii) units, or a combination of linear (i) units and branched (ii) units. Preferred specific examples will be described later.

Among the above examples, it is preferable to use structural units that do not contain Cl, since they are more stable and do not undergo a base-induced HCl removal reaction.

More preferred fluorinated alkyl groups having an ether bond (b) include those represented by the general formula (b-1):
R ³ - (OR ⁴ ) _n1 - (b-1)
(In the formula, ^R3 may have a fluorine atom and is preferably an alkyl group having 1 to 6 carbon atoms; ^R4 may have a fluorine atom and is preferably an alkylene group having 1 to 4 carbon atoms; n1 is an integer of 1 to 3; with the proviso that at least one of ^R3 and ^R4 has a fluorine atom).

Examples of ^R3 and ^R4 include the following, which can be appropriately combined to form a fluorinated alkyl group (b) having an ether bond represented by general formula (b-1) above, but are not limited to these.

(1) R ³ is preferably an alkyl group represented by the general formula: X ^c ₃ C-(R ⁵ ) _n2 - (wherein the three X ^{c 's} are the same or different and all are H or F; R ⁵ is an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; and n2 is 0 or 1).

When n2 is 0, R ³ includes CH ₃ —, CF ₃ —, HCF ₂ —, and H ₂ CF—.

Specific examples when n2 is 1 include those in which R ³ is linear, such as CF ₃ CH ₂ -, CF ₃ CF ₂ -, CF ₃ CH ₂ CH ₂ -, CF ₃ CF 2 CH 2 -, CF ₃ CF ₂ CF ₂ -, CF ₃ CH ₂ CF ₂ -, CF ₃ CH ₂ CH ₂ CH ₂ -, CF 3 CF ₂ CH ₂ CH 2 -, CF ₃ CF ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CF ₂ -, CF ₃ CF ₂ CH 2 CF 2 -, CF 3 CF 2 CH ₂ CF ₂ -, CF ₃ CF ₂ CH ₂ CF ₂ -, CF ₃ CH ₂ CH ₂ CH _2. CH ₂ -, CF ₃ CF ₂ CH ₂ CH _{2 CH 2} -, CF ₃ CH ₂ CF ₂ CH 2 CH ₂ -, CF ₃ CF ₂ CF ₂ CH ₂ CH ₂ -, CF _{3 CF 2} CF ₂ CF _{2 CH 2} -, CF 3 ₂ CH ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ CH 2 -, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ -, HCF ₂ CF ₂ -, HCF ₂ CH ₂ CH ₂ -, HCF ₂ CF ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ -, HCF ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ -, HCF ₂ CF ₂ CH ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ -, FCH ₂ CH ₂ -, FCH ₂ CF ₂ -, FCH ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ -, CH ₃ CH ₂ -, CH ₃ CF ₂ CH ₂ -, CH _{3 CF 2 CF 2} -, CH ₃ CH ₂ CH _{2 -} , CH _{3 CF 2} CH _{2 CF 2 -} , CH _{3 CF 2 C F2CF2- , CH3CH2CF2CF2- , CH3CH2CH2CH2- , CH3CF2CH2CF2CH2- , CH3CF2CF2CF2CH2- , CH3CF2CF2} CH _{2 CH 2 -} , _{CH 3 CH 2 CF 2 Examples include CF2CH2- , CH3CF2CH2CF2CH2CH2- , CH3CH2CF2CF2CH2CH2- , CH3CF2CH2CF2CF2CH2CH2- , CH3CF2CH2CF2CH2CF2CH2CH2- , and the like . ​ ​ ​ ​}

Examples of the group in which n2 is 1 and ^R3 is branched include

These include:

However, since the presence of a branch such as CH ₃ — or CF ₃ — tends to increase viscosity, it is more preferable that R ³ is linear.

(2) In the above general formula (b-1) -(OR ⁴ ) _n1 -, n1 is an integer of 1 to 3, and preferably 1 or 2. When n1=2 or 3, R ⁴ may be the same or different.

Preferable specific examples of ^R4 include the following straight-chain or branched-chain groups.

Examples _of linear ones include _-CH2- , _-CHF- , -CF2- _{, -CH2CH2- , -CF2CH2- , -CF2CF2- , -CH2CF2-} , _{-CH2CH2CH2- , -CH2CH2CF2- , -CH2CF2CH2- , -CH2CF2CF2-} , _-CH2CF2CH2- , _{-CH2CF2CF2- , -CF2CH2CH2- , -CF2CF2CF2- , -CF2CF2CH2CH2- , -CF2CF2CH2- , -CF2CF2CH2- , -CF2CF2CF2- ,} and the _like .

As branched chains,

These include:

The fluorinated alkoxy group (c) is an alkoxy group in which at least one hydrogen atom has been replaced with a fluorine atom. The fluorinated alkoxy group (c) preferably has 1 to 17 carbon atoms. More preferably, it has 1 to 6 carbon atoms.

The fluorinated alkoxy group (c) is particularly preferably _a fluorinated alkoxy group represented by the general formula: ^Xd3C- ( ^R6 ) _n3 -O- (wherein the three Xd ^'s are the same or different and all are H or F; ^R6 is preferably an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; n3 is 0 or 1; provided that one of the three Xd ^'s contains a fluorine atom).

Specific examples of the fluorinated alkoxy group (c) include fluorinated alkoxy groups in which an oxygen atom is bonded to the terminal of the alkyl group exemplified as R ^a1 in the general formula (a-1) above.

The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group (b) having an ether bond, and the fluorinated alkoxy group (c) in the fluorinated saturated cyclic carbonate is preferably 10% by mass or more. If the fluorine content is too low, the effect of reducing viscosity at low temperatures and the effect of increasing the flash point may not be sufficiently obtained. From this viewpoint, the fluorine content is more preferably 12% by mass or more, and even more preferably 15% by mass or more. The upper limit is usually 76% by mass.
The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group having an ether bond (b), and the fluorinated alkoxy group (c) is a value calculated based on the structural formula of each group by {(number of fluorine atoms×19)/formula weight of each group}×100(%).

From the viewpoint of obtaining good dielectric constant and oxidation resistance, the fluorine content of the entire fluorinated saturated cyclic carbonate is preferably 10% by mass or more, more preferably 15% by mass or more, and the upper limit is usually 76% by mass.
The fluorine content of the above fluorinated saturated cyclic carbonate is a value calculated based on the structural formula of the fluorinated saturated cyclic carbonate by {(number of fluorine atoms×19)/molecular weight of fluorinated saturated cyclic carbonate}×100(%).

Specific examples of the above-mentioned fluorinated saturated cyclic carbonates include the following:

Specific examples of the fluorinated saturated cyclic carbonate in which at least one of X ¹ to X ⁴ is —F include:

等が挙げられる。これらの化合物は、耐電圧が高く、電解質塩の溶解性も良好である。

These compounds have a high withstand voltage and good solubility of electrolyte salt.

Others:

etc. can also be used.

Specific examples of the fluorinated saturated cyclic carbonate in which at least one of X ¹ to X ⁴ is a fluorinated alkyl group (a) and the rest are all -H include:

These include:

Specific examples of fluorinated saturated cyclic carbonates in which at least one of X ¹ to X ⁴ is a fluorinated alkyl group (b) having an ether bond or a fluorinated alkoxy group (c) and the rest are all -H include:

These include:

Among these, the fluorinated saturated cyclic carbonate is preferably any of the following compounds:

Other examples of the fluorinated saturated cyclic carbonates include trans-4,5-difluoro-1,3-dioxolane-2-one, 5-(1,1-difluoroethyl)-4,4-difluoro-1,3-dioxolane-2-one, 4-methylene-1,3-dioxolane-2-one, 4-methyl-5-trifluoromethyl-1,3-dioxolane-2-one, 4-ethyl-5-fluoro-1,3-dioxolane-2-one, 4-ethyl-5,5-difluoro-1,3-dioxolane-2-one, Examples include dioxolan-2-one, 4-ethyl-4,5-difluoro-1,3-dioxolan-2-one, 4-ethyl-4,5,5-trifluoro-1,3-dioxolan-2-one, 4,4-difluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-trifluoromethyl-1,3-dioxolan-2-one, and 4,4-difluoro-1,3-dioxolan-2-one.

Of the above fluorinated saturated cyclic carbonates, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethylethylene carbonate (3,3,3-trifluoropropylene carbonate), and 2,2,3,3,3-pentafluoropropylethylene carbonate are more preferred.

The above-mentioned fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom, and is preferably a fluorinated ethylene carbonate derivative substituted with an aromatic ring or a substituent having a carbon-carbon double bond. Specific examples include 4,4-difluoro-5-phenylethylene carbonate, 4,5-difluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate.

The above fluorinated cyclic carbonates may be used alone or in any combination and ratio of two or more kinds.

When the fluorinated cyclic carbonate is included, the content of the fluorinated cyclic carbonate is preferably 5 to 90% by volume relative to the solvent, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume.

The chain carbonate may be a non-fluorinated chain carbonate or a fluorinated chain carbonate.

Examples of the non-fluorinated chain carbonate include hydrocarbon chain carbonates such as CH ₃ OCOOCH ₃ (dimethyl carbonate: DMC), CH ₃ CH ₂ OCOOCH ₂ CH ₃ (diethyl carbonate: DEC), CH ₃ CH ₂ OCOOCH ₃ (ethyl methyl carbonate: EMC), CH ₃ OCOOCH ₂ CH ₂ CH ₃ (methyl propyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl isopropyl carbonate, methyl-2-phenylphenyl carbonate, phenyl-2-phenylphenyl carbonate, trans-2,3-pentylene carbonate, trans-2,3-butylene carbonate, and ethyl phenyl carbonate. Among these, at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate is preferred.

The above non-fluorinated chain carbonates may be used alone or in any combination and ratio of two or more kinds.

When the non-fluorinated chain carbonate is included, the content of the non-fluorinated chain carbonate is preferably 10 to 90% by volume, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume, relative to the solvent.

The above-mentioned fluorinated chain carbonate is a chain carbonate having fluorine atoms. A solvent containing a fluorinated chain carbonate can be suitably used even under high voltage.

The fluorinated chain carbonate may be a fluorinated chain carbonate represented by the general formula (B):
Rf ² OCOOR ⁷ (B)
(wherein ^Rf2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and ^R7 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom) can be mentioned.

^Rf2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and ^R7 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom.
The fluorinated alkyl group is an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom. When ^R7 is an alkyl group containing a fluorine atom, it becomes a fluorinated alkyl group.
^Rf2 and ^R7 each preferably have 1 to 7 carbon atoms, and more preferably 1 or 2 carbon atoms, in terms of low viscosity.
If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and even an increase in viscosity.

Examples of the fluorinated alkyl group having one carbon atom include CFH ₂ —, CF ₂ H—, CF ₃ —, etc. In particular, CFH ₂ — or CF ₃ — is preferred in terms of high-temperature storage properties.

The fluorinated alkyl group having two or more carbon atoms may be represented by the following general formula (d-1):
R ^d1 -R ^d2 - (d-1)
(wherein R ^d1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom; R ^d2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that at least one of R ^d1 and R ^d2 has a fluorine atom) is a preferred example from the viewpoint of good solubility of the electrolyte salt.
R ^d1 and R ^d2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

R ^d1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. R ^d1 is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. The number of carbon atoms in R ^d1 is more preferably 1 to 3.

Specific examples of R ^d1 include a linear or branched alkyl group such as CH ₃ -, CF ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, CH ₃ CH 2 CH _{2 CH 2 -} ,

These include:

When R ^d1 is a linear alkyl group having a fluorine atom, examples of the alkyl group include CF ₃ -, CF ₃ CH ₂ -, CF ₃ CF ₂ -, CF ₃ CH ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ -, CF ₃ CH ₂ CF ₂ -, CF ₃ CH ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CF ₂ -, CF ₃ CF ₂ CH ₂ CF ₂ -, CF ₃ CF ₂ CH ₂ CF ₂ -, CF ₃ CH ₂ CH ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ -, CF ₃ CH ₂ CF _{2 CH 2} CH ₂ -, CF ₃ CF ₂ CF ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ - ₃ CF ₂ CH ₂ CF ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ -, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ - ₂ -, HCF ₂ CH ₂ -, HCF ₂ CF ₂ -, HCF ₂ CH ₂ CH ₂ -, HCF ₂ CF ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ -, HCF ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ -, HCF ₂ CF ₂ CH ₂ CH ₂ CH ₂ -, HCF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ -, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ -, FCH ₂ -, FCH ₂ CH ₂ -, FCH ₂ CF ₂ -, FCH ₂ CF ₂ CH ₂ -, FCH ₂ CF ₂ CF ₂ -, CH ₃ CF ₂ CH ₂ -, CH ₃ CF ₂ CF ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ -, CH ₃ CF ₂ CF ₂ CF ₂ -, CH ₃ CH ₂ CF ₂ CF ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ CF ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ CF ₂ CH ₂ CH ₂ -, CH ₃ CH ₂ CF ₂ CF ₂ CH ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ -, HCFClCF ₂ CH ₂ -, HCF ₂ CFClCH ₂ -, HCF ₂ CFClCF ₂ CFClCH ₂ -, HCFClC Examples include F ₂ CFClCF ₂ CH ₂ -.

When R ^d1 is a branched alkyl group having a fluorine atom,

However, since the presence of branches such as CH ₃ — or CF ₃ — tends to increase the viscosity, it is more preferable that the number of branches is small (one) or zero.

R ^d2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom. R ^d2 may be linear or branched. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below. R ^d2 is composed of these alone or in combination.

(i) A linear minimum structural unit:
-CH ₂ -, -CHF-, -CF ₂ -, -CHCl-, -CFCl-, -CCl ₂ -

(ii) Smallest branched structural unit:

Among the above examples, it is preferable to use structural units that do not contain Cl, since they are more stable and do not undergo a base-induced HCl removal reaction.

When R ^d2 is linear, it is composed only of the above-mentioned linear minimum structural unit, and among them, -CH ₂ -, -CH ₂ CH ₂ - or -CF ₂ - is preferable. -CH ₂ - or -CH ₂ CH ₂ - is more preferable from the viewpoint of further improving the solubility of the electrolyte salt.

When R ^d2 is branched, it contains at least one of the above-mentioned branched minimum structural units, and a preferred example is one represented by the general formula -(CX ^a X ^b )- (X ^a is H, F, CH ₃ or CF ₃ ; X ^b is CH ₃ or CF ₃ ; however, when X ^b is CF ₃ , X ^a is H or CH ₃ ). These can particularly further improve the solubility of the electrolyte salt.

_{Specific examples of preferred} fluorinated alkyl groups include _{CF3CF2- , HCF2CF2- , H2CFCF2- , CH3CF2- , CF3CH2- , CF3CF2CF2- , HCF2CF2CF2- , H2CFCF2CF2- , CH3CF2CF2- ,}

These include:

Among these, the fluorinated alkyl groups for Rf ² and R ⁷ are preferably CF ₃ --, CF ₃ CF ₂ --, (CF ₃ ) ₂ CH --, CF ₃ CH ₂ --, C ₂ F ₅ CH ₂ --, CF ₃ CF ₂ CH ₂ --, HCF ₂ CF ₂ CH ₂ --, CF ₃ CFHCF ₂ CH ₂ --, CFH ₂ -- and CF ₂ H-, and from the standpoint of high flame retardancy and good rate characteristics and oxidation resistance, CF ₃ CH ₂ --, CF ₃ CF ₂ CH ₂ --, HCF ₂ CF ₂ CH ₂ --, CFH ₂ -- and CF ₂ H- are more preferred.

When ^R7 is an alkyl group not containing a fluorine atom, it is an alkyl group having a carbon number of 1 to 7. ^R7 preferably has a carbon number of 1 to 4, and more preferably has a carbon number of 1 to 3, in terms of low viscosity.

Examples of the alkyl group not containing a fluorine atom include CH ₃ —, CH ₃ CH ₂ —, (CH ₃ ) ₂ CH—, C ₃ H ₇ —, etc. Among these, CH ₃ — and CH ₃ CH ₂ — are preferred from the viewpoints of low viscosity and good rate characteristics.

The fluorine content of the fluorinated chain carbonate is preferably 15 to 70% by mass. When the fluorine content is within the above range, compatibility with the solvent and solubility of the salt can be maintained. The fluorine content is more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 35% by mass or more, more preferably 60% by mass or less, and even more preferably 50% by mass or less.
In the present disclosure, the fluorine content is based on the structural formula of the fluorinated chain carbonate as follows:
{(number of fluorine atoms×19)/molecular weight of fluorinated chain carbonate}×100(%)
This value was calculated using the following formula.

The above-mentioned fluorinated chain carbonate is preferably any of the following compounds, because they have low viscosity.

As the above-mentioned fluorinated chain carbonate, methyl 2,2,2-trifluoroethyl carbonate (F ₃ CH ₂ COC(═O)OCH ₃ ) is particularly preferable.

The above fluorinated chain carbonates may be used alone or in any combination and ratio of two or more kinds.

When the fluorinated chain carbonate is included, the content of the fluorinated chain carbonate is preferably 10 to 90% by volume relative to the solvent, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume.

The carboxylic acid ester may be a cyclic carboxylic acid ester or a chain carboxylic acid ester.

The cyclic carboxylic acid ester may be a non-fluorinated cyclic carboxylic acid ester or a fluorinated cyclic carboxylic acid ester.

The non-fluorinated cyclic carboxylic acid ester may be a non-fluorinated saturated cyclic carboxylic acid ester, and preferably a non-fluorinated saturated cyclic carboxylic acid ester having an alkylene group having 2 to 4 carbon atoms.

Specific examples of non-fluorinated saturated cyclic carboxylic acid esters having an alkylene group with 2 to 4 carbon atoms include β-propiolactone, γ-butyrolactone, ε-caprolactone, δ-valerolactone, and α-methyl-γ-butyrolactone. Among these, γ-butyrolactone and δ-valerolactone are particularly preferred in terms of improving the degree of lithium ion dissociation and improving load characteristics.

The non-fluorinated saturated cyclic carboxylic acid esters may be used alone or in any combination of two or more in any ratio.

When the non-fluorinated saturated cyclic carboxylic acid ester is included, the content of the non-fluorinated saturated cyclic carboxylic acid ester relative to the solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

The chain carboxylate ester may be a non-fluorinated chain carboxylate ester or a fluorinated chain carboxylate ester. When the solvent contains the chain carboxylate ester, the increase in resistance of the electrolyte solution after storage at high temperatures can be further suppressed.

Examples of the non-fluorinated chain carboxylate esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, tert-butyl propionate, tert-butyl butyrate, sec-butyl propionate, sec-butyl butyrate, n-butyl butyrate, methyl pyrophosphate, ethyl pyrophosphate, tert-butyl formate, tert-butyl acetate, sec-butyl formate, sec-butyl acetate, n-hexyl pivalate, n-propyl formate, n-propyl butyl ester ... Examples of such esters include propyl acetate, n-butyl formate, n-butyl pivalate, n-octyl pivalate, ethyl 2-(dimethoxyphosphoryl)acetate, ethyl 2-(dimethylphosphoryl)acetate, ethyl 2-(diethoxyphosphoryl)acetate, ethyl 2-(diethylphosphoryl)acetate, isopropyl propionate, isopropyl acetate, ethyl formate, ethyl 2-propynyl oxalate, isopropyl formate, isopropyl butyrate, isobutyl formate, isobutyl propionate, isobutyl butyrate, and isobutyl acetate.

Among these, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate are preferred, and ethyl propionate and propyl propionate are particularly preferred.

The non-fluorinated chain carboxylic acid esters may be used alone or in any combination of two or more in any ratio.

When the non-fluorinated chain carboxylic acid ester is included, the content of the non-fluorinated chain carboxylic acid ester relative to the solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

The above-mentioned fluorinated chain carboxylate ester is a chain carboxylate ester having a fluorine atom. A solvent containing the fluorinated chain carboxylate ester can be suitably used even under high voltage.

The fluorinated chain carboxylate ester may be represented by the following general formula:
R ³¹ COOR ³²
(wherein R ³¹ and R ³² are each independently an alkyl group having 1 to 4 carbon atoms which may contain a fluorine atom, and at least one of R ³¹ and R ³² contains a fluorine atom) is preferred from the viewpoints of compatibility with other solvents and oxidation resistance.

Examples of R ³¹ and R ³² include non-fluorinated alkyl groups such as a methyl group (-CH ₃ ), an ethyl group (-CH ₂ CH ₃ ), a propyl group (-CH ₂ CH ₂ CH ₃ ), an isopropyl group (-CH(CH ₃ ) ₂ ), a normal butyl group (-CH ₂ CH ₂ CH ₂ CH ₃ ), and a tertiary butyl group (-C(CH ₃ ) ₃ ); -CF ₃ , -CF ₂ H, -CFH ₂ , -CF ₂ CF ₃ , -CF ₂ CF ₂ H, -CF ₂ CFH ₂ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CF ₂ CF ₂ CF ₃ , -CF ₂ CF ₂ CF _{2 H} , _{-CF2CF2CFH2 ,} -CH2CF2CF3 _{, -CH2CF2CF2H} , _{-CH2CF2CFH2 , -CH2CH2CF3} , -CH2CH2CF2H _, -CH2CH2CFH ₂ , -CF _{( CF3} ) ₂ , -CF(CF2H) _{2, -CF(CFH2)2 , -CH ( CF3 ) 2 , -CH} ( _CF2H ) _{2 , -CH} ( _{CFH2 ) 2 , -CF ( OCH3 ) CF3 , -CF2CF2CF2} CF ₃ , _{-CF 2} CF2CF2CF2H, -CF2CF2CF2CFH2 _{, -CH2CF2CF2CF3 ,} -CH2CF2CF2CF2H _, -CH2CF2CF2CFH2, -CH2CH2CF 2 _CF 3 , -CH ₂ CH ₂ CF _{2 CF 2 H} , -CH ₂ CH _{2 CF 2 CFH 2 , -CH 2} CH ₂ CH _{2 CF 3} , -CH _{2 CH 2 CH 2 CF 2 H , -CH 2 CH 2 CH 2 CFH 2 F ( CF3 ) CF2CF3} , -CF( _CF2H ) _{CF2CF3 ,} -CF( _CFH2 )CF2CF3, -CF( _CF3 )CF2CF2H, -CF( _CF3 ) _CF2CFH2 , -CF(CF3)CH2CF3, -CF( _CF3 )CH ₂ CF _{2 H} , -CF(CF ₃ )CH ₂ CFH ₂ , -CH(CF ₃ ) _{CF 2 CF 3} , -CH(CF _{2 H} )CF _{2 CF 3} , -CH( _{CFH 2} ) _{CF 2 CF 3 ,} -CH(CF ₃ )CF ₂ CF ₂ H, -CH( _{C F3 )} CF ₂ CFH ₂ , -CH(CF ₃ )CH ₂ CF ₃ , -CH(CF ₃ )CH ₂ CF ₂ H, -CH(CF ₃ )CH ₂ CFH ₂ , -CF ₂ CF (CF ₃ ) CF ₃ , _{-CF 2} CF ( _{CF 2 H} ) CF ₃ , -CF ₂ CF( _CFH2 )CF3, _-CF2CF ( _CF3 ) _CF2H , -CF2CF ₍ CF3) _CFH2 , _-CH2CF ( _CF3 ) _CF3 , _{-CH2CF(CF2H)CF3, -CH2CF ( CFH2 ) CF3} , _-CH2 CF( _CF3 ) _CF2H , _-CH2CF ( _CF3 )CFH2, -CH2CH( _CF3 ) _CF3 , _{-CH2CH (} CF2H) _CF3 , -CH2CH( _CFH2 ) _CF3 , _-CH2CH ( _CF3 ) _CF2 H, _-CH2CH ( _CF3 ) _CFH2 , -CF2CH( _CF3 ) _{CF3 , -CF2CH} ( _CF2H ) _{CF3 ,} -CF2CH _{(CFH2)CF3, -CF2CH(CF3)CF2H, -CF2CH ( CF 3 ) CFH 2 , -C ( CF} Examples of the fluorinated alkyl group include _-CF3 ) ₃ , -C( _CF2H ) _{3 ,} and _-C ( _CFH2 ) _{3 .} Among these _, methyl group, ethyl group _{, -CF3, -CF2H , -CF2CF3 , -CH2CF3 , -CH2CF2H , -CH2CFH2 , -CH2CH2CF3} , _{-CH2CF2CF3 , -CH2CF2CF2H} , _{and -CH2CF2CFH2} are particularly preferred in terms of compatibility with other solvents, _viscosity , and oxidation resistance.

Specific examples of the fluorinated chain carboxylate include, for example, CF ₃ CH ₂ C(═O)OCH ₃ (methyl 3,3,3-trifluoropropionate), HCF ₂ C(═O)OCH ₃ (methyl difluoroacetate), HCF ₂ C(═O)OC ₂ H ₅ (ethyl difluoroacetate), CF ₃ C(═O)OCH ₂ CH ₂ CF ₃ , CF ₃ C(═O)OCH ₂ C ₂ F ₅ , CF ₃ C(═O)OCH ₂ CF ₂ CF ₂ H (2,2,3,3-tetrafluoropropyl trifluoroacetate), CF ₃ C(═O)OCH ₂ CF ₃ , CF ₃ C(═O)OCH(CF ₃ ) ₂ , ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH ₃ C(═O)OCH ₂ CF ₃ Examples of the ethyl 4,4,4-trifluorobutyrate include 2,2,2-trifluoroethyl acetate, 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-difluorobutyl acetate, methyl 2,2,3,3-tetrafluoropropionate, 2-(trifluoromethyl)-3,3,3-methyl trifluoropropionate, and methyl heptafluorobutyrate.
Among them, _CF3CH2C ( _{= O} ) _OCH3 , _HCF2C ( _{= O ) OCH3} , _HCF2C ( ₌ O) _OC2H5 , _CF3C ( ₌ O) _OCH2C2F5 , _CF3C (= _O )OCH2CF2CF2H, CF3C (= _O ) _OCH2CF3 , _CF3C (=O)OCH( _CF3 ) ₂ , ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH ₃ C(═O)OCH ₂ CF ₃ , 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-difluorobutyl acetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate are preferred from the viewpoints of good compatibility with other solvents and rate characteristics, and CF ₃ CH ₂ C( _═O )OCH ₃ , HCF ₂ C(═O)OCH ₃ , HCF 2 C(═O)OC ₂ H ₅ , CH ₃ C(═O)OCH _{2 CF3} is more preferred, _{and HCF2C} (=O) _OCH3 , _HCF2C (=O) _OC2H5 , and _CH3C (=O) _{OCH2CF3 are} particularly preferred.

The above fluorinated chain carboxylic acid esters may be used alone or in any combination and ratio of two or more kinds.

When the fluorinated chain carboxylate ester is included, the content of the fluorinated chain carboxylate ester is preferably 10 to 90% by volume relative to the solvent, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume.

The solvent preferably contains at least one selected from the group consisting of the cyclic carbonate, the chain carbonate, and the chain carboxylate, and more preferably contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylate. The cyclic carbonate is preferably a saturated cyclic carbonate.
An electrolyte solution containing a solvent having the above composition can further improve the high-temperature storage characteristics and cycle characteristics of an electrochemical device.

When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester, it preferably contains 10 to 100% by volume of the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester in total, more preferably 30 to 100% by volume, and even more preferably 50 to 100% by volume.

When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester, the volume ratio of the cyclic carbonate to at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester is preferably 5/95 to 95/5, more preferably 10/90 or more, even more preferably 15/85 or more, particularly preferably 20/80 or more, more preferably 90/10 or less, even more preferably 60/40 or less, and particularly preferably 50/50 or less.

The solvent also preferably contains at least one selected from the group consisting of the non-fluorinated saturated cyclic carbonate, the non-fluorinated chain carbonate, and the non-fluorinated chain carboxylic acid ester, and more preferably contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester. An electrolyte solution containing a solvent of the above composition can be suitably used in electrochemical devices used at relatively low voltages.

When the solvent contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the solvent preferably contains 5 to 100% by volume of the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester in total, more preferably 20 to 100% by volume, and even more preferably 30 to 100% by volume.

When the electrolyte solution contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the volume ratio of the non-fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester is preferably 5/95 to 95/5, more preferably 10/90 or more, even more preferably 15/85 or more, particularly preferably 20/80 or more, more preferably 90/10 or less, even more preferably 60/40 or less, and particularly preferably 50/50 or less.

The solvent also preferably contains at least one selected from the group consisting of the fluorinated saturated cyclic carbonate, the fluorinated chain carbonate, and the fluorinated chain carboxylic acid ester, and more preferably contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester. An electrolyte solution containing a solvent of the above composition can be suitably used not only in electrochemical devices used at relatively low voltages, but also in electrochemical devices used at relatively high voltages.

When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester, the solvent preferably contains 5 to 100% by volume of the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester in total, more preferably 10 to 100% by volume, and even more preferably 30 to 100% by volume.

When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester, the volume ratio of the fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester is preferably 5/95 to 95/5, more preferably 10/90 or more, even more preferably 15/85 or more, particularly preferably 20/80 or more, more preferably 90/10 or less, even more preferably 60/40 or less, and particularly preferably 50/50 or less.

Ionic liquids can also be used as the solvent. "Ionic liquids" are liquids that consist of ions that combine organic cations and anions.

The organic cation is not particularly limited, but examples thereof include imidazolium ions such as dialkylimidazolium cations and trialkylimidazolium cations; tetraalkylammonium ions; alkylpyridinium ions; dialkylpyrrolidinium ions; and dialkylpiperidinium ions.

The anion serving as a counter to these organic cations is not particularly limited, and examples thereof include _PF6 anion, _PF3 ( _C2F5 ) ₃ anion, _PF3 ( _CF3 ) ₃ anion, _BF4 anion, _BF2 ( _{CF3 ) 2} anion, _BF3 ( _CF3 ) anion, bisoxalatoborate anion, P( _C2O4 ) _F2 anion, Tf(trifluoromethanesulfonyl) anion, Nf(nonafluorobutanesulfonyl) anion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide _anion , dicyanoamine anion, and halide anions.

The solvent is preferably a non-aqueous solvent, and the electrolyte solution of the present disclosure is preferably a non-aqueous electrolyte solution.
The content of the solvent in the electrolytic solution is preferably 70 to 99.999% by mass, more preferably 80% by mass or more, and more preferably 92% by mass or less.

The electrolyte solution of the present disclosure preferably further contains an electrolyte salt. As the electrolyte salt, any salt that can be used in an electrolyte solution can be used, such as lithium salt, ammonium salt, metal salt, liquid salt (ionic liquid), inorganic polymer salt, organic polymer salt, etc.

As the electrolyte salt of the electrolyte for the lithium ion secondary battery, a lithium salt is preferred.
Any lithium salt can be used as the lithium salt, and specific examples thereof include the _following : inorganic lithium salts such as _LiPF6 , _LiBF4 , LiClO4, _LiAlF4 , _LiSbF6 , _LiTaF6 , _LiWF7 , _LiAsF6 , _LiAlCl4 , LiI, _{LiBr ,} LiCl, _LiB10Cl10 , _Li2SiF6 , _Li2PFO3 , _{and LiPO2F2 ;}
Lithium tungstates such as _LiWOF5 ;
_{Lithium carboxylates such as HCO2Li} , _{CH3CO2Li , CH2FCO2Li , CHF2CO2Li , CF3CO2Li , CF3CH2CO2Li , CF3CF2CO2Li , CF3CF2CF2CO2Li , CF3CF2CF2CF2CO2Li , and CF3CF2CF2CF2CF2CO2Li ;
Lithium salts having an S =} O group, _{such as} FSO3Li, _{CH3SO3Li , CH2FSO3Li} , _CHF2SO3Li , _{CF3SO3Li , CF3CF2SO3Li , CF3CF2CF2CF2SO3Li, CF3CF2CF2CF2CF2SO3Li, lithium methyl sulfate, lithium ethyl sulfate (C2H5OSO3Li ) , and lithium 2,2,2 - trifluoroethyl sulfate} ;
LiN(FCO) ₂ , LiN(FCO)(FSO ₂ ), LiN(FSO ₂ ) ₂ , LiN(FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , lithium bisperfluoroethanesulfonylimide, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, lithium cyclic 1,2-ethanedisulfonylimide, lithium cyclic 1,3-propanedisulfonylimide, lithium cyclic 1,4-perfluorobutanedisulfonylimide, LiN(CF ₃ SO ₂ )(FSO ₂ ), LiN(CF ₃ SO ₂ )(C ₃ F ₇ SO ₂ ), LiN(CF ₃ SO ₂ )(C Lithium imide salts such as LiN( _POF2 ) ₂ , LiN( _POF2 ) _{2, etc} .;
Lithium methide salts such as LiC _{( FSO2} ) ₃ , _LiC ( _CF3SO2 ) ₃ , LiC( _C2F5SO2 ) _{3 ;}
Other examples include salts represented by the formula LiPF _a (C _n F _2n+1 ) _6-a (wherein a is an integer from 0 to 5, and n is an integer from 1 to 6) (e.g., LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ), LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ ), LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₃ CF ₃ , LiBF _{3 Fluorine} -containing organic _lithium salts _{such as C2F5 , LiBF3C3F7} , _LiBF2 ( _CF3 ) ₂ , LiBF2( _{C2F5 ) 2} , _{LiBF2 (CF3SO2)2, and LiBF2(C2F5SO2)2, LiSCN, LiB(CN)4 , LiB ( C6H5 ) 4 , Li2(C2O4), LiP(C2O4)3 , and Li2B12FbH12 - b ( b is an integer of 0} to ₃ ) _, etc.

Among them, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiTaF ₆ , LiPO ₂ F ₂ , FSO ₃ Li, CF ₃ SO ₃ Li, LiN(FSO ₂ ) ₂ , LiN(FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC(FSO ₂ ) ₃ , LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , LiBF ₃ CF ₃ , LiBF _{3 C2F5} , _LiPF3 ( _CF3 ) ₃ , _LiPF3 ( _C2F5 ) _{3 ,} and _the like are particularly preferred because they have the effect of improving output characteristics, high-rate charge/discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like, and at least one lithium salt selected from the group consisting of _LiPF6 , LiN( _FSO2 ) ₂ , and _LiBF4 is most preferred.

These electrolyte salts may be used alone or in combination of two or more. A preferred example of a combination of two or more is a combination of _{LiPF6 and LiBF4, or a combination of LiPF6 and LiPO2F2, C2H5OSO3Li or FSO3Li , which has the effect} of improving high-temperature storage characteristics, load characteristics and cycle characteristics.

In this case, there is no restriction on the amount of LiBF ₄ , LiPO ₂ F ₂ , C ₂ H ₅ OSO ₃ Li or FSO ₃ Li relative to 100 mass% of the entire electrolyte solution, and it is any amount as long as it does not significantly impair the effects of the present disclosure; however, relative to the electrolyte solution of the present disclosure, it is usually 0.01 mass% or more, preferably 0.1 mass% or more, and also usually 30 mass% or less, preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 5 mass% or less.

Another example is the combined use of an inorganic lithium salt and an organic lithium salt, which has the effect of suppressing deterioration due to storage at high temperatures. _The organic lithium salt is preferably _CF3SO3Li , LiN( _FSO2 ) _{2 , LiN} ( _FSO2 ) ₍ CF3SO2), _LiN (CF3SO2) ₂ , LiN( _C2F5SO2 ) ₂ , lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide _, LiC( _FSO2 ) ₃ , LiC( _CF3SO2 ) _{3 , LiC ( C2F5SO2 )3 , LiBF3CF3 , LiBF3C2F5 , LiPF3} ( _CF3 ) ₃ , _LiPF3 ( _C2F5 ) _{3 ,} or the _like . In this case, the ratio of the organic lithium salt to the total electrolyte solution (100 mass %) is preferably 0.1 mass % or more, particularly preferably 0.5 mass % or more, and is preferably 30 mass % or less, particularly preferably 20 mass % or less.

The concentration of these electrolyte salts in the electrolyte is not particularly limited as long as it does not impair the effects of the present disclosure. In order to keep the electrical conductivity of the electrolyte in a good range and ensure good battery performance, the total molar concentration of lithium in the electrolyte is preferably 0.3 mol/L or more, more preferably 0.4 mol/L or more, even more preferably 0.5 mol/L or more, and is preferably 3 mol/L or less, more preferably 2.5 mol/L or less, even more preferably 2.0 mol/L or less.

If the total molar concentration of lithium is too low, the electrical conductivity of the electrolyte may be insufficient, while if the concentration is too high, the electrical conductivity may decrease due to increased viscosity, which may result in reduced battery performance.

The electrolyte salt of the electrolyte for the electric double layer capacitor is preferably an ammonium salt.
Examples of the ammonium salt include the following (IIa) to (IIe).
(IIa) Tetraalkyl quaternary ammonium salt General formula (IIa):

（式中、Ｒ^１ａ、Ｒ^２ａ、Ｒ^３ａ及びＲ^４ａは同じか又は異なり、いずれも炭素数１～６のエーテル結合を含んでいてもよいアルキル基；Ｘ^－はアニオン）
で示されるテトラアルキル４級アンモニウム塩が好ましく例示できる。また、このアンモニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１～４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^1a , R ^2a , R ^3a and R ^4a are the same or different, and each is an alkyl group having 1 to 6 carbon atoms which may contain an ether bond; X ⁻ is an anion.)
Preferred examples of the tetraalkyl quaternary ammonium salts include those represented by the following formula: In addition, ammonium salts in which some or all of the hydrogen atoms have been substituted with fluorine atoms and/or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

Specific examples include general formula (IIa-1):

（式中、Ｒ^１ａ、Ｒ^２ａ及びＸ^－はアニオン；ｘ及びｙは同じか又は異なり０～４の整数で、かつｘ＋ｙ＝４）
で示されるテトラアルキル４級アンモニウム塩、一般式（ＩＩａ－２）：

(wherein R ^1a , R ^2a and X ⁻ are anions; x and y are the same or different and are integers from 0 to 4, and x+y=4).
Tetraalkyl quaternary ammonium salts represented by general formula (IIa-2):

（式中、Ｒ^５ａは炭素数１～６のアルキル基；Ｒ^６ａは炭素数１～６の２価の炭化水素基；Ｒ^７ａは炭素数１～４のアルキル基；ｚは１又は２；Ｘ^－はアニオン）
で示されるアルキルエーテル基含有トリアルキルアンモニウム塩、
等が挙げられる。アルキルエーテル基を導入することにより、粘性の低下を図ることができる。

(In the formula, R ^5a is an alkyl group having 1 to 6 carbon atoms; R ^6a is a divalent hydrocarbon group having 1 to 6 carbon atoms; R ^7a is an alkyl group having 1 to 4 carbon atoms; z is 1 or 2; and X ⁻ is an anion.)
an alkyl ether group-containing trialkylammonium salt represented by the formula:
By introducing an alkyl ether group, it is possible to reduce the viscosity.

The anion ^X- may be _an inorganic anion or an organic anion. Examples of inorganic anions include _AlCl4- ^, _BF4- , ^{PF6- ,} _AsF6- ^, _TaF6- ^, I- ^, and _SbF6- ^. Examples of organic anions include bisoxalatoborate _anion , difluorooxalatoborate anion, tetrafluorooxalatophosphate anion _{, difluorobisoxalatophosphate} anion _{, CF3COO-} ^, _{CF3SO3- ,} ( _CF3SO2 ) ^2N- , ^and ( _C2F5SO2 ) _2N- ^.

Among these, BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ and SbF ₆ ⁻ are preferred because of their excellent oxidation resistance and ionic dissociation properties.

_{Specific examples of suitable} tetraalkyl quaternary ammonium salts include _{Et4NBF4 , Et4NClO4} , _{Et4NPF6 , Et4NAsF6 , Et4NSbF6} , Et4NCF3SO3, _{Et4N ( CF3SO2 ) 2N , Et4NC4F9SO3} , _{Et3MeNBF4 , Et3MeNClO4 , Et3MeNPF6 , Et3MeNAsF6 , Et3MeNSbF6 , Et3MeNCF3SO3 , Et3MeN ( CF3SO2 ) 2N , Et 3} MeNC ₄ F ₉ SO ₃ may be used, and in particular, Et ₄ NBF ₄ , Et ₄ NPF ₆ , Et ₄ NSbF ₆ , Et ₄ NAsF ₆ , Et ₃ MeNBF ₄ , N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium salt, and the like may be mentioned.

(IIb) Spirocyclic bipyrrolidinium salt General formula (IIb-1):

（式中、Ｒ^８ａ及びＲ^９ａは同じか又は異なり、いずれも炭素数１～４のアルキル基；Ｘ^－はアニオン；ｎ１は０～５の整数；ｎ２は０～５の整数）
で示されるスピロ環ビピロリジニウム塩、一般式（ＩＩｂ－２）：

(wherein R ^8a and R ^9a are the same or different and each is an alkyl group having 1 to 4 carbon atoms; X ⁻ is an anion; n1 is an integer of 0 to 5; and n2 is an integer of 0 to 5).
spirocyclic bipyrrolidinium salts represented by the general formula (IIb-2):

（式中、Ｒ^１０ａ及びＲ^１１ａは同じか又は異なり、いずれも炭素数１～４のアルキル基；Ｘ^－はアニオン；ｎ３は０～５の整数；ｎ４は０～５の整数）
で示されるスピロ環ビピロリジニウム塩、又は、一般式（ＩＩｂ－３）：

(In the formula, R ^10a and R ^11a are the same or different and each is an alkyl group having 1 to 4 carbon atoms; X ⁻ is an anion; n3 is an integer of 0 to 5; and n4 is an integer of 0 to 5.)
or a spiro ring bipyrrolidinium salt represented by the general formula (IIb-3):

（式中、Ｒ^１２ａ及びＲ^１３ａは同じか又は異なり、いずれも炭素数１～４のアルキル基；Ｘ^－はアニオン；ｎ５は０～５の整数；ｎ６は０～５の整数）
で示されるスピロ環ビピロリジニウム塩が好ましく挙げられる。また、このスピロ環ビピロリジニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１～４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^12a and R ^13a are the same or different and each is an alkyl group having 1 to 4 carbon atoms; X ⁻ is an anion; n5 is an integer of 0 to 5; and n6 is an integer of 0 to 5.)
In addition, spiro ring bipyrrolidinium salts in which some or all of the hydrogen atoms are substituted with fluorine atoms and/or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

Preferred specific examples of the anion ^X- are the same as those in the case of (IIa). Among them, _BF4- , _PF6- , ( _{CF3SO2 ) 2N-} or ( _C2F5SO2 ) _2N- are preferred because of their high dissociation property and low internal resistance under _{high voltage} .

等が挙げられる。 Preferable specific examples of the spiro ring bipyrrolidinium salt include, for example,

etc.

This spirocyclic bipyrrolidinium salt has excellent solubility in solvents, oxidation resistance, and ionic conductivity.

(IIc) Imidazolium salts General formula (IIc):

（式中、Ｒ^１４ａ及びＲ^１５ａは同じか又は異なり、いずれも炭素数１～６のアルキル基；Ｘ^－はアニオン）
で示されるイミダゾリウム塩が好ましく例示できる。また、このイミダゾリウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１～４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(wherein R ^14a and R ^15a may be the same or different and each represents an alkyl group having 1 to 6 carbon atoms; X ⁻ represents an anion).
In addition, imidazolium salts in which some or all of the hydrogen atoms of the imidazolium salts have been substituted with fluorine atoms and/or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

Preferred examples of the anion X ^{1 −} are the same as those in (IIa).

Preferred examples include, for example,

等が挙げられる。

etc.

This imidazolium salt is excellent in that it has low viscosity and good solubility.

(IId): N-alkylpyridinium salt General formula (IId):

（式中、Ｒ^１６ａは炭素数１～６のアルキル基；Ｘ^－はアニオン）
で示されるＮ－アルキルピリジニウム塩が好ましく例示できる。また、このＮ－アルキルピリジニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１～４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(wherein R ^16a is an alkyl group having 1 to 6 carbon atoms; X ⁻ is an anion).
In addition, N-alkylpyridinium salts in which some or all of the hydrogen atoms of the N-alkylpyridinium salts have been substituted with fluorine atoms and/or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

Preferred examples of the anion X ^{1 −} are the same as those in (IIa).

Preferred examples include, for example,

等が挙げられる。

etc.

These N-alkylpyridinium salts are excellent in that they have low viscosity and good solubility.

(IIe) N,N-dialkylpyrrolidinium salts General formula (IIe):

（式中、Ｒ^１７ａ及びＲ^１８ａは同じか又は異なり、いずれも炭素数１～６のアルキル基；Ｘ^－はアニオン）
で示されるＮ，Ｎ－ジアルキルピロリジニウム塩が好ましく例示できる。また、このＮ，Ｎ－ジアルキルピロリジニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１～４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(wherein R ^17a and R ^18a may be the same or different and each represents an alkyl group having 1 to 6 carbon atoms; X ⁻ represents an anion).
Preferred examples of the N,N-dialkylpyrrolidinium salts include those represented by the following formula: In addition, N,N-dialkylpyrrolidinium salts in which some or all of the hydrogen atoms have been substituted with fluorine atoms and/or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

Preferred examples of the anion X ^{1 −} are the same as those in (IIa).

Preferred examples include, for example,

等が挙げられる。

etc.

This N,N-dialkylpyrrolidinium salt is excellent in that it has low viscosity and good solubility.

Among these ammonium salts, (IIa), (IIb) and (IIc) are preferred because of their good solubility, oxidation resistance and ionic conductivity, and furthermore

（式中、Ｍｅはメチル基；Ｅｔはエチル基；Ｘ^－、ｘ、ｙは式（ＩＩａ－１）と同じ）
が好ましい。

(In the formula, Me is a methyl group; Et is an ethyl group; X ⁻ , x, and y are the same as those in formula (IIa-1).)
is preferred.

Furthermore, a lithium salt may be used as the electrolyte salt for the electric double layer capacitor. As the lithium salt, for example, _LiPF6 , _LiBF4 , LiN _{( FSO2} ) ₂ , _LiAsF6 , _LiSbF6 , and LiN _{( SO2C2H5} ) ₂ are preferable.
To further improve the capacity, a magnesium salt may be used, and as the magnesium salt, for example, Mg(ClO ₄ ) ₂ , Mg(OOC ₂ H ₅ ) ₂ and the like are preferable.

When the electrolyte salt is the ammonium salt, the concentration is preferably 0.7 mol/L or more. If the concentration is less than 0.7 mol/L, not only the low-temperature characteristics may deteriorate but also the initial internal resistance may become high. The concentration of the electrolyte salt is more preferably 0.9 mol/L or more.
The upper limit of the concentration is preferably 2.0 mol/L or less, and more preferably 1.5 mol/L or less, from the viewpoint of low-temperature characteristics.
When the ammonium salt is triethylmethylammonium tetrafluoroborate (TEMABF ₄ ), the concentration is preferably 0.7 to 1.5 mol/L in terms of excellent low-temperature characteristics.
In the case of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄ ), the concentration is preferably 0.7 to 2.0 mol/liter.

（式中、Ｘ^２１は少なくともＨ又はＣを含む基、ｎ２１は１～３の整数、Ｙ^２１及びＺ^２１は、同じか又は異なり、少なくともＨ、Ｃ、Ｏ又はＦを含む基、ｎ２２は０又は１、Ｙ^２１及びＺ^２１はお互いに結合して環を形成してもよい。）で示される化合物（２）を更に含むことが好ましい。上記電解液が化合物（２）を含むと、高温で保管した場合でも、容量保持率が一層低下しにくく、ガスの発生量が更に増加しにくい。 The electrolyte solution of the present disclosure has the general formula (2):

(wherein X ²¹ is a group containing at least H or C, n21 is an integer of 1 to 3, Y ²¹ and Z ²¹ are the same or different and are a group containing at least H, C, O or F, n22 is 0 or 1, and Y ²¹ and Z ²¹ may be bonded to each other to form a ring.) When the electrolyte solution contains compound (2), the capacity retention rate is further prevented from decreasing and the amount of gas generated is further prevented from increasing, even when stored at high temperatures.

When n21 is 2 or 3, two or three ^X21 may be the same or different.
When a plurality of Y ²¹ and a plurality of Z ²¹ are present, the plurality of Y ²¹ and the plurality of Z ²¹ may be the same or different.

X ²¹ is preferably a group represented by -CY ²¹ Z ²¹ - (wherein Y ²¹ and Z ²¹ are as defined above) or -CY ²¹ ═CZ ²¹ - (wherein Y ²¹ and Z ²¹ are as defined above).

Y ²¹ is preferably at least one selected from the group consisting of H-, F-, CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, CF ₃ -, CF ₃ CF ₂ -, CH ₂ FCH ₂ - and CF ₃ CF ₂ CF ₂ -.
Z ²¹ is preferably at least one selected from the group consisting of H-, F-, CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, CF ₃ -, CF ₃ CF ₂ -, CH ₂ FCH ₂ - and CF ₃ CF ₂ CF ₂ -.

Alternatively, Y ²¹ and Z ²¹ may be bonded to each other to form a carbocyclic or heterocyclic ring which may contain an unsaturated bond and may have aromaticity. The ring preferably has 3 to 20 carbon atoms.

Next, specific examples of compound (2) will be described. In the following examples, "analog" refers to an acid anhydride obtained by replacing part of the structure of the exemplified acid anhydride with another structure within the scope of the present disclosure, such as a dimer, trimer, or tetramer composed of multiple acid anhydrides, or structural isomers such as those having the same number of carbon atoms in the substituent but a branched chain, or those in which the substituent is bonded to the acid anhydride at a different site, etc.

Specific examples of acid anhydrides forming a five-membered ring structure include succinic anhydride, methylsuccinic anhydride (4-methylsuccinic anhydride), dimethylsuccinic anhydride (4,4-dimethylsuccinic anhydride, 4,5-dimethylsuccinic anhydride, etc.), 4,4,5-trimethylsuccinic anhydride, 4,4,5,5-tetramethylsuccinic anhydride, 4-vinylsuccinic anhydride, 4,5-divinylsuccinic anhydride, phenylsuccinic anhydride (4-phenylsuccinic anhydride), 4,5-diphenylsuccinic anhydride, Examples of such anhydrides include hydrates, 4,4-diphenylsuccinic anhydride, citraconic anhydride, maleic anhydride, methylmaleic anhydride (4-methylmaleic anhydride), 4,5-dimethylmaleic anhydride, phenylmaleic anhydride (4-phenylmaleic anhydride), 4,5-diphenylmaleic anhydride, itaconic anhydride, 5-methylitaconic anhydride, 5,5-dimethylitaconic anhydride, phthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, and their analogs.

Specific examples of acid anhydrides that form a six-membered ring structure include cyclohexanedicarboxylic anhydride (cyclohexane-1,2-dicarboxylic anhydride, etc.), 4-cyclohexene-1,2-dicarboxylic anhydride, glutaric anhydride, glutaconic anhydride, 2-phenylglutaric anhydride, etc., and their analogues.

Specific examples of acid anhydrides that form other cyclic structures include 5-norbornene-2,3-dicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic anhydride, diglycolic anhydride, and their analogues.

Specific examples of acid anhydrides that form a cyclic structure and are substituted with halogen atoms include monofluorosuccinic anhydride (4-fluorosuccinic anhydride, etc.), 4,4-difluorosuccinic anhydride, 4,5-difluorosuccinic anhydride, 4,4,5-trifluorosuccinic anhydride, trifluoromethylsuccinic anhydride, tetrafluorosuccinic anhydride (4,4,5,5-tetrafluorosuccinic anhydride), 4-fluoromaleic anhydride, 4,5-difluoromaleic anhydride, trifluoromethylmaleic anhydride, 5-fluoroitaconic anhydride, 5,5-difluoroitaconic anhydride, and the like, and their analogs.

Examples of compound (2) include, among others, glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride, 2-phenylglutaric anhydride, maleic anhydride, methylmaleic anhydride, trifluoromethyl Preferred are maleic anhydride, phenylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, dimethylsuccinic anhydride, trifluoromethylsuccinic anhydride, monofluorosuccinic anhydride, and tetrafluorosuccinic anhydride, and more preferred are maleic anhydride, methylmaleic anhydride, trifluoromethylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, trifluoromethylsuccinic anhydride, and tetrafluorosuccinic anhydride, and even more preferred are maleic anhydride and succinic anhydride.

Compound (2) is represented by the general formula (3):

（式中、Ｘ^３１～Ｘ^３４は、同じか又は異なり、少なくともＨ、Ｃ、Ｏ又はＦを含む基）で示される化合物（３）、及び、一般式（４）：

(wherein X ³¹ to X ³⁴ are the same or different and each is a group containing at least H, C, O or F), and a compound represented by the general formula (4):

（式中、Ｘ^４１及びＸ^４２は、同じか又は異なり、少なくともＨ、Ｃ、Ｏ又はＦを含む基）で示される化合物（４）からなる群より選択される少なくとも１種であることが好ましい。

(wherein X ⁴¹ and X ⁴² are the same or different and each is a group containing at least H, C, O or F)

X ³¹ to X ³⁴ are the same or different and each preferably represents at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group. X ³¹ to X ³⁴ each preferably have 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms.

X ³¹ to X ³⁴ may be the same or different and are more preferably at least one selected from the group consisting of H-, F-, CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, CF ₃ -, CF ₃ CF ₂ -, CH ₂ FCH ₂ - and CF ₃ CF ₂ CF ₂ -.

X ⁴¹ and X ⁴² are the same or different and are preferably at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group. X ⁴¹ and X ⁴² each preferably have 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms.

X ⁴¹ and X ⁴² may be the same or different and are more preferably at least one selected from the group consisting of H-, F-, CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, CF ₃ -, CF ₃ CF ₂ -, CH ₂ FCH ₂ - and CF ₃ CF ₂ CF ₂ -.

Compound (3) is preferably any of the following compounds:

Compound (4) is preferably any of the following compounds:

The electrolyte solution preferably contains 0.0001 to 15% by mass of compound (2) because the capacity retention rate is unlikely to decrease and the amount of gas generated is unlikely to increase even when stored at high temperatures. The content of compound (2) is more preferably 0.01 to 10% by mass, even more preferably 0.1 to 3% by mass, and particularly preferably 0.1 to 1.0% by mass.

When the electrolyte contains both compounds (3) and (4), even when stored at high temperatures, the capacity retention rate is unlikely to decrease and the amount of gas generated is unlikely to increase. Therefore, the electrolyte preferably contains 0.08 to 2.50 mass% of compound (3) and 0.02 to 1.50 mass% of compound (4), and more preferably contains 0.80 to 2.50 mass% of compound (3) and 0.08 to 1.50 mass% of compound (4).

（式中、Ｒ^ａ及びＲ^ｂは、それぞれ独立して、水素原子、シアノ基（ＣＮ）、ハロゲン原子、アルキル基、又は、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基を表す。ｎは１～１０の整数を表す。）

（式中、Ｒ^ｃは、水素原子、ハロゲン原子、アルキル基、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基、又は、ＮＣ－Ｒ^ｃ１－Ｘ^ｃ１－（Ｒ^ｃ１はアルキレン基、Ｘ^ｃ１は酸素原子又は硫黄原子を表す。）で表される基を表す。Ｒ^ｄ及びＲ^ｅは、それぞれ独立して、水素原子、ハロゲン原子、アルキル基、又は、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基を表す。ｍは１～１０の整数を表す。）

（式中、Ｒ^ｆ、Ｒ^ｇ、Ｒ^ｈ及びＲ^ｉは、それぞれ独立して、シアノ基（ＣＮ）を含む基、水素原子（Ｈ）、ハロゲン原子、アルキル基、又は、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基を表す。ただし、Ｒ^ｆ、Ｒ^ｇ、Ｒ^ｈ及びＲ^ｉのうち少なくとも１つはシアノ基を含む基である。ｌは１～３の整数を表す。）
これにより、電気化学デバイスの高温保存特性を向上させることができる。上記ニトリル化合物を単独で用いてもよく、２種以上を任意の組み合わせ及び比率で併用してもよい。 The electrolyte solution of the present disclosure may contain at least one selected from the group consisting of nitrile compounds represented by the following general formulas (1a), (1b), and (1c).

(In the formula, R ^a and R ^b each independently represent a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom; and n represents an integer of 1 to 10.)

(In the formula, R ^c represents a hydrogen atom, a halogen atom, an alkyl group, a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with halogen atoms, or a group represented by NC-R ^c1 -X ^c1 - (R ^c1 represents an alkylene group, and X ^c1 represents an oxygen atom or a sulfur atom). ^{R d} and R ^e each independently represent a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with halogen atoms. m represents an integer of 1 to 10.)

(In the formula, R ^f , R ^g , R ^h and R ⁱ each independently represent a group containing a cyano group (CN), a hydrogen atom (H), a halogen atom, an alkyl group, or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with halogen atoms, provided that at least one of R ^f , R ^g , R ^h and R ⁱ is a group containing a cyano group, and l represents an integer of 1 to 3.)
This can improve the high-temperature storage characteristics of the electrochemical device. The above nitrile compounds may be used alone or in any combination of two or more kinds in any ratio.

In the above general formula (1a), R ^a and R ^b each independently represent a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom.
Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, with a fluorine atom being preferred.
The alkyl group preferably has a carbon number of 1 to 5. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.
Examples of the alkyl group in which at least a portion of the hydrogen atoms have been substituted with halogen atoms include the above-mentioned alkyl groups in which at least a portion of the hydrogen atoms have been substituted with the above-mentioned halogen atoms.
When R ^a and R ^b are each an alkyl group or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom, R ^a and R ^b may be bonded to each other to form a ring structure (for example, a cyclohexane ring).
R ^a and R ^b are preferably a hydrogen atom or an alkyl group.

In the above general formula (1a), n is an integer of 1 to 10. When n is 2 or more, n R ^a may all be the same or at least some may be different. The same applies to R ^b . n is preferably an integer of 1 to 7, and more preferably an integer of 2 to 5.

As the nitrile compound represented by the above general formula (1a), dinitriles and tricarbonitriles are preferred.
Specific examples of dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2,4-dimethylsuccinonitrile, 2,5-dimethylsuccinonitrile, 2,6-dimethylsuccinonitrile, 2,7-dimethylsuccinonitrile, 2,8-dimethylsuccinonitrile, 2,9-dimethylsuccinonitrile, 2,10-dimethylsuccinonitrile, 2,11-dimethylsuccinonitrile, 2,12-dimethylsuccinonitrile, 2,13-dimethylsuccinonitrile, 2,14-dimethylsuccinonitrile, 2,15-dimethylsuccinonitrile, 2,16-dimethylsuccinonitrile, 2,17-dimethylsuccinonitrile, 2,18-dimethylsuccinonitrile, 2,20-dimethylsuccinonitrile, 2,21-dimethylsuccinonitrile, 2,22-dimethylsuccinonitrile, 2,31-dimethylsuccinonitrile, 2,23-dimethylsuccinonitrile, 2,32-dimethylsuccinonitrile, 2,33-dimethylsuccinonitrile, 2,34-dimethylsuccinonitrile, 2,35-dimethylsuccinonitrile, 2,36-dimethylsuccinonitrile, 2,37-dimethylsuccinonitrile, 2,38-dimethylsuccinonitrile, 2,39-dimethylsuccinonitrile, 2,40-dimethylsuccinonitrile, 2, ,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3- Dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-dicyanopentane, Examples include anoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, phthalonitrile, etc. Among these, succinonitrile, glutaronitrile, and adiponitrile are particularly preferred.
Specific examples of tricarbonitrile include pentanetricarbonitrile, propanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,6-hexanetricarbonitrile, heptanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, cyclohexanetricarbonitrile, triscyanoethylamine, triscyanoethoxypropane, tricyanoethylene, tris(2-cyanoethyl)amine, and the like. Particularly preferred are 1,3,6-hexanetricarbonitrile and cyclohexanetricarbonitrile, and most preferred is cyclohexanetricarbonitrile.

In the above general formula (1b), R ^c is a hydrogen atom, a halogen atom, an alkyl group, a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with halogen atoms, or a group represented by NC-R ^c1 -X ^c1 - (R ^c1 is an alkylene group, and X ^c1 is an oxygen atom or a sulfur atom), and R ^d and R ^e are each independently a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with halogen atoms.
Examples of the halogen atom, the alkyl group, and the alkyl group in which at least a part of the hydrogen atoms have been substituted with halogen atoms include those exemplified for the above general formula (1a).
In the above formula NC-R ^c1 -X ^c1 -, R ^c1 is an alkylene group, preferably an alkylene group having 1 to 3 carbon atoms.
It is preferable that R ^c , R ^d and R ^e each independently represent a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom.
At least one of R ^c , R ^d and R ^e is preferably a halogen atom or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with a halogen atom, and more preferably a fluorine atom or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with a fluorine atom.
When R ^d and R ^e are each an alkyl group or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom, R ^d and R ^e may be bonded to each other to form a ring structure (for example, a cyclohexane ring).

In the above general formula (1b), m is an integer of 1 to 10. When m is 2 or more, m ^Rd 's may all be the same, or at least some of them may be different. The same applies to R ^e . m is preferably an integer of 2 to 7, and more preferably an integer of 2 to 5.

Examples of the nitrile compound represented by the above general formula (1b) include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, lauronitrile, 3-methoxypropionitrile, 2-methylbutyronitrile, trimethylacetonitrile, hexanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile, 3-fluoropropionitrile, 2,2-difluoropropionitrile, 2,3-difluoropropionitrile, 3,3-difluoropropionitrile, 2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile, pentafluoropropionitrile, methoxyacetonitrile, benzonitrile, and the like. Among these, 3,3,3-trifluoropropionitrile is particularly preferred.

In the above general formula (1c), ^Rf , ^Rg , ^Rh and ^Ri are each independently a group containing a cyano group (CN), a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group have been substituted with halogen atoms.
Examples of the halogen atom, the alkyl group, and the alkyl group in which at least a part of the hydrogen atoms have been substituted with halogen atoms include those exemplified for the above general formula (1a).
Examples of the group containing a cyano group include a cyano group and an alkyl group in which at least some of the hydrogen atoms are substituted with a cyano group. In this case, examples of the alkyl group include those exemplified for the above general formula (1a).
At least one of ^Rf , ^Rg , ^Rh and ^Ri is a group containing a cyano group. Preferably, at least two of ^Rf , ^Rg , ^Rh and ^Ri are groups containing a cyano group, more preferably, ^Rh and ^Ri are groups containing a cyano group. When ^Rh and ^Ri are groups containing a cyano group, ^Rf and ^Rg are preferably hydrogen atoms.

In the above general formula (1c), l is an integer of 1 to 3. When l is 2 or more, l ^Rf may all be the same, or at least some of them may be different. The same applies to ^Rg . l is preferably an integer of 1 to 2.

Examples of the nitrile compound represented by the above general formula (1c) include 3-hexenedinitrile, mucononitrile, maleonitrile, fumaronitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, 2-hexenenitrile, etc., with 3-hexenedinitrile and mucononitrile being preferred, and 3-hexenedinitrile being particularly preferred.

The content of the nitrile compounds is preferably 0.2 to 7 mass% relative to the electrolyte. This can further improve the high-temperature storage characteristics and safety of the electrochemical device at high voltages. The lower limit of the total content of the nitrile compounds is more preferably 0.3 mass%, and even more preferably 0.5 mass%. The upper limit is more preferably 5 mass%, even more preferably 2 mass%, and particularly preferably 0.5 mass%.

The electrolyte solution of the present disclosure may contain a compound having an isocyanato group (hereinafter, may be abbreviated as "isocyanate"). The above-mentioned isocyanate is not particularly limited, and any isocyanate can be used. Examples of isocyanates include monoisocyanates, diisocyanates, triisocyanates, etc.

Specific examples of monoisocyanates include isocyanatomethane, isocyanatoethane, 1-isocyanatopropane, 1-isocyanatobutane, 1-isocyanatopentane, 1-isocyanatohexane, 1-isocyanatoheptane, 1-isocyanatooctane, 1-isocyanatononane, 1-isocyanatodecane, isocyanatocyclohexane, methoxycarbonyl isocyanate, ethoxycarbonyl isocyanate, propoxycarbonyl isocyanate, butoxycarbonyl isocyanate, methoxysulfonyl isocyanate, ethoxysulfonyl isocyanate, propoxysulfonyl isocyanate, butoxysulfonyl isocyanate, fluorosulfonyl isocyanate, methyl isocyanate, butyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and ethyl isocyanate.

Specific examples of diisocyanates include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,7-diisocyanatoheptane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3-diisocyanatopropene, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, and 1,4-diisocyanato-2,3-difluorobutane. 1,5-diisocyanato-2-pentene, 1,5-diisocyanato-2-methylpentane, 1,6-diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-3,4-difluorohexane, toluene diisocyanate, xylene diisocyanate, tolylene diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-1,1'-diisocyanate, dicyclohexylmethane-2,2'-diisocyanate, dicyclohexylmethane-3,3'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate bis(methyl isocyanate), bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, octamethylene diisocyanate, tetramethylene diisocyanate, etc.

Specific examples of triisocyanates include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylene diisocyanate, 1,3,5-triisocyanatomethylbenzene, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 4-(isocyanatomethyl)octamethylene diisocyanate.

Among these, 1,6-diisocyanatohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,4-trimethylhexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate are preferred because they are easily available industrially and can keep the manufacturing costs of the electrolyte low, and from a technical standpoint, they can contribute to the formation of a stable film-like structure, and are therefore more preferably used.

The content of isocyanate is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure, but is preferably 0.001% by mass or more and 1.0% by mass or less with respect to the electrolyte. If the content of isocyanate is equal to or more than this lower limit, a sufficient cycle characteristic improvement effect can be brought about in the nonaqueous electrolyte secondary battery. If the content is equal to or less than this upper limit, an initial increase in resistance of the nonaqueous electrolyte secondary battery can be avoided. The content of isocyanate is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and more preferably 0.8% by mass or less, even more preferably 0.7% by mass or less, particularly preferably 0.6% by mass or less.

The electrolyte solution of the present disclosure may contain a cyclic sulfonate ester. The cyclic sulfonate ester is not particularly limited, and any cyclic sulfonate ester can be used. Examples of cyclic sulfonate esters include saturated cyclic sulfonate esters, unsaturated cyclic sulfonate esters, saturated cyclic disulfonate esters, and unsaturated cyclic disulfonate esters.

Specific examples of saturated cyclic sulfonic acid esters include 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 1-fluoro-1,4-butane sultone, 2-fluoro-1,4-butane sultone, 3-fluoro-1,4-butane sultone, 4-fluoro-1,4-butane sultone, 1-methyl-1,4-butane sultone, 2-methyl-1,4-butane sultone, 3-methyl-1,4-butane sultone, 4-methyl-1,4-butane sultone, and 2,4-butane sultone.

Specific examples of unsaturated cyclic sulfonic acid esters include 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene 1-Butene-1,4-sultone, 2-Butene-1,4-sultone, 3-Butene-1,4-sultone, 1-Fluoro-1-butene-1,4-sultone, 2-Fluoro-1-butene-1,4-sultone, 3-Fluoro-1-butene-1,4-sultone, 4-Fluoro-1-butene-1,4-sultone, 5-Fluoro-1-butene-1,4-sultone, 6-Fluoro-1-butene-1,4-sultone, 7-Fluoro-1-butene-1,4-sultone, 8-Fluoro-1-butene-1,4-sultone, 9-Fluoro-1-butene-1,4-sultone, 10-Fluoro-1-butene-1,4-sultone, 11-Fluoro-1-butene-1,4-sultone, 12-Fluoro-1-butene-1,4-sultone, 13-Fluoro-1-butene-1,4-sultone, 14-Fluoro-1-butene-1,4-sultone, 15-Fluoro-1-butene-1,4-sultone, 16-Fluoro-1-butene-1,4-sultone, 17-Fluoro-1-butene-1,4-sultone, 18-Fluoro-1-butene-1,4-sultone, 19-Fluoro-1-butene-1,4-sultone, 20-Fluoro-1-butene-1,4-sultone, 21-Fluoro-1-butene-1,4-sultone, 22-Fluoro-1-butene-1,4-sultone, 23-Fluoro-1-butene-1,4-sultone, 24-Fluoro-1-butene-1,4-sult -sultone, 1-fluoro-2-butene-1,4-sultone, 2-fluoro-2-butene-1,4-sultone, 3-fluoro-2-butene-1,4-sultone, 4-fluoro-2-butene-1,4-sultone, 1,3-propene sultone, 1-fluoro-3-butene-1,4-sultone, 2-fluoro-3-butene-1,4-sultone, 3-fluoro-3-butene-1,4-sultone, 4-fluoro-3-butene-1,4-sultone, 1-methyl-1-butene-1,4-sultone, 2-methyl-1-butene -1,4-sultone, 3-methyl-1-butene-1,4-sultone, 4-methyl-1-butene-1,4-sultone, 1-methyl-2-butene-1,4-sultone, 2-methyl-2-butene-1,4-sultone, 3-methyl-2-butene-1,4-sultone, 4-methyl-2-butene-1,4-sultone, 1-methyl-3-butene-1,4-sultone, 2-methyl-3-butene-1,4-sultone, 3-methyl-3-butene-1,4-sultone, 4-methyl-3-butene-14-sultone, etc.

Among these, 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, and 1-propene-1,3-sultone are more preferably used because they are easily available and can contribute to the formation of a stable coating structure. The content of the cyclic sulfonate ester is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present disclosure, but is preferably 0.001% by mass or more and 3.0% by mass or less with respect to the electrolyte.

When the content of the cyclic sulfonic acid ester is equal to or greater than this lower limit, the nonaqueous electrolyte secondary battery can be provided with a sufficient effect of improving the cycle characteristics. When the content is equal to or less than this upper limit, an increase in the manufacturing cost of the nonaqueous electrolyte secondary battery can be avoided. The content of the cyclic sulfonic acid ester is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and more preferably 2.5% by mass or less, even more preferably 2.0% by mass or less, particularly preferably 1.8% by mass or less.

The electrolyte solution of the present disclosure may further contain polyethylene oxide having a weight average molecular weight of 2000 to 4000 and having —OH, —OCOOH, or —COOH at its terminal.
By containing such a compound, the stability of the electrode interface is improved, and the characteristics of the electrochemical device can be improved.
Examples of the polyethylene oxide include polyethylene oxide monool, polyethylene oxide carboxylic acid, polyethylene oxide diol, polyethylene oxide dicarboxylic acid, polyethylene oxide triol, polyethylene oxide tricarboxylic acid, etc. These may be used alone or in combination of two or more kinds.
Among these, a mixture of polyethylene oxide monol and polyethylene oxide diol, and a mixture of polyethylene carboxylic acid and polyethylene dicarboxylic acid are preferred in terms of improving the properties of the electrochemical device.

If the weight-average molecular weight of the polyethylene oxide is too small, it may be easily decomposed by oxidation.
The weight average molecular weight can be measured in terms of polystyrene by gel permeation chromatography (GPC).

The content of the polyethylene oxide in the electrolyte is preferably 1×10 ⁻⁶ to 1×10 ⁻² mol/kg. If the content of the polyethylene oxide is too high, the characteristics of the electrochemical device may be impaired.
The content of the polyethylene oxide is more preferably 5×10 ⁻⁶ mol/kg or more.

The electrolyte solution of the present disclosure may further contain, as an additive, a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an overcharge inhibitor, or other known auxiliary agents. This can suppress deterioration of the characteristics of the electrochemical device.

The fluorinated saturated cyclic carbonate may be a compound represented by the general formula (A) described above. Among them, fluoroethylene carbonate, difluoroethylene carbonate, monofluoromethylethylene carbonate, trifluoromethylethylene carbonate, and 2,2,3,3,3-pentafluoropropylethylene carbonate (4-(2,2,3,3,3-pentafluoro-propyl)-[1,3]dioxolan-2-one) are preferred. The fluorinated saturated cyclic carbonate may be used alone or in any combination and ratio of two or more kinds.

The content of the fluorinated saturated cyclic carbonate is preferably 0.001 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.1 to 3% by mass, relative to the electrolyte.

Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, and catechol carbonates.

Examples of vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-divinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, 4-fluoro vinylene carbonate, 4-fluoro-5-methyl vinylene carbonate, 4-fluoro-5-phenyl vinylene carbonate, 4-fluoro-5-vinyl vinylene carbonate, 4-allyl-5-fluoro vinylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, methyl vinylene carbonate, and dimethyl vinylene carbonate.

Specific examples of ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ethylene carbonate, 4-allyl-5-ethynyl Examples of such ethylene carbonates include 4,5-diphenylethylene carbonate, 4-phenyl-5-vinylethylene carbonate, 4-allyl-5-phenylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one, and 4-methyl-5-allylethylene carbonate.

Among these, preferred unsaturated cyclic carbonates are vinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate, vinylvinylene carbonate, 4,5-vinylvinylene carbonate, allylvinylene carbonate, 4,5-diallylvinylene carbonate, vinylethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynylethylene carbonate, 4,5-diethynylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, and 4-vinyl-5-ethynylethylene carbonate. Additionally, vinylene carbonate, vinyl ethylene carbonate, and ethynyl ethylene carbonate are particularly preferred because they form more stable interface protective coatings, with vinylene carbonate being the most preferred.

The molecular weight of the unsaturated cyclic carbonate is not particularly limited and may be any value as long as it does not significantly impair the effects of the present disclosure. The molecular weight is preferably 50 or more and 250 or less. Within this range, it is easy to ensure the solubility of the unsaturated cyclic carbonate in the electrolyte solution, and the effects of the present disclosure are easily achieved. The molecular weight of the unsaturated cyclic carbonate is more preferably 80 or more and more preferably 150 or less.

The method for producing the unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production.

The unsaturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

The content of the unsaturated cyclic carbonate is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure. The content of the unsaturated cyclic carbonate is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, based on 100% by mass of the electrolyte. The content is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. If it is within the above range, an electrochemical device using the electrolyte is likely to exhibit a sufficient cycle characteristic improvement effect, and it is also easy to avoid situations such as a decrease in high-temperature storage characteristics, an increase in the amount of gas generated, and a decrease in the discharge capacity retention rate.

As the unsaturated cyclic carbonate, in addition to the above-mentioned non-fluorinated unsaturated cyclic carbonates, fluorinated unsaturated cyclic carbonates can also be suitably used.
The fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom. The number of fluorine atoms in the fluorinated unsaturated cyclic carbonate is not particularly limited as long as it is 1 or more. Among them, the number of fluorine atoms is usually 6 or less, preferably 4 or less, and most preferably 1 or 2.

Examples of fluorinated unsaturated cyclic carbonates include fluorinated vinylene carbonate derivatives, and fluorinated ethylene carbonate derivatives substituted with a substituent having an aromatic ring or a carbon-carbon double bond.

Examples of fluorinated vinylene carbonate derivatives include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, and 4-fluoro-5-vinylvinylene carbonate.

Fluorinated ethylene carbonate derivatives substituted with a substituent having an aromatic ring or a carbon-carbon double bond include 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-arylethylene carbonate, Examples of such ethylene carbonates include 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, and 4,5-difluoro-4-phenylethylene carbonate.

Among these, examples of fluorinated unsaturated cyclic carbonates include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, and 4,4-difluoro-4-vinylethylene carbonate. Carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate are more preferably used because they form a stable interface protective coating.

The molecular weight of the fluorinated unsaturated cyclic carbonate is not particularly limited and may be any as long as it does not significantly impair the effects of the present disclosure. The molecular weight is preferably 50 or more and 500 or less. Within this range, it is easy to ensure the solubility of the fluorinated unsaturated cyclic carbonate in the electrolyte.

The method for producing the fluorinated unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production. The molecular weight is more preferably 100 or more, and more preferably 200 or less.

The fluorinated unsaturated cyclic carbonate may be used alone or in any combination and ratio of two or more kinds. The content of the fluorinated unsaturated cyclic carbonate is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure. The content of the fluorinated unsaturated cyclic carbonate is usually, in 100 mass% of the electrolyte, preferably 0.001 mass% or more, more preferably 0.01 mass% or more, even more preferably 0.1 mass% or more, and preferably 5 mass% or less, more preferably 4 mass% or less, and even more preferably 3 mass% or less. Within this range, an electrochemical device using the electrolyte is likely to exhibit a sufficient cycle characteristic improvement effect, and it is also easy to avoid situations such as a decrease in high-temperature storage characteristics, an increase in gas generation, and a decrease in discharge capacity retention rate.

The electrolyte solution of the present disclosure may contain a compound having a triple bond. The type of the compound is not particularly limited as long as the compound has one or more triple bonds in the molecule.
Specific examples of the compound having a triple bond include the following compounds.
Hydrocarbon compounds such as 1-pentyne, 2-pentyne, 1-hexyne, 2-hexyne, 3-hexyne, 1-heptyne, 2-heptyne, 3-heptyne, 1-octyne, 2-octyne, 3-octyne, 4-octyne, 1-nonyne, 2-nonyne, 3-nonyne, 4-nonyne, 1-dodecyne, 2-dodecyne, 3-dodecyne, 4-dodecyne, 5-dodecyne, phenylacetylene, 1-phenyl-1-propyne, 1-phenyl-2-propyne, 1-phenyl-1-butyne, 4-phenyl-1-butyne, 4-phenyl-1-butyne, 1-phenyl-1-pentyne, 5-phenyl-1-pentyne, 1-phenyl-1-hexyne, 6-phenyl-1-hexyne, diphenylacetylene, 4-ethynyltoluene, and dicyclohexylacetylene;

2-propynyl methyl carbonate, 2-propynyl ethyl carbonate, 2-propynyl propyl carbonate, 2-propynyl butyl carbonate, 2-propynyl phenyl carbonate, 2-propynyl cyclohexyl carbonate, di-2-propynyl carbonate, 1-methyl-2-propynyl methyl carbonate, 1,1-dimethyl-2-propynyl methyl carbonate, 2-butynyl methyl carbonate, 3-butynyl methyl carbonate, 2-pentynyl methyl carbonate Monocarbonates such as 2-butyne-1,4-diol dimethyl dicarbonate, 2-butyne-1,4-diol diethyl dicarbonate, 2-butyne-1,4-diol dipropyl dicarbonate, 2-butyne-1,4-diol dibutyl dicarbonate, 2-butyne-1,4-diol diphenyl dicarbonate, and 2-butyne-1,4-diol dicyclohexyl dicarbonate;

2-propynyl acetate, 2-propynyl propionate, 2-propynyl butyrate, 2-propynyl benzoate, 2-propynyl cyclohexylcarboxylate, 1,1-dimethyl-2-propynyl acetate, 1,1-dimethyl-2-propynyl propionate, 1,1-dimethyl-2-propynyl butyrate, 1,1-dimethyl-2-propynyl benzoate, 1,1-dimethyl-2-propynyl cyclohexylcarboxylate, 2-butynyl acetate, 3-butynyl acetate, 2-pentynyl acetate, 3-pentynyl acetate, 4-pentynyl acetate, methyl acrylate, Ethyl acrylate, propyl acrylate, vinyl acrylate, 2-propenyl acrylate, 2-butenyl acrylate, 3-butenyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, vinyl methacrylate, 2-propenyl methacrylate, 2-butenyl methacrylate, 3-butenyl methacrylate, methyl 2-propynoate, ethyl 2-propynoate, propyl 2-propynoate, vinyl 2-propynoate, 2-propenyl 2-propynoate, 2-butenyl 2-propynoate, 3-butenyl 2-propynoate, 2 methyl 2-butynoate, ethyl 2-butynoate, propyl 2-butynoate, vinyl 2-butynoate, 2-propenyl 2-butynoate, 2-butenyl 2-butynoate, 3-butenyl 2-butynoate, methyl 3-butynoate, ethyl 3-butynoate, propyl 3-butynoate, vinyl 3-butynoate, 2-propenyl 3-butynoate, 2-butenyl 3-butynoate, 3-butenyl 3-butynoate, methyl 2-pentynoate, ethyl 2-pentynoate, propyl 2-pentynoate, vinyl 2-pentynoate, 2-propenyl 2-pentynoate, 2-butenyl 2-pentynoate, Monocarboxylic acid esters such as 3-butenyl 2-pentynoate, methyl 3-pentynoate, ethyl 3-pentynoate, propyl 3-pentynoate, vinyl 3-pentynoate, 2-propenyl 3-pentynoate, 2-butenyl 3-pentynoate, 3-butenyl 3-pentynoate, methyl 4-pentynoate, ethyl 4-pentynoate, propyl 4-pentynoate, vinyl 4-pentynoate, 2-propenyl 4-pentynoate, 2-butenyl 4-pentynoate, 3-butenyl 4-pentynoate, fumaric acid esters, methyl trimethylacetate, ethyl trimethylacetate;

Dicarboxylic acid esters such as 2-butyne-1,4-diol diacetate, 2-butyne-1,4-diol dipropionate, 2-butyne-1,4-diol dibutyrate, 2-butyne-1,4-diol dibenzoate, 2-butyne-1,4-diol dicyclohexanecarboxylate, hexahydrobenzo[1,3,2]dioxathiolan-2-oxide (1,2-cyclohexanediol, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, 2,2-dioxide-1,2-oxathiolan-4-yl acetate;

Oxalic acid diesters such as methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, propyl 2-propynyl oxalate, vinyl 2-propynyl oxalate, allyl 2-propynyl oxalate, di-2-propynyl oxalate, 2-butynylmethyl oxalate, 2-butynylethyl oxalate, 2-butynylpropyl oxalate, vinyl 2-butynyl oxalate, allyl 2-butynyl oxalate, di-2-butynyl oxalate, 3-butynylmethyl oxalate, 3-butynylethyl oxalate, 3-butynylpropyl oxalate, vinyl 3-butynyl oxalate, allyl 3-butynyl oxalate, and di-3-butynyl oxalate;

Phosphine oxides such as methyl(2-propynyl)(vinyl)phosphine oxide, divinyl(2-propynyl)phosphine oxide, di(2-propynyl)(vinyl)phosphine oxide, di(2-propenyl)2(-propynyl)phosphine oxide, di(2-propynyl)(2-propenyl)phosphine oxide, di(3-butenyl)(2-propynyl)phosphine oxide, and di(2-propynyl)(3-butenyl)phosphine oxide;

2-propynyl methyl(2-propenyl)phosphinate, 2-propynyl 2-butenyl(methyl)phosphinate, 2-propynyl di(2-propenyl)phosphinate, 2-propynyl di(3-butenyl)phosphinate, 1,1-dimethyl-2-propynyl methyl(2-propenyl)phosphinate, 1,1-dimethyl-2-propynyl 2-butenyl(methyl)phosphinate, 1,1-dimethyl-2-propynyl di(2-propenyl)phosphinate, and Phosphinic acid esters such as 1,1-dimethyl-2-propynyl di(3-butenyl)phosphinate, 2-propenyl methyl(2-propynyl)phosphinate, 3-butenyl methyl(2-propynyl)phosphinate, 2-propenyl di(2-propynyl)phosphinate, 3-butenyl di(2-propynyl)phosphinate, 2-propenyl 2-propenyl (2-propenyl)phosphinate, and 3-butenyl 2-propynyl (2-propenyl)phosphinate;

2-propenylphosphonic acid methyl 2-propynyl, 2-butenylphosphonic acid methyl (2-propynyl), 2-propenylphosphonic acid (2-propynyl) (2-propenyl), 3-butenylphosphonic acid (3-butenyl) (2-propynyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-butenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and 3-butenylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), methyl Phosphonic acid esters such as ethylphosphonic acid (2-propynyl) (2-propenyl), methylphosphonic acid (3-butenyl) (2-propynyl), methylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), methylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), ethylphosphonic acid (2-propynyl) (2-propenyl), ethylphosphonic acid (3-butenyl) (2-propynyl), ethylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and ethylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl);

Phosphate esters such as (methyl)(2-propenyl)(2-propynyl) phosphate, (ethyl)(2-propenyl)(2-propynyl) phosphate, (2-butenyl)(methyl)(2-propynyl) phosphate, (2-butenyl)(ethyl)(2-propynyl) phosphate, (1,1-dimethyl-2-propynyl)(methyl)(2-propenyl) phosphate, (1,1-dimethyl-2-propynyl)(ethyl)(2-propenyl) phosphate, (2-butenyl)(1,1-dimethyl-2-propynyl)(methyl) phosphate, and (2-butenyl)(ethyl)(1,1-dimethyl-2-propynyl) phosphate;

Among these, compounds having an alkynyloxy group are preferred because they form a more stable negative electrode coating in the electrolyte.

Furthermore, compounds such as 2-propynyl methyl carbonate, di-2-propynyl carbonate, 2-butyne-1,4-diol dimethyl dicarbonate, 2-propynyl acetate, 2-butyne-1,4-diol diacetate, methyl 2-propynyl oxalate, and di-2-propynyl oxalate are particularly preferred in terms of improving storage properties.

The above-mentioned compound having a triple bond may be used alone or in any combination and ratio of two or more kinds. There is no limit to the amount of the compound having a triple bond in the entire electrolyte solution of the present disclosure, and it is arbitrary as long as it does not significantly impair the effects of the present disclosure. However, the compound is usually contained in the electrolyte solution of the present disclosure at a concentration of 0.01 mass% or more, preferably 0.05 mass% or more, more preferably 0.1 mass% or more, and usually 5 mass% or less, preferably 3 mass% or less, more preferably 1 mass% or less. When the above range is satisfied, the effects of output characteristics, load characteristics, cycle characteristics, high-temperature storage characteristics, etc. are further improved.

In the electrolyte of the present disclosure, an overcharge inhibitor can be used to effectively prevent the battery from exploding or catching fire when an electrochemical device using the electrolyte is overcharged or otherwise affected.

Overcharge inhibitors include unsubstituted or alkyl group-substituted terphenyl derivatives such as biphenyl, o-terphenyl, m-terphenyl, and p-terphenyl, partial hydrogenation products of unsubstituted or alkyl group-substituted terphenyl derivatives, aromatic compounds such as cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindane, cyclopentylbenzene, cyclohexylbenzene, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, t-butylbenzene, t-amylbenzene, t-hexylbenzene, and anisole; 2-fluorobiphenyl, 4-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, Examples of the aromatic compounds include partially fluorinated compounds of the above aromatic compounds such as hexylfluorobenzene, fluorotoluene, and benzotrifluoride; fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 1,6-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; aromatic acetates such as 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, and phenethylphenyl acetate; aromatic carbonates such as diphenyl carbonate and methylphenyl carbonate, toluene derivatives such as toluene and xylene, and biphenyl derivatives substituted with an unsubstituted or alkyl group, such as 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, and o-cyclohexylbiphenyl. Among these, preferred are aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindane, 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, diphenyl carbonate, and methylphenyl carbonate. These may be used alone or in combination of two or more. When two or more types are used in combination, it is particularly preferable to use a combination of cyclohexylbenzene with t-butylbenzene or t-amylbenzene, or a combination of at least one type selected from oxygen-free aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, and t-amylbenzene with at least one type selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran, in terms of the balance between overcharge prevention properties and high-temperature storage properties.

The electrolyte solution of the present disclosure may further contain a compound (5) represented by general formula (5).

（式中、Ａ^ａ＋は金属イオン、水素イオン又はオニウムイオン。ａは１～３の整数、ｂは１～３の整数、ｐはｂ／ａ、ｎ２０３は１～４の整数、ｎ２０１は０～８の整数、ｎ２０２は０又は１、Ｚ^２０１は遷移金属、周期律表のＩＩＩ族、ＩＶ族又はＶ族の元素。
Ｘ^２０１は、Ｏ、Ｓ、炭素数１～１０のアルキレン基、炭素数１～１０のハロゲン化アルキレン基、炭素数６～２０のアリーレン基又は炭素数６～２０のハロゲン化アリーレン基（アルキレン基、ハロゲン化アルキレン基、アリーレン基、及び、ハロゲン化アリーレン基はその構造中に置換基、ヘテロ原子を持っていてもよく、またｎ２０２が１でｎ２０３が２～４のときにはｎ２０３個のＸ^２０１はそれぞれが結合していてもよい）。
Ｌ^２０１は、ハロゲン原子、シアノ基、炭素数１～１０のアルキル基、炭素数１～１０のハロゲン化アルキル基、炭素数６～２０のアリール基、炭素数６～２０のハロゲン化アリール基（アルキレン基、ハロゲン化アルキレン基、アリーレン基、及び、ハロゲン化アリーレン基はその構造中に置換基、ヘテロ原子を持っていてもよく、またｎ２０１が２～８のときにはｎ２０１個のＬ^２０１はそれぞれが結合して環を形成してもよい）又は－Ｚ^２０３Ｙ^２０３。
Ｙ^２０１、Ｙ^２０２及びＺ^２０３は、それぞれ独立でＯ、Ｓ、ＮＹ^２０４、炭化水素基又はフッ素化炭化水素基。Ｙ^２０３及びＹ^２０４は、それぞれ独立でＨ、Ｆ、炭素数１～１０のアルキル基、炭素数１～１０のハロゲン化アルキル基、炭素数６～２０のアリール基又は炭素数６～２０のハロゲン化アリール基（アルキル基、ハロゲン化アルキル基、アリール基及びハロゲン化アリール基はその構造中に置換基、ヘテロ原子を持っていてもよく、Ｙ^２０３又はＹ^２０４が複数個存在する場合にはそれぞれが結合して環を形成してもよい）。 General formula (5):

(In the formula, A ^a+ represents a metal ion, a hydrogen ion or an onium ion. a represents an integer of 1 to 3, b represents an integer of 1 to 3, p represents b/a, n203 represents an integer of 1 to 4, n201 represents an integer of 0 to 8, n202 represents 0 or 1, and Z ²⁰¹ represents a transition metal or an element of Group III, IV or V of the periodic table.
X ²⁰¹ is O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (the alkylene group, halogenated alkylene group, arylene group, and halogenated arylene group may have a substituent or a heteroatom in the structure, and when n202 is 1 and n203 is 2 to 4, each of the n203 X ²⁰¹ may be bonded).
L ²⁰¹ is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms (an alkylene group, a halogenated alkylene group, an arylene group, and a halogenated arylene group may have a substituent or a heteroatom in the structure, and when n201 is 2 to 8, the n201 L ²⁰¹ may be bonded to each other to form a ring), or -Z ²⁰³ Y ²⁰³ .
Y ²⁰¹ , Y ²⁰² and Z ²⁰³ are each independently O, S, NY ²⁰⁴ , a hydrocarbon group or a fluorinated hydrocarbon group. Y ²⁰³ and Y ²⁰⁴ are each independently H, F, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms or a halogenated aryl group having 6 to 20 carbon atoms (the alkyl group, halogenated alkyl group, aryl group and halogenated aryl group may have a substituent or a hetero atom in the structure, and when a plurality of Y ²⁰³ or Y ²⁰⁴ are present, they may be bonded to each other to form a ring).

Examples of A ^a+ include a lithium ion, a sodium ion, a potassium ion, a magnesium ion, a calcium ion, a barium ion, a cesium ion, a silver ion, a zinc ion, a copper ion, a cobalt ion, an iron ion, a nickel ion, a manganese ion, a titanium ion, a lead ion, a chromium ion, a vanadium ion, a ruthenium ion, a yttrium ion, a lanthanoid ion, an actinoid ion, a tetrabutylammonium ion, a tetraethylammonium ion, a tetramethylammonium ion, a triethylmethylammonium ion, a triethylammonium ion, a pyridinium ion, an imidazolium ion, a hydrogen ion, a tetraethylphosphonium ion, a tetramethylphosphonium ion, a tetraphenylphosphonium ion, a triphenylsulfonium ion, and a triethylsulfonium ion.

When used in applications such as electrochemical devices, A ^a+ is preferably a lithium ion, a sodium ion, a magnesium ion, a tetraalkylammonium ion, or a hydrogen ion, and is particularly preferably a lithium ion. The valence a of the cation of A ^a+ is an integer of 1 to 3. If it is greater than 3, the crystal lattice energy becomes large, causing a problem that it becomes difficult to dissolve in a solvent. Therefore, when solubility is required, 1 is more preferable. The valence b of the anion is also an integer of 1 to 3, and is particularly preferably 1. The constant p representing the ratio of the cation to the anion is inevitably determined by the ratio of the valences of the two, b/a.

Next, the ligand portion of the general formula (5) will be described. In this specification, the organic or inorganic portion bonded to Z ²⁰¹ in the general formula (5) is called a ligand.

Z ²⁰¹ is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb, and more preferably Al, B or P.

X ²⁰¹ represents O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups and arylene groups may have a substituent or a heteroatom in their structure. Specifically, instead of hydrogen on the alkylene group and arylene group, a halogen atom, a linear or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group may be substituted, or instead of carbon on the alkylene and arylene, nitrogen, sulfur, or oxygen may be introduced. When n202 is 1 and n203 is 2 to 4, n203 X ²⁰¹ may be bonded to each other. An example of such a ligand is ethylenediaminetetraacetic acid.

L ²⁰¹ represents a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms, or -Z ²⁰³ Y ²⁰³ (Z ²⁰³ and Y ²⁰³ will be described later). The alkyl group and aryl group here may also have a substituent or a heteroatom in the structure, similar to X ²⁰¹ , and when n201 is 2 to 8, n201 L ²⁰¹ may be bonded to each other to form a ring. L ²⁰¹ is preferably a fluorine atom or a cyano group. This is because in the case of a fluorine atom, the solubility and dissociation degree of the salt of the anion compound are improved, and the ionic conductivity is improved accordingly. In addition, the oxidation resistance is improved, and the occurrence of side reactions can be suppressed.

Y ²⁰¹ , Y ²⁰² and Z ²⁰³ each independently represent O, S, NY ²⁰⁴ , a hydrocarbon group or a fluorinated hydrocarbon group. Y ²⁰¹ and Y ²⁰² are preferably O, S or NY ²⁰⁴ , more preferably O. The characteristic of compound (5) is that Y ²⁰¹ and Y ²⁰² are bonded to Z ²⁰¹ in the same ligand, so that these ligands form a chelate structure with Z ^201. Due to the effect of this chelate, the heat resistance, chemical stability and hydrolysis resistance of this compound are improved. The constant n202 in this ligand is 0 or 1, and in particular, when it is 0, the chelate ring becomes a 5-membered ring, so that the chelate effect is most strongly exerted and stability is increased, which is preferable.
In this specification, a fluorinated hydrocarbon group is a group in which at least one hydrogen atom of a hydrocarbon group has been substituted with a fluorine atom.

Y ²⁰³ and Y ²⁰⁴ are each independently H, F, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms. These alkyl and aryl groups may have a substituent or a heteroatom in the structure. When a plurality of Y ²⁰³ or Y ²⁰⁴ are present, they may be bonded to each other to form a ring.

The constant n203 related to the number of ligands described above is an integer from 1 to 4, preferably 1 or 2, and more preferably 2. The constant n201 related to the number of ligands described above is an integer from 0 to 8, preferably an integer from 0 to 4, and more preferably 0, 2, or 4. It is further preferred that when n203 is 1, n201 is 2, and when n203 is 2, n201 is 0.

In general formula (5), the alkyl group, halogenated alkyl group, aryl group, and halogenated aryl group also include those having other functional groups such as branches, hydroxyl groups, and ether bonds.

（式中、Ａ^ａ＋、ａ、ｂ、ｐ、ｎ２０１、Ｚ^２０１及びＬ^２０１は上述したとおり）で示される化合物、又は、一般式：

（式中、Ａ^ａ＋、ａ、ｂ、ｐ、ｎ２０１、Ｚ^２０１及びＬ^２０１は上述したとおり）で示される化合物であることが好ましい。 Compound (5) has the general formula:

(wherein A ^a+ , a, b, p, n 201, Z ²⁰¹ and L ²⁰¹ are as defined above), or a compound represented by the general formula:

(wherein A ^a+ , a, b, p, n 201, Z ²⁰¹ and L ²⁰¹ are as defined above) are preferred.

で示されるリチウムビス（オキサラト）ボレート（ＬＩＢＯＢ）、下記式：

で示されるリチウムジフルオロオキサラトボレート（ＬＩＤＦＯＢ）、下記式：

で示されるリチウムジフルオロオキサラトホスファナイト（ＬＩＤＦＯＰ）、下記式：

で示されるリチウムテトラフルオロオキサラトホスファナイト（ＬＩＴＦＯＰ）、下記式：

で示されるリチウムビス（オキサラト）ジフルオロホスファナイト等が挙げられる。 Compound (5) includes lithium oxalatoborate salts, and is represented by the following formula:

Lithium bis(oxalato)borate (LIBOB) represented by the following formula:

Lithium difluorooxalatoborate (LIDFOB) represented by the following formula:

Lithium difluorooxalatophosphanite (LIDFOP) represented by the following formula:

Lithium tetrafluorooxalatophosphanite (LITFOP) represented by the following formula:

Examples of the lithium bis(oxalato)difluorophosphanite include those represented by the following formula:

Compound (5) also includes dicarboxylic acid complex salts in which the central complex element is boron, such as lithium bis(malonato)borate, lithium difluoro(malonato)borate, lithium bis(methylmalonato)borate, lithium difluoro(methylmalonato)borate, lithium bis(dimethylmalonato)borate, and lithium difluoro(dimethylmalonato)borate.

Examples of compound (5) also include dicarboxylic acid complex salts in which the central complex element is phosphorus, such as lithium tris(oxalato)phosphate, lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate, lithium tris(methylmalonato)phosphate, lithium difluorobis(methylmalonato)phosphate, lithium tetrafluoro(methylmalonato)phosphate, lithium tris(dimethylmalonato)phosphate, lithium difluorobis(dimethylmalonato)phosphate, and lithium tetrafluoro(dimethylmalonato)phosphate.

Compound (5) also includes dicarboxylic acid complex salts in which the central element of the complex is aluminum, such as LiAl(C ₂ O ₄ ) ₂ and LiAlF ₂ (C ₂ O ₄ ).

Among these, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate are more preferably used because of their ease of availability and their ability to contribute to the formation of a stable coating structure.
The compound (5) is particularly preferably lithium bis(oxalato)borate.

The content of compound (5) is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and is preferably 10% by mass or less, and more preferably 3% by mass or less, relative to the solvent, since this provides even better cycle characteristics.

The electrolyte used in the present disclosure may contain a carboxylic acid anhydride (excluding compound (2)). As the carboxylic acid anhydride, compound (6) represented by the following general formula (6) is preferable. The method for producing the carboxylic acid anhydride is not particularly limited, and it is possible to produce the carboxylic acid anhydride by any known method.
General formula (6):

（一般式（６）中、Ｒ^６１、Ｒ^６２はそれぞれ独立に、置換基を有していてもよい、炭素数１以上１５以下の炭化水素基を表す。）

(In formula (6), R ⁶¹ and R ⁶² each independently represent a hydrocarbon group having 1 to 15 carbon atoms which may have a substituent.)

R ⁶¹ and R ⁶² are not particularly limited in type as long as they are monovalent hydrocarbon groups. For example, they may be aliphatic hydrocarbon groups or aromatic hydrocarbon groups, or may be groups in which an aliphatic hydrocarbon group and an aromatic hydrocarbon group are bonded. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or may contain an unsaturated bond (carbon-carbon double bond or carbon-carbon triple bond). The aliphatic hydrocarbon group may be chain-like or cyclic, and if chain-like, it may be linear or branched. Furthermore, it may be a group in which a chain and a ring are bonded. R ⁶¹ and R ⁶² may be the same or different from each other.

In addition, when the hydrocarbon group of R ⁶¹ and R ⁶² has a substituent, the type of the substituent is not particularly limited as long as it is not contrary to the purpose of the present disclosure, but examples include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom, and preferably fluorine atom. In addition, examples of the substituent other than halogen atom include substituents having functional groups such as ester group, cyano group, carbonyl group, and ether group, and preferably cyano group and carbonyl group. The hydrocarbon group of R ⁶¹ and R ⁶² may have only one of these substituents, or may have two or more. When it has two or more substituents, those substituents may be the same or different from each other.

The carbon number of each of the hydrocarbon groups of R ⁶¹ and R ⁶² is usually 1 or more, and usually 15 or less, preferably 12 or less, more preferably 10 or less, and even more preferably 9 or less. When R ⁶¹ and R ⁶² are bonded to each other to form a divalent hydrocarbon group, the carbon number of the divalent hydrocarbon group is usually 1 or more, and usually 15 or less, preferably 13 or less, more preferably 10 or less, and even more preferably 8 or less. When the hydrocarbon groups of R ⁶¹ and R ⁶² have a substituent containing a carbon atom, it is preferable that the total carbon number of R ⁶¹ and R ⁶² including the substituent satisfies the above range.

Next, specific examples of the above compound (6) will be described. In the following examples, "analog" refers to an acid anhydride obtained by replacing a part of the structure of the exemplified acid anhydride with another structure within the scope of the present disclosure, such as a dimer, trimer, or tetramer composed of multiple acid anhydrides, or structural isomers such as those having the same number of carbon atoms in the substituent but a branched chain, or those in which the substituent is bonded to the acid anhydride at a different site, etc.

First, specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are the same are listed below.

Specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are chain alkyl groups include acetic anhydride, propionic anhydride, butanoic anhydride, 2-methylpropionic anhydride, 2,2-dimethylpropionic anhydride, 2-methylbutanoic anhydride, 3-methylbutanoic anhydride, 2,2-dimethylbutanoic anhydride, 2,3-dimethylbutanoic anhydride, 3,3-dimethylbutanoic anhydride, 2,2,3-trimethylbutanoic anhydride, 2,3,3-trimethylbutanoic anhydride, 2,2,3,3-tetramethylbutanoic anhydride, 2-ethylbutanoic anhydride, and the like, and their analogs.

Specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are cyclic alkyl groups include cyclopropanecarboxylic anhydride, cyclopentanecarboxylic anhydride, cyclohexanecarboxylic anhydride, and analogs thereof.

Specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are alkenyl groups include acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 2,3,3-trimethylacrylic anhydride, 2-phenylacrylic anhydride, 3-phenylacrylic anhydride, 2,3-diphenylacrylic anhydride, 3,3-diphenylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, 2,2-dimethyl-3-butenoic anhydride, 3-methyl-3-enoic anhydride, 2-methyl-3-methyl-3-butenoic anhydride, 2,2-dimethyl-3-methyl-3-butenoic anhydride, 3-pentenoic anhydride, 4-pentenoic anhydride, 2-cyclopentenecarboxylic anhydride, 3-cyclopentenecarboxylic anhydride, 4-cyclopentenecarboxylic anhydride, and the like, and analogs thereof.

Specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are alkynyl groups include propynoic anhydride, 3-phenylpropynoic anhydride, 2-butynoic anhydride, 2-pentynoic anhydride, 3-butynoic anhydride, 3-pentynoic anhydride, 4-pentynoic anhydride, and analogs thereof.

Specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are aryl groups include benzoic anhydride, 4-methylbenzoic anhydride, 4-ethylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 2-methylbenzoic anhydride, 2,4,6-trimethylbenzoic anhydride, 1-naphthalenecarboxylic anhydride, 2-naphthalenecarboxylic anhydride, and analogs thereof.

In addition, as examples of acid anhydrides in which R ⁶¹ and R ⁶² are substituted with halogen atoms, examples of acid anhydrides mainly substituted with fluorine atoms are given below, but acid anhydrides obtained by substituting some or all of these fluorine atoms with chlorine atoms, bromine atoms, or iodine atoms are also included in the exemplified compounds.

Examples of acid anhydrides in which R ⁶¹ and R ⁶² are chain alkyl groups substituted with halogen atoms include fluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, 2-fluoropropionic anhydride, 2,2-difluoropropionic anhydride, 2,3-difluoropropionic anhydride, 2,2,3-trifluoropropionic anhydride, 2,3,3-trifluoropropionic anhydride, 2,2,3,3-tetrapropionic anhydride, 2,3,3,3-tetrapropionic anhydride, 3-fluoropropionic anhydride, 3,3-difluoropropionic anhydride, 3,3,3-trifluoropropionic anhydride, perfluoropropionic anhydride, and analogs thereof.

Examples of acid anhydrides in which R ⁶¹ and R ⁶² are cyclic alkyl groups substituted with halogen atoms include 2-fluorocyclopentane carboxylic anhydride, 3-fluorocyclopentane carboxylic anhydride, 4-fluorocyclopentane carboxylic anhydride, and analogs thereof.

Examples of acid anhydrides in which R ⁶¹ and R ⁶² are alkenyl groups substituted with halogen atoms include 2-fluoroacrylic anhydride, 3-fluoroacrylic anhydride, 2,3-difluoroacrylic anhydride, 3,3-difluoroacrylic anhydride, 2,3,3-trifluoroacrylic anhydride, 2-(trifluoromethyl)acrylic anhydride, 3-(trifluoromethyl)acrylic anhydride, 2,3-bis(trifluoromethyl)acrylic anhydride, 2,3,3-tris(trifluoromethyl)acrylic anhydride, 2-(4- fluorophenyl)acrylic anhydride, 3-(4-fluorophenyl)acrylic anhydride, 2,3-bis(4-fluorophenyl)acrylic anhydride, 3,3-bis(4-fluorophenyl)acrylic anhydride, 2-fluoro-3-butenoic anhydride, 2,2-difluoro-3-butenoic anhydride, 3-fluoro-2-butenoic anhydride, 4-fluoro-3-butenoic anhydride, 3,4-difluoro-3-butenoic anhydride, 3,3,4-trifluoro-3-butenoic anhydride, and the like, and their analogs.

Examples of acid anhydrides in which R ⁶¹ and R ⁶² are alkynyl groups substituted with halogen atoms include 3-fluoro-2-propynoic anhydride, 3-(4-fluorophenyl)-2-propynoic anhydride, 3-(2,3,4,5,6-pentafluorophenyl)-2-propynoic anhydride, 4-fluoro-2-butynoic anhydride, 4,4-difluoro-2-butynoic anhydride, 4,4,4-trifluoro-2-butynoic anhydride, and analogs thereof.

Examples of acid anhydrides in which R ⁶¹ and R ⁶² are aryl groups substituted with halogen atoms include 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, 4-trifluoromethylbenzoic anhydride, and analogs thereof.

Examples of acid anhydrides in which R ⁶¹ and R ⁶² have a substituent having a functional group such as an ester, a nitrile, a ketone, or an ether include methoxyformic anhydride, ethoxyformic anhydride, methyloxalic anhydride, ethyloxalic anhydride, 2-cyanoacetic anhydride, 2-oxopropionic anhydride, 3-oxobutanoic anhydride, 4-acetylbenzoic anhydride, methoxyacetic anhydride, 4-methoxybenzoic anhydride, and analogs thereof.

Next, specific examples of acid anhydrides in which R ⁶¹ and R ⁶² are different from each other are listed below.

Although all combinations of the above-mentioned examples and analogues thereof are possible for R ⁶¹ and R ⁶² , representative examples are given below.

Examples of combinations of chain alkyl groups include acetic acid propionic anhydride, acetic acid butanoic anhydride, butanoic acid propionic anhydride, and acetic acid 2-methylpropionic anhydride.

Examples of combinations of linear alkyl groups and cyclic alkyl groups include acetic acid cyclopentanoic anhydride, acetic acid cyclohexanoic anhydride, and cyclopentanoic acid propionic anhydride.

Examples of combinations of linear alkyl groups and alkenyl groups include acetic acid acrylic anhydride, acetic acid 3-methylacrylic anhydride, acetic acid 3-butenoic anhydride, acrylic acid propionic anhydride, etc.

Examples of combinations of chain alkyl groups and alkynyl groups include acetic acid propynoic anhydride, acetic acid 2-butynoic anhydride, acetic acid 3-butynoic anhydride, acetic acid 3-phenylpropynoic anhydride, propionic acid propynoic anhydride, etc.

Examples of combinations of linear alkyl groups and aryl groups include acetic acid benzoic anhydride, acetic acid 4-methylbenzoic anhydride, acetic acid 1-naphthalenecarboxylic anhydride, and benzoic acid propionic anhydride.

Examples of combinations of chain alkyl groups and hydrocarbon groups having functional groups include acetic acid fluoroacetic anhydride, acetic acid trifluoroacetic anhydride, acetic acid 4-fluorobenzoic anhydride, fluoroacetic acid propionic anhydride, acetic acid alkyl oxalic anhydride, acetic acid 2-cyanoacetic anhydride, acetic acid 2-oxopropionic anhydride, acetic acid methoxyacetic anhydride, and methoxyacetic acid propionic anhydride.

Examples of combinations of cyclic alkyl groups include cyclopentanoic acid and cyclohexanoic acid anhydride.

Examples of combinations of cyclic alkyl groups and alkenyl groups include acrylic acid cyclopentanoic anhydride, 3-methylacrylic acid cyclopentanoic anhydride, 3-butenoic acid cyclopentanoic anhydride, acrylic acid cyclohexanoic anhydride, etc.

Examples of combinations of cyclic alkyl groups and alkynyl groups include propynoic acid cyclopentanoic acid anhydride, 2-butynoic acid cyclopentanoic acid anhydride, propynoic acid cyclohexanoic acid anhydride, etc.

Examples of combinations of cyclic alkyl groups and aryl groups include benzoic acid cyclopentanoic acid anhydride, 4-methylbenzoic acid cyclopentanoic acid anhydride, and benzoic acid cyclohexanoic acid anhydride.

Examples of combinations of a cyclic alkyl group and a hydrocarbon group having a functional group include cyclopentanoic fluoroacetic anhydride, cyclopentanoic trifluoroacetic anhydride, cyclopentanoic 2-cyanoacetic anhydride, cyclopentanoic methoxyacetic anhydride, and cyclohexanoic fluoroacetic anhydride.

Examples of combinations of alkenyl groups include acrylic acid 2-methylacrylic anhydride, acrylic acid 3-methylacrylic anhydride, acrylic acid 3-butenoic anhydride, 2-methylacrylic acid 3-methylacrylic anhydride, etc.

Examples of combinations of alkenyl and alkynyl groups include acrylic acid propynoic anhydride, acrylic acid 2-butynoic anhydride, and 2-methylacrylic acid propynoic anhydride.

Examples of combinations of alkenyl and aryl groups include acrylic acid benzoic anhydride, acrylic acid 4-methylbenzoic anhydride, 2-methylacrylic acid benzoic anhydride, etc.

Examples of combinations of alkenyl groups and hydrocarbon groups having functional groups include acrylic acid fluoroacetic anhydride, acrylic acid trifluoroacetic anhydride, acrylic acid 2-cyanoacetic anhydride, acrylic acid methoxyacetic anhydride, 2-methylacrylic acid fluoroacetic anhydride, etc.

Examples of combinations of alkynyl groups include propynoic acid 2-butynoic anhydride, propynoic acid 3-butynoic anhydride, 2-butynoic acid 3-butynoic anhydride, etc.

Examples of combinations of alkynyl and aryl groups include benzoic acid propynoic anhydride, 4-methylbenzoic acid propynoic anhydride, and benzoic acid 2-butynoic anhydride.

Examples of combinations of alkynyl groups and hydrocarbon groups having functional groups include propynoic acid fluoroacetic anhydride, propynoic acid trifluoroacetic anhydride, propynoic acid 2-cyanoacetic anhydride, propynoic acid methoxyacetic anhydride, and 2-butynoic acid fluoroacetic anhydride.

Examples of combinations of aryl groups include benzoic acid 4-methylbenzoic acid anhydride, benzoic acid 1-naphthalenecarboxylic acid anhydride, and 4-methylbenzoic acid 1-naphthalenecarboxylic acid anhydride.

Examples of combinations of aryl groups and hydrocarbon groups having functional groups include benzoic acid fluoroacetic anhydride, benzoic acid trifluoroacetic anhydride, benzoic acid 2-cyanoacetic anhydride, benzoic acid methoxyacetic anhydride, and 4-methylbenzoic acid fluoroacetic anhydride.

Examples of combinations of hydrocarbon groups having functional groups include fluoroacetic acid trifluoroacetic anhydride, fluoroacetic acid 2-cyanoacetic anhydride, fluoroacetic acid methoxyacetic anhydride, trifluoroacetic acid 2-cyanoacetic anhydride, etc.

Among the acid anhydrides forming the above chain structure, preferred are acetic anhydride, propionic anhydride, 2-methylpropionic anhydride, cyclopentane carboxylic anhydride, cyclohexane carboxylic anhydride, etc., acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, propynoic anhydride, 2-butynoic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, trifluoroacetic anhydride, 3,3,3-trifluoroacetic anhydride, 4-tert-butylbenzoic ... fluoropropionic anhydride, 2-(trifluoromethyl)acrylic anhydride, 2-(4-fluorophenyl)acrylic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride, and more preferably acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride.

These compounds are preferable because they can appropriately form bonds with lithium oxalate salts to form a coating with excellent durability, thereby improving charge/discharge rate characteristics, input/output characteristics, and impedance characteristics, particularly after durability tests.

The molecular weight of the carboxylic acid anhydride is not limited and may be any value as long as it does not significantly impair the effects of the present disclosure, but is usually 90 or more, preferably 95 or more, and usually 300 or less, preferably 200 or less. When the molecular weight of the carboxylic acid anhydride is within the above range, the increase in the viscosity of the electrolyte can be suppressed, and the film density can be optimized, thereby appropriately improving durability.

The method for producing the carboxylic acid anhydride is not particularly limited, and any known method can be selected for production. The nonaqueous electrolyte solution of the present disclosure may contain any one of the carboxylic acid anhydrides described above, or may contain two or more of them in any combination and ratio.

In addition, there is no particular limit to the content of the carboxylic acid anhydride in the electrolyte solution of the present disclosure, and it can be any amount as long as it does not significantly impair the effects of the present disclosure. However, it is desirable to include the carboxylic acid anhydride in the electrolyte solution of the present disclosure at a concentration of usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less. When the content of the carboxylic acid anhydride is within the above range, the effect of improving cycle characteristics is easily manifested, and the reactivity is favorable, so that the battery characteristics are easily improved.

Other known auxiliary agents can be used in the electrolyte solution of the present disclosure, such as hydrocarbon compounds such as pentane, heptane, octane, nonane, decane, cycloheptane, benzene, furan, naphthalene, 2-phenylbicyclohexyl, cyclohexane, 2,4,8,10-tetraoxaspiro[5.5]undecane, and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane;
Fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene, benzotrifluoride, monofluorobenzene, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-4-tert-butylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-2-cyclohexylbenzene, and fluorinated biphenyls;
Carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, and methoxyethyl-methyl carbonate;
Ether compounds such as dioxolane, dioxane, 2,5,8,11-tetraoxadodecane, 2,5,8,11,14-pentaoxapentadecane, ethoxymethoxyethane, trimethoxymethane, glyme, and ethyl monoglyme;
Ketone compounds such as dimethyl ketone, diethyl ketone, and 3-pentanone;
Acid anhydrides such as 2-allyl succinic anhydride;
Ester compounds such as dimethyl oxalate, diethyl oxalate, ethyl methyl oxalate, di(2-propynyl) oxalate, methyl 2-propynyl oxalate, dimethyl succinate, di(2-propynyl) glutarate, methyl formate, ethyl formate, 2-propynyl formate, 2-butyne-1,4-diyl diformate, 2-propynyl methacrylate, and dimethyl malonate;
Amide compounds such as acetamide, N-methylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide;
Ethylene sulfate, vinylene sulfate, ethylene sulfite, methyl fluorosulfonate, ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, sulfolene, diphenyl sulfone, N,N-dimethylmethanesulfonamide, N,N-diethylmethanesulfonamide, methyl vinylsulfonate, ethyl vinylsulfonate, allyl vinylsulfonate, propargyl vinylsulfonate, methyl allylsulfonate, ethyl allylsulfonate, allyl allylsulfonate, propargyl allylsulfonate, 1,2-bis(vinylsulfonyloxy)ethane, propanedisulfonic anhydride, sulfobutyric anhydride, sulfobenzoic anhydride, sulfopropionic anhydride, ethanedisulfonic anhydride, methylenemethanedisulfonate, 2-propynyl methanesulfonate, pentenesulfite, pentafluorophenylmethanesulfonate, propylene sulfate, propylene sulfite, propane sultone, butylene sulfite, butane-2,3-diyl dimethanesulfonate, 2-butyne-1,4-diyl dimethanesulfonate, 2-propynyl vinylsulfonate, bis(2-vinylsulfonylethyl)ether, 5-vinyl-hexahydro-1,3,2-benzodioxathiol-2-oxide, 2-(methanesulfonyloxy)propionate 2-propynyl, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxy sulfur-containing compounds such as 3-sulfo-propionic anhydride trimethylenemethane disulfonate 2-methyltetrahydrofuran, trimethylenemethane disulfonate, tetramethylene sulfoxide, dimethylenemethane disulfonate, difluoroethyl methyl sulfone, divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, ethylene bis(methyl sulfonate), ethylene bis(ethyl sulfonate), ethylene sulfate, and thiophene 1-oxide;
Nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide, nitromethane, nitroethane, and ethylenediamine;
Trimethyl phosphite, triethyl phosphite, triphenyl phosphite, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl vinylphosphonate, diethyl vinylphosphonate, ethyl diethylphosphonoacetate, methyl dimethylphosphinate, ethyl diethylphosphinate, trimethylphosphine oxide, triethylphosphine oxide, bis(2,2-difluoroethyl) phosphate 2,2,2-trifluoroethyl, bis(2,2,3,3-tetrafluoroethyl)phosphate 2,2,2-trifluoroethyl phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate, bis(2,2,2-trifluoroethyl)ethyl phosphate, bis(2,2,2-trifluoroethyl)2,2-difluoroethyl phosphate, bis(2,2,2-trifluoroethyl)2,2,3,3-tetrafluoropropyl phosphate, tributyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, tris(1,1,1,3,3,3-hexafluoropropan-2-yl)phosphate, trioctyl phosphate, 2-phenyl phosphate nylphenyldimethyl, 2-phenylphenyldiethyl phosphate, (2,2,2-trifluoroethyl)(2,2,3,3-tetrafluoropropyl)methyl phosphate, methyl 2-(dimethoxyphosphoryl)acetate, methyl 2-(dimethylphosphoryl)acetate, methyl 2-(diethoxyphosphoryl)acetate, methyl 2-(diethylphosphoryl)acetate, methyl methylenebisphosphonate, ethyl methylenebisphosphonate, methyl ethylenebisphosphonate, ethyl ethylenebisphosphonate, methyl butylenebisphosphonate phosphorus-containing compounds such as ethyl butylene bisphosphonate, 2-propynyl 2-(dimethoxyphosphoryl) acetate, 2-propynyl 2-(dimethylphosphoryl) acetate, 2-propynyl 2-(diethoxyphosphoryl) acetate, 2-propynyl 2-(diethylphosphoryl) acetate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(trimethoxysilyl) phosphate, tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(trimethoxysilyl) phosphite, and trimethylsilyl polyphosphate;
boron-containing compounds such as tris(trimethylsilyl) borate and tris(trimethoxysilyl) borate;
silane compounds such as dimethoxyaluminoxytrimethoxysilane, diethoxyaluminoxytriethoxysilane, dipropoxyaluminoxytriethoxysilane, dibutoxyaluminoxytrimethoxysilane, dibutoxyaluminoxytriethoxysilane, titanium tetrakis(trimethylsiloxide), titanium tetrakis(triethylsiloxide), and tetramethylsilane;
These may be used alone or in combination of two or more. By adding these auxiliary agents, the capacity retention characteristics and cycle characteristics after high-temperature storage can be improved.
Of the other auxiliaries, phosphorus-containing compounds are preferred, with tris(trimethylsilyl) phosphate and tris(trimethylsilyl) phosphite being preferred.

The amount of the other auxiliary agent is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present disclosure. The amount of the other auxiliary agent is preferably 0.01% by mass or more and 5% by mass or less in 100% by mass of the electrolyte. Within this range, the effect of the other auxiliary agent is easily exerted, and it is easy to avoid a situation in which the battery characteristics such as high-load discharge characteristics are deteriorated. The amount of the other auxiliary agent is more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and more preferably 3% by mass or less, even more preferably 1% by mass or less.

The electrolyte solution of the present disclosure may further contain additives such as cyclic and chain carboxylic acid esters, ether compounds, nitrogen-containing compounds, boron-containing compounds, organosilicon-containing compounds, flame-retardant (flame-retardant) agents, surfactants, high-dielectric additives, cycle property and rate property improvers, sulfone-based compounds, etc., within the scope of the present disclosure that does not impair the effects of the present disclosure.

The above-mentioned cyclic carboxylic acid esters include those having a total of 3 to 12 carbon atoms in their structural formula. Specific examples include gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone, epsilon-caprolactone, and 3-methyl-γ-butyrolactone. Among these, gamma-butyrolactone is particularly preferred from the viewpoint of improving the characteristics of electrochemical devices due to the improved degree of lithium ion dissociation.

The amount of the cyclic carboxylic acid ester as an additive is usually preferably 0.1% by mass or more, more preferably 1% by mass or more, based on 100% by mass of the solvent. This range improves the electrical conductivity of the electrolyte and makes it easier to improve the large-current discharge characteristics of the electrochemical device. In addition, the amount of the cyclic carboxylic acid ester is preferably 10% by mass or less, more preferably 5% by mass or less. By setting an upper limit in this way, the viscosity of the electrolyte is kept in an appropriate range, a decrease in electrical conductivity is avoided, an increase in the negative electrode resistance is suppressed, and the large-current discharge characteristics of the electrochemical device are easily kept in a good range.

Furthermore, as the cyclic carboxylic acid ester, a fluorinated cyclic carboxylic acid ester (fluorine-containing lactone) can also be suitably used. Examples of the fluorine-containing lactone include those represented by the following formula (C):

(wherein, X ¹⁵ to X ²⁰ are the same or different and each is —H, —F, —Cl, —CH ₃ or a fluorinated alkyl group; provided that at least one of X ¹⁵ to X ²⁰ is a fluorinated alkyl group).
Examples of fluorine-containing lactones include those represented by the following formula:

Examples of the fluorinated alkyl group represented by X ¹⁵ to X ²⁰ include -CFH ₂ , -CF ₂ H, -CF ₃ , -CH ₂ CF ₃ , -CF ₂ CF ₃ , -CH ₂ CF ₂ CF ₃ , -CF(CF ₃ ) ₂ and the like, of which -CH ₂ CF ₃ and -CH ₂ CF ₂ CF ₃ are preferred from the viewpoints of high oxidation resistance and safety improvement effect.

When at least one of X ¹⁵ to X ²⁰ is a fluorinated alkyl group, -H, -F, -Cl, -CH ₃ or a fluorinated alkyl group may be substituted at only one position of X ¹⁵ to X ²⁰ or at multiple positions thereof, preferably 1 to 3 positions, more preferably 1 to 2 positions, from the viewpoint of good solubility of the electrolyte salt.

The substitution position of the fluorinated alkyl group is not particularly limited, but in terms of good synthesis yield, it is preferable that X ¹⁷ and/or X ¹⁸ , particularly X ¹⁷ or X ¹⁸ , is a fluorinated alkyl group, especially -CH ₂ CF ₃ or -CH ₂ CF ₂ CF _3. X ¹⁵ to X ²⁰ other than the fluorinated alkyl group are -H, -F, -Cl or CH ₃ , and in terms of good solubility of the electrolyte salt, -H is particularly preferred.

In addition to those represented by the above formula, fluorine-containing lactones include, for example, those represented by the following formula (D):

(In the formula, either one of A and B is CX ²²⁶ X ²²⁷ (X ²²⁶ and X ²²⁷ are the same or different and each is -H, -F, -Cl, -CF ₃ , -CH ₃ or an alkylene group in which a hydrogen atom may be substituted with a halogen atom and which may contain a heteroatom in the chain), and the other is an oxygen atom; Rf ¹² is a fluorinated alkyl group or a fluorinated alkoxy group which may have an ether bond; X ²²¹ and X ²²² are the same or different and each is -H, -F, -Cl, -CF ₃ or CH ₃ ; X ²²³ to X ²²⁵ are the same or different and each is -H, -F, -Cl or an alkyl group in which a hydrogen atom may be substituted with a halogen atom and which may contain a heteroatom in the chain; n=0 or 1)
Also included are fluorine-containing lactones represented by the following formula:

The fluorine-containing lactone represented by formula (D) is represented by the following formula (E):

(In the formula, A, B, Rf ¹² , X ²²¹ , X ²²² and X ²²³ are the same as in formula (D).
A five-membered ring structure represented by the following formula (F):

(In the formula, Rf ¹² , X ²²¹ , X ²²² , X ²²³ , X ²²⁶ and X ²²⁷ are the same as in formula (D).
and a fluorine-containing lactone represented by the following formula (G):

(In the formula, Rf ¹² , X ²²¹ , X ²²² , X ²²³ , X ²²⁶ and X ²²⁷ are the same as in formula (D).
There is a fluorine-containing lactone represented by the formula:

Among these, the excellent properties of high dielectric constant and high voltage resistance can be particularly exhibited, and the solubility of electrolyte salts and reduction of internal resistance are also favorable, improving the properties of the electrolyte solution in this disclosure.

等が挙げられる。
フッ素化環状カルボン酸エステルを含有させることにより、イオン伝導度の向上、安全性の向上、高温時の安定性向上といった効果が得られる。

etc.
By incorporating a fluorinated cyclic carboxylate, effects such as improved ion conductivity, improved safety, and improved stability at high temperatures can be obtained.

The chain carboxylate esters include those having a total carbon number of 3 to 7 in their structural formula. Specific examples include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isobutyl propionate, n-butyl propionate, methyl butyrate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate.

Among these, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, etc. are preferred in terms of improving ionic conductivity by reducing viscosity.

As the ether compound, a chain ether having 2 to 10 carbon atoms and a cyclic ether having 3 to 6 carbon atoms are preferred.
Examples of chain ethers having 2 to 10 carbon atoms include dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, and diisopropyl ether.

As the ether compound, fluorinated ethers (excluding the fluorine-containing ether compounds (1) and (2)) can also be suitably used.
The fluorinated ether is represented by the following general formula (I):
Rf ³ -O-Rf ⁴ (I)
(In the formula, Rf ³ and Rf ⁴ are the same or different and are an alkyl group having 1 to 10 carbon atoms or a fluorinated alkyl group having 1 to 10 carbon atoms, provided that at least one of Rf ³ and Rf ⁴ is a fluorinated alkyl group.)
The inclusion of the fluorinated ether (I) improves the flame retardancy of the electrolyte solution, and also improves the stability and safety at high temperatures and high voltages.

In the above general formula (I), at least one of Rf ³ and Rf ⁴ may be a fluorinated alkyl group having 1 to 10 carbon atoms, but from the viewpoint of further improving the flame retardancy of the electrolyte and the stability and safety at high temperature and high voltage, it is preferable that Rf ³ and Rf ⁴ are both fluorinated alkyl groups having 1 to 10 carbon atoms. In this case, Rf ³ and Rf ⁴ may be the same or different from each other.
Among these, it is more preferable that Rf ³ and Rf ⁴ are the same or different, Rf ³ is a fluorinated alkyl group having 3 to 6 carbon atoms, and Rf ⁴ is a fluorinated alkyl group having 2 to 6 carbon atoms.

If the total carbon number of ^Rf3 and ^Rf4 is too small, the boiling point of the fluorinated ether becomes too low, and if the carbon number of ^Rf3 or ^Rf4 is too large, the solubility of the electrolyte salt decreases, the compatibility with other solvents begins to be adversely affected, and the viscosity increases, resulting in reduced rate characteristics. When the carbon number of ^Rf3 is 3 or 4 and the carbon number of ^Rf4 is 2 or 3, it is advantageous in terms of excellent boiling point and rate characteristics.

The fluorinated ether (I) preferably has a fluorine content of 40 to 75 mass %. When the fluorine content is in this range, the balance between non-flammability and compatibility is particularly excellent. In addition, this is also preferred in terms of good oxidation resistance and safety.
The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass, and the upper limit is more preferably 70% by mass, and further preferably 66% by mass.
The fluorine content of the fluorinated ether (I) is a value calculated based on the structural formula of the fluorinated ether (I) by {(number of fluorine atoms×19)/molecular weight of the fluorinated ether (I)}×100(%).

Examples of Rf ³ include CF ₃ CF ₂ CH ₂ --, CF ₃ CFHCF ₂ --, HCF ₂ CF ₂ CF ₂ --, HCF ₂ CF ₂ CH ₂ --, CF ₃ CF ₂ CH ₂ CH ₂ --, CF ₃ CFHCF ₂ CH ₂ --, HCF ₂ CF ₂ CF ₂ CF ₂ --, HCF ₂ CF ₂ CF ₂ CH ₂ --, HCF ₂ CF ₂ CH ₂ CH ₂ --, HCF ₂ CF(CF ₃ )CH ₂ --, and the like. Examples of Rf ⁴ include -CH ₂ CF ₂ CF ₃ , -CF ₂ CFHCF ₃ , -CF ₂ CF ₂ CF ₂ H, -CH ₂ CF ₂ CF ₂ H, -CH ₂ CH ₂ CF ₂ CF ₃ , -CH ₂ CF ₂ CFHCF ₃ , -CF ₂ CF ₂ CF ₂ CF ₂ H, -CH ₂ CF ₂ CF ₂ CF ₂ H, -CH ₂ CH ₂ CF ₂ CF ₂ H, -CH ₂ CF(CF ₃ )CF ₂ H, -CF ₂ CF ₂ H, -CH ₂ CF ₂ H, -CF ₂ CH ₃ , and the like.

_{Specific examples of the fluorinated ether ( I ) include , for example , CF3CF2CH2OCF2CF2H , CF3CF2CH2OCF2CFHCF3} , _{C6F13OCH3 , C6F13OC2H5 , C8F17OCH3 , C8F17OC2H5 , CF3CFHCF2CH ( CH3 ) OCF2CFHCF3 , HCF2CF2OCH ( C2H5 ) 2 , HCF2CF2OC4H9 , HCF2CF2OCH2CH ( C2H5 )} ) ₂ , HCF ₂ CF ₂ OCH ₂ CH(CH ₃ ) ₂ , etc.

Among these, those containing HCF ₂ - or CF ₃ CFH- at one or both ends have excellent polarizability and can give a fluorinated ether (I) having a high boiling point. The boiling point of the fluorinated ether (I) is preferably 67 to 120°C, more preferably 80°C or higher, and even more preferably 90°C or higher.

_{Examples of such} fluorinated ethers _{( I ) include one or more of CF3CH2OCF2CFHCF3 , CF3CF2CH2OCF2CFHCF3 , HCF2CF2CH2OCH2CF2CF2CF2H , CF3CFHCF2CH2OCF2CFHCF3 , CF3CF2CH2OCF2CF2CF2H , and the like .}
Among these, at least one _selected from _the group _consisting of _{CF3CF2CH2OCF2CFHCF3} (boiling point 82°C) _{and CF3CF2CH2OCF2CF2CF2H} (boiling point 68°C) is preferred, since it has advantages in terms of a high _boiling point _, compatibility with other solvents, and good _{solubility of} electrolyte salts.

Cyclic ethers having 3 to 6 carbon atoms include 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, metaformaldehyde, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane 2,2,-bis(trifluoromethyl)-1,3-dioxolane, and fluorinated compounds thereof. Among these, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ether are preferred in terms of their high solvation ability for lithium ions and their improved degree of ion dissociation, and dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have low viscosity and provide high ionic conductivity.

The nitrogen-containing compounds include nitriles, fluorine-containing nitriles, carboxylic acid amides, fluorine-containing carboxylic acid amides, sulfonic acid amides, fluorine-containing sulfonic acid amides, acetamides, formamides, and the like. 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxaziridinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide can also be used. However, the nitrile compounds represented by the general formulae (1a), (1b), and (1c) above are not included in the nitrogen-containing compounds.

Examples of the boron-containing compounds include boric acid esters such as trimethyl borate and triethyl borate, boric acid ethers, and alkyl borates.

Examples of the organosilicon-containing compound include (CH ₃ ) ₄ --Si, (CH ₃ ) ₃ --Si--Si(CH ₃ ) ₃ , and silicone oil.

Examples of the flame retardant (fire resistant) agent include phosphate esters and phosphazene compounds. Examples of the phosphate esters include fluorine-containing alkyl phosphate esters, non-fluorine-based alkyl phosphate esters, and aryl phosphate esters. Among these, fluorine-containing alkyl phosphate esters are preferred because they can exert a flame retardant effect in small amounts.

Examples of the phosphazene compounds include methoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, dimethylaminopentafluorocyclotriphosphazene, diethylaminopentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

Specific examples of the fluorine-containing alkyl phosphate ester include the fluorine-containing dialkyl phosphate ester described in JP-A-11-233141, the cyclic alkyl phosphate ester described in JP-A-11-283669, and the fluorine-containing trialkyl phosphate ester.

As the non-combustible (flame retardant) agent, ( _CH3O ) _3P =O _, (CF3CH2O) _{3P =} O, ( _HCF2CH2O ) _{3P = O} , ( _{CF3CF2CH2 ) 3P} =O, ( _{HCF2CF2CH2 ) 3P} =O, and the like are _preferred .

The surfactant may be any of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants, but it is preferable that the surfactant contains a fluorine atom in order to improve cycle characteristics and rate characteristics.

Examples of such a surfactant containing a fluorine atom include a surfactant represented by the following formula (30):
Rf ⁵ COO ^- M ⁺ (30)
(In the formula, Rf ⁵ is a fluorine-containing alkyl group having 3 to 10 carbon atoms which may contain an ether bond; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR' ₃ ⁺ (R' may be the same or different and both are H or an alkyl group having 1 to 3 carbon atoms).
or a fluorine-containing carboxylate represented by the following formula (40):
Rf ⁶ SO ₃ ⁻ M ⁺ (40)
(In the formula, Rf ⁶ is a fluorine-containing alkyl group having 3 to 10 carbon atoms which may contain an ether bond; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR' ₃ ⁺ (R' may be the same or different and both are H or an alkyl group having 1 to 3 carbon atoms).
Preferred is a fluorine-containing sulfonate represented by the following formula:

The content of the surfactant in the electrolyte is preferably 0.01 to 2 mass % because it can reduce the surface tension of the electrolyte without reducing the charge/discharge cycle characteristics.

Examples of the high dielectric additives include sulfolane, methylsulfolane, gamma-butyrolactone, gamma-valerolactone, etc.

Examples of the cycle characteristic and rate characteristic improver include methyl acetate, ethyl acetate, tetrahydrofuran, 1,4-dioxane, etc.

The electrolyte solution of the present disclosure may also be combined with a polymeric material to form a gel-like (plasticized) gel electrolyte solution.

Such polymeric materials include conventionally known polyethylene oxide, polypropylene oxide, and modified products thereof (JP Patent Publication Nos. 8-222270 and 2002-100405); polyacrylate polymers, polyacrylonitrile, fluororesins such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers (JP Patent Publication Nos. 4-506726, 8-507407, and 10-294131); and composites of such fluororesins and hydrocarbon resins (JP Patent Publication Nos. 11-35765 and 11-86630). In particular, it is desirable to use polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers as polymeric materials for gel electrolytes.

In addition, the electrolyte solution of the present disclosure may also contain the ion-conducting compound described in Japanese Patent Application No. 2004-301934.

The ion-conducting compound has the formula (101):
A-(D)-B (101)
[Wherein, D represents formula (201):
-(D1) _n -(FAE) _m -(AE) _p -(Y) _q - (201)
(Wherein, D1 is a compound represented by formula (2a):

(In the formula, Rf is a fluorine-containing ether group which may have a crosslinkable functional group; ^R10 is a group or bond which bonds Rf to the main chain.)
an ether unit having a fluorine-containing ether group in a side chain, represented by the following formula:
FAE is represented by the formula (2b):

(In the formula, Rfa represents a hydrogen atom or a fluorinated alkyl group which may have a crosslinkable functional group; ^R11 represents a group or bond which bonds Rfa to the main chain.)
an ether unit having a fluorinated alkyl group at a side chain, represented by the formula:
AE is a compound represented by the formula (2c):

(In the formula, R ¹³ represents a hydrogen atom, an alkyl group which may have a crosslinkable functional group, an aliphatic cyclic hydrocarbon group which may have a crosslinkable functional group, or an aromatic hydrocarbon group which may have a crosslinkable functional group; R ¹² represents a group or bond which bonds R ¹³ to the main chain.)
Ether unit represented by:
Y is represented by the formulas (2d-1) to (2d-3):

A unit including at least one of the following:
n is an integer of 0 to 200; m is an integer of 0 to 200; p is an integer of 0 to 10,000; q is an integer of 1 to 100; provided that n+m is not 0, and the bonding order of D1, FAE, AE, and Y is not specified;
A and B are the same or different and each are a hydrogen atom, an alkyl group which may contain a fluorine atom and/or a crosslinkable functional group, a phenyl group which may contain a fluorine atom and/or a crosslinkable functional group, a -COOH group, -OR (R is a hydrogen atom or an alkyl group which may contain a fluorine atom and/or a crosslinkable functional group), an ester group or a carbonate group (however, when the terminal of D is an oxygen atom, it is not a -COOH group, -OR, an ester group or a carbonate group)
The compound is an amorphous fluorine-containing polyether compound having a fluorine-containing group in the side chain represented by the formula:

The electrolyte solution of the present disclosure may contain a sulfone-based compound. As the sulfone-based compound, cyclic sulfones having 3 to 6 carbon atoms and chain sulfones having 2 to 6 carbon atoms are preferred. The number of sulfonyl groups in one molecule is preferably 1 or 2.

Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoint of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

Preferable sulfolanes are sulfolane and/or sulfolane derivatives (hereinafter, sulfolane may be abbreviated as "sulfolanes"). Preferred sulfolane derivatives are those in which one or more of the hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with a fluorine atom or an alkyl group.

Among them, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,2-difluorosulfolane, 2,3-difluorosulfolane, 2,4-difluorosulfolane, 2,5-difluorosulfolane, 3,4-difluorosulfolane, 2-fluoro-3-methylsulfolane, 2-fluoro-2-methylsulfolane, 3-fluoro-3-methylsulfolane, 3-fluoro-2-methylsulfolane, 4-fluoro-3-methylsulfolane, 4-fluoro-2-methylsulfolane, 5-fluoro-3-methylsulfolane , 5-fluoro-2-methylsulfolane, 2-fluoromethylsulfolane, 3-fluoromethylsulfolane, 2-difluoromethylsulfolane, 3-difluoromethylsulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, 2-fluoro-3-(trifluoromethyl)sulfolane, 3-fluoro-3-(trifluoromethyl)sulfolane, 4-fluoro-3-(trifluoromethyl)sulfolane, 3-sulfolene, 5-fluoro-3-(trifluoromethyl)sulfolane, etc. are preferred because of their high ionic conductivity and high input/output.

Furthermore, examples of chain sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, n-propyl ethyl sulfone, di-n-propyl sulfone, isopropyl methyl sulfone, isopropyl ethyl sulfone, diisopropyl sulfone, n-butyl methyl sulfone, n-butyl ethyl sulfone, t-butyl methyl sulfone, t-butyl ethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, and perfluoroethyl methyl sulfone. , ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, di(trifluoroethyl)sulfone, perfluorodiethyl sulfone, fluoromethyl-n-propyl sulfone, difluoromethyl-n-propyl sulfone, trifluoromethyl-n-propyl sulfone, fluoromethyl isopropyl sulfone, difluoromethyl isopropyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-propyl sulfone, trifluoroethyl isopropyl sulfone, pentafluoroethyl-n-propyl sulfone, pentafluoroethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, pentafluoroethyl-n-butyl sulfone, pentafluoroethyl-t-butyl sulfone, and the like.

Among them, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, t-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl-n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, trifluoromethyl-n-butyl sulfone, trifluoromethyl-t-butyl sulfone, etc. are preferred because of their high ionic conductivity and high input/output.

The content of the sulfone-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure, but is usually 0.3 vol% or more, preferably 0.5 vol% or more, more preferably 1 vol% or more, and is usually 40 vol% or less, preferably 35 vol% or less, more preferably 30 vol% or less, based on 100 vol% of the solvent. If the content of the sulfone-based compound is within the above range, it is easy to obtain an effect of improving durability such as cycle characteristics and storage characteristics, and the viscosity of the nonaqueous electrolyte can be set to an appropriate range, a decrease in electrical conductivity can be avoided, and the input/output characteristics and charge/discharge rate characteristics of the nonaqueous electrolyte secondary battery can be set to an appropriate range.

From the viewpoint of improving output characteristics, the electrolyte solution of the present disclosure also preferably contains, as an additive, at least one compound (7) selected from the group consisting of lithium fluorophosphate salts (excluding _LiPF6 ) and lithium salts having an S═O group.
When compound (7) is used as an additive, it is preferable to use a compound other than compound (7) as the above-mentioned electrolyte salt.

Examples of the lithium fluorophosphate salts include lithium monofluorophosphate (LiPO ₃ F) and lithium difluorophosphate (LiPO ₂ F ₂ ).
Examples of the lithium salts having an S═O group include lithium monofluorosulfonate (FSO ₃ Li), lithium methylsulfate (CH ₃ OSO ₃ Li), lithium ethylsulfate (C ₂ H ₅ OSO ₃ Li), and lithium 2,2,2-trifluoroethylsulfate.
Of these, the compound (7) is preferably LiPO ₂ F ₂ , FSO ₃ Li, or C ₂ H ₅ OSO ₃ Li.

The content of compound (7) is preferably 0.001 to 20% by mass, more preferably 0.01 to 15% by mass, even more preferably 0.1 to 10% by mass, and particularly preferably 0.1 to 7% by mass, relative to the electrolyte.

The electrolyte solution of the present disclosure may further contain other additives as necessary. Examples of other additives include metal oxides, glass, etc.

The electrolyte solution of the present disclosure preferably contains, as an additive, at least one selected from the group consisting of unsaturated cyclic carbonates, compound (2), nitrile compounds, fluorinated saturated cyclic carbonates, lithium salts having an S=O group, lithium imide salts, lithium fluorophosphate salts (excluding _LiPF6 ), and compound (5). By containing these additives, the increase in resistance during high-temperature storage can be further suppressed.
The additive is preferably at least one selected from the group consisting of unsaturated cyclic carbonates, compound (4), a nitrile compound represented by general formula (1a), a fluorinated saturated cyclic carbonate, a lithium sulfonate compound, LiN(FSO ₂ ) ₂ , lithium difluorophosphate (LiPO ₂ F ₂ ), lithium bis(oxalato)borate (LIBOB), and lithium difluorooxalatoborate (LIDFOB);
More preferably, the organic solvent is at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, maleic anhydride, adiponitrile, fluoroethylene carbonate, FSO ₃ Li, LiN(FSO ₂ ) ₂ , LiPO ₂ F ₂ , LIBOB, and LIDFOB.

The electrolyte of the present disclosure preferably contains 1 to 1000 ppm of hydrogen fluoride (HF). By containing HF, the film formation of the above-mentioned additive can be promoted. If the HF content is too low, the film forming ability on the negative electrode decreases, and the characteristics of the electrochemical device tend to decrease. In addition, if the HF content is too high, the oxidation resistance of the electrolyte tends to decrease due to the influence of HF. Even if the electrolyte of the present disclosure contains HF in the above range, it does not decrease the high-temperature storage recovery capacity rate of the electrochemical device.
The HF content is more preferably 5 ppm or more, even more preferably 10 ppm or more, and particularly preferably 20 ppm or more. The HF content is also more preferably 200 ppm or less, even more preferably 100 ppm or less, even more preferably 80 ppm or less, and particularly preferably 50 ppm or less.
The HF content can be measured by neutralization titration.

The electrolyte solution of the present disclosure may be prepared by any method using the components described above.

The electrolyte solution of the present disclosure can be suitably applied to electrochemical devices such as secondary batteries such as lithium ion secondary batteries, lithium ion capacitors, hybrid capacitors, electric double layer capacitors, etc. Hereinafter, a nonaqueous electrolyte battery using the electrolyte solution of the present disclosure will be described.
The nonaqueous electrolyte battery may have a known structure, and typically includes a positive electrode and a negative electrode capable of absorbing and releasing ions (e.g., lithium ions) and the electrolyte of the present disclosure. An electrochemical device including such an electrolyte of the present disclosure also constitutes the present disclosure.

Examples of the electrochemical device include secondary batteries such as lithium ion secondary batteries, lithium ion capacitors, capacitors (hybrid capacitors and electric double layer capacitors), radical batteries, solar cells (particularly dye-sensitized solar cells), lithium ion primary batteries, fuel cells, various electrochemical sensors, electrochromic elements, electrochemical switching elements, aluminum electrolytic capacitors, and tantalum electrolytic capacitors, of which secondary batteries such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors are preferred.
The present disclosure also provides a module including the electrochemical device.

The present disclosure also relates to a secondary battery comprising the electrolyte of the present disclosure.
The secondary battery preferably comprises a positive electrode, a negative electrode, and the above-mentioned electrolyte solution.
The secondary battery is preferably a lithium ion secondary battery.

<Positive electrode>
The positive electrode is composed of a positive electrode active material layer containing a positive electrode active material and a current collector.

The positive electrode active material is not particularly limited as long as it can electrochemically absorb and release lithium ions, but examples include lithium-containing transition metal composite oxides, lithium-containing transition metal phosphate compounds, sulfur-based materials, conductive polymers, and the like. Among these, lithium-containing transition metal composite oxides and lithium-containing transition metal phosphate compounds are preferred as positive electrode active materials, and lithium-containing transition metal composite oxides that produce high voltage are particularly preferred.

The transition metal of the lithium-containing transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples include lithium cobalt composite oxides such as _LiCoO2 , lithium nickel composite oxides such as _LiNiO2 , lithium manganese composite oxides such as _LiMnO2 , _{LiMn2O4 , and Li2MnO4} , and those in which a part of the transition metal atoms that are the main components of these lithium transition metal composite oxides has been replaced with other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W, etc. _{Specific examples of the substituted ones include LiNi0.5Mn0.5O2 , LiNi0.85Co0.10Al0.05O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.6Co0.2Mn0.2O2 , LiNi0.33Co0.33Mn0.33O2 , LiNi0.8Co0.1Mn0.1O2 , LiNi0.45Co0.10Al0.45O2 , LiMn1.8Al0.2O4 , and LiMn1.5Ni0.5O . ​ ​ ​ ​ ​ ​ 4,} etc.

_{Among these} , the lithium _- containing transition metal composite oxide is preferably _{LiMn1.5Ni0.5O4 , LiNi0.5Co0.2Mn0.3O2} , _{or LiNi0.6Co0.2Mn0.2O2 , which} have high energy density even at high voltages. Among these, _{LiMn1.5Ni0.5O4} is _preferred for high voltages of 4.4 V or _{more .}

Among them, the lithium _- containing transition metal composite oxide is _{preferably LiNi0.6Co0.2Mn0.2O2 , LiNi0.8Co0.1Mn0.1O2} , or _{LiNi0.85Co0.10Al0.05O2} , since it can provide _{a high -} capacity lithium _{ion secondary battery} .

The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples include iron phosphates such as _LiFePO4 , _Li3Fe2 ( _PO4 ) ₃ , _{LiFeP2O7 , cobalt} phosphates such as _LiCoPO4 , and lithium transition metal phosphate compounds in which a part of the transition metal atoms that constitute the main components of these compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

Examples of the lithium-containing transition metal composite oxide include:
a lithium manganese spinel composite oxide represented by the formula Li _a Mn _2-b M ¹ _b O ₄ (wherein 0.9≦a; 0≦b≦1.5; M ¹ is at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge);
A lithium _{-nickel composite oxide represented by the formula: LiNi1- cM2cO2 (} ^wherein 0≦c≦0.5; ^M2 is at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge), or
Examples of the lithium-cobalt composite _oxide include those represented by the formula LiCo1 _- ^dM3dO2 (wherein 0≦d≦ _0.5 ; ^M3 is at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge).

Among these, _LiCoO2 , _LiMnO2 , LiNiO2 _{, LiMn2O4 ,} LiNi0.8Co0.15Al0.05O2, or LiNi1 _{/3Co1/ 3Mn1 / 3O2 is preferred} because it provides a lithium ion secondary battery with high energy _density and high _output .

Other examples _of the positive _electrode active material _{include LiFePO4 , LiNi0.8Co0.2O2 , Li1.2Fe0.4Mn0.4O2 , LiNi0.5Mn0.5O2 , LiV3O6} , _{and Li2MnO3 .}

The sulfur-based material may be, for example, a material containing a sulfur atom, and is preferably at least one selected from the group consisting of elemental sulfur, metal sulfides, and organic sulfur compounds, and more preferably elemental sulfur. The metal sulfide may be a metal polysulfide. The organic sulfur compound may be an organic polysulfide.

Examples of the metal sulfides include compounds represented by LiS _x (0<x≦8); compounds represented by Li ₂ S _x (0<x≦8); compounds having a two-dimensional layered structure such as TiS ₂ and MoS ₂ ; and Chevrel compounds having a strong three-dimensional framework structure represented by the general formula Me _x Mo ₆ S ₈ (Me is various transition metals including Pb, Ag, and Cu).

Examples of the organic sulfur compounds include carbon sulfide compounds.

The organic sulfur compound may be supported on a material having fine pores such as carbon and used as a carbon composite material. The content of sulfur contained in the carbon composite material is preferably 10 to 99% by mass, more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 40% by mass or more, and is preferably 85% by mass or less, based on the carbon composite material, because the cycle performance is more excellent and the overvoltage is further reduced.
When the positive electrode active material is the elemental sulfur, the content of sulfur contained in the positive electrode active material is equal to the content of the elemental sulfur.

Conductive polymers include p-doped conductive polymers and n-doped conductive polymers. Conductive polymers include polyacetylenes, polyphenylenes, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

In addition, it is preferable to include lithium phosphate in the positive electrode active material, since this improves the continuous charging characteristics. There is no restriction on the use of lithium phosphate, but it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, with respect to the total of the positive electrode active material and lithium phosphate, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

In addition, a material having a different composition may be attached to the surface of the positive electrode active material. Examples of surface-attached materials include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent, impregnating and adding them to the positive electrode active material, and drying them; dissolving or suspending a surface-attaching substance precursor in a solvent, impregnating and adding them to the positive electrode active material, and then reacting them by heating or the like; or adding them to a positive electrode active material precursor and simultaneously baking them. When attaching carbon, a method of mechanically attaching carbonaceous material in the form of, for example, activated carbon, etc., afterwards can also be used.

The amount of the surface-attached substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, and preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less, by mass relative to the positive electrode active material. The surface-attached substance can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving the battery life, but if the amount of attachment is too small, the effect is not fully manifested, and if it is too large, the movement of lithium ions is inhibited, which may increase resistance.

The shape of the particles of the positive electrode active material may be, as conventionally used, a block, polyhedron, sphere, oval sphere, plate, needle, column, etc. Primary particles may also aggregate to form secondary particles.

The tap density of the positive electrode active material is usually 1.5 g/cm ³ or more, preferably 2.0 g/cm ³ or more, more preferably 2.5 g/cm ³ or more, and most preferably 3.0 g/cm ³ or more. If the tap density of the positive electrode active material is below the lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, and the amount of conductive material and binder required increases, which may restrict the filling rate of the positive electrode active material in the positive electrode active material layer and restrict the battery capacity. By using a metal composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. The tap density is generally preferably as high as possible and has no particular upper limit, but is usually 4.5 g/cm ³ or less, preferably 4.3 g/cm ³ or less.
In the present disclosure, the tap density is determined as the powder packing density (tap density) g/cm3 when 5 to 10 g of the positive electrode active material powder is placed in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of about ²⁰ mm.

The median diameter d50 of the particles of the positive electrode active material (secondary particle diameter when primary particles are aggregated to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more, and is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it is below the lower limit, a high tap density product may not be obtained, and if it exceeds the upper limit, it may take time for lithium to diffuse within the particles, resulting in a decrease in battery performance, or problems such as streaking may occur when preparing the positive electrode of a battery, i.e., when the active material, conductive material, binder, etc. are slurried with a solvent and applied in a thin film. Here, by mixing two or more types of the above positive electrode active materials having different median diameters d50, the filling property during preparation of the positive electrode can be further improved.

In this disclosure, the median diameter d50 is measured using a known laser diffraction/scattering particle size distribution measuring device. When using the HORIBA LA-920 as the particle size distribution measuring device, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

When the primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it is difficult to form spherical secondary particles, which may adversely affect powder packing and significantly reduce the specific surface area, increasing the possibility of a decrease in battery performance such as output characteristics. Conversely, if the lower limit is exceeded, problems such as poor reversibility of charge and discharge may occur due to underdeveloped crystals.

In this disclosure, the primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at 10,000x magnification, the longest intercept value of the horizontal line between the left and right boundaries of the primary particle is determined for any 50 primary particles, and the average value is calculated.

The BET specific surface area of the positive electrode active material is preferably 0.1 ^m2 /g or more, more preferably 0.2 ^m2 /g or more, and even more preferably 0.3 ^m2 /g or more, and the upper limit is preferably 50 ^m2 /g or less, more preferably 40 ^m2 /g or less, and even more preferably 30 ^m2 /g or less. If the BET specific surface area is smaller than this range, the battery performance is likely to decrease, and if it is larger, it is difficult to increase the tap density, and problems may easily occur in the application when forming the positive electrode active material layer.

In this disclosure, the BET specific surface area is defined as the value measured by a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after which the sample is pre-dried at 150°C for 30 minutes using a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) and the value measured by a nitrogen adsorption BET single point method using a gas flow method.

When the secondary battery of the present disclosure is used as a large-scale lithium-ion secondary battery for hybrid automobiles or distributed power sources, high output is required, so that the particles of the positive electrode active material are preferably mainly secondary particles.
The positive electrode active material particles preferably contain 0.5 to 7.0 volume % of fine particles having an average secondary particle size of 40 μm or less and an average primary particle size of 1 μm or less. By including fine particles having an average primary particle size of 1 μm or less, the contact area with the electrolyte increases, and the diffusion of lithium ions between the electrode and the electrolyte can be made faster, resulting in improved output performance of the battery.

The manufacturing method of the positive electrode active material is a general method for manufacturing inorganic compounds.In particular, various methods can be considered for making spherical or elliptical active material, for example, the raw material of transition metal is dissolved or crushed and dispersed in a solvent such as water, and the pH is adjusted while stirring to make and recover spherical precursor, which is dried as necessary, and then LiOH, _Li2CO3 , _LiNO3 , _or other Li source is added and calcined at high temperature to obtain active material.

For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more different compositions may be used in any combination or _ratio . In this case, preferred combinations include a combination of _LiCoO2 with _LiMn2O4 such as _{LiNi0.33Co0.33Mn0.33O2} or a _combination of LiCoO2 or a combination of _LiMn2O4 with a part of Mn replaced with another transition metal or _the like, or a combination of _LiCoO2 or a combination of LiCoO2 with a part of Co replaced with another transition metal or the like.

The content of the positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, more preferably 80 to 99% by mass, in terms of high battery capacity. The content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electrical capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

The positive electrode mixture preferably further contains a binder, a thickener, and a conductive material.
Any material may be used as the binder as long as it is safe against the solvent and electrolyte used in the production of the electrodes. Examples of the binder include resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrogenated products thereof; EPDM (ethylene propylene glycol dimethyl ether (EPDM)); Examples of suitable polymers include thermoplastic elastomeric polymers such as styrene-ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-styrene copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof; soft resinous polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymers, and tetrafluoroethylene-ethylene copolymers; and polymer compositions having ionic conductivity for alkali metal ions (particularly lithium ions). These may be used alone or in any combination and ratio of two or more.

The content of the binder, expressed as the proportion of the binder in the positive electrode active material layer, is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 1.2% by mass or more, and is usually 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently held, resulting in insufficient mechanical strength of the positive electrode, which may deteriorate battery performance such as cycle characteristics. On the other hand, if the proportion is too high, it may lead to a decrease in battery capacity and conductivity.

The thickeners include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein, polyvinylpyrrolidone, and salts thereof. One type may be used alone, or two or more types may be used in any combination and ratio.

The ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. If it is below this range, the coating properties may be significantly reduced. If it is above this range, the ratio of the active material in the positive electrode active material layer may decrease, which may cause problems such as a decrease in battery capacity or an increase in resistance between the positive electrode active materials.

As the conductive material, any known conductive material can be used. Specific examples include metal materials such as copper, nickel, and gold; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; and carbon materials such as needle coke, carbon nanotubes, fullerene, and amorphous carbon such as VGCF. These may be used alone or in any combination and ratio of two or more. The conductive material is used so that it is contained in the positive electrode active material layer in an amount of usually 0.01% by mass or more, preferably 0.1% by mass or more, and more preferably 1% by mass or more, and usually 50% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

There are no particular limitations on the type of solvent used to form the slurry, and either an aqueous or organic solvent may be used as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed. Examples of aqueous solvents include water and a mixture of alcohol and water. Examples of organic solvents include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide.

The material of the positive electrode current collector may be metals such as aluminum, titanium, tantalum, stainless steel, nickel, or metal materials such as alloys thereof; or carbon materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum or its alloys, are preferred.

The shape of the current collector may be, for example, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, expanded metal, punched metal, or foamed metal, for a metal material, or a carbon plate, a carbon thin film, or a carbon cylinder, for example. Of these, a metal thin film is preferred. The thin film may be formed into a mesh shape as appropriate. The thickness of the thin film is optional, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and is usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the thin film is thicker than this range, handling may be impaired.

It is also preferable that a conductive assistant is applied to the surface of the current collector in order to reduce the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive assistants include carbon and precious metals such as gold, platinum, and silver.

The thickness ratio of the current collector to the positive electrode active material layer is not particularly limited, but the value of (thickness of the positive electrode active material layer on one side immediately before electrolyte injection)/(thickness of the current collector) is preferably 20 or less, more preferably 15 or less, and most preferably 10 or less, and is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charging and discharging. If it is below this range, the volume ratio of the current collector to the positive electrode active material increases, and the battery capacity may decrease.

The positive electrode may be manufactured by a conventional method. For example, the positive electrode active material may be mixed with the binder, thickener, conductive material, solvent, etc., to form a slurry-like positive electrode mixture, which is then applied to a current collector, dried, and pressed to increase density.

The densification can be performed by hand pressing, roller pressing, etc. The density of the positive electrode active material layer is preferably 1.0 g/cm ³ or more, more preferably 1.3 g/cm ³ or more, and even more preferably 1.5 g/cm ³ or more, and is preferably 5 g/cm ³ or less, more preferably 3.0 g/cm ³ or less, and even more preferably 2.5 g/cm ³ or less. If it exceeds this range, the permeability of the electrolyte solution near the current collector/active material interface decreases, and the charge/discharge characteristics at high current density in particular may decrease, and high output may not be obtained. If it is below this range, the conductivity between the active materials decreases, the battery resistance increases, and high output may not be obtained.

When the electrolyte solution of the present disclosure is used, from the viewpoint of increasing the stability at high output and high temperatures, it is preferable that the area of the positive electrode active material layer is larger than the external surface area of the battery exterior case. Specifically, it is preferable that the total electrode area of the positive electrode is 15 times or more, and more preferably 40 times or more, in terms of area ratio, relative to the surface area of the exterior of the secondary battery. In the case of a bottomed rectangular shape, the external surface area of the battery exterior case refers to the total area calculated from the vertical, horizontal, and thickness dimensions of the case part filled with the power generating element excluding the protruding part of the terminal. In the case of a bottomed cylindrical shape, it is the geometric surface area of the case part filled with the power generating element excluding the protruding part of the terminal as a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which a positive electrode mixture layer is formed on both sides via a collector foil, it refers to the sum of the areas calculated separately for each side.

The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer minus the thickness of the metal foil of the core material is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit on one side of the current collector, and is preferably 500 μm or less, more preferably 450 μm or less.

In addition, a material having a different composition may be attached to the surface of the positive electrode plate. Examples of surface-attached materials include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

<Negative Electrode>
The negative electrode is composed of a negative electrode active material layer containing a negative electrode active material and a current collector.

There are no particular limitations on the negative electrode material, so long as it is capable of electrochemically absorbing and releasing lithium ions. Specific examples include carbon materials, alloy-based materials, lithium-containing metal composite oxide materials, conductive polymers, and the like. These may be used alone or in any combination of two or more.

The above-mentioned negative electrode active materials include carbonaceous materials capable of absorbing and releasing lithium, such as pyrolysis products of organic matter under various pyrolysis conditions, artificial graphite, and natural graphite; metal oxide materials capable of absorbing and releasing lithium, such as tin oxide and silicon oxide; lithium metal; various lithium alloys; lithium-containing metal composite oxide materials; and the like. Two or more of these negative electrode active materials may be mixed and used.

As the carbonaceous material capable of absorbing and releasing lithium, artificial graphite or purified natural graphite produced by high-temperature treatment of graphitizable pitch obtained from various raw materials, or those obtained by surface-treating these graphites with pitch or other organic substances and then carbonizing them are preferable. Carbonaceous materials obtained by heat-treating natural graphite, artificial graphite, artificial carbonaceous substances, and artificial graphite substances at least once in the range of 400 to 3200°C, carbonaceous materials in which the negative electrode active material layer is made of carbonaceous materials having at least two or more different types of crystallinity and/or has an interface where the carbonaceous materials of the different crystallinity are in contact, and carbonaceous materials in which the negative electrode active material layer has an interface where the carbonaceous materials of at least two or more different orientations are in contact are more preferable because they have a good balance between initial irreversible capacity and high current density charge/discharge characteristics. In addition, these carbonaceous materials may be used alone or in any combination and ratio of two or more.

The above-mentioned artificial carbonaceous substances and artificial graphite substances are heat-treated at least once in the range of 400 to 3200°C as carbonaceous materials, which include coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch and these pitches that have been oxidized, needle coke, pitch coke and carbon agents obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fiber and other organic matter pyrolysis products, carbonizable organic matter and their charcoal products, or solutions of carbonizable organic matter dissolved in low-molecular organic solvents such as benzene, toluene, xylene, quinoline, n-hexane and other low-molecular organic solvents and their charcoal products.

The metal material (excluding lithium titanium composite oxide) used as the negative electrode active material is not particularly limited, and may be any of lithium alone, elemental metals and alloys that form lithium alloys, or compounds such as oxides, carbides, nitrides, silicides, sulfides, or phosphides thereof, as long as it is capable of absorbing and releasing lithium. The elemental metals and alloys that form lithium alloys are preferably materials containing metals and semimetallic elements of Groups 13 and 14, and more preferably elemental metals such as aluminum, silicon, and tin (hereinafter abbreviated as "specific metal elements") and alloys or compounds containing these atoms. These may be used alone or in any combination and ratio of two or more.

Anode active materials having at least one atom selected from specific metal elements include a single metal of any one of the specific metal elements, an alloy of two or more specific metal elements, an alloy of one or more specific metal elements and one or more other metal elements, and a compound containing one or more specific metal elements, as well as composite compounds such as oxides, carbides, nitrides, silicides, sulfides, or phosphides of the compounds. By using these single metals, alloys, or metal compounds as the anode active material, it is possible to increase the capacity of the battery.

Furthermore, these composite compounds may be compounds in which several elements, such as simple metals, alloys, or nonmetallic elements, are intricately bonded. Specifically, for example, with silicon or tin, alloys of these elements and metals that do not function as negative electrodes can be used. For example, with tin, complex compounds containing five to six elements in combination with tin, a metal other than silicon that acts as a negative electrode, a metal that does not function as a negative electrode, and a nonmetallic element can also be used.

Specifically, Si alone, _SiB4 , _SiB6 , _Mg2Si , _Ni2Si , _{TiSi2 , MoSi2} , CoSi2, _NiSi2 , _CaSi2 , _CrSi2 , _Cu6Si , _FeSi2 , _MnSi2 , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0<v≦2), LiSiO or tin alone, SnSiO ₃ , LiSnO, Mg ₂ Examples include Sn and SnO _w (0<w≦2).
In addition, there is a composite material containing Si or Sn as a first constituent element and further containing a second and a third constituent element. The second constituent element is, for example, cobalt, iron, magnesium, titanium, or vanadium. The third constituent element is, for example, at least one of boron, carbon, aluminum, and phosphorus.
In particular, the metal material is preferably silicon or tin (which may contain a trace amount of impurities), SiO _v (0<v≦2), SnO _w (0 ≦w≦2), Si—Co—C composite material, Si—Ni—C composite material, Sn—Co—C composite material, and Sn—Ni—C composite material are preferred.

The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium, but from the viewpoint of high current density charge/discharge characteristics, materials containing titanium and lithium are preferred, and lithium-containing composite metal oxide materials containing titanium are more preferred, with composite oxides of lithium and titanium (hereinafter abbreviated as "lithium titanium composite oxides") being even more preferred. In other words, when lithium titanium composite oxides having a spinel structure are used as negative electrode active materials for electrolyte batteries, the output resistance is significantly reduced, and this is particularly preferred.

The lithium titanium composite oxide has the general formula:
Li _x Ti _y M _z O ₄
[In the formula, M represents at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.]
It is preferable that the compound is represented by the following formula:
Among the above compositions,
(i) 1.2≦x≦1.4, 1.5≦y≦1.7, z=0
(ii) 0.9≦x≦1.1, 1.9≦y≦2.1, z=0
(iii) 0.7≦x≦0.9, 2.1≦y≦2.3, z=0
The structure of is particularly preferred because it has a good balance of battery performance.

Particularly preferred representative compositions of the above compounds are (i) Li4 _{/ 3Ti5/ 3O4} , ₍ ii) _Li1Ti2O4 , and (iii) Li4 _{/5Ti11 / 5O4} . As for the structure where Z≠0, Li4 _{/ 3Ti4/ 3Al1 / 3O4} is preferred, for example.

The negative electrode mixture preferably further contains a binder, a thickener, and a conductive material.

The binder may be the same as the binder that can be used for the positive electrode described above. The ratio of the binder to the negative electrode active material is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and particularly preferably 0.6 mass% or more, and is preferably 20 mass% or less, more preferably 15 mass% or less, even more preferably 10 mass% or less, and particularly preferably 8 mass% or less. If the ratio of the binder to the negative electrode active material exceeds the above range, the ratio of the binder that does not contribute to the battery capacity increases, which may lead to a decrease in the battery capacity. Also, if it is below the above range, it may lead to a decrease in the strength of the negative electrode.

In particular, when the main component is a rubber-like polymer such as SBR, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. In addition, when the main component is a fluorine-based polymer such as polyvinylidene fluoride, the ratio to the negative electrode active material is usually 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, and usually 15% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less.

The thickener may be the same as the thickener that can be used for the positive electrode described above. The ratio of the thickener to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. If the ratio of the thickener to the negative electrode active material is below the above range, the coating property may be significantly reduced. If the ratio exceeds the above range, the ratio of the negative electrode active material in the negative electrode active material layer may decrease, causing problems such as a decrease in the capacity of the battery and an increase in resistance between the negative electrode active materials.

Conductive materials for the negative electrode include metal materials such as copper and nickel; carbon materials such as graphite and carbon black; etc.

The solvent for forming the slurry is not particularly limited as long as it is capable of dissolving or dispersing the negative electrode active material, the binder, and the thickener and conductive material used as needed, and either an aqueous solvent or an organic solvent may be used.
Examples of the aqueous solvent include water and alcohol, and examples of the organic solvent include N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphatamide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane.

Examples of materials for the negative electrode current collector include copper, nickel, and stainless steel. Among these, copper foil is preferred because it is easy to process into a thin film and is cost-effective.

The thickness of the current collector is usually 1 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less. If the thickness of the negative electrode current collector is too thick, the overall capacity of the battery may be too low, and conversely, if it is too thin, it may be difficult to handle.

The negative electrode may be manufactured by a conventional method. For example, the negative electrode material may be made into a slurry by adding the above-mentioned binder, thickener, conductive material, solvent, etc., and the like, which is then applied to a current collector, dried, and pressed to increase density. In addition, when an alloy material is used, a method of forming a thin film layer (negative electrode active material layer) containing the above-mentioned negative electrode active material by a method such as vapor deposition, sputtering, or plating may also be used.

The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the negative electrode active material present on the current collector is preferably 1 g cm ⁻³ or more, more preferably 1.2 g cm ⁻³ or more, particularly preferably 1.3 g cm ⁻³ or more, and also preferably 2.2 g cm ⁻³ or less, more preferably 2.1 g cm −3 or less, even more preferably 2.0 g cm ⁻³ or less, and particularly preferably 1.9 g cm ^{−3 or} less. If the density of the negative electrode active material present on the current collector exceeds the above range, the negative electrode active material particles are destroyed, which may lead to an increase in initial irreversible capacity and a deterioration in high current density charge and discharge characteristics due to a decrease in the permeability of the electrolyte near the current collector/negative electrode active material interface. If the density is below the above range, the conductivity between the negative electrode active materials may decrease, the battery resistance may increase, and the capacity per unit volume may decrease.

The thickness of the negative electrode plate is designed to match the positive electrode plate to be used, and is not particularly limited, but the thickness of the composite layer minus the thickness of the metal foil of the core material is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and is usually 300 μm or less, preferably 280 μm or less, more preferably 250 μm or less.

In addition, a substance having a different composition may be attached to the surface of the negative electrode plate. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

<Separator>
The secondary battery of the present disclosure preferably further includes a separator.
The material and shape of the separator are not particularly limited as long as they are stable to the electrolyte and have excellent liquid retention, and any known material can be used. Among them, it is preferable to use a material formed of a material stable to the electrolyte of the present disclosure, such as a resin, glass fiber, or inorganic material, and to use a porous sheet or nonwoven fabric having excellent liquid retention.

As materials for the resin and glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters, etc. can be used. These materials may be used alone or in any combination and ratio, such as polypropylene/polyethylene two-layer film and polypropylene/polyethylene/polypropylene three-layer film. Among them, the separator is preferably a porous sheet or nonwoven fabric made of polyolefins such as polyethylene and polypropylene, because of its good electrolyte permeability and shutdown effect.

The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is thinner than the above range, the insulating properties and mechanical strength may decrease. Furthermore, if the separator is thicker than the above range, not only may the battery performance such as rate characteristics decrease, but the energy density of the electrolyte battery as a whole may decrease.

Furthermore, when a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is optional, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, and is usually 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too small below the above range, the membrane resistance tends to increase and the rate characteristics tend to deteriorate. Also, if the porosity is too large above the above range, the mechanical strength of the separator tends to decrease, and the insulating properties tend to decrease.

The average pore size of the separator can also be any value, but is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size exceeds the above range, short circuits are more likely to occur. If it is below the above range, the membrane resistance increases and the rate characteristics may deteriorate.

On the other hand, inorganic materials include, for example, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate, and are used in particulate or fibrous form.

As for the form, a thin film shape such as a nonwoven fabric, woven fabric, or microporous film is used. In the thin film shape, a film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above independent thin film shape, a separator can be used in which a composite porous layer containing the above inorganic particles is formed on the surface layer of the positive electrode and/or negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

<Battery design>
The electrode group may be either a laminated structure of the positive electrode plate and the negative electrode plate with the separator interposed therebetween, or a structure of the positive electrode plate and the negative electrode plate wound in a spiral shape with the separator interposed therebetween. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less.

If the electrode group occupancy rate falls below the above range, the battery capacity will be small. On the other hand, if it exceeds the above range, there will be little void space, and the battery will become hot, causing the components to expand and the vapor pressure of the electrolyte liquid components to increase, resulting in an increase in internal pressure, which will reduce the battery's various characteristics such as repeated charge/discharge performance and high-temperature storage, and may even activate the gas release valve that releases internal pressure to the outside.

The current collection structure is not particularly limited, but in order to more effectively achieve improved high current density charge/discharge characteristics using the electrolyte of the present disclosure, it is preferable to use a structure that reduces the resistance of the wiring and joint parts. When the internal resistance is reduced in this way, the effect of using the electrolyte of the present disclosure is particularly good.

When the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core parts of each electrode layer and welding them to a terminal is preferably used. When the surface area of a single electrode is large, the internal resistance increases, so it is also preferably used to reduce the resistance by providing multiple terminals within the electrode. When the electrode group has the above-mentioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive and negative electrodes and bundling them to a terminal.

The material of the exterior case is not particularly limited as long as it is stable against the electrolyte used. Specifically, metals such as nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminate film of resin and aluminum foil can be used. From the viewpoint of weight reduction, metals such as aluminum or aluminum alloy, and laminate films are preferably used.

In the case of an exterior case using metals, the metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed structure, or the metals are used via a resin gasket to form a crimped structure. In the case of an exterior case using the above-mentioned laminate film, the resin layers are heat-sealed to form a sealed structure. In order to improve the sealing property, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when the resin layers are heat-sealed via a current collecting terminal to form a sealed structure, a bond is formed between the metal and the resin, so a resin having a polar group or a modified resin into which a polar group has been introduced is preferably used as the interposed resin.

The shape of the secondary battery of the present disclosure is arbitrary, and examples of such shapes include cylindrical, square, laminated, coin, large, etc. The shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery.

A module equipped with the secondary battery of the present disclosure is also part of the present disclosure.

The present disclosure also includes an electric double layer capacitor comprising the electrolyte solution of the present disclosure.
The electric double layer capacitor may include a positive electrode, a negative electrode, and the above-mentioned electrolyte solution.
In the electric double layer capacitor, at least one of the positive electrode and the negative electrode is a polarizable electrode, and as the polarizable electrode and the non-polarizable electrode, the following electrodes described in detail in JP-A-9-7896 can be used.

The polarizable electrode mainly made of activated carbon used in this disclosure preferably contains inert carbon with a large specific surface area and a conductive agent such as carbon black that imparts electronic conductivity. The polarizable electrode can be formed by various methods. For example, a polarizable electrode made of activated carbon and carbon black can be formed by mixing activated carbon powder, carbon black, and a phenolic resin, pressing the mixture, and then firing and activating the mixture in an inert gas atmosphere and a water vapor atmosphere. Preferably, the polarizable electrode is joined to a current collector with a conductive adhesive or the like.

Also, activated carbon powder, carbon black, and a binder can be kneaded in the presence of alcohol, formed into a sheet, and dried to form a polarizable electrode. For example, polytetrafluoroethylene is used as the binder. Also, activated carbon powder, carbon black, a binder, and a solvent can be mixed to form a slurry, which can be coated onto a metal foil current collector and dried to form a polarizable electrode integrated with the current collector.

An electric double layer capacitor can be made by using polarizable electrodes mainly made of activated carbon on both poles, but it is also possible to use a non-polarizable electrode on one side, for example, a combination of a positive electrode mainly made of a battery active material such as a metal oxide and a negative electrode that is a polarizable electrode mainly made of activated carbon, or a combination of a negative electrode mainly made of a carbon material that can reversibly absorb and release lithium ions, or a negative electrode made of lithium metal or a lithium alloy and a polarizable positive electrode mainly made of activated carbon.

In addition, carbonaceous materials such as carbon black, graphite, expanded graphite, porous carbon, carbon nanotubes, carbon nanohorns, and Ketjen black may be used in place of or in combination with activated carbon.

The non-polarizable electrode is preferably made mainly of a carbon material that can reversibly absorb and release lithium ions, and this carbon material with lithium ions absorbed is used as the electrode. In this case, a lithium salt is used as the electrolyte. With an electric double layer capacitor of this configuration, an even higher withstand voltage of over 4V can be obtained.

The solvent used to prepare the slurry for producing the electrodes is preferably one that dissolves the binder, and N-methylpyrrolidone, dimethylformamide, toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, dimethyl phthalate, ethanol, methanol, butanol, or water is appropriately selected according to the type of binder.

Activated carbon used in polarizable electrodes includes phenolic resin-based activated carbon, coconut shell-based activated carbon, and petroleum coke-based activated carbon. Of these, it is preferable to use petroleum coke-based activated carbon or phenolic resin-based activated carbon because they can provide a large capacity. Activation methods for activated carbon include steam activation and molten KOH activation, and it is preferable to use activated carbon produced by the molten KOH activation method because they can provide a larger capacity.

Preferred conductive agents for use in polarizable electrodes include carbon black, ketjen black, acetylene black, natural graphite, artificial graphite, metal fiber, conductive titanium oxide, and ruthenium oxide. The amount of conductive agent such as carbon black used in polarizable electrodes is preferably 1 to 50 mass% of the total amount with activated carbon to obtain good conductivity (low internal resistance), and since too much reduces the capacity of the product.

As the activated carbon used for the polarizable electrode, it is preferable to use activated carbon having an average particle size of 20 μm or less and a specific surface area of 1500 to 3000 m ² /g so as to obtain an electric double layer capacitor with a large capacity and low internal resistance. Preferable carbon materials for constituting an electrode mainly made of a carbon material capable of reversibly absorbing and releasing lithium ions include natural graphite, artificial graphite, graphitized mesocarbon microspheres, graphitized whiskers, vapor-grown carbon fiber, a fired product of furfuryl alcohol resin, or a fired product of novolac resin.

The current collector may be any material that is chemically and electrochemically resistant to corrosion. Stainless steel, aluminum, titanium, or tantalum is preferably used as the current collector for a polarizable electrode that is mainly made of activated carbon. Of these, stainless steel or aluminum is particularly preferred in terms of both the properties and price of the resulting electric double layer capacitor. Stainless steel, copper, or nickel is preferably used as the current collector for an electrode that is mainly made of a carbon material that can reversibly absorb and release lithium ions.

In addition, there are several ways to absorb lithium ions in advance into a carbon material that can reversibly absorb and release lithium ions: (1) mixing powdered lithium with the carbon material that can reversibly absorb and release lithium ions; (2) placing lithium foil on an electrode made of a carbon material that can reversibly absorb and release lithium ions and a binder, and electrically contacting the electrode, immersing the electrode in an electrolyte solution containing a lithium salt to ionize the lithium and incorporate the lithium ions into the carbon material; and (3) placing an electrode made of a carbon material that can reversibly absorb and release lithium ions and a binder on the negative side, placing lithium metal on the positive side, and immersing the electrode in a non-aqueous electrolyte solution containing lithium salt as an electrolyte, and passing a current through the electrode to electrochemically incorporate lithium in an ionized state into the carbon material.

Generally known electric double layer capacitors include wound electric double layer capacitors, laminated electric double layer capacitors, and coin-type electric double layer capacitors, and the above electric double layer capacitor can also be of these types.

For example, a wound type electric double layer capacitor is assembled by winding a positive electrode and a negative electrode, each of which is a laminate (electrode) of a current collector and an electrode layer, with a separator between them to produce a wound element, placing this wound element in a case made of aluminum or the like, filling it with an electrolyte, preferably a non-aqueous electrolyte, and then sealing it with a rubber seal.

Separators can be made of conventionally known materials and configurations. Examples include porous polyethylene membranes, polytetrafluoroethylene, polypropylene fibers, glass fibers, and nonwoven fabrics of cellulose fibers.

In addition, it is also possible to make a laminate type electric double layer capacitor in which sheet-shaped positive and negative electrodes are laminated with an electrolyte and a separator between them by using a known method, or a coin type electric double layer capacitor in which the positive and negative electrodes are fixed with a gasket and arranged in a coin shape with an electrolyte and a separator between them.

The electrolyte of the present disclosure is useful as an electrolyte for large lithium-ion secondary batteries for hybrid vehicles and distributed power sources, and for electric double-layer capacitors.

Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

The present disclosure will now be described with reference to examples, but the present disclosure is not limited to these examples.

(Preparation of Electrolyte)
Examples 1 to 31 and Comparative Examples 1 to 5
FE1 or FE4 and FE2, FE3 or FE5 were mixed in a volume ratio shown in Table 1 to obtain an electrolyte composition. Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed into this composition in a volume ratio shown in Table 1, and _LiPF6 was added to this mixture to a concentration of 1.0 mol/L. Further, the additives shown in Table 1 were added in the amounts shown in Table 1 to obtain a nonaqueous electrolyte.

(Preparation of aluminum laminated lithium ion secondary battery)
[Preparation of Positive Electrode]
93% by mass of _{LiNi0.5Co0.2Mn0.3O2} ( _NMC532 ) as a positive electrode active material, 3 _% by mass of acetylene black as a conductive material, and 4 _% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent to form a slurry. The obtained slurry was applied to one side of a 15 μm thick aluminum foil that had been previously coated with a conductive assistant, dried, and roll-pressed with a press machine, and the active material layer was cut to a width of 50 mm and a length of 30 mm to form a positive electrode.

[Preparation of negative electrode]
98 parts by mass of carbonaceous material (graphite) was mixed with 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) as a thickener and binder, and the mixture was mixed with a disperser to form a slurry. The obtained slurry was applied to a copper foil having a thickness of 15 μm and dried. This was rolled with a press machine and cut into an active material layer size of 52 mm wide and 32 mm long to form a negative electrode.

[Preparation of aluminum laminate cell]
The positive electrode and the negative electrode were opposed to each other via a 20 μm-thick microporous polyethylene film (separator), the nonaqueous electrolyte obtained above was injected, and after the nonaqueous electrolyte sufficiently permeated the separator and the like, the battery was sealed, pre-charged, and aged to prepare a lithium ion secondary battery.

(Measurement of battery characteristics)
[High temperature storage test]
The secondary battery prepared above was sandwiched between plates and pressurized, and then at 25°C, it was charged at a constant current-constant voltage (hereinafter referred to as CC/CV charging, 0.1C cut) to 4.4V at a current equivalent to 0.2C, and then discharged to 3V at a constant current of 0.2C, which constitutes one cycle, and the initial discharge capacity was calculated from the discharge capacity of the third cycle. Here, 1C represents the current value at which the reference capacity of the battery is discharged in one hour, and for example, 0.2C represents 1/5 of that current value. After CC/CV charging (0.1C cut) to 4.4V at 0.2C again, it was stored at a high temperature of 80°C for 72 hours.
[Evaluation of IV resistance]
The battery was charged to SOC 50%, and discharged for 10 seconds at 1, 3, and 5 C rates, and the voltage drop (V) was measured. The resistance value was calculated from the slope using the equation V = IR from the obtained voltage and current values. The resistance value was measured before and after the high-temperature storage test, and the resistance increase rate was calculated from the following equation.
{(resistance value after storage) - (resistance value before storage)} / (resistance value before storage) = resistance increase rate (%)
The SOC indicates a state of charge, and SOC 100% is the capacity when charged to 4.4 V. For example, SOC 50% indicates half the capacity of SOC 100%.
The results are shown in Table 1.

The abbreviations in the table are as follows.
_{FE1 : HCF2CF2CH2OCF2CF2H ​ ​
FE2 : HCF2CF2CH2OCF2CHFCF3 ​ ​
FE3 : CF3CF2CH2OCH2CF2CF3 ​ ​ ​
FE4 : CH3CH2CH2OCF2CF2H ​ ​
FE5 : CH3CH2CH2OCF2CHFCF3 ​ ​}
EC: Ethylene carbonate EMC: Ethyl methyl carbonate VC: Vinylene carbonate LiFSI: Lithium bis(fluorosulfonyl)imide FEC: Fluoroethylene carbonate VEC: Vinyl ethylene carbonate LiBOB: Lithium bis(oxalate)borate LiDFOB: Lithium difluorooxalate borate

Claims (10)

The composition for an electrolyte solution contains a fluorinated ether compound (1) represented by the following formula (1) and a fluorinated ether compound (2) represented by the following formula (2), in which the content of the fluorinated ether compound (2) is 0.001 to 5% by volume based on the fluorinated ether compound (1).
Formula (1): HCF ₂ -CF ₂ -O-Rf ¹
(In the formula, Rf ¹ is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.)
Formula (2): CF ₃ -CHF-CF ₂ -O-Rf ²
(In the formula, ^Rf2 is an optionally fluorinated alkyl group having 1 to 5 carbon atoms.) The composition for an electrolyte solution according to claim 1, wherein Rf ¹ in the formula (1) is a fluorinated alkyl group having 1 to 3 carbon atoms, and Rf ² in the formula (2) is a fluorinated alkyl group having 1 to 3 carbon atoms. The electrolyte solution composition _according to claim 1 _{or 2} , wherein the _fluorine -containing _ether compound ( ₁ ) is at least one selected from _the group consisting of _{HCF2CF2OCH2CF2CF2H and CH3CH2CH2OCF2CF2H , and the fluorine - containing} ether compound (2) is at _least one selected from the _group consisting of _{CF3CHFCF2OCH2CF2CF2CF2H} and _{CH3CH2CH2OCF2CHFCF3 . The electrolyte} solution composition according to claim 1 or _{2 ,} wherein the _fluorine -containing ether compound (1) is _{HCF2CF2OCH2CF2CF2CF2H} , and the _fluorine -containing ether compound ( ₂ ) _{is CF3CHFCF2OCH2CF2CF2CF2H} . An electrolyte solution comprising the electrolyte solution composition according to claim 1 or 2. The electrolyte solution according to claim 5, wherein the total content of the fluorine-containing ether compounds (1) and (2) is 5 to 90% by volume of the electrolyte solution. The electrolyte solution according to claim 5, wherein the content of the fluorine-containing ether compound (1) is 1 to 90% by volume relative to the electrolyte solution, and the content of the fluorine-containing ether compound (2) is 0.00001 to 4.5% by volume relative to the electrolyte solution. The electrolyte solution according to claim 5, wherein the content of the fluorine-containing ether compound (1) is 8 to 80% by volume relative to the electrolyte solution, and the content of the fluorine-containing ether compound (2) is 0.00008 to 4% by volume relative to the electrolyte solution. The electrolyte solution according to claim 5, further comprising at least one solvent selected from the group consisting of carbonates and carboxylic acid esters, and a lithium salt. A secondary battery comprising the electrolyte solution according to claim 5.