JP7423889B2 - Nonaqueous electrolytes for batteries and lithium ion secondary batteries - Google Patents

Description

The present disclosure relates to a non-aqueous electrolyte for batteries and a lithium ion secondary battery.

In recent years, lithium ion secondary batteries have been widely used in electronic devices such as mobile phones and notebook computers, or as power sources for electric vehicles and power storage. Particularly recently, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be installed in hybrid vehicles and electric vehicles.
A lithium ion secondary battery includes, for example, a positive electrode and a negative electrode containing a material capable of inserting and extracting lithium, and a non-aqueous battery electrolyte containing a lithium salt and a non-aqueous solvent.
As the positive electrode active material used in the positive electrode, for example, lithium metal oxides such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and LiFePO ₄ are used.
In addition, as a non-aqueous electrolyte for batteries, a mixed solvent (non-aqueous solvent) of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ), etc. ₂ , a solution containing a Li electrolyte such as LiN(SO ₂ CF ₂ CF ₃ ) ₂ is used.
On the other hand, as negative electrode active materials used in negative electrodes, metal lithium, metal compounds that can absorb and release lithium (such as simple metals, oxides, alloys with lithium, etc.), and carbon materials are known. Lithium-ion secondary batteries that use coke, artificial graphite, and natural graphite, which can be absorbed and released, have been put into practical use.

In order to improve the performance of batteries (for example, lithium ion secondary batteries) containing nonaqueous battery electrolytes, various additives have been incorporated into the battery nonaqueous electrolytes.
As a nonaqueous electrolyte for batteries that can improve the charge/discharge characteristics and life characteristics of batteries, a nonaqueous electrolyte for batteries containing a sultone compound with a specific structure is known (for example, see Patent Document 1 below) .
In addition, we have developed a non-aqueous electrolyte for batteries that contains a cyclic sulfate ester compound with a specific structure as a non-aqueous electrolyte for batteries that can improve battery capacity maintenance performance and suppress the drop in open-circuit voltage during battery storage. Liquids are known (for example, see Patent Document 2 below).

JP2004-087437A International Publication 2012/053644

However, with respect to conventional non-aqueous electrolytes and batteries, it may be required to further reduce the battery resistance after storage.
Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte for batteries that can reduce battery resistance after storage, and a lithium ion secondary battery using this nonaqueous electrolyte for batteries.

<1>
An electrolyte containing lithium hexafluorophosphate, additive A which is lithium bis(fluorosulfonyl)imide, additive B which is vinylene carbonate, a compound represented by the following formula (C1), and the following formula (C2) A non-aqueous electrolyte for a battery, comprising: an additive C which is at least one selected from the group consisting of compounds represented by:

[In formula (C1), R ^c11 to R ^c14 are each independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b) represents a group. In formulas (a) and (b), * represents the bonding position. In formula (C2), R ^c21 to R ^c24 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms. ]
<2>
The nonaqueous electrolyte for a battery according to <1>, wherein the content of the additive A is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the nonaqueous electrolyte.
<3>
The nonaqueous electrolyte for a battery according to <1> or <2>, wherein the content of the additive B is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the nonaqueous electrolyte.
<4>
The nonaqueous battery according to any one of <1> to <3>, wherein the content of the additive C is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the nonaqueous electrolyte. Water electrolyte.
<5>
The non-aqueous electrolyte for a battery according to any one of <1> to <4>, wherein the concentration of the electrolyte is 0.1 mol/L or more and 3 mol/L or less based on the total amount of the non-aqueous electrolyte.
<6>
A positive electrode including a positive electrode active material layer containing a positive electrode active material, a negative electrode including a negative electrode active material layer containing a negative electrode active material, and a non-aqueous electrolyte for batteries according to any one of <1> to <5>. liquid and
A lithium-ion secondary battery equipped with.
<7>
The lithium ion secondary battery according to <6>, wherein the positive electrode active material contains a lithium nickel manganese cobalt composite oxide.
<8>
The lithium ion secondary battery according to <6> or <7>, wherein the negative electrode active material contains a carbon material.
<9>
A lithium ion secondary battery obtained by charging and discharging the lithium ion secondary battery according to any one of <6> to <8>.

According to the present disclosure, a non-aqueous electrolyte for batteries that can reduce battery resistance after storage, and a lithium ion secondary battery using this non-aqueous electrolyte for batteries are provided.

1 is a schematic perspective view showing an example of a laminate type battery, which is an example of a lithium ion secondary battery of the present disclosure. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the laminated battery shown in FIG. 1. FIG. FIG. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the lithium ion secondary battery of the present disclosure.

In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as lower and upper limits.
In this specification, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition. means.

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte for batteries (hereinafter also simply referred to as "non-aqueous electrolyte") of the present disclosure comprises additive A which is lithium bis(fluorosulfonyl)imide, additive B which is vinylene carbonate, and the following formula ( It contains an additive C which is at least one selected from the group consisting of a compound represented by C1) and a compound represented by the following formula (C2).
According to the nonaqueous electrolyte of the present disclosure, battery resistance after storage in a battery can be reduced.
Although the reason for this effect is not clear, it is presumed as follows.
The non-aqueous electrolyte of the present disclosure contains Additives A to C, and it is thought that the combination of these additives can improve battery characteristics after storage.

<Additive A>
Additive A is lithium bis(fluorosulfonyl)imide (hereinafter also referred to as "LiFSI").

The content of additive A is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 3% by mass, and even more preferably 0% by mass, based on the total amount of the nonaqueous electrolyte. .1% to 2% by weight, more preferably 0.1% to 1.5% by weight.

<Additive B>
Additive B is vinylene carbonate (hereinafter also referred to as "VC").

The content of additive B is preferably 0.01% by mass to 3% by mass, more preferably 0.05% by mass to 2% by mass, and even more preferably 0% by mass, based on the total amount of the nonaqueous electrolyte. .1% by mass to 1.5% by mass, more preferably 0.1% by mass to 1% by mass.

<Additive C>
Additive C is at least one selected from the group consisting of a compound represented by the following formula (C1) and a compound represented by the following formula (C2).

The compound represented by formula (C1) is as follows.

In formula (C1), R ^c11 to R ^c14 each independently represent a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b). represents. In formulas (a) and (b), * represents the bonding position.

In formula (C1), the hydrocarbon group having 1 to 6 carbon atoms represented by R ^c11 to R ^c14 is preferably an alkyl group, an alkenyl group, or an alkynyl group, more preferably an alkyl group or an alkenyl group, and an alkyl group is particularly preferred.
In formula (C1), the number of carbon atoms in the hydrocarbon group having 1 to 6 carbon atoms represented by R ^c11 to R ^c14 is preferably 1 or 2, and particularly preferably 1.

Specific examples of the compound represented by formula (C1) include compounds represented by the following formulas (C1-1) to (C1-4) (hereinafter, compound (C1-1) to compound (C1), respectively). -4)), but the compound represented by formula (C1) is not limited to these specific examples.
Among these, compounds (C1-1) to (C1-3) are particularly preferred.

The compound represented by formula (C2) is as follows.

In formula (C2), R ^c21 to R ^c24 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms.

In formula (C2), R ^c21 to R ^c24 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms.

In formula (C2), the hydrocarbon group having 1 to 3 carbon atoms represented by R ^c21 to R ^c24 may be a straight chain hydrocarbon group or a hydrocarbon group having a branched and/or ring structure. It may be.
The hydrocarbon group having 1 to 3 carbon atoms represented by R ^c21 to R ^c24 is preferably an alkyl group or an aryl group, and more preferably an alkyl group.
The number of carbon atoms in the hydrocarbon group having 1 to 3 carbon atoms represented by R ^c21 to R ^c24 is preferably 1 or 2, and more preferably 1.

In formula (C2), the fluorinated hydrocarbon group having 1 to 3 carbon atoms represented by R ^c21 to R ^c24 may be a straight chain fluorinated hydrocarbon group, or may have a branched and/or ring structure. It may also be a fluorinated hydrocarbon group.
The fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^c21 to R ^c24 is preferably a fluorinated alkyl group or a fluorinated aryl group, and more preferably a fluorinated alkyl group.
The number of carbon atoms in the fluorinated hydrocarbon group having 1 to 3 carbon atoms represented by R ^c21 to R ^c24 is preferably 1 or 2, and more preferably 1.

Specific examples of the compound represented by formula (C2) include compounds represented by the following formulas (C2-1) to (C2-21) (hereinafter, compound (C2-1) to compound (C2), respectively). -21)), but the compound represented by formula (C2) is not limited to these specific examples.
Among these, compound (C2-1) is particularly preferred.

The content of additive C is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 3% by mass, even more preferably 0. .1% to 2% by weight, more preferably 0.1% to 1.5% by weight.

The non-aqueous electrolyte of the present disclosure may contain at least one of additives D to H, which will be described later.

<Additive D>
The nonaqueous electrolyte of the present disclosure may contain an additive D that is at least one selected from the group consisting of compounds represented by formula (D1).

In formula (D1), R ^d11 to R ^d14 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

In formula (D1), the hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 may be a straight chain hydrocarbon group, or a hydrocarbon group having a branched and/or ring structure. It may be.
The hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 is preferably an alkyl group or an aryl group, and more preferably an alkyl group.

In formula (D1), the number of carbon atoms in the hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 is more preferably 1 to 3, still more preferably 1 or 2, and particularly preferably 1.

In formula (D1), the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 may be a linear fluorinated hydrocarbon group, or may have a branched and/or ring structure. It may also be a fluorinated hydrocarbon group.
The fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 is preferably a fluorinated alkyl group or a fluorinated aryl group, and more preferably a fluorinated alkyl group.

In formula (D1), the number of carbon atoms in the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 is more preferably 1 to 3, still more preferably 1 or 2, and particularly preferably 1. .

Specific examples of the compound represented by formula (D1) include compounds represented by the following formulas (D1-1) to (D1-9) (hereinafter, compound (D1-1) to compound (D1), respectively). -9)), but the compound represented by formula (D1) is not limited to these specific examples.
Among these, compound (D1-1) or compound (D1-2) is particularly preferred.

When the nonaqueous electrolyte of the present disclosure contains additive D, the content of additive D with respect to the total amount of the nonaqueous electrolyte is preferably 0.001% by mass to 10% by mass, and preferably 0.005% by mass to 10% by mass. It is more preferably 5% by mass, even more preferably 0.01% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass.

<Additive E>
The nonaqueous electrolyte of the present disclosure may contain an additive E that is at least one selected from the group consisting of compounds represented by the following formula (E1).

In formula (E1), R ^e11 to R ^e14 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. However, R ^e11 to R ^e14 do not become hydrogen atoms at the same time.

In formula (E1), a preferable embodiment of the hydrocarbon group having 1 to 6 carbon atoms represented by R ^e11 to R ^e14 is the hydrocarbon group having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 in formula (D1). Same as hydrocarbon group.
However, the hydrocarbon group having 1 to 6 carbon atoms represented by R ^e11 to R ^e14 is also preferably an alkenyl group.
The number of carbon atoms in the hydrocarbon group having 1 to 6 carbon atoms represented by R ^e11 to R ^e14 is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

Preferred embodiments of the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^e11 to R ^e14 in formula (E1) are those having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 in formula (D1). This is the same as the preferred embodiment of the fluorinated hydrocarbon group in No. 6.
However, the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^e11 to R ^e14 is also preferably a fluorinated alkenyl group.
The number of carbon atoms in the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^e11 to R ^e14 is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

Specific examples of the compound represented by formula (E1) include compounds represented by the following formulas (E1-1) to (E1-5) (hereinafter, compound (E1-1) to compound (E1), respectively). -5)), but the compound represented by formula (E1) is not limited to these specific examples.
Among these, compound (E1-1) or compound (E1-2) is particularly preferred.

When the nonaqueous electrolyte of the present disclosure contains additive E, the content of additive E relative to the total amount of the nonaqueous electrolyte is preferably 0.001% by mass to 10% by mass, and preferably 0.005% by mass to 10% by mass. It is more preferably 5% by mass, even more preferably 0.01% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass.

<Additive F>
The non-aqueous electrolyte of the present disclosure may contain an additive F that is at least one selected from the group consisting of compounds represented by the following formula (F1).

In formula (F1), R ^f11 to R ^f13 each independently represent a fluorine atom or an -OLi group, and at least one of R ^f11 to R ^f13 is an -OLi group.

Specific examples of the compound represented by the formula (F1) include compounds represented by the following formula (F1-1) and the following formula (F1-2) (hereinafter referred to as compound (F1-1) and compound (F1), respectively). -2)), but the compound represented by formula (F1) is not limited to these specific examples.

When the nonaqueous electrolyte of the present disclosure contains additive F, the content of additive F with respect to the total amount of the nonaqueous electrolyte is preferably 0.001% by mass to 10% by mass, and 0.005% by mass to It is more preferably 5% by mass, even more preferably 0.01% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass.

<Additive G>
The non-aqueous electrolyte of the present disclosure may contain an additive G that is at least one selected from the group consisting of compounds represented by the following formula (G1).

In formula (G1), R ^g11 to R ^g16 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms.

In formula (G1), a preferable embodiment of the hydrocarbon group having 1 to 3 carbon atoms represented by R ^g11 to R ^g16 is R ^d11 in formula (D1), except that the hydrocarbon group has 1 to 3 carbon atoms. The preferred embodiments of the hydrocarbon group having 1 to 6 carbon atoms represented by ~R ^d14 are the same.
The number of carbon atoms in the hydrocarbon group having 1 to 3 carbon atoms represented by R ^g11 to R ^g16 is preferably 1 or 2, and more preferably 1.

Preferred embodiments of the fluorinated hydrocarbon group having 1 to 3 carbon atoms represented by R ^g11 to R ^g16 in formula (G1) are those in formula (D1), except that the number of carbon atoms is 1 to 3. The preferred embodiments are the same as the preferred embodiments of the fluorinated hydrocarbon groups having 1 to 6 carbon atoms represented by R ^d11 to R ^d14 .
The number of carbon atoms in the fluorinated hydrocarbon group having 1 to 3 carbon atoms represented by R ^g11 to R ^g16 is preferably 1 or 2, and more preferably 1.

Specific examples of the compound represented by formula (G1) include compounds represented by the following formulas (G1-1) to (G1-21) (hereinafter, compound (G1-1) to compound (G1), respectively). -21)), but the compound represented by formula (G1) is not limited to these specific examples.
Among these, compound (G1-1) is particularly preferred.

When the nonaqueous electrolyte of the present disclosure contains additive G, the content of additive G relative to the total amount of the nonaqueous electrolyte is preferably 0.001% by mass to 10% by mass, and 0.005% by mass to It is more preferably 5% by mass, even more preferably 0.01% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass.

<Additive H>
The non-aqueous electrolyte of the present disclosure may contain an additive H that is at least one selected from the group consisting of compounds represented by the following formula (H1).

In formula (H1), M represents an alkali metal, Y represents a transition element, or an element of Group 13, Group 14, or Group 15 of the periodic table, b is an integer of 1 to 3, and m is 1 to 4. , n is an integer of 0 to 8, and q is 0 or 1. R ^h11 is 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 groups are may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, m R ^h11 may each be bonded. ^h12 is a halogen atom, 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 (these groups are , may contain a substituent or a heteroatom in the structure, and when n is 2 to 8, n R ^h12s may be bonded together to form a ring), or -X ³ R ^h13 . X ¹ , X ² and X ³ each independently represent O, S or NR ^h14 , and R ^h13 and R ^h14 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a C 1 to 10 alkyl group. 10 halogenated alkyl group, aryl group having 6 to 20 carbon atoms, or halogenated aryl group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in the structure, R When a plurality of ^h13 or R ^h14 are present, each may be combined to form a ring.).

In formula (H1), M is an alkali metal, and Y is a transition metal or an element of Group 13, Group 14, or Group 15 of the periodic table. Among these, Y is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb. , Al, B or P are more preferable. When Y is Al, B or P, the anionic compound can be synthesized relatively easily and manufacturing costs can be reduced. b, which represents the valence of the anion and the number of cations, is an integer of 1 to 3, preferably 1. If b is larger than 3, it is not preferable because the salt of the anionic compound tends to be difficult to dissolve in the mixed organic solvent. Further, the constants m and n are values related to the number of ligands and are determined depending on the type of M, where m is an integer of 1 to 4 and n is an integer of 0 to 8. Constant q is 0 or 1. When q is 0, the chelate ring is a five-membered ring, and when q is 1, the chelate ring is a six-membered ring.

R ^h11 represents 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, halogenated alkylene groups, arylene groups, or halogenated arylene groups may contain a substituent or a heteroatom in their structure. Specifically, instead of the hydrogen atom of these groups, a halogen atom, a chain 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, It may contain an acyl group, amide group, or hydroxyl group as a substituent. Furthermore, a structure may be adopted in which a nitrogen atom, a sulfur atom, or an oxygen atom is introduced instead of the carbon element in these groups. Further, when q is 1 and m is 2 to 4, each of the m R ^h11s may be bonded. Such an example may include a ligand such as ethylenediaminetetraacetic acid.

R ^h12 is a halogen atom, 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 -X ³ R ^h13 (X ³ and R ^h13 will be described later).
The alkyl group, halogenated alkyl group, aryl group, or halogenated aryl group in R ^h12 may contain a substituent or a heteroatom in its structure, and n is 2 to 2, as in R ^h11 . When R 12 is 8, n R ^12s may be bonded to each other to form a ring. R ⁹² is preferably an electron-withdrawing group, particularly preferably a fluorine atom.

X ¹ , X ² and X ³ each independently represent O, S or NR ^h14 . In other words, the ligand will be bonded to Y via these heteroatoms.

R ^h13 and R ^h14 are each independently a hydrogen atom, 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 aryl group having 6 to 20 carbon atoms. Represents a halogenated aryl group. These alkyl groups, halogenated alkyl groups, aryl groups, or halogenated aryl groups may contain a substituent or a heteroatom in their structure, similar to R ^h11 . Furthermore, when a plurality of R ^h13 and R ^h14 are present, each may be combined to form a ring.

Examples of the alkali metal represented by M include lithium, sodium, potassium, and the like. Among these, lithium is particularly preferred.
As n, an integer of 0 to 4 is preferable.

Examples of the compound represented by the formula (H1) include a compound represented by the following formula (H1-1), a compound represented by the following formula (H1-2), and a compound represented by the following formula (H1-3). , a compound represented by the following formula (H1-4), and a compound represented by the following formula (H1-5).

In formulas (H1-1) to (H1-5), M has the same meaning as M in formula (H1), and preferred embodiments are also the same.

The compound represented by formula (H1) is particularly preferably a compound represented by formula (H1-1) in which M is lithium, or a compound represented by formula (H1-4). and M is lithium.

When the nonaqueous electrolyte of the present disclosure contains additive H, the content of additive H relative to the total amount of the nonaqueous electrolyte is preferably 0.001% by mass to 10% by mass, and preferably 0.005% by mass to 10% by mass. It is more preferably 5% by mass, even more preferably 0.01% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass.

<Electrolyte>
The non-aqueous electrolyte of the present disclosure contains an electrolyte containing lithium hexafluorophosphate (also referred to as “LiPF ₆ ”).
The proportion of LiPF ₆ in the electrolyte is preferably 10% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass.

The concentration of electrolyte in the non-aqueous electrolyte of the present disclosure is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 2 mol/L.
Further, the concentration of LiPF ₆ in the non-aqueous electrolyte of the present disclosure is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 2 mol/L.

The electrolyte may contain compounds other than _LiPF6 .
As compounds other than LiPF ₆ ;
_{( C2H5 ) 4NPF6 ,} ( _{C2H5 ) 4NBF4 ,} ( _{C2H5 ) 4NClO4 ,} ( _{C2H5 ) 4NAsF6 , ( C2H5} ) _{4N2SiF 6} , (C ₂ H ₅ ) ₄ NOSO ₂ C _k F _(2k+1) (k=integer from 1 to 8), (C ₂ H ₅ ) ₄ NPF _n [C _k F _(2k+1) ] _(6-n) ( tetraalkylammonium salts such as n = integer of 1 to 5, k = integer of 1 to 8);
LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _(2k+1) (k=integer from 1 to 8), LiPF _n [C _k F _(2k+1) ] _(6-n) (n= (integer from 1 to 5, k = integer from 1 to 8), LiC (SO ₂ R ⁷ ) (SO ₂ R ⁸ ) (SO ₂ R ⁹ ), LiN (SO ₂ OR ¹⁰ ) (SO ₂ OR ¹¹ ), LiN Lithium salts such as (SO ₂ R ¹² ) (SO ₂ R ¹³ ) (where R ⁷ to R ¹³ may be the same or different and are a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms) (i.e., lithium salts other than LiPF ₆ );
etc.

<Non-aqueous solvent>
The non-aqueous electrolyte of the present disclosure may contain a non-aqueous solvent.
The number of non-aqueous solvents may be one, or two or more.
As the non-aqueous solvent, various known ones can be appropriately selected.
As the nonaqueous solvent, for example, the nonaqueous solvents described in paragraphs 0069 to 0087 of JP 2017-45723A can be used.

Preferably, the nonaqueous solvent contains a cyclic carbonate compound and a chain carbonate compound.
In this case, the number of cyclic carbonate compounds and chain carbonate compounds contained in the nonaqueous solvent may be one, or two or more.

Examples of the cyclic carbonate compound include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.
Among these, ethylene carbonate and propylene carbonate, which have a high dielectric constant, are preferred. In the case of a battery using a negative electrode active material containing graphite, the nonaqueous solvent more preferably contains ethylene carbonate.

Examples of chain carbonate compounds include dimethyl carbonate, methylethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylisopropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, methylbutyl carbonate, ethylbutyl carbonate, dibutyl carbonate, methylpentyl carbonate, and ethylpentyl. carbonate, dipentyl carbonate, methylheptyl carbonate, ethylheptyl carbonate, diheptyl carbonate, methylhexyl carbonate, ethylhexyl carbonate, dihexyl carbonate, methyloctyl carbonate, ethyl octyl carbonate, dioctyl carbonate, and the like.

Examples of combinations of cyclic carbonate and linear carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, propylene carbonate and Diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate and diethyl carbonate , ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and the like.

The mixing ratio of the cyclic carbonate compound and the chain carbonate compound, expressed in mass ratio, is cyclic carbonate compound:chain carbonate compound, for example, 5:95 to 80:20, preferably 10:90 to 70:30, more preferably is from 15:85 to 55:45. By setting such a ratio, it is possible to suppress the increase in viscosity of the non-aqueous electrolyte and increase the degree of dissociation of the electrolyte, thereby increasing the conductivity of the non-aqueous electrolyte, which is related to the charging and discharging characteristics of the battery. . Furthermore, the solubility of the electrolyte can be further increased. Therefore, a non-aqueous electrolyte having excellent electrical conductivity at room temperature or low temperature can be obtained, so that the load characteristics of the battery at room temperature or low temperature can be improved.

The non-aqueous solvent may contain other compounds than the cyclic carbonate compound and the chain carbonate compound.
In this case, the number of other compounds contained in the nonaqueous solvent may be one, or two or more.
Other compounds include cyclic carboxylic acid ester compounds (e.g. γ-butyrolactone), cyclic sulfone compounds, cyclic ether compounds, chain carboxylic acid ester compounds, chain ether compounds, chain phosphate ester compounds, amide compounds, and chain carbamates. compounds, cyclic amide compounds, cyclic urea compounds, boron compounds, polyethylene glycol derivatives, and the like.
Regarding these compounds, the descriptions in paragraphs 0069 to 0087 of JP 2017-45723 A can be appropriately referred to.

The proportion of the cyclic carbonate compound and the chain carbonate compound in the nonaqueous solvent is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more.
The proportion of the cyclic carbonate compound and the chain carbonate compound in the nonaqueous solvent may be 100% by mass.

The proportion of the nonaqueous solvent in the nonaqueous electrolyte is preferably 60% by mass or more, more preferably 70% by mass or more.
The upper limit of the proportion of the nonaqueous solvent in the nonaqueous electrolyte depends on the content of other components (electrolytes, additives, etc.), but the upper limit is, for example, 99% by mass, preferably 97% by mass. The content is more preferably 90% by mass.

[Lithium ion secondary battery]
The lithium ion secondary battery of the present disclosure includes:
a positive electrode including a positive electrode active material layer containing a positive electrode active material;
a negative electrode including a negative electrode active material layer containing a negative electrode active material;
The above-mentioned non-aqueous electrolyte for batteries according to the present disclosure,
Equipped with.
In the lithium ion secondary battery of the present disclosure, deterioration in battery characteristics after storage is reduced.
This effect is brought about by the combination of additives A to C contained in the non-aqueous electrolyte.

<Positive electrode>
The positive electrode includes a positive electrode active material layer containing a positive electrode active material. It is preferable that a lithium nickel manganese cobalt composite oxide is included as the positive electrode active material. As the lithium nickel manganese cobalt composite oxide, a compound represented by the following formula (P1) is preferable.

_{LiNix Mny Coz} O ₂ … (P1)
[In formula (P1), x, y and z are each independently greater than 0 and less than 1.00, and the sum of x, y and z is 0.99 to 1.00. ]

In formula (P1), x is preferably 0.10 to 0.90, more preferably 0.30 to 0.90, still more preferably 0.50 to 0.90, even more preferably It is more than 0.50 and not more than 0.90, more preferably 0.55 to 0.90, and even more preferably 0.60 to 0.80.
In formula (P1), y is preferably 0.10 to 0.90, more preferably 0.10 to 0.50, and still more preferably 0.20 to 0.40.
In formula (P1), z is preferably 0.10 to 0.90, more preferably 0.10 to 0.50, and still more preferably 0.10 to 0.30.

Examples of the compound represented by formula (P1) include LiNi _0.33 Mn _0.33 Co _0.33 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.6 Mn _0.2 Co _0.2 O ₂ or LiNi _0.8 Mn _0.1 Co _0.1 O ₂ is preferred, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.6 Mn _0.2 Co _{0 .2} O ₂ or LiNi _0.8 Mn _0.1 Co _0.1 O ₂ is more preferred, and LiNi _0.6 Mn _0.2 Co _0.2 O ₂ or LiNi _0.8 Mn _0.1 Co _{0. 1} O ₂ is more preferred.

The positive electrode may contain components other than the lithium nickel manganese cobalt composite oxide as a positive electrode active material.
Ingredients other than lithium nickel manganese cobalt composite oxide are:
Transition metal oxides or transition _metal sulfides such as _MoS2 , _TiS2 , _MnO2 , _V2O5 ;
Composite oxides made of lithium and transition metals, such _as LiCoO ₂ , LiMnO 2 , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _X Co _(1-X) O ₂ [0<X<1], LiFePO ₄ , LiMnPO ₄ (However, excluding lithium nickel manganese cobalt composite oxide);
Conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, polyaniline composite;
etc.

The proportion of the lithium nickel manganese cobalt composite oxide in the positive electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.
The proportion of the lithium nickel manganese cobalt composite oxide in the positive electrode active material may be 100% by mass or less than 100% by mass.

The positive electrode preferably includes a positive electrode active material layer containing a positive electrode active material.
The positive electrode active material layer may contain components other than the positive electrode active material.
Components other than the positive electrode active material include a conductive aid, a binder, and the like.
Examples of the conductive aid include carbon materials such as carbon black (eg, acetylene black), amorphous whiskers, and graphite.
Examples of the binder include polyvinylidene fluoride.

The positive electrode active material layer can be formed by applying a positive electrode mixture slurry containing a positive electrode active material and a solvent onto a positive electrode current collector, which will be described later, and drying the slurry.
The positive electrode mixture slurry may contain components other than the positive electrode active material (for example, a conductive auxiliary agent, a binder, etc.).
Examples of the solvent in the positive electrode mixture slurry include organic solvents such as N-methylpyrrolidone.

The proportion of the positive electrode active material in the total solid content of the positive electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.
The proportion of the positive electrode active material in the total solid content of the positive electrode active material layer may be 100% by mass.
Here, the total solid content of the positive electrode active material layer means the total amount of the positive electrode active material layer excluding the solvent, if the solvent remains in the positive electrode active material layer. If there is no remaining amount, it means the entire amount of the positive electrode active material layer.

The proportion of the lithium nickel manganese cobalt composite oxide in the total solid content of the positive electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more.
The proportion of the lithium nickel manganese cobalt composite oxide in the total solid content of the positive electrode active material layer may be 100% by mass or less than 100% by mass.

The positive electrode preferably includes a positive electrode current collector.
The material of the positive electrode current collector is not particularly limited, and any known material can be used.
Specific examples of the positive electrode current collector include metal materials such as aluminum, aluminum alloy, stainless steel, nickel, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and the like.

<Negative electrode>
The negative electrode includes a negative electrode active material layer containing a negative electrode active material.
Examples of negative electrode active materials include metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped and dedoped with lithium ions, and oxides that can be doped and dedoped with lithium ions. At least one member selected from the group consisting of transition metal nitrides and carbon materials capable of doping and dedoping with lithium ions can be used.
Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, and tin alloys.
Examples of oxides that can be doped and dedoped with lithium ions include lithium titanate, silicon oxide (preferably SiOx (X represents 0.5 or more and less than 1.6), more preferably SiO), etc. Can be done.
Among these, carbon materials that can be doped and dedoped with lithium ions are preferred.
Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The carbon material may be in any of fibrous, spherical, potato-like, and flake-like forms.

Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or lower, and mesophase pitch carbon fiber (MCF).
Examples of the graphite material include natural graphite and artificial graphite. As the artificial graphite, graphitized MCMB, graphitized MCF, etc. are used. Further, as the graphite material, one containing boron can also be used. Further, as the graphite material, those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those coated with a mixture of amorphous carbon and graphite can also be used.

These carbon materials may be used alone or in combination of two or more.
The above-mentioned carbon material is particularly preferably a carbon material in which the interplanar spacing d(002) of the (002) plane measured by X-ray analysis is 0.340 nm or less. Further, as the carbon material, graphite having a true density of 1.70 g/cm ³ or more or a highly crystalline carbon material having properties similar to graphite is also preferable. By using carbon materials such as those described above, it is possible to further increase the energy density of the battery.

The proportion of the carbon material (preferably graphite material) in the negative electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.
The proportion of the carbon material (preferably graphite material) in the negative electrode active material may be 100% by mass or less than 100% by mass.

The negative electrode preferably includes a negative electrode active material layer containing a negative electrode active material.
The negative electrode active material layer may contain components other than the negative electrode active material.
Components other than the negative electrode active material include a binder.
Examples of the binder include carboxymethyl cellulose and SBR latex.

The negative electrode active material layer may be formed by applying a negative electrode mixture slurry containing a negative electrode active material and a solvent onto a negative electrode current collector, which will be described later, and drying the slurry.
The negative electrode mixture slurry may contain components other than the negative electrode active material (for example, a binder).
Examples of the solvent in the negative electrode mixture slurry include water.

The proportion of the negative electrode active material in the total solid content of the negative electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.
The proportion of the negative electrode active material in the total solid content of the negative electrode active material layer may be 100% by mass.
Here, the total solid content of the negative electrode active material layer means the total amount of the negative electrode active material layer excluding the solvent when the solvent remains in the negative electrode active material layer. If there is no remaining amount, it means the entire amount of the negative electrode active material layer.

The proportion of the carbon material (preferably graphite material) in the total solid content of the negative electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. .
The proportion of the carbon material (preferably graphite material) in the total solid content of the negative electrode active material layer may be 100% by mass.

The negative electrode preferably includes a negative electrode current collector.
The material of the negative electrode current collector is not particularly limited, and any known material can be used.
Specific examples of the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is particularly preferred from the viewpoint of ease of processing.

<Separator>
The lithium ion secondary battery of the present disclosure preferably includes a separator between the negative electrode and the positive electrode.
The separator is a membrane that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and examples thereof include a porous membrane and a polymer electrolyte.
A microporous polymer film is preferably used as the porous membrane, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, and polyester.
Particularly preferred are porous polyolefins, and specific examples include porous polyethylene films, porous polypropylene films, and multilayer films of porous polyethylene films and polypropylene films. Other resins having excellent thermal stability may be coated on the porous polyolefin film.
Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, a polymer swollen with an electrolytic solution, and the like.
The non-aqueous electrolyte of the present disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

<Battery configuration>
The lithium ion secondary battery of the present disclosure can take various known shapes, such as a cylindrical shape, a coin shape, a square shape, a laminate shape, a film shape, and other arbitrary shapes. However, the basic structure of a battery is the same regardless of its shape, and the design can be changed depending on the purpose.

An example of the lithium ion secondary battery of the present disclosure is a laminate type battery.
FIG. 1 is a schematic perspective view showing an example of a laminate type battery, which is an example of a lithium ion secondary battery of the present disclosure, and FIG. FIG. 3 is a schematic cross-sectional view in the horizontal direction.
The laminated battery shown in FIG. 1 contains a non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1), and has a sealed peripheral edge. The device includes a laminate exterior body 1 whose interior is hermetically sealed. As the laminate exterior body 1, for example, a laminate exterior body made of aluminum is used.
As shown in FIG. 2, the laminated electrode body housed in the laminate exterior body 1 includes a laminated body in which positive electrode plates 5 and negative electrode plates 6 are alternately laminated with separators 7 in between, and a laminated body of this laminated body. A separator 8 surrounding the periphery is provided. The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the nonaqueous electrolyte of the present disclosure. The positive electrode plate 5 includes a positive electrode current collector and a positive electrode active material layer. The negative electrode plate 5 includes a negative electrode current collector and a negative electrode active material layer.
Each of the plurality of positive electrode plates 5 in the laminated electrode body is electrically connected to the positive electrode terminal 2 via a positive electrode tab (not shown), and a part of the positive electrode terminal 2 is connected to the laminate exterior body 1. It protrudes outward from the peripheral edge (Figure 1). A portion of the peripheral end of the laminate exterior body 1 from which the positive electrode terminal 2 protrudes is sealed with an insulating seal 4.
Similarly, each of the plurality of negative electrode plates 6 in the laminated electrode body is electrically connected to the negative electrode terminal 3 via a negative electrode tab (not shown), and a part of the negative electrode terminal 3 is connected to the laminate exterior. It protrudes outward from the peripheral end of the body 1 (Fig. 1). A portion of the peripheral end of the laminate exterior body 1 from which the negative electrode terminal 3 protrudes is sealed with an insulating seal 4.
In addition, in the laminated battery according to the above example, the number of positive electrode plates 5 is five and the number of negative electrode plates 6 is six, and the positive electrode plates 5 and the negative electrode plates 6 are connected to the uppermost part of both sides with a separator 7 in between. The outer layers are laminated in such a manner that each of them becomes a negative electrode plate 6. However, it goes without saying that the number of positive electrode plates, the number of negative electrode plates, and their arrangement in the laminate type battery are not limited to this example, and various changes may be made.

Another example of the lithium ion secondary battery of the present disclosure includes a coin type battery.
FIG. 3 is a schematic perspective view showing an example of a coin-type battery that is another example of the lithium ion secondary battery of the present disclosure.
In the coin-type battery shown in FIG. 3, a disc-shaped negative electrode 12, a separator 15 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 11, and spacer plates 17 and 18 made of stainless steel or aluminum, if necessary, are arranged in this order. The stacked state is stored between the positive electrode can 13 (hereinafter also referred to as "battery can") and the sealing plate 14 (hereinafter also referred to as "battery can lid"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed via a gasket 16.
In this example, the nonaqueous electrolyte of the present disclosure is used as the nonaqueous electrolyte injected into the separator 15. The disk-shaped positive electrode 11 includes a positive electrode current collector and a positive electrode active material layer. The disc-shaped negative electrode 12 includes a negative electrode current collector and a negative electrode active material layer.

Note that the lithium ion secondary battery of the present disclosure is a lithium ion secondary battery (a lithium ion secondary battery before charging and discharging) that includes a positive electrode, a negative electrode, and a nonaqueous electrolyte of the present disclosure. It may also be a lithium ion secondary battery obtained by
That is, in the lithium ion secondary battery of the present disclosure, first, a lithium ion secondary battery before charging and discharging that includes a positive electrode, a negative electrode, and the nonaqueous electrolyte of the present disclosure is produced, and then, the lithium ion secondary battery before charging and discharging is prepared. The lithium ion secondary battery may be a lithium ion secondary battery (charged and discharged lithium ion secondary battery) produced by charging and discharging a lithium ion secondary battery one or more times.

The use of the lithium ion secondary battery of the present disclosure is not particularly limited, and it can be used for various known uses. For example, notebook computers, mobile computers, mobile phones, headphone stereos, video movies, LCD TVs, handy cleaners, electronic notebooks, calculators, radios, backup power supplies, motors, automobiles, electric vehicles, motorcycles, electric motorcycles, bicycles, electric It can be widely used in bicycles, lighting equipment, game consoles, watches, power tools, cameras, etc., regardless of whether they are small portable devices or large devices.

Examples of the present disclosure will be shown below, but the present disclosure is not limited to the following examples.
In the following examples, the "addition amount" means the content in the finally obtained non-aqueous electrolyte (that is, the amount relative to the total amount of the finally obtained non-aqueous electrolyte).
Moreover, "wt%" means mass %.

[Example 1]
A coin-type battery (test battery), which is a lithium ion secondary battery, was produced using the following procedure.
<Preparation of negative electrode>
A paste-like negative electrode mixture slurry was prepared by kneading amorphous coated natural graphite (97 parts by mass), carboxymethyl cellulose (1 part by mass), and SBR latex (2 parts by mass) with a water solvent.
Next, this negative electrode mixture slurry is applied to a 10 μm thick strip-shaped copper foil negative electrode current collector, dried, and then compressed with a roll press to form a sheet-like negative electrode consisting of the negative electrode current collector and negative electrode active material layer. I got it. The coating density of the negative electrode active material layer at this time was 12 mg/cm ² and the packing density was 1.5 g/mL.

<Preparation of positive electrode>
LiNi _0.5 Mn _0.3 Co _0.2 O ₂ (90 parts by mass), acetylene black (5 parts by mass) and polyvinylidene fluoride (5 parts by mass) were kneaded using N-methylpyrrolidinone as a solvent to form a paste. A positive electrode mixture slurry was prepared.
Next, this positive electrode mixture slurry is applied to a positive electrode current collector made of a strip of aluminum foil with a thickness of 20 μm, dried, and then compressed with a roll press to form a sheet-like positive electrode consisting of a positive electrode current collector and a positive electrode active material layer. I got it. The coating density of the positive electrode active material layer at this time was 22 mg/cm ² and the packing density was 2.5 g/ml.

<Preparation of non-aqueous electrolyte>
As a nonaqueous solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:35:35 (mass ratio), respectively, to obtain a mixed solvent.
LiPF ₆ as an electrolyte was dissolved in the obtained mixed solvent so that the electrolyte concentration in the finally prepared non-aqueous electrolyte was 1 mol/liter.
LiFSI, VC, and a compound represented by formula (C1-1) (hereinafter also referred to as "compound (C1-1)") were added to the resulting solution as additives. The non-aqueous electrolyte was added in such a manner that the content thereof based on the total mass of the non-aqueous electrolyte was 0.5% by mass, 0.3% by mass, and 0.5% by mass to obtain a non-aqueous electrolyte.

<Production of coin-type battery>
The above-mentioned negative electrode was punched out into a disk shape with a diameter of 14 mm, and the above-mentioned positive electrode was punched out into a disk shape with a diameter of 13 mm to obtain a coin-shaped negative electrode and a coin-shaped positive electrode, respectively. Further, a 20 μm thick microporous polyethylene film was punched out into a disc shape with a diameter of 17 mm to obtain a separator.
The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode were stacked in this order in a stainless steel battery can (2032 size), and then 20 μL of the above-mentioned non-aqueous electrolyte was poured into the battery can. It was injected into the separator, positive electrode, and negative electrode.
Next, an aluminum plate (thickness: 1.2 mm, diameter: 16 mm) and a spring were placed on the positive electrode, and a battery can lid was caulked through a polypropylene gasket to seal the battery.
As a result, a coin-shaped battery (ie, a coin-shaped lithium ion secondary battery) having the configuration shown in FIG. 3 and having a diameter of 20 mm and a height of 3.2 mm was obtained.

<Evaluation>
The following evaluations were performed on the obtained coin-type battery.
The evaluation results are shown in Table 1.
Table 1 shows the initial resistance (that is, the resistance before storage), the resistance after storage, and the rate of increase in resistance during storage of the coin-shaped batteries obtained in each example.

In the following,
"Conditioning" means repeating charging and discharging of a coin-type battery three times between 2.75V and 4.25V at 25°C in a constant temperature bath,
"Storage" means an operation in which the coin-type battery is stored at 60° C. for 10 days in a constant temperature bath.
Hereinafter, the DC resistance was measured at a temperature of 25°C.

(Measurement of initial resistance)
After conditioning, the SOC (State of Charge) of the coin-type battery is adjusted to 50%, and then the initial (i.e., before storage) DCIR (Direct current internal resistance) of the coin-type battery is adjusted by the following method. It was measured.
CC discharge was performed for 10 seconds at a discharge rate of 0.2C to 5C using the above-mentioned coin-type battery adjusted to SOC 50%.
Here, CC10s discharge means discharging at a constant current for 10 seconds.
In the above "CC discharge at a discharge rate of 0.2C to 5C", each current value (that is, the current value corresponding to a discharge rate of 0.2C to 5C) and each voltage drop amount corresponding to each current value (= discharge start The DC resistance (Ω) was determined based on the previous voltage (voltage at 10 seconds after the start of discharge). The obtained DC resistance (Ω) was defined as the initial resistance (ie, the resistance before storage) (Ω). The results are shown in Table 1.

(Measurement of resistance after storage)
After conditioning, but before adjusting the SOC to 50%, the coin-type battery is CC-CV charged to 4.25V at a charging rate of 0.2C in a thermostatic chamber, and then subjected to "storage" under the above conditions. The resistance (Ω) after storage was measured in the same manner as the initial resistance measurement described above except that . The results are shown in Table 1.
Here, CC-CV charging means constant current-constant voltage.

(Calculation of resistance increase rate during storage)
The rate of increase in resistance during storage was calculated using the following formula.
Resistance increase rate during storage = ((Resistance after storage (Ω) / Initial resistance (Ω)) x 100)

Table 1 shows the resistance increase rate (also simply referred to as "increase rate") during storage.
Here, the increase rate means that if the value exceeds 100, the DC resistance of the battery after storage has increased compared to the initial resistance, and if the value is less than 100, the DC resistance of the battery after storage has increased. This means that the resistance has decreased compared to the initial resistance.

[Examples 2 to 8, Comparative Examples 1 to 6]
The same operation as in Example 1 was performed except that the combinations of types and amounts of additives contained in the non-aqueous electrolyte were changed as shown in Table 1.
The results are shown in Table 1.
In Table 1, "-" means that the corresponding additive is not contained.

As shown in Table 1, in Examples 1 to 8 containing all of Additives A to C in the non-aqueous electrolyte, the increase in battery resistance due to storage was reduced compared to Comparative Examples 1 to 6 (Table 1 (See “Increase rate”).

Claims (10)

an electrolyte containing lithium hexafluorophosphate;
Additive A, which is lithium bis(fluorosulfonyl)imide;
Additive B, which is vinylene carbonate;
an additive C which is at least one selected from the group consisting of a compound represented by the following formula (C1) and a compound represented by the following formula (C2);
Contains
A non-aqueous electrolyte for a battery, wherein the content of the additive A is more than 1.0% by mass based on the total amount of the non-aqueous electrolyte .

[In formula (C1), R ^c11 to R ^c14 are each independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b) represents a group. In formulas (a) and (b), * represents the bonding position.
In formula (C2), R ^c21 to R ^c24 each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms. ] The nonaqueous electrolyte for a battery according to claim 1, wherein the content of the additive A is more than 1.0% by mass and 2.0% by mass or less based on the total amount of the nonaqueous electrolyte. The non-aqueous electrolyte for a battery according to claim 1 or 2, wherein the content of the additive A is 1.5% by mass or more based on the total amount of the non-aqueous electrolyte. The nonaqueous battery according to any one of claims 1 to 3 , wherein the content of the additive B is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the nonaqueous electrolyte. Water electrolyte. The nonaqueous battery according to any one of claims 1 to 4 , wherein the content of the additive C is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the nonaqueous electrolyte. Water electrolyte. The nonaqueous electrolyte for a battery according to any one of claims 1 to 5, wherein the concentration of the electrolyte is 0.1 mol/L or more and 3 mol/L or less based on the total amount of the nonaqueous electrolyte. a positive electrode including a positive electrode active material layer containing a positive electrode active material;
a negative electrode including a negative electrode active material layer containing a negative electrode active material;
The non-aqueous electrolyte for batteries according to any one of claims 1 to 6 ,
A lithium-ion secondary battery equipped with. The lithium ion secondary battery according to claim 7, wherein the positive electrode active material includes a lithium nickel manganese cobalt composite oxide. The lithium ion secondary battery according to claim 7 or 8, wherein the negative electrode active material contains a carbon material. A lithium ion secondary battery obtained by charging and discharging the lithium ion secondary battery according to any one of claims 7 to 9 .