JP2022126851A - Non-aqueous electrolyte for batteries and lithium secondary batteries - Google Patents

Abstract

The present invention provides a nonaqueous electrolyte for a battery that can improve the capacity retention rate of the battery after storage. [Solution] Contains additive A which is a compound represented by formula (A), additive B which is a compound represented by formula (B), and an electrolyte which is a lithium salt other than additive B. A non-aqueous electrolyte for batteries, wherein the content of the additive B is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte for batteries. R1 is an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms, substituted with at least one fluorine atom Represents a hydrocarbon oxy group having 1 to 6 carbon atoms or a fluorine atom. R2 represents a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom. JPEG2022126851000009.jpg31164 [Selection diagram] None

Description

TECHNICAL FIELD The present disclosure relates to non-aqueous electrolytes for batteries and lithium secondary batteries.

In recent years, lithium secondary batteries have been widely used as power sources for electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage. In recent years, in particular, 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 secondary battery includes, for example, a positive electrode and a negative electrode containing a material capable of intercalating and deintercalating lithium, and a non-aqueous battery electrolyte containing a lithium salt and a non-aqueous solvent.
As the positive electrode active material used for the positive electrode, for example, lithium metal oxides such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ and LiFePO ₄ are used.
As the non-aqueous electrolyte for batteries, LiPF ₆ , LiBF ₄ and LiN(SO ₂ CF ₃ ) are added to a mixed solvent (non-aqueous solvent) of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate and ethyl methyl carbonate. ₂ and LiN(SO ₂ CF ₂ CF ₃ ) ₂ solutions mixed with Li electrolytes are used.
On the other hand, as negative electrode active materials used for the negative electrode, metallic lithium, metallic compounds capable of intercalating and deintercalating lithium (elemental metals, oxides, alloys with lithium, etc.) and carbon materials are known. Lithium secondary batteries using coke, artificial graphite, and natural graphite, which are capable of absorbing and desorbing, have been put to practical use.

In order to improve the performance of a battery containing a non-aqueous battery electrolyte (for example, a lithium secondary battery), various additives are added to the non-aqueous battery electrolyte.
For example, additive A, which is a five-membered cyclic sulfate compound having a specific structure, is used as a non-aqueous electrolyte for batteries capable of improving low-temperature cycle characteristics and suppressing deposition of metallic lithium after low-temperature cycles. and an additive B that is a sulfonyl fluoride compound having a specific structure (see, for example, Patent Document 1).

JP 2016-66481 A

However, in some cases, it is required to further improve the capacity retention rate after storage for a battery containing a non-aqueous electrolyte containing an additive that is a sulfonyl fluoride compound with a specific structure.
Therefore, an object of the present disclosure is to provide a non-aqueous electrolyte for batteries that can improve the capacity retention rate of batteries after storage, and a lithium secondary battery using this non-aqueous electrolyte for batteries. be.

Means for solving the above problems include the following aspects.
<1> an additive A which is a compound represented by formula (A);
an additive B which is a compound represented by formula (B);
an electrolyte that is a lithium salt other than additive B;
A non-aqueous electrolyte for batteries containing

[In the formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms, a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a hydrocarbon oxy group having 1 to 6 carbon atoms. , represents a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom.
In formula (B), R ² is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or represents a fluorine atom. ]

<2> The nonaqueous electrolyte for batteries according to <1>, wherein the content of the additive A is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for batteries.
<3> The non-aqueous electrolyte for batteries according to <1> or <2>, wherein the content of the additive B is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries. .
<4> The battery according to any one of <1> to <3>, further comprising an additive C that is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. Non-aqueous electrolyte.
<5> The non-aqueous electrolyte for batteries according to <4>, wherein the content of the additive C is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries.

<6> a positive electrode;
Metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, transition metal nitrides that can be doped/dedoped with lithium ions, and lithium a negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of ion doping and dedoping;
The non-aqueous electrolyte for batteries according to any one of <1> to <5>,
Lithium secondary battery including.
<7> A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to <6>.

Advantageous Effects of Invention According to the present disclosure, a non-aqueous electrolyte for batteries capable of improving the capacity retention rate of batteries after storage, and a lithium 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 secondary battery of the present disclosure; FIG. FIG. 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. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure;

In this specification, a numerical range represented by "to" means a range including the numerical values before and after "to" as lower and upper limits.
As used herein, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. means

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte for a battery of the present disclosure (hereinafter also simply referred to as “non-aqueous electrolyte”) is an additive A that is a compound represented by formula (A) and a compound represented by formula (B). It contains an additive B and an electrolyte other than the additive B, which is a lithium salt.

In formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms, a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms, represents a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom;
In formula (B), R ² is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or represents a fluorine atom.

According to the non-aqueous electrolyte solution of the present disclosure, it is possible to improve the capacity retention rate of the battery after storage.
Although the reason for such an effect is not clear, it is believed that the combination of additive A and additive B forms a highly durable film on the electrode surface of the battery.

Each component of the non-aqueous electrolyte of the present disclosure will be described below.

<Additive A>
The non-aqueous electrolytic solution of the present disclosure contains additive A, which is a compound represented by formula (A) below.
The additive A may be only one selected from the group consisting of compounds represented by the following formula (A), or may be two or more.

In formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms, a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms, represents a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom;

The “hydrocarbon group having 1 to 6 carbon atoms” represented by R ¹ represents an unsubstituted hydrocarbon group having 1 to 6 carbon atoms.
The “hydrocarbon group having 1 to 6 carbon atoms” represented by R ¹ may be a linear hydrocarbon group, a branched hydrocarbon group, or a cyclic hydrocarbon group.
The “hydrocarbon group having 1 to 6 carbon atoms” represented by R ¹ is preferably an alkyl group or an alkenyl group, more preferably an alkyl group.
The number of carbon atoms in the “hydrocarbon group having 1 to 6 carbon atoms” represented by R ¹ is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

Examples of the "hydrocarbon group having 1 to 6 carbon atoms" represented by R ¹ include methyl group, ethyl group, n-propyl group, isopropyl group, 1-ethylpropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, 2-methylbutyl group, 3,3-dimethylbutyl group, n-pentyl group, isopentyl group, neopentyl group, 1-methylpentyl group, n-hexyl group, isohexyl group, sec- Alkyl groups such as hexyl group and tert-hexyl group; vinyl group, 1-propenyl group, allyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, pentenyl group, hexenyl group, isopropenyl group, 2- alkenyl groups such as methyl-2-propenyl group, 1-methyl-2-propenyl group, 2-methyl-1-propenyl group;

Examples of the "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by R ¹ include the above-mentioned "hydrocarbon group having 1 to 6 carbon atoms" represented by R ¹ (i.e. , an unsubstituted hydrocarbon group having 1 to 6 carbon atoms) is substituted with at least one fluorine atom.

Examples of the "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by R ¹ include fluoromethyl group, difluoromethyl group, trifluoromethyl group, 2,2,2- fluoroalkyl groups such as trifluoroethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, perfluoroisopropyl group, perfluoroisobutyl group; 2-fluoroethenyl group, 2,2-difluoroethenyl group, 2-fluoro-2-propenyl group, 3,3-difluoro-2-propenyl group, 2,3-difluoro-2-propenyl group, 3,3-difluoro-2- fluoroalkenyl groups such as methyl-2-propenyl group, 3-fluoro-2-butenyl group, perfluorovinyl group, perfluoropropenyl group and perfluorobutenyl group;

In formula (A), the portion of the hydrocarbon group in the structure of the “hydrocarbon oxy group having 1 to 6 carbon atoms” represented by R ¹ is the “hydrocarbon oxy group having 1 to 6 carbon atoms” represented by R ¹ above. It is synonymous with "hydrocarbon group".
The “hydrocarbonoxy group having 1 to 6 carbon atoms” represented by R ¹ is preferably an alkoxy group or an alkenyloxy group, more preferably an alkoxy group.

Examples of the "hydrocarbonoxy group having 1 to 6 carbon atoms" represented by R ¹ include methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, 2-butoxy and tert-butoxy. , an alkoxy group such as a cyclopropyloxy group and a cyclopentyloxy group; an alkenyloxy group such as an allyloxy group and a vinyloxy group; and the like.

In formula (A), the "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by R ¹ includes the above-mentioned "C ¹ to 6 (ie, an unsubstituted hydrocarbon oxy group having 1 to 6 carbon atoms) is substituted with at least one fluorine atom.

In formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms (that is, an unsubstituted hydrocarbon group having 1 to 6 carbon atoms), or a carbon number substituted with at least one fluorine atom. A hydrocarbon group having 1 to 6 carbon atoms is preferred, a hydrocarbon group having 1 to 6 carbon atoms is more preferred, and an alkyl group having 1 to 6 carbon atoms is particularly preferred.

As the compound represented by formula (A),
methanesulfonyl fluoride, ethanesulfonyl fluoride, propanesulfonyl fluoride, 2-propanesulfonyl fluoride, butanesulfonyl fluoride, 2-butanesulfonyl fluoride, hexanesulfonyl fluoride, trifluoromethanesulfonyl fluoride, perfluoroethanesulfonyl fluoride , perfluoropropanesulfonyl fluoride, perfluorobutanesulfonyl fluoride, ethenesulfonyl fluoride, 1-propene-1-sulfonyl fluoride, or 2-propene-1-sulfonyl fluoride,
methanesulfonyl fluoride, ethanesulfonyl fluoride, propanesulfonyl fluoride, 2-propanesulfonyl fluoride, butanesulfonyl fluoride, 2-butanesulfonyl fluoride, hexanesulfonyl fluoride, trifluoromethanesulfonyl fluoride, perfluoroethanesulfonyl fluoride is more preferred, perfluoropropanesulfonyl fluoride, or perfluorobutanesulfonyl fluoride,
More preferably, methanesulfonyl fluoride, ethanesulfonyl fluoride, propanesulfonyl fluoride, 2-propanesulfonyl fluoride, butanesulfonyl fluoride, 2-butanesulfonyl fluoride, or hexanesulfonyl fluoride,
more preferably methanesulfonyl fluoride, ethanesulfonyl fluoride or propanesulfonyl fluoride,
Methanesulfonyl fluoride is particularly preferred.

The content of additive A is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 10% by mass, and 0.05% by mass to 5% by mass, relative to the total amount of the non-aqueous electrolyte. More preferably 0.1% by mass to 5% by mass, more preferably 0.5% by mass to 5% by mass, still more preferably 0.5% by mass to 3% by mass, 0.5% by mass ~2% by mass is more preferred, and 0.5% to 1% by mass is even more preferred.

<Additive B>
The non-aqueous electrolyte of the present disclosure contains additive B, which is a compound represented by the following formula (B).
The additive B may be only one selected from the group consisting of compounds represented by the following formula (B), or may be two or more.

In formula (B), R ² is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or represents a fluorine atom.

In formula (B), the “hydrocarbon group having 1 to 6 carbon atoms substituted with at least ^one fluorine atom” represented by R ² is the “at least It is synonymous with "a hydrocarbon group having 1 to 6 carbon atoms substituted with one fluorine atom".
In formula (B), the "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by R ² is represented by R ¹ in formula (A) described above. A hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom".

In formula (B), R ² is preferably a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, and an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom. More preferably, a perfluoroalkyl group having 1 to 6 carbon atoms is more preferable, a perfluoromethyl group (also known as trifluoromethyl group) or a perfluoroethyl group (also known as pentafluoroethyl group) is more preferred, and a perfluoromethyl group (alias: trifluoromethyl group) is particularly preferred.

The compound represented by formula (B) preferably contains at least one selected from the group consisting of lithium trifluoromethanesulfonate and lithium pentafluoroethanesulfonate, and lithium trifluoromethanesulfonate is particularly preferred.

The content of additive B is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 10% by mass, and 0.05% by mass to 5% by mass, relative to the total amount of the non-aqueous electrolyte. More preferably 0.1% by mass to 5% by mass, more preferably 0.5% by mass to 5% by mass, still more preferably 0.5% by mass to 3% by mass, 0.5% by mass ~2% by mass is more preferred, and 0.5% to 1% by mass is even more preferred.

<Electrolyte>
The non-aqueous electrolytic solution of the present disclosure contains an electrolyte that is a lithium salt other than additive B (hereinafter also referred to as “specific lithium salt”).
Only one kind of specific lithium salt as an electrolyte may be used, or two or more kinds thereof may be used.

Specific examples of the specific lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiPF _n [C _k F _(2k+1) ] _(6−n) (n=1 to 5, k= an integer of 1 to 8).
Lithium salts represented by the following general formula can also be used.

^LiC ( _SO2R27 ) ( ^SO2R28 ) ( _SO2R29 ), ^LiN ₍ ^SO2OR30 ) _{( SO2OR31} ), ^LiN ₍ ^SO2R32 ) ₍ ^SO2R33 ) (where R ²⁷ to R ³³ may be the same or different and are perfluoroalkyl groups having 1 to 8 carbon atoms). These electrolytes may be used alone or in combination of two or more.

The specific lithium salt preferably contains at least one of LiPF ₆ and LiBF ₄ , more preferably LiPF ₆ .
When the specific lithium salt contains LiPF ₆ , the ratio of LiPF ₆ in the specific lithium salt is preferably 10% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, and 70% by mass to 100% by mass. is particularly preferred.

The concentration of the electrolyte in the nonaqueous electrolytic solution is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 2 mol/L.

<Additive C>
The non-aqueous electrolytic solution of the present disclosure preferably contains an additive C that is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate.
When the non-aqueous electrolyte of the present disclosure contains additive C, the resistance of the battery before and after storage can be reduced. Furthermore, an increase in battery resistance due to storage can be suppressed.
Additive C preferably comprises lithium difluorophosphate.

The content of additive C is preferably 0.001% by mass to 10% by mass, preferably 0.01% by mass to 10% by mass, relative to the total amount of the nonaqueous electrolyte. More preferably 0.05% by mass to 5% by mass, still more preferably 0.1% by mass to 5% by mass, still more preferably 0.5% by mass to 5% by mass, 0.5% by mass to 3% by mass %, more preferably 0.5% by mass to 2% by mass, even more preferably 0.5% by mass to 1% by mass.

<Additive D>
The non-aqueous electrolyte of the present disclosure may contain an additive D, which is a compound represented by formula (D) below.
The additive D may be only one selected from the group consisting of compounds represented by the following formula (D), or may be two or more.

^In formula (D), Y1 and Y2 ^each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

Examples of the compound represented by formula (D) include vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, bropylvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, dipropylvinylene carbonate, and the like.
Of these, vinylene carbonate is particularly preferred.

The content of additive D is preferably 0.001% by mass to 10% by mass, preferably 0.01% by mass to 10% by mass, relative to the total amount of the nonaqueous electrolyte. More preferably 0.05% by mass to 5% by mass, still more preferably 0.1% by mass to 5% by mass, still more preferably 0.5% by mass to 5% by mass, 0.5% by mass to 3% by mass %, more preferably 0.5% by mass to 2% by mass, even more preferably 0.5% by mass to 1% by mass.

<Other additives>
The nonaqueous electrolytic solution of the present disclosure contains additives other than additive A, additive B, additive C, and additive D (also referred to herein as “other additives”). good too.
When the non-aqueous electrolytic solution of the present disclosure contains other additives, the other additives contained may be one type only, or may be two or more types.
Other additives include fluorophosphate compounds (excluding lithium monofluorophosphate and lithium difluorophosphate), carbonate compounds having carbon-carbon unsaturated bonds (excluding additive D), fluorine atoms and at least one selected from the group consisting of a carbonate compound having and a cyclic sultone compound.

(Fluorophosphate compound)
Fluorophosphoric acid compounds (excluding lithium monofluorophosphate and lithium difluorophosphate) include difluorophosphoric acid, monofluorophosphoric acid, methyl difluorophosphate, ethyl difluorophosphate, dimethyl fluorophosphate, fluorophosphoric acid diethyl and the like. Among these, lithium difluorophosphate and lithium monofluorophosphate are preferred.

(Carbon-carbon unsaturated bond-containing carbonate compound)
Carbon-carbon unsaturated bond-containing carbonate compounds (excluding additive D) include methyl vinyl carbonate, ethyl vinyl carbonate, divinyl carbonate, methyl propynyl carbonate, ethyl propynyl carbonate, dipropynyl carbonate, methyl phenyl carbonate, ethyl chain carbonates such as phenyl carbonate and diphenyl carbonate; vinylethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, ethynylethylene carbonate, 4,4-diethynylethylene carbonate, 4,5-di cyclic carbonates such as ethynylethylene carbonate, propynylethylene carbonate, 4,4-dipropynylethylene carbonate, 4,5-dipropynylethylene carbonate; Among these, preferred are methylphenyl carbonate, ethylphenyl carbonate, diphenyl carbonate, vinylethylene carbonate, 4,4-divinylethylene carbonate and 4,5-divinylethylene carbonate, and more preferred is vinylethylene carbonate.

(Carbonate compound having fluorine atom)
Carbonate compounds having a fluorine atom include methyltrifluoromethyl carbonate, ethyltrifluoromethyl carbonate, bis(trifluoromethyl) carbonate, methyl (2,2,2-trifluoroethyl) carbonate, ethyl (2,2,2 -trifluoroethyl)carbonate, bis(2,2,2-trifluoroethyl)carbonate and other linear carbonates; 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4 - Cyclic carbonates such as trifluoromethylethylene carbonate; Among these, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate and 4,5-difluoroethylene carbonate are preferred.

(Cyclic sultone compound)
Cyclic sultone compounds include 1,3-propanesultone, 1,4-butanesultone, 1,3-propenesultone, 1-methyl-1,3-propenesultone, 2-methyl-1,3-propenesultone, 3- and sultones such as methyl-1,3-propene sultone. Among these, 1,3-propanesultone and 1,3-propenesultone are preferred.

When the non-aqueous electrolytic solution of the present disclosure contains other additives, the content (the total content if two or more types) is not particularly limited, but the effect of the present disclosure is more effective. From the viewpoint of performance, the total amount of the non-aqueous electrolyte is preferably 0.001% by mass to 10% by mass, and 0.05% by mass to 5% by mass. more preferably 0.1% by mass to 4% by mass, still more preferably 0.1% by mass to 2% by mass, and 0.1% by mass to 1% by mass is particularly preferred.

<Non-aqueous solvent>
A non-aqueous electrolyte generally contains a non-aqueous solvent.
As the non-aqueous solvent, various known solvents can be appropriately selected, but it is preferable to use at least one selected from cyclic aprotic solvents and chain aprotic solvents.

When aiming to improve the flash point of the solvent in order to improve battery safety, it is preferable to use a cyclic aprotic solvent as the non-aqueous solvent.

(Cyclic aprotic solvent)
Cyclic aprotic solvents that can be used include cyclic carbonates, cyclic carboxylic acid esters, cyclic sulfones, and cyclic ethers.

Cyclic aprotic solvents may be used singly or in combination.
The mixing ratio of the cyclic aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass. By setting such a ratio, the conductivity of the electrolytic solution, which is related to the charge/discharge characteristics of the battery, can be increased.

Specific examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate and 2,3-pentylene carbonate. Of these, ethylene carbonate and propylene carbonate, which have high dielectric constants, are preferably used. Ethylene carbonate is more preferable for batteries using graphite as the negative electrode active material. Moreover, these cyclic carbonates may be used in combination of two or more.

Specific examples of cyclic carboxylic acid esters include γ-butyrolactone, δ-valerolactone, and alkyl-substituted compounds such as methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.

A cyclic carboxylic acid ester has a low vapor pressure, a low viscosity, and a high dielectric constant, and can lower the viscosity of the electrolyte without lowering the flash point of the electrolyte and the dissociation degree of the electrolyte. For this reason, it has the feature that the conductivity of the electrolyte, which is an index related to the discharge characteristics of the battery, can be increased without increasing the flammability of the electrolyte. It is preferred to use a cyclic carboxylic acid ester as the cyclic aprotic solvent. Among the cyclic carboxylic acid esters, γ-butyrolactone is most preferred.

Moreover, the cyclic carboxylic acid ester is preferably used by being mixed with another cyclic aprotic solvent. Examples include mixtures of cyclic carboxylic acid esters with cyclic carbonates and/or chain carbonates.

Examples of cyclic sulfones include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, dipropylsulfone, methylethylsulfone, methylpropylsulfone, and the like.
Dioxolane can be mentioned as an example of a cyclic ether.

(chain-like aprotic solvent)
As the chain aprotic solvent, chain carbonates, chain carboxylic acid esters, chain ethers, chain phosphates, and the like can be used.

The mixing ratio of the linear aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.

Specific examples of chain carbonates include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, Ethylpentyl carbonate, dipentyl carbonate, methylheptyl carbonate, ethylheptyl carbonate, diheptyl carbonate, methylhexyl carbonate, ethylhexyl carbonate, dihexyl carbonate, methyloctyl carbonate, ethyloctyl carbonate, dioctyl carbonate, methyltrifluoroethyl carbonate and the like. These chain carbonates may be used in combination of two or more.

Specific examples of chain carboxylic acid esters include methyl pivalate.
Specific examples of chain ethers include dimethoxyethane and the like.
Specific examples of chain phosphates include trimethyl phosphate and the like.

(combination of solvents)
The non-aqueous solvent used in the non-aqueous electrolytic solution of the present disclosure may be used singly or in combination of multiple types. Further, even if only one or more kinds of cyclic aprotic solvents are used, or only one or more kinds of chain aprotic solvents are used, or both cyclic aprotic solvents and chain protic solvents are used. A solvent may be mixed and used. When especially intended to improve the load characteristics and low-temperature characteristics of the battery, it is preferable to use a combination of a cyclic aprotic solvent and a chain aprotic solvent as the non-aqueous solvent.

Furthermore, from the electrochemical stability of the electrolytic solution, it is most preferable to apply a cyclic carbonate to the cyclic aprotic solvent and a chain carbonate to the chain aprotic solvent. Also, the combination of the cyclic carboxylic acid ester and the cyclic carbonate and/or the chain carbonate can increase the conductivity of the electrolytic solution, which is related to the charge/discharge characteristics of the battery.

Specific examples of combinations of cyclic carbonate and chain carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methylethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methylethyl 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 Carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate and the like.

The mixing ratio of the cyclic carbonate and the chain carbonate is 5:95 to 80:20, more preferably 10:90 to 70:30, particularly preferably 15:85, in terms of a mass ratio of cyclic carbonate:chain carbonate. ~55:45. By setting such a ratio, it is possible to suppress an increase in the viscosity of the electrolytic solution and increase the degree of dissociation of the electrolyte, so that the conductivity of the electrolytic solution, which is related to the charge/discharge characteristics of the battery, can be increased. Also, the solubility of the electrolyte can be further increased. Therefore, the electrolytic solution having excellent electrical conductivity at room temperature or low temperature can be obtained, so that the load characteristics of the battery at room temperature to low temperature can be improved.

Specific examples of combinations of cyclic carboxylic acid esters and cyclic carbonates and/or chain carbonates include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and methylethyl carbonate, γ-butyrolactone and ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and propylene carbonate and dimethyl carbonate, γ-butyrolactone and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and propylene carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and sulfolane, γ-butyrolactone and ethylene carbonate and sulfolane, γ-butyrolactone and propylene carbonate Sulfolane, γ-butyrolactone, ethylene carbonate, propylene carbonate, sulfolane, γ-butyl Lolactone, sulfolane, dimethyl carbonate and the like.

(Other solvents)
Examples of non-aqueous solvents include solvents other than those mentioned above.
Specific examples of other solvents include amides such as dimethylformamide, chain carbamates such as methyl-N,N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, and N,N-dimethylimidazolidinone. Examples include boron compounds such as cyclic urea, trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, and trimethylsilyl borate, and polyethylene glycol derivatives represented by the following general formula.
HO _{( CH2CH2O} ) _aH
HO[ _{CH2CH ( CH3} )O]bH
_{CH3O ( CH2CH2O} ) _cH
CH3O[ _{CH2CH ( CH3} )O] _{dH
CH3O ( CH2CH2O ) eCH3
CH3O} [ _{CH2CH ( CH3} )O] _{fCH3
C9H19PhO ( CH2CH2O} ) _g [ _{CH ( CH3} )O] _hCH3
(Ph is a phenyl group)
_CH3O [ _CH2CH ( _CH3 )O] _iCO [OCH _{( CH3} ) _CH2 ] _jOCH3
In the above formula, a to f are integers of 5 to 250, g to j are integers of 2 to 249, 5≦g+h≦250, and 5≦i+j≦250.

The nonaqueous electrolyte of the present disclosure is not only suitable as a nonaqueous electrolyte for lithium secondary batteries, but also a nonaqueous electrolyte for primary batteries, a nonaqueous electrolyte for electrochemical capacitors, and an electric double layer capacitor. It can also be used as an electrolyte for aluminum electrolytic capacitors.

[Lithium secondary battery]
A lithium secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte of the present disclosure.

(negative electrode)
The negative electrode may include a negative electrode active material and a negative electrode current collector.
The negative electrode active material in the negative electrode includes metal lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, and lithium ions that can be doped/dedoped. At least one selected from the group consisting of transition metal nitrides and carbon materials capable of doping and dedoping lithium ions (may be used alone, or a mixture containing two or more of these may be used. good) 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. Lithium titanate may also be used.
Among these, a carbon material capable of doping/dedoping lithium ions is preferable. 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 fibrous, spherical, potato-like, or flake-like.

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. Graphitized MCMB, graphitized MCF, and the like are used as artificial graphite. As the graphite material, one containing boron can also be used. As the graphite material, those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those in which amorphous carbon and graphite are mixed can be used.

These carbon materials may be used singly or in combination of two or more.
As the above-mentioned carbon material, 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 is particularly preferable. 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 close thereto is also preferable. The energy density of the battery can be increased by using the above carbon materials.

The material of the negative electrode current collector in the negative electrode 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 them, copper is particularly preferable from the viewpoint of ease of processing.

(positive electrode)
The positive electrode may include a positive electrode active material and a positive electrode current collector.
Examples of positive electrode active materials for the positive electrode include transition metal oxides or sulfides such as MoS ₂ , TiS ₂ , MnO ₂ and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , _{LiNiXCo (1−X)} O ₂ [0<X<1], α-NaFeO Li _1+α Me _1-α O ₂ having a ₂ -type crystal structure (Me is a transition metal element including Mn, Ni and Co, 1.0 ≦(1+α)/(1−α)≦1.6), LiNi _x Co _y Mn _z O ₂ [x+y+z=1, 0<x<1, 0<y<1, 0<z<1] (for example, composite _{oxides composed} of _lithium and a transition _metal such as _{LiNi0.33Co0.33Mn0.33O2} , _{LiNi0.5Co0.2Mn0.3O2 , LiFePO4} , _{LiMnPO4 ;} Examples thereof include conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline complexes. Among these, a composite oxide composed of lithium and a transition metal is particularly preferred. Carbon materials can also be used as the positive electrode when the negative electrode is lithium metal or a lithium alloy. A mixture of a composite oxide of lithium and a transition metal and a carbon material can also be used as the positive electrode.
One type of positive electrode active material may be used, or two or more types may be mixed and used. If the positive electrode active material has insufficient conductivity, it can be used together with a conductive aid to form the positive electrode. Examples of conductive aids include carbon materials such as carbon black, amorphous whiskers, and graphite.

The material of the positive electrode current collector in the positive electrode 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 alloys, stainless steel, nickel, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and the like.

(separator)
The lithium secondary battery of the present disclosure preferably includes a separator between the negative electrode and the positive electrode.
The separator is a film that electrically insulates the positive electrode and the negative electrode and allows lithium ions to pass through, and is exemplified by a porous film 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, polyester, and the like.
In particular, porous polyolefin is preferable, and specific examples include porous polyethylene film, porous polypropylene film, or multilayer film of porous polyethylene film and polypropylene film. Other resins having excellent thermal stability may be coated on the porous polyolefin film.
Examples of polymer electrolytes include polymers in which lithium salts are dissolved and polymers swollen with an electrolytic solution.
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 secondary battery of the present disclosure can take various known shapes, such as cylindrical, coin, square, laminate, film, and other arbitrary shapes. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed depending on the purpose.

An example of the lithium secondary battery (non-aqueous electrolyte 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 the lithium secondary battery of the present disclosure, and FIG. 2 shows the thickness of the laminated electrode body housed in the laminate type battery shown in FIG. 1 is a schematic sectional view in a direction; FIG.
The laminated battery shown in FIG. 1 contains a non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode assembly (not shown in FIG. 1), and the peripheral portion is sealed. It has a laminated exterior body 1 whose inside is sealed by. As the laminated exterior body 1, for example, a laminated exterior body made of aluminum is used.
As shown in FIG. 2, the laminated electrode body housed in the laminated outer package 1 is composed of a laminated body in which a positive electrode plate 5 and a negative electrode plate 6 are alternately laminated with separators 7 interposed therebetween, and this laminated body. a surrounding separator 8; The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the non-aqueous electrolyte of the present disclosure.
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 the laminated outer body 1. It protrudes outward from the peripheral edge (Fig. 1). A portion of the peripheral end portion of the laminate package 1 where 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). It protrudes outward from the peripheral edge of the body 1 (Fig. 1). A portion where the negative terminal 3 protrudes from the peripheral end portion of the laminate outer package 1 is sealed with an insulating seal 4 .
In the laminate type 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. The outer layers are laminated in such a manner that all of them serve as the negative electrode plate 6 . However, the number of positive plates and the number and arrangement of negative plates in the laminate type battery are not limited to this example, and it goes without saying that various modifications may be made.

Another example of the lithium secondary battery of the present disclosure is a coin-type battery.
FIG. 3 is a schematic perspective view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure.
In the coin-type battery shown in FIG. 3, a disk-shaped negative electrode 12, a separator 15 filled with a non-aqueous electrolyte, a disk-shaped positive electrode 11, and optionally spacer plates 17 and 18 made of stainless steel or aluminum are arranged in this order. In a stacked state, they are accommodated 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 cover"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed with a gasket 16 interposed therebetween.
In this example, the non-aqueous electrolytic solution of the present disclosure is used as the non-aqueous electrolytic solution injected into the separator 15 .

The lithium secondary battery of the present disclosure is obtained by charging and discharging a lithium secondary battery (lithium secondary battery before charging and discharging) containing the negative electrode, the positive electrode, and the non-aqueous electrolyte of the present disclosure. It may be a lithium secondary battery.
That is, in the lithium secondary battery of the present disclosure, first, a lithium secondary battery before charging and discharging including the negative electrode, the positive electrode, and the non-aqueous electrolyte of the present disclosure is produced, and then the lithium secondary battery before charging and discharging is produced. It may be a lithium secondary battery produced by charging and discharging a lithium secondary battery one or more times (charged and discharged lithium secondary battery).

Applications of the lithium secondary battery of the present disclosure are not particularly limited, and can be used for various known applications. For example, notebook computers, mobile computers, mobile phones, headphone stereos, video movies, liquid crystal televisions, handy cleaners, electronic notebooks, calculators, radios, backup power supply applications, motors, automobiles, electric vehicles, motorcycles, electric motorcycles, bicycles, electric It can be widely used in small mobile devices and large devices such as bicycles, lighting equipment, game machines, clocks, power tools, and cameras.

Examples of the present disclosure are shown below, but the present disclosure is not limited to the following examples.
In the following examples, the "addition amount" represents 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 secondary battery, was produced in the following procedure.
<Production of negative electrode>
20 parts by mass of artificial graphite, 80 parts by mass of natural graphite, 1 part by mass of carboxymethyl cellulose, and 2 parts by mass of SBR latex were kneaded with a water solvent to prepare a pasty negative electrode mixture slurry.
Next, this negative electrode mixture slurry is applied to a negative electrode current collector made of strip-shaped copper foil with a thickness of 18 μm, dried, and then compressed by a roll press to form a sheet-like negative electrode comprising the negative electrode current collector and the negative electrode active material layer. got At this time, the negative electrode active material layer had a coating density of 10 mg/cm ² and a filling density of 1.5 g/ml.

<Preparation of positive electrode>
90 parts by mass of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , 5 parts by mass of acetylene black and 5 parts by mass of polyvinylidene fluoride were kneaded using N-methylpyrrolidinone as a solvent to prepare a pasty positive electrode mixture. A slurry was prepared.
Next, this positive electrode mixture slurry is applied to a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to form a sheet-like positive electrode comprising the positive electrode current collector and the positive electrode active material. Obtained. At this time, the coating density of the positive electrode active material layer was 30 mg/cm ² and the filling density was 2.5 g/ml.

<Preparation of non-aqueous electrolyte>
As non-aqueous solvents, 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 concentration of the electrolyte in the finally obtained non-aqueous electrolyte was 1 mol/liter.
For the solution obtained above,
Methanesulfonyl fluoride (hereinafter also referred to as "MSF") as additive A (addition amount 0.5% by mass), and lithium trifluoromethanesulfonate (hereinafter also referred to as "TFMSLi") as additive B (addition amount 0 .5% by mass)
was added to obtain a non-aqueous electrolyte.

<Production of coin-type battery>
Coin-shaped electrodes (negative electrode and positive electrode) were obtained by punching the above-described negative electrode with a diameter of 14 mm and the above-described positive electrode with a diameter of 13 mm, respectively. A disk-shaped separator having a diameter of 17 mm was obtained by punching a microporous polyethylene film having a thickness of 20 μm.
The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode were stacked in this order in a battery can made of stainless steel (2032 size), and 20 μl of the above non-aqueous electrolyte was poured into the separator, positive electrode, and negative electrode. soaked.
Furthermore, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring are placed on the positive electrode, and the battery can lid is crimped through a polypropylene gasket to seal the battery. A 3.2 mm coin-type battery having the configuration shown in FIG. 3 (hereinafter sometimes referred to as "test battery") was fabricated.

<Measurement of capacity retention rate after high temperature storage>
The coin-type battery is charged to 4.25 V at a charge rate of 0.2 C in a 25 ° C. constant temperature bath, discharged to 2.85 V at a discharge rate of 0.2 C in this 25 ° C. constant temperature bath, and discharged The discharge capacity was measured, and this discharge capacity was defined as the discharge capacity [mAh] before high temperature storage.
The coin-type battery whose discharge capacity [mAh] before high temperature storage was measured was charged to 4.25 V at a charge rate of 0.2 C in a constant temperature bath at 25 ° C., and then the temperature of the constant temperature bath was raised to 60 ° C. The temperature was raised and the coin-shaped battery was stored in a constant temperature bath at 60° C. for 5 days (high temperature storage).
After the high temperature storage, the temperature of the constant temperature bath is returned to 25 ° C., the coin type battery is discharged to 2.85 V at a discharge rate of 2 C in the constant temperature bath at 25 ° C., the discharge capacity at the time of discharging is measured, and this discharge is performed. The capacity was taken as the discharge capacity [mAh] after high temperature storage.
From these results, the "capacity retention rate [%] after high-temperature storage" was determined by the following formula.
Table 1 shows the results.

Capacity retention rate after high temperature storage [%]
= (Discharge capacity after high temperature storage [mAh]/Discharge capacity before high temperature storage [mAh]) × 100 [%]

[Comparative Example 1]
In the preparation of the non-aqueous electrolyte, the same operation as in Example 1 was performed except that additive A was not added and the amount of additive B added was changed to 1.0% by mass. Table 1 shows the results.

[Comparative Example 2]
In the preparation of the non-aqueous electrolyte, the same operation as in Example 1 was performed except that additive B was not added and the amount of additive A added was changed to 1.0% by mass. Table 1 shows the results.

As shown in Table 1, in Example 1 using a non-aqueous electrolyte containing both additive A and additive B, a non-aqueous electrolyte containing neither additive A nor additive B was used. Compared with Comparative Examples 1 and 2, the capacity retention rate after high temperature storage was excellent.
More specifically, in Example 1, 0.5 wt% of Additive B (1.0 wt%) is replaced with Additive A in the non-aqueous electrolytic solution of Comparative Example 1 that does not contain Additive A. As a result, the capacity retention rate after high-temperature storage was improved.
Further, in Example 1, by replacing 0.5 wt% of Additive A (1.0 wt%) with Additive B in the non-aqueous electrolytic solution of Comparative Example 2 that does not contain Additive B, The capacity retention rate after high temperature storage was improved.

[Example 2]
In the preparation of the non-aqueous electrolyte, the same operation as in Example 1 except that lithium difluorophosphate (hereinafter also referred to as "LiDFP") as additive C (addition amount 0.5% by mass) was added. did
Table 2 shows the results of the capacity retention rate after high-temperature storage.
For comparison, Table 2 also shows the capacity retention rate after high-temperature storage in Example 1 described above.

For the coin-type batteries of Examples 1 and 2, the DC resistance before storage (−20° C.), the DC resistance after storage (−20° C.), and the rate of increase in DC resistance (%) due to storage were measured. It was measured. Table 2 shows the results.

<DC resistance before storage (-20°C)>
The coin-type battery was charged and discharged three times at a constant voltage of 4.2 V, then charged to a constant voltage of 3.9 V, and then cooled to −20° C. in a constant temperature bath. A coin-type battery cooled to -20°C is discharged at a constant current of 0.2 mA at -20°C, and the potential drop for 10 seconds from the start of discharge is measured to measure the DC resistance [Ω] of the coin-type battery. did. The obtained measured value was taken as the DC resistance (−20° C.) (Ω) before storage.

<DC resistance after storage (-20°C)>
The coin-type battery whose direct current resistance (−20° C.) before storage was measured was charged at a constant voltage of 4.25 V, and the charged coin-type battery was stored in a constant temperature bath at 60° C. for 5 days.
After storage for 5 days, the coin-type battery was charged to a constant voltage of 3.9 V and then cooled to -20°C in a constant temperature bath. A coin-type battery cooled to -20°C is discharged at a constant current of 0.2 mA at -20°C, and the potential drop for 10 seconds from the start of discharge is measured to measure the DC resistance [Ω] of the coin-type battery. did. The obtained measured value was taken as the DC resistance (-20°C) (Ω) after storage.

<Increase rate of DC resistance due to storage (%)>
Based on the DC resistance (−20° C.) before storage and the DC resistance (−20° C.) after storage, the increase rate (%) of DC resistance due to storage was calculated by the following formula.

Rate of increase in DC resistance due to storage (%) = ((DC resistance after storage (-20°C) - DC resistance before storage (-20°C))/DC resistance before storage (-20°C)) x 100

As shown in Table 2, according to the non-aqueous electrolytic solution of Example 2 in which the additive C was further added to the non-aqueous electrolytic solution of Example 1, the capacity retention rate after high-temperature storage hardly decreased, The direct current resistance before and after high temperature storage and the increase in direct current resistance due to high temperature storage could be significantly reduced.

1 Laminated exterior body 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulating seal 5 Positive electrode plate 6 Negative electrode plates 7, 8 Separator 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gaskets 17, 18 Spacer plate

Claims (6)

an additive A which is a compound represented by formula (A);
an additive B which is a compound represented by formula (B);
an electrolyte that is a lithium salt other than additive B;
contains
The content of the additive B is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries,
Non-aqueous electrolyte for batteries.

[In formula (A), R ¹ is an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms, or at least represents a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with one fluorine atom, or a fluorine atom;
In formula (B), R ² is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or represents a fluorine atom. ] 2. The non-aqueous electrolyte for batteries according to claim 1, wherein the content of said additive A is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries. 3. The non-aqueous electrolyte for a battery according to claim 1, further comprising an additive C which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. 4. The nonaqueous electrolyte for battery according to claim 3, wherein the content of said additive C is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for battery. a positive electrode;
Metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, transition metal nitrides that can be doped/dedoped with lithium ions, and lithium a negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of ion doping and dedoping;
The non-aqueous electrolyte for batteries according to any one of claims 1 to 4,
Lithium secondary battery including. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 5 .

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