Non-aqueous electrolytic solution and lithium ion secondary battery

Abstract

This non-aqueous electrolytic solution for a lithium ion secondary battery comprises a compound represented by formula (1), a cyclic sulfonic acid ester, a compound represented by formula (2), and a non-aqueous solvent.　(1): LiN(R1SO2)(R2SO2) [In formula (1), R1 and R2 each independently represent a fluorine atom or an alkyl group which has 1-6 carbon atoms and which may be substituted with a fluorine atom.]　(2): FSO2NHR3 [In formula (2), R3 represents a hydrogen atom or a hydrocarbon group which has 1-18 carbon atoms and which may be substituted.]

Description

Nonaqueous electrolyte and lithium ion secondary battery

[0001] The present invention relates to a non-aqueous electrolyte and a lithium ion secondary battery.

[0002] Lithium-ion secondary batteries are used as power sources for electronic devices such as smartphones and personal computers, as well as for automobiles, etc. Research into the batteries used in these applications has been extensively conducted with the aim of improving various battery characteristics, such as higher output, higher energy density, cycle characteristics, and rate characteristics.

[0003] Various additives have been investigated to improve battery characteristics. For example, Patent Documents 1 to 3 disclose additives such as cyclic disulfonic acid esters, -SO ２ It has been proposed to add a cyclic compound containing a - bond or a cyclic sulfonate ester such as a γ-sultone compound as an additive to a non-aqueous electrolyte.

[0004] Japanese Patent Application Laid-Open No. 2012-094454 Japanese Patent Application Laid-Open No. 2021-532531 Japanese Patent Application Laid-Open No. 2000-235866

[0005] However, as a result of intensive studies by the present inventors, it has become clear that conventional lithium ion secondary batteries containing a cyclic sulfonate ester as an additive have problems in that the resistance increases significantly during high-temperature storage and during cycle charge / discharge, resulting in significant deterioration of battery performance.

[0006] Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte solution containing a cyclic sulfonic acid ester that can sufficiently suppress an increase in resistance during high-temperature storage and cyclic charge / discharge, and a lithium-ion secondary battery including the same.

[0007] The present disclosure relates to, for example, the following items [1] to

[11] . [1] A non-aqueous electrolyte solution for a lithium ion secondary battery, comprising a compound represented by the following formula (1), a cyclic sulfonic acid ester, a compound represented by the following formula (2), and a non-aqueous solvent: LiN(R １ SO ２ ) (R ２ SO ２ )...(1) [In formula (1), R １ and R ２each independently represents a fluorine atom or an alkyl group having 1 to 6 carbon atoms which may be substituted with a fluorine atom.] FSO ２ NHR ３ ...(2) [In formula (2), R ３ represents a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 18 carbon atoms.] [2] The compound represented by the above formula (1) is LiN(FSO ２ ) ２ and LiN(CF ３ SO ２ ) ２ [3] The nonaqueous electrolyte solution according to [1], wherein the compound represented by formula (1) is LiN(FSO ２ ) ２ [4] The nonaqueous electrolyte solution according to any one of [1] to [3], wherein the cyclic sulfonate ester comprises at least one selected from the group consisting of a compound represented by the following formula (3) and a compound represented by the following formula (4): [In formulas (3) and (4), R ４ ~R ６ each independently represents a divalent saturated hydrocarbon group having 1 to 10 carbon atoms or a divalent unsaturated hydrocarbon group having 2 to 10 carbon atoms.] [5] The nonaqueous electrolyte solution according to [4], wherein the cyclic sulfonate ester contains a compound represented by the above formula (3). [6] The nonaqueous electrolyte solution according to [5], wherein the cyclic sulfonate ester contains a compound represented by the following formula (3-1): [In formula (3-1), R １１ ~R １６ each independently represents a hydrogen atom or a methyl group.] [7] In formula (3-1), R １１ ~R １６ [8] The nonaqueous electrolyte solution according to [5], wherein at least one of the cyclic sulfonate esters is a methyl group. [In formula (3-2), R １７ ~R ２４ R each independently represents a hydrogen atom or a methyl group. １７ ~R ２４the total number of carbon atoms contained therein is 0 to 6. [9] The non-aqueous electrolyte solution according to any one of [1] to [8], wherein the content of the cyclic sulfonic acid ester in the total amount of the non-aqueous electrolyte solution is 0.05% by mass or more and 5% by mass or less.

[10] The non-aqueous electrolyte solution according to any one of [1] to [9], wherein the content of the compound represented by formula (2) in the total amount of the non-aqueous electrolyte solution is 0.005% by mass or more and 15% by mass or less.

[11] A lithium ion secondary battery comprising the non-aqueous electrolyte solution according to any one of [1] to

[10] , a positive electrode having a positive electrode mixture layer and a positive electrode current collector, and a negative electrode having a negative electrode mixture layer and a negative electrode current collector, wherein the positive electrode contains at least one positive electrode active material selected from the group consisting of a positive electrode active material represented by the following formula (A) and a positive electrode active material represented by the following formula (B): Li ｖ Ni ｘ Co ｙ Mn ｚ O （２＋ｗ） ...(A) [In formula (A), 0.2≦v≦1.2, 0.6≦x≦0.9, 0<y≦0.3, 0<z<0.4, x+y+z=1, and −0.2≦w≦0.2.] LiMPO ４ ...(B) [In formula (B), M represents Ni, Mn, Co, or Fe.]

[0008] The nonaqueous electrolyte solution and the lithium ion secondary battery including the same according to the present disclosure can sufficiently suppress an increase in resistance during high-temperature storage and cyclic charge / discharge. Furthermore, the nonaqueous electrolyte solution and the lithium ion secondary battery improve self-discharge during high-temperature storage and further improve low-temperature discharge capacity after high-temperature storage.

[0009] Modes for carrying out the invention included in this disclosure will be described below, but the invention included in this disclosure is not limited to the following embodiments. Note that when a numerical range is indicated as X to Y, it means X or more and Y or less. Furthermore, unless otherwise specified, the materials, components, or methods exemplified in this specification can be used alone or in combination of two or more.

[0010] <Non-aqueous electrolyte solution for lithium ion secondary battery> One embodiment of the present disclosure is a non-aqueous electrolyte solution for lithium ion secondary battery (hereinafter also simply referred to as "nonaqueous electrolyte solution") containing a compound represented by formula (1) described below, a cyclic sulfonic acid ester, a compound represented by formula (2) described below, and a non-aqueous solvent.

[0011] <Compound Represented by Formula (1)> The non-aqueous electrolyte solution according to this embodiment contains a compound represented by the following formula (1). Hereinafter, the compound represented by the following formula (1) will also be referred to as the "compound of formula (1)". LiN(R １ SO ２ ) (R ２ SO ２ ) … (1)

[0012] In formula (1), R １ and R ２ each independently represents a fluorine atom or an alkyl group having 1 to 6 carbon atoms which may be substituted with a fluorine atom. The number of carbon atoms in the alkyl group may be 1 to 6, 1 to 5, 1 to 4, 1 to 3, 1 to 2, or 1. The number of fluorine atoms substituted in the alkyl group may be, for example, 1 to 13, 1 to 9, 1 to 8, 1 to 5, 1 to 3, 1 to 2, or 1. The alkyl group having 1 to 6 carbon atoms which may be substituted with a fluorine atom may be a perfluoroalkyl group having 1 to 6 carbon atoms.

[0013] For example, in formula (1), R １ and R ２ may each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, may each independently represent a fluorine atom, trifluoromethyl, or pentafluoroethyl, may each independently represent a fluorine atom, trifluoromethyl, or may each independently represent a fluorine atom. １ and R ２ The compound where is a fluorine atom is lithium bis(fluorosulfonyl)imide, also known as LiFSI.

[0014] The compound of formula (1) is LiN(FSO ２ ) ２ and LiN(CF ３ SO ２ ) ２It is preferable that the material contains at least one selected from the group consisting of LiN(FSO ２ ) ２ It is more preferred that the composition contains:

[0015] The content of the compound of formula (1) in the non-aqueous electrolyte may be, for example, 0.01 mol / L to 10.0 mol / L, 0.05 mol / L to 4.00 mol / L, 0.10 mol / L to 2.00 mol / L, 0.15 mol / L to 1.20 mol / L, 0.20 mol / L to 1.00 mol / L, or 0.40 mol / L to 0.80 mol / L. When the molar concentration of the compound of formula (1) is within the above range, self-discharge during high-temperature storage is less likely to occur.

[0016] <Cyclic Sulfonate Ester> The non-aqueous electrolyte solution according to this embodiment contains a cyclic sulfonate ester. The cyclic sulfonate ester is a sulfonate ester having at least one sulfonate ester moiety (—S(═O) ２ O-), for example, compounds represented by the following formulas (3) to (7).

[0017]

[0018] In formulas (3) to (7), R ４ ~R １０ are each independently a divalent saturated hydrocarbon group having 1 to 10 carbon atoms or a divalent unsaturated hydrocarbon group having 2 to 10 carbon atoms.

[0019] The compounds represented by formulas (3) to (7) may be, for example, cyclic sulfonic acid esters having a 5- to 10-membered ring, a 5- to 8-membered ring, or a 5- to 6-membered ring.

[0020] The divalent saturated hydrocarbon group having 1 to 10 carbon atoms may be a linear or branched saturated hydrocarbon group. The number of carbon atoms in the saturated hydrocarbon group may be, for example, 1 to 8, 1 to 5, 1 to 4, 1 to 3, 1 to 2, or 1.

[0021] Specific examples of divalent saturated hydrocarbon groups having 1 to 10 carbon atoms include a methylene group, an ethylene group, a 1,2-propylene group, an n-propylene group, a 1,2-butylene group, a 1,3-butylene group, an n-butylene group, a 2,3-butylene group, an n-pentylene group, and an n-hexylene group.

[0022] The divalent unsaturated hydrocarbon group having 2 to 10 carbon atoms may be a linear or branched unsaturated hydrocarbon group. The number of carbon atoms in the unsaturated hydrocarbon group may be, for example, 2 to 8, 2 to 5, 2 to 4, or 2 to 3.

[0023] Specific examples of the divalent unsaturated hydrocarbon group having 2 to 10 carbon atoms include a vinylene group, a propenylene group, and a methylvinylene group.

[0024] Specific examples of the compound represented by formula (3) include 1,3-propane sultone (PS), 2-methyl-1,3-propane sultone (2Me-PS), 1,3-butane sultone (1,3-BS), 2,4-butane sultone (2,4-BS), 1,4-butane sultone (1,4-BS), 1-propene-1,3-sultone (PRS), and 3H-1,2-oxathiol-2,2-dioxide.

[0025] Specific examples of the compound represented by formula (4) include methylenemethane disulfonate (MMDS), dimethylenemethane disulfonate, and trimethylenemethane disulfonate.

[0026] Specific examples of the compound represented by formula (5) include 1,2,4-oxadithietane-2,2,4,4-tetraoxide, 1,2,5-oxadithiane-2,2,5,5-tetraoxide, 1,2,5-oxadithiol-2,2,5,5-tetraoxide, and 1,2,6-oxadithiane-2,2,6,6-tetraoxide.

[0027] Specific examples of the compound represented by formula (6) include 1,2,4-oxadithiolane-2,2,4,4-tetraoxide and 1,2,4-oxadithiane-2,2,4,4-tetraoxide.

[0028] Specific examples of the compound represented by formula (7) include 1,3,2,4-dioxadithiolane-2,2,4,4-tetraoxide, 1,3,2,4-dioxadithiane-2,2,4,4-tetraoxide, and 1,3,2,4-dioxadithiin-2,2,4,4-tetraoxide.

[0029] The cyclic sulfonate ester preferably contains at least one selected from the group consisting of a compound represented by formula (3) and a compound represented by formula (4), and more preferably contains a compound represented by formula (3).

[0030] The cyclic sulfonate ester more preferably contains a compound represented by the following formula (3-1):

[0031]

[0032] In formula (3-1), R １１ ~R １６ R each independently represents a hydrogen atom or a methyl group. １１ ~R １６ At least one of R is preferably a methyl group. １１ R １３ R １５ It is more preferable that at least one of the groups is a methyl group.

[0033] Furthermore, it is more preferable that the cyclic sulfonate ester contains a compound represented by the following formula (3-2).

[0034]

[0035] In formula (3-2), R １７ ~R ２４ R each independently represents a hydrogen atom or a methyl group. １７ ~R ２４ The total number of carbon atoms contained in the ring is 0 to 6.

[0036] The content of the cyclic sulfonate ester in the non-aqueous electrolyte may be 0.005% by mass to 15% by mass, 0.01% by mass to 10% by mass, or 0.05% by mass to 5% by mass. When the content of the cyclic sulfonate ester is within the above range, self-discharge during high-temperature storage is more unlikely to occur.

[0037] <Compound Represented by Formula (2)> The non-aqueous electrolyte solution according to this embodiment contains a compound represented by the following formula (2). Hereinafter, the compound represented by the following formula (2) will also be referred to as the "compound of formula (2)". FSO ２ NHR ３ …(2)

[0038] In formula (2), R ３ represents a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 18 carbon atoms. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or may be an aliphatic hydrocarbon group. The hydrocarbon group may be a chain or cyclic hydrocarbon group, or may be a chain hydrocarbon group, or may be a chain aliphatic hydrocarbon group. The chain hydrocarbon group may be a linear or branched hydrocarbon group, or may be a linear hydrocarbon group, or may be a linear aliphatic hydrocarbon group. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, or may be a saturated hydrocarbon group. The number of carbon atoms in the hydrocarbon group may be, for example, 1 to 18, 1 to 8, 1 to 5, 1 to 4, 1 to 3, 1 to 2, or 1.

[0039] In formula (2), R ３ The number of substituents on the hydrocarbon group in may be, for example, 1 to 18, 1 to 6, 1 to 4, 1 to 3, 1 to 2, or 1.

[0040] In formula (2), R ３ The substituents of the hydrocarbon group in may each independently be, for example, a group selected from the group consisting of a halogen atom, a hydroxy group, a nitro group, a cyano group, an aryl group, an alkoxy group, an acyl group, an alkoxycarbonyl group, and a carbamoyl group.

[0041] R ３ may be a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms (i.e., a hydrocarbon group having no substituent). ３ may be a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or an alkenyl group having 2 to 18 carbon atoms. ３ may be a hydrogen atom or an alkyl group having 1 to 18, 1 to 8, 1 to 5, 1 to 4, 1 to 3, 1 to 2, or 1 carbon atom. ３may be a hydrogen atom, methyl, ethyl, propyl, isopropyl, cyclopropyl, vinyl or allyl, may be a hydrogen atom, methyl or ethyl, or may be a hydrogen atom or methyl. ３ is a hydrogen atom, the compound of formula (2) has the chemical formula FSO ２ NH ２ It is expressed as: R ３ The compound of formula (2) where is methyl has the chemical formula FSO ２ NHCH ３ That is, the compound of formula (2) is represented by FSO ２ NH ２ or FSO ２ NHCH ３ The compound of formula (2) may contain one or two hydrogen atoms as substituents on the nitrogen atom, and thus may be able to suppress self-discharge during high-temperature storage to a greater extent than a compound that does not contain a hydrogen atom as a substituent on the nitrogen atom.

[0042] The content of the compound of formula (2) in the non-aqueous electrolyte may be, for example, 0.005% by mass to 15% by mass, 0.01% by mass to 10% by mass, 0.05% by mass to 5% by mass, 0.05% by mass to 3% by mass, or 0.1% by mass to 1% by mass. When the content of the compound of formula (2) is within the above range, self-discharge during high-temperature storage is less likely to occur.

[0043] The content of the compound of formula (2) in the nonaqueous electrolyte solution may be, for example, 1 part by mol to 10,000 parts by mol, 5 parts by mol to 5,000 parts by mol, 10 parts by mol to 1,000 parts by mol, 20 parts by mol to 500 parts by mol, or 50 parts by mol to 200 parts by mol, relative to 100 parts by mol of the compound of formula (1).

[0044] <Non-aqueous solvent> The non-aqueous solvent is an organic solvent that is not water. A non-aqueous solvent that is commonly used by those skilled in the art as a solvent for electrolytes in secondary batteries can be used. The non-aqueous solvent may contain at least one solvent selected from the group consisting of, for example, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), dimethyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, butyl propionate, isopropyl propionate, propyl propionate, ethyl acetate, methyl acetate, propyl acetate, and isopropyl acetate, in a proportion of 90% by volume or more of the total amount of non-aqueous solvent contained in the non-aqueous electrolyte. When these solvents are contained in a proportion of 90% by volume or more, storage stability at high temperatures is improved. From the viewpoint of further improving storage stability at high temperatures, these solvents may be contained in a proportion of 95% by volume or more, or even 100% by volume.

[0045] Furthermore, from the viewpoint of further improving storage stability at high temperatures, the nonaqueous solvent may contain at least one solvent selected from the group consisting of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, fluoroethylene carbonate, methyl propionate, and dimethyl carbonate in a proportion of 90% by volume or more, 95% by volume or more, or 100% by volume of the total amount of nonaqueous solvent contained in the nonaqueous electrolyte.

[0046] The solvent contained in the non-aqueous electrolyte may also contain other organic solvents. Specific examples thereof include saturated cyclic carbonate (carbonate ester) solvents such as 2,3-dimethylethylene carbonate, 1,2-butylene carbonate, and erythritan carbonate; chain carbonate (carbonate ester) solvents such as diphenyl carbonate and methyl phenyl carbonate; ether solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane, and 1,3-dioxolane; cyclic carbonate (carbonate ester) solvents having an unsaturated bond such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 2-vinyl ethylene carbonate, and phenyl ethylene carbonate; fluorine-containing cyclic carbonate (carbonate ester) solvents such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and trifluoropropylene carbonate; methyl benzoate, ethyl benzoate, and the like. aromatic carboxylic acid ester solvents such as butyl; lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone; phosphate ester solvents such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, triethyl phosphate; nitrile solvents such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone Examples of suitable solvents include sulfur compound solvents such as benzene, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane; aromatic nitrile solvents such as benzonitrile and tolunitrile; aromatic solvents such as toluene, amylbenzene, cyclohexylbenzene, fluorobenzene, anisole, 2,4-difluoroanisole, and trifluoromethoxybenzene; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, and 3-methyl-2-oxazolidinone. The solvent in the nonaqueous electrolyte does not need to contain water.

[0047] <Fluorine-Containing Lithium Salt> The non-aqueous electrolyte preferably further contains, in addition to the compound of formula (1), a fluorine-containing lithium salt other than the compound of formula (1).

[0048] The fluorine-containing lithium salt is a salt composed of an anion having a fluorine atom and a lithium ion. A specific example of the fluorine-containing lithium salt is LiPF ６ , LiBF ４ , LiPO ２ F ２ , FSO ３ Li, lithium difluorooxalatoborate (LiBF ２ (C ２ O ４ ), LiDFOB), lithium difluorooxalate phosphate (LiPF ２ (C ２ O ４ ), LiDFOP), (SO ２ CF ２ CF ２ SO ２ ) NLi, (SO ２ CF ２ CF ２ CF ２ SO ２ )NLi, LiFSO ２ (CH ３ SO ２ ) N, LiFSO ２ (C ２ F ５ SO ２ ) N, LiFSO ２ (C ２ H ５ SO ２ ) N, and LiAsF ６ At least one selected from the group consisting of (SO ２ CF ２ CF ２ SO ２ ) NLi and (SO ２ CF ２ CF ２ CF ２ SO ２ ) NLi is a salt consisting of a cyclic sulfonimide anion and a lithium ion.

[0049] Among these, the fluorine-containing lithium salt is LiPF ６ , LiBF ４ , LiPO ２ F ２ , FSO ３ Li, LiBF ２ (C ２ O ４ ), LiPF ２ (C ２ O ４ ), and LiPF ６ may be.

[0050] The content of the fluorine-containing lithium salt in the nonaqueous electrolyte may be, for example, 0.01 mol / L to 10.0 mol / L, 0.05 mol / L to 4.00 mol / L, 0.10 mol / L to 2.00 mol / L, 0.15 mol / L to 1.20 mol / L, 0.20 mol / L to 1.00 mol / L, or 0.40 mol / L to 0.80 mol / L. When the molar concentration of the fluorine-containing lithium salt is within the above range, self-discharge during high-temperature storage is more unlikely to occur.

[0051] <Other Additives> The nonaqueous electrolyte may further contain other additives in addition to the components described above. For example, the nonaqueous electrolyte may contain at least one additive selected from the group consisting of unsaturated cyclic carbonates, nitrile compounds, ester compounds, and fluorine-containing lithium salts.

[0052] The unsaturated cyclic carbonate may be, for example, at least one selected from the group consisting of vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 2-vinylethylene carbonate, and phenylethylene carbonate. For example, the unsaturated cyclic carbonate may be vinylene carbonate.

[0053] A nitrile compound is a compound having a cyano group in its molecule. The nitrile compound according to the present invention may be, for example, a compound having one cyano group in its molecule (mononitrile compound), a compound having two cyano groups in its molecule (dinitrile compound), or a compound having three or more cyano groups in its molecule. The nitrile compound according to the present invention is preferably a compound having two or more cyano groups in its molecule. The compound having two or more cyano groups in its molecule may be a dinitrile compound or a compound having three or more cyano groups in its molecule.

[0054] Dinitrile compounds are compounds having two cyano groups in the molecule, such as succinonitrile, malononitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, and 2,3-dimethylsuccinonitrile. , 2,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3-dimethylsuccinonitrile succinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, maleonitrile, fumaronitrile, 1,4-dicyanopentane, 2,6 The dinitrile compound may be at least one selected from the group consisting of 1,3-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, and 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane. The dinitrile compound may be at least one selected from the group consisting of succinonitrile, malononitrile, glutaronitrile, adiponitrile, pimelonitrile, and suberonitrile. For example, the dinitrile compound may be succinonitrile.

[0055] The compound having three or more cyano groups in the molecule may be at least one selected from the group consisting of, for example, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, tris(2-cyanoethyl)amine, 1,3,5-cyclohexanetricarbonitrile, 1,3,5-cyclohexanetricyanobenzene, tris(2-cyanoethyl)amine, tris(2-cyanoethyl)phosphine, 7,7,8,8-tetracyanoquinodimethane, 2,5-dimethyl-7,7,7,8-tetracyanoquinodimethane, 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane, and 1,2,3,4-butanetetracarbonitrile.

[0056] The mononitrile compound may be at least one selected from the group consisting of, for example, acetonitrile, propionitrile, butyronitrile, pentanenitrile, hexanenitrile, heptanenitrile, octanenitrile, pelargononitrile, decanenitrile, undecanenitrile, dodecanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, and 2-hexenenitrile.

[0057] The ester compound is a compound having an ester bond in the molecule. The ester compound may be a carbonate ester compound. The carbonate ester compound is a compound having a divalent group represented by -O-C(=O)-O- in the molecule. The carbonate ester compound according to this embodiment may be a compound having two divalent groups represented by -O-C(=O)-O- in the molecule. For example, the ester compound may be a compound represented by the following formula (8): [In formula (8), R １１ and R １２R each independently represents an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an alkynyl group having 2 to 6 carbon atoms which may have a substituent. １３ represents an alkylene group having 1 to 6 carbon atoms which may have a substituent, an alkenylene group having 2 to 6 carbon atoms which may have a substituent, an alkynylene group having 2 to 6 carbon atoms which may have a substituent, or a bridged ring which may have a substituent. The substituent represents a halogen atom or an alkyl group.] For example, the ester compound may be dimethyl 2,5-dioxahexanedioate.

[0058] As described above, the non-aqueous electrolyte may further contain at least one additive selected from the group consisting of vinylene carbonate, succinonitrile, and dimethyl 2,5-dioxahexanedioate. The non-aqueous electrolyte may also contain additives other than those described above. Examples of such additives include carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, and phenylsuccinic anhydride; sulfur-containing compounds such as ethylene sulfite, methyl methanesulfonate, busulfan, sulfolene, tetramethylthiuram monosulfide, and trimethylene glycol sulfate; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, and N-methylsuccinimide; saturated hydrocarbon compounds such as heptane, octane, and cycloheptane; sulfamic acid (amidosulfuric acid, H ３ NSO ３ ); sulfamates (e.g., alkali metal salts such as lithium salts, sodium salts, potassium salts, etc.; alkaline earth metal salts such as calcium salts, strontium salts, barium salts, etc.; other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts, nickel salts, etc.; ammonium salts; guanidine salts, etc.); sodium fluorosulfonate (NaFSO ３ ), potassium fluorosulfonate (KFSO ３ ), magnesium fluorosulfonate (Mg(FSO ３ )２ ) and other fluorosulfonic acid compounds.

[0059] When the non-aqueous electrolyte contains at least one additive selected from the group consisting of unsaturated cyclic carbonates, nitrile compounds, and ester compounds, the total content of these additives may be 0.1% by mass or more and 10% by mass or less, or 0.3% by mass or more and 5% by mass or less. When the content of these additives is 0.1% by mass or more, the effects derived from the additives tend to be easily obtained, and when the content of these additives is 10% by mass or less, an increase in the viscosity of the non-aqueous electrolyte tends to be suppressed.

[0060] The non-aqueous electrolyte contains carbon dioxide (CO ２ ), carbon monoxide (CO), bicarbonate ion (HCO ３ － ) and carbonate ions (CO ３ ２－ ) may be dissolved in the solution.

[0061] The non-aqueous electrolyte solution is added with carbon dioxide (CO ２ ), carbon monoxide (CO), bicarbonate ion (HCO ３ － ) and carbonate ions (CO ３ ２－ When at least one selected from the group consisting of carbon dioxide (CO ２ ), carbon monoxide (CO), bicarbonate ion (HCO ３ － ) and carbonate ions (CO ３ ２－ The total dissolved amount of at least one selected from the group consisting of may be 20 ppm by mass or more, 100 ppm by mass or more, or 250 ppm by mass or more, and may be the saturated dissolved amount at 25°C or less.

[0062] <Lithium-ion secondary battery> Another aspect of the present invention is a lithium-ion secondary battery including the nonaqueous electrolyte solution according to one embodiment of the present invention, a positive electrode having a positive electrode composite layer and a positive electrode current collector, and a negative electrode having a negative electrode composite layer and a negative electrode current collector.

[0063] <Positive Electrode> The positive electrode of the lithium ion secondary battery according to this embodiment may be one in which a positive electrode mixture layer is formed on a positive electrode current collector.

[0064] The positive electrode of the lithium ion secondary battery according to one embodiment includes at least one positive electrode active material selected from the group consisting of a positive electrode active material represented by the following formula (A) and a positive electrode active material represented by the following formula (B): Li ｖ Ni ｘ Co ｙ Mn ｚ O （２＋ｗ） …(A) LiMPO ４ …(B)

[0065] In formula (A), 0.2≦v≦1.2, 0.6≦x≦0.9, 0<y≦0.3, 0<z<0.4, x+y+z=1, and −0.2≦w≦0.2.

[0066] In formula (A), v is preferably 0.5 or more and 1.2 or less, more preferably 0.8 or more and 1.1 or less, and further preferably 1.

[0067] In formula (A), w is preferably −0.1 or more and 0.1 or less, and more preferably 0.

[0068] The positive electrode active material represented by formula (A) is LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．７ Co ０．２ Mn ０．１ O ２ , or LiNi ０．８ Co ０．１ Mn ０．１ O ２ is preferred, and LiNi ０．６ Co ０．２ Mn ０．２ O ２ , or LiNi ０．８ Co ０．１ Mn ０．１ O ２ is more preferred.

[0069] In formula (B), M represents Ni, Mn, Co, or Fe. In other words, in formula (B), M represents a transition metal, and the transition metal is selected from the group consisting of Ni (nickel), Mn (manganese), Co (cobalt), and Fe (iron).

[0070] The positive electrode active material represented by formula (B) is LiFePO ４ , LiNiPO ４ , LiMnPO ４ or LiCoPO ４ may be.

[0071] From the viewpoint of improving the output characteristics and electrical characteristics of the lithium-ion secondary battery according to this embodiment, the content of the positive electrode active material in the positive electrode composite layer is preferably 75% by mass or more and 99% by mass or less, and more preferably 85% by mass or more and 95% by mass or less.

[0072] The positive electrode mixture layer may further contain a conductive additive such as carbon black (e.g., ketjen black or acetylene black), carbon fiber, or graphite, with acetylene black and graphite being preferred.

[0073] From the viewpoint of improving the output characteristics and electrical characteristics of the lithium-ion secondary battery according to this embodiment, the content of the conductive additive in the positive electrode mixture layer is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 5% by mass or less.

[0074] The positive electrode mixture layer may further contain a binder. Examples of the binder include fluorine-based resins such as polyvinylidene fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide-based resins such as polyamideimide; polyolefin-based resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; and cellulose-based resins such as carboxymethyl cellulose, with polyvinylidene fluoride being preferred.

[0075] The content of the binder in the positive electrode mixture layer is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 5% by mass or less.

[0076] The positive electrode mixture layer may further contain other components as necessary. Examples of other components include polymers such as non-fluorinated polymers such as (meth)acrylic polymers, nitrile polymers, and diene polymers, and fluorinated polymers such as polytetrafluoroethylene; emulsifiers such as anionic emulsifiers, nonionic emulsifiers, and cationic emulsifiers; dispersants such as polymer dispersants such as styrene-maleic acid copolymers and polyvinylpyrrolidone; thickeners such as carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyacrylic acid (salts), and alkali-soluble (meth)acrylic acid-(meth)acrylic acid ester copolymers; and preservatives.

[0077] The content of the other components in the positive electrode may be 0% by mass or more and 15% by mass or less, or 0% by mass or more and 10% by mass or less.

[0078] Examples of the positive electrode current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum, with aluminum being preferred.

[0079] The positive electrode is not particularly limited and can be produced by a known method. For example, the positive electrode may be produced by dispersing a positive electrode active material, a conductive additive, and a binder in a solvent to form a slurry, applying the slurry to a positive electrode current collector, drying the slurry, and then performing roll pressing.

[0080] Examples of the solvent include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, and water, with N-methylpyrrolidone being preferred.

[0081] <Negative Electrode> The negative electrode of the lithium ion secondary battery according to this embodiment may be one in which a negative electrode mixture layer is formed on a negative electrode current collector.

[0082] The negative electrode mixture layer may contain, as a negative electrode active material, graphite such as artificial graphite or natural graphite, a mesophase fired body made from coal or petroleum pitch, a carbon material such as non-graphitizable carbon, Si-based negative electrode materials such as Si, Si alloys, and SiO, Sn-based negative electrode materials such as Sn alloys, lithium metal, lithium alloys such as lithium-aluminum alloys, and the like, and preferably contains graphite.

[0083] The content of the negative electrode active material in the negative electrode mixture layer is preferably 80% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less.

[0084] The negative electrode mixture layer may further contain a conductive additive. The conductive additive may be the same as that in the positive electrode mixture layer, and is preferably carbon fiber. The content of the conductive additive in the negative electrode mixture layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less.

[0085] The negative electrode mixture layer may further contain a binder. The binder may be the same as that in the positive electrode mixture layer, and is preferably styrene-butadiene rubber or carboxymethyl cellulose. The content of the binder in the negative electrode mixture layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less.

[0086] The negative electrode mixture layer may further contain other components as necessary. The other components may be the same as those in the positive electrode mixture layer. The content of the other components in the negative electrode mixture layer may be the same as that in the positive electrode mixture layer.

[0087] The negative electrode current collector may be the same as the positive electrode current collector, and is preferably made of copper.

[0088] The negative electrode can be produced by any known method without any particular limitation, for example, it may be produced in the same manner as the positive electrode, and in this case, the solvent is preferably water.

[0089] <Separator> The lithium ion secondary battery according to this embodiment may include a separator. The separator is disposed to separate the positive electrode from the negative electrode. Examples of the separator include a porous sheet made of a polymer capable of absorbing and retaining a non-aqueous electrolyte (e.g., a polyolefin-based microporous separator, a cellulose-based separator, etc.), a nonwoven fabric separator, a porous metal body, etc. Examples of materials for the porous sheet include polyethylene, polypropylene, and a laminate having a three-layer structure of polypropylene / polyethylene / polypropylene. Examples of materials for the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc. A porous sheet made of polyethylene is preferred as the separator.

[0090] <Battery Exterior Material> The lithium ion secondary battery according to this embodiment may be housed in a battery exterior material. The material of the battery exterior material is not particularly limited, and any conventionally known exterior material may be used. If necessary, the battery exterior material may contain an overcurrent prevention element such as an expanded metal, a fuse, or a PTC element, a lead plate, or the like, to prevent pressure buildup within the battery and overcharging and discharging.

[0091] The shape of the lithium ion secondary battery according to this embodiment is not particularly limited, and may be any known shape, such as a cylindrical shape, a square shape, a laminated shape, a coin shape, or a large shape.

[0092] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples.

[0093] (Fabrication of Positive Electrode) LiNi, a ternary positive electrode active material ０．８ Co ０．１ Mn ０．１ O ２(Beijing Dangsheng), acetylene black (AB, Denka Co., Ltd., product name: Denka Black (registered trademark)), graphite (Nippon Graphite Industries Co., Ltd., product number: SP270), and polyvinylidene fluoride (PVdF, Kureha Corporation, product number: KF1120) were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry (positive electrode active material: AB: graphite: PVdF = 93:3:3:3 (solid content mass ratio)). Subsequently, the obtained positive electrode mixture slurry was applied to an aluminum foil (positive electrode current collector, Nippon Foil Co., Ltd., thickness 15 μm) so that the coating weight after drying was 19.4 mg / cm ２ The mixture was coated on one side with an applicator so that the density was 3.1 g / cm 3 and dried on a hot plate at 110° C. for 10 minutes. The mixture was further dried in a vacuum drying oven at 110° C. for 12 hours. Thereafter, the density was adjusted to 3.1 g / cm 3 using a roll press. ３ The mixture was pressed and molded until a sheet-like positive electrode was obtained.

[0094] (Preparation of Negative Electrode) Graphite (natural graphite (O-MAC)) as a negative electrode active material, carbon fiber (VGCF) as a conductive additive, and styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders were dispersed in ultrapure water to prepare a negative electrode composite slurry (negative electrode active material: conductive additive: SBR: CMC = 100: 2: 1: 1 (solid content mass ratio)). Subsequently, the obtained negative electrode composite slurry was applied to a copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil & Powder Co., Ltd., thickness 15 μm) so that the coating weight after drying was 10.8 mg / cm ２ The mixture was coated on one side with an applicator so that the density was 1.2 g / cm 3 and dried on a hot plate at 80° C. for 10 minutes. The mixture was then dried in a vacuum drying oven at 100° C. for 12 hours. Thereafter, the density was adjusted to 1.2 g / cm 3 using a roll press. ３ The mixture was pressed and molded until it reached a thickness of 88 μm, thereby obtaining a sheet-like negative electrode (thickness: 88 μm).

[0095] (Preparation of Non-Aqueous Electrolyte) A mixed solvent (manufactured by Kishida Chemical Co., Ltd., the same applies hereinafter) having a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (volume ratio) was used as an electrolyte solvent, and LiFSI (manufactured by Nippon Shokubai Co., Ltd., the same applies hereinafter) and LiPF ６(manufactured by Kishida Chemical Co., Ltd., the same applies hereinafter) or LiPF ６ A nonaqueous electrolyte solution (hereinafter also simply referred to as "electrolyte solution") was prepared by dissolving an electrolyte salt having a simple salt composition containing only ammonium hydroxide, a first additive, and a second additive shown below to the concentrations shown in Tables 1 to 6.

[0096] As the first additive, 1,3-propane sultone (PS) (manufactured by Tokyo Chemical Industry Co., Ltd.), 1,3-butane sultone (1,3-BS) (manufactured by Chemexpress), 2-methyl-1,3-propane sultone (manufactured by AccelaChemBio), 2,4-butane sultone (2,4-BS) (manufactured by Angene International), 1,4-butane sultone (1,4-BS) (manufactured by BLDPharmatech), 1-propene-1,3-sultone (PRS) (manufactured by Tokyo Chemical Industry Co., Ltd.), and methylenemethane disulfonate (MMDS) (manufactured by Tokyo Chemical Industry Co., Ltd.) were used.

[0097] The second additive is FSO ２ NH ２ (Nippon Shokubai Co., Ltd.) or FSO ２ NHCH ３ (manufactured by Enamine) was used.

[0098] (Preparation of Laminated Battery) The prepared positive electrode was placed on a laminated battery with an effective area of ​​12 cm ２ The negative electrode was cut at 13.44 cm², and a polarity lead was welded to the cut positive electrode using an ultrasonic welder. ２The battery was cut to a length of 1 / 3, and a polarity lead was welded to the ultrasonically cut negative electrode. The positive and negative electrodes were placed opposite each other with a 25 μm-thick polyethylene separator between them, and the three sides were sealed with a laminate exterior to produce an unfilled battery. Subsequently, 700 μL of each electrolyte solution listed in Tables 1 to 6 was added to one of the unsealed sides of the unfilled battery. After the electrolyte was injected, the battery was vacuum sealed to produce a 4.2 V, 30 mAh capacity laminate battery (cell). The resulting cell was charged at a constant current of 0.1 C (3 mA) for 3 hours at room temperature (25°C, hereinafter) using a charge / discharge tester (ASKA Electronics Co., Ltd., product number: ACD-01, hereinafter the same) and then left at room temperature for 36 hours. After leaving the battery, it was charged at a constant current / constant voltage (CCCV) of 4.2 V at room temperature for 5 hours at 0.5 C (15 mA). The cell was then discharged at a constant current of 0.2 C (6 mA) to a discharge cutoff voltage of 2.75 V at room temperature, the excess laminate was cleaved, and the cell was vacuum sealed to degas the cell. After degassing, the cell was charged at a constant current and constant voltage under the same conditions as above, and then discharged at a constant current of 1 C (30 mA) to a discharge cutoff voltage of 2.75 V at room temperature. This was the aging process for the cell.

[0099] [Battery Evaluation] The self-discharge after high-temperature storage (capacity retention rate after high-temperature storage), the resistance increase rate after high-temperature storage, the low-temperature characteristics after high-temperature storage (low-temperature charge-discharge characteristics), and the charge-discharge cycle characteristics (resistance increase rate after cycle test) were evaluated by the methods described below. The results are shown in Tables 1 to 6.

[0100] (Self-discharge: Capacity Retention Rate after High-Temperature Storage) The aged cell was charged at 4.2 V, 0.5 C (15 mA) by constant current / constant voltage (CCCV) at room temperature. Subsequently, a constant current discharge of 0.1 C (3 mA) at room temperature with a cutoff voltage of 2.75 V was performed. The discharge capacity at this time was designated as the "discharge capacity before high-temperature storage." The discharged cell was again charged at 4.2 V, 0.5 C (15 mA) by constant current / constant voltage (CCCV) at room temperature to a fully charged state. After storage at 80°C for 15 days, a constant current discharge of 0.1 C (3 mA) at room temperature with a cutoff voltage of 2.75 V was performed. The discharge capacity at this time was designated as the "discharge capacity after high-temperature storage." The capacity retention rate after high-temperature storage was calculated based on the following formula (2): Capacity retention rate after high-temperature storage (%) = (discharge capacity after high-temperature storage / discharge capacity before high-temperature storage) × 100 (2). It should be noted that the greater the capacity retention rate after high-temperature storage, the more the self-discharge of the battery is suppressed.

[0101] (Rate of Resistance Increase After High-Temperature Storage) The aged cell was charged at room temperature at 1 C (30 mA) and a constant current / constant voltage of 0.02 C (0.6 mA) at 4.2 V, and fully charged (SOC 100%). Subsequently, the cell was discharged at 6 mA for 10 seconds after leaving it for 30 minutes from the fully charged state (SOC 100%), then discharged at 30 mA for 10 seconds after leaving it for 30 minutes, and then discharged at 90 mA for 10 seconds after leaving it for another 30 minutes. Each discharge current was plotted on the horizontal axis, and the difference (ΔV) in closed-circuit voltage at the start of discharge and after 10 seconds at each discharge current was plotted on the vertical axis. The slope of the IV line was taken as the "initial DCR" of the cell. After the self-discharge evaluation described above, the same operation was performed again to determine the DCR after high-temperature storage. The resistance increase rate after high-temperature storage was calculated based on the following formula (3): Resistance increase rate after high-temperature storage (%) = (DCR after high-temperature storage / initial DCR) × 100 (3) A smaller DCR after high-temperature storage means that the increase in resistance of the battery is more suppressed.

[0102] (Low-temperature discharge capacity after high-temperature storage: low-temperature charge-discharge characteristics) After high-temperature storage and DCR measurement, the cell was discharged to 2.75 V at 0.2 C (6 mA) at 25 ° C., and then charged to 4.2 V at 25 ° C. at 1 C (30 mA) with a 0.02 C (0.6 mA) termination. The charged cell was then left at -20 ° C. for 3 hours, and the constant current discharge capacity at 1 C (30 mA) and 2.75 V termination was measured at -20 ° C. Subsequently, the cell was left at room temperature for 3 hours, and then a constant current discharge at 0.2 C (6 mA) and 2.75 V termination was performed at 25 ° C. The discharged cell was then left at -20 ° C. for 3 hours, and the constant current charge capacity at 1 C (30 mA) and 4.2 V termination was measured at -20 ° C.

[0103] (Charge-Discharge Cycle Characteristics: Resistance Increase Rate After Cycle Test) The aged cell was subjected to constant current / constant voltage charging at room temperature with a termination of 0.02C (0.6mA) at 4.2V at 1C (30mA) to achieve a fully charged state (SOC 100%). Subsequently, after leaving the cell for 30 minutes from the fully charged state (SOC 100%), the cell was discharged at 6mA for 10 seconds, then left for 30 minutes, and then discharged at 30mA for 10 seconds. After leaving the cell for another 30 minutes, the cell was discharged at 90mA for 10 seconds. Each discharge current was plotted on the horizontal axis, and the difference (ΔV) in closed-circuit voltage at the start of discharge and after 10 seconds at each discharge current was plotted on the vertical axis. The slope of the IV line was taken as the "initial DCR" of the cell. A total of 500 cycles of cycle testing was performed at 45°C under the following charge-discharge conditions (cycle conditions). Charge: Constant current / constant voltage charge at 4.2 V, 1 C (30 mA), terminated at 0.02 C (0.6 mA), 10-minute rest. Discharge: Constant current (CC) discharge at 1 C (30 mA), terminated at 2.75 V, 10-minute rest. After the cycle test, the DCR was measured in the same manner as described above and recorded as "post-cycle DCR." The post-cycle resistance increase rate was calculated using the following formula (4): Post-cycle resistance increase rate (%) = (post-cycle DCR / initial DCR) × 100 (4). Note that a smaller post-cycle DCR indicates a more suppressed increase in battery resistance.

[0104]

Claims

1. A non-aqueous electrolyte solution for a lithium ion secondary battery, comprising a compound represented by the following formula (1), a cyclic sulfonic acid ester, a compound represented by the following formula (2), and a non-aqueous solvent: LiN(R １ SO ２ ) (R ２ SO ２ )...(1) [In formula (1), R １ and R ２ each independently represents a fluorine atom or an alkyl group having 1 to 6 carbon atoms which may be substituted with a fluorine atom.] FSO ２ NHR ３ ...(2) [In formula (2), R ３ represents a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 18 carbon atoms.

2. The compound represented by the formula (1) is LiN(FSO ２ ) ２ and LiN(CF ３ SO ２ ) ２ 2. The nonaqueous electrolyte solution according to claim 1, comprising at least one selected from the group consisting of:

3. The compound represented by the formula (1) is LiN(FSO ２ ) ２ The nonaqueous electrolyte according to claim 1 , comprising:

4. The non-aqueous electrolyte solution according to claim 1, wherein the cyclic sulfonate ester comprises at least one selected from the group consisting of compounds represented by the following formula (3) and compounds represented by the following formula (4): [In formulas (3) and (4), R ４ ~R ６ each independently represents a divalent saturated hydrocarbon group having 1 to 10 carbon atoms or a divalent unsaturated hydrocarbon group having 2 to 10 carbon atoms.] 5. The non-aqueous electrolyte according to claim 4, wherein the cyclic sulfonate ester comprises a compound represented by formula (3).

6. The nonaqueous electrolyte according to claim 5, wherein the cyclic sulfonate ester comprises a compound represented by the following formula (3-1): [In formula (3-1), R １１ ~R １６ each independently represents a hydrogen atom or a methyl group.

7. In formula (3-1), R １１ ~R １６ 7. The nonaqueous electrolyte solution according to claim 6, wherein at least one of the groups is a methyl group.

8. The nonaqueous electrolyte according to claim 5, wherein the cyclic sulfonate ester comprises a compound represented by the following formula (3-2): [In formula (3-2), R １７ ~R ２４ R each independently represents a hydrogen atom or a methyl group. １７ ~R ２４ The total number of carbon atoms contained in 9. The non-aqueous electrolyte according to claim 1, wherein the content of the cyclic sulfonate ester in the total amount of the non-aqueous electrolyte is 0.05% by mass or more and 5% by mass or less.

10. The non-aqueous electrolyte according to claim 1, wherein the content of the compound represented by formula (2) is 0.005% by mass or more and 15% by mass or less based on the total amount of the non-aqueous electrolyte.

11. A lithium ion secondary battery comprising the nonaqueous electrolyte solution according to any one of claims 1 to 10, a positive electrode having a positive electrode mixture layer and a positive electrode current collector, and a negative electrode having a negative electrode mixture layer and a negative electrode current collector, wherein the positive electrode contains at least one positive electrode active material selected from the group consisting of a positive electrode active material represented by the following formula (A) and a positive electrode active material represented by the following formula (B): Li ｖ Ni ｘ Co ｙ Mn ｚ O （２＋ｗ） ...(A) [In formula (A), 0.2≦v≦1.2, 0.6≦x≦0.9, 0<y≦0.3, 0<z<0.4, x+y+z=1, and −0.2≦w≦0.2.] LiMPO ４ ...(B) [In formula (B), M represents Ni, Mn, Co, or Fe.]

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