Non-aqueous electrolytic solution for lithium ion secondary battery and lithium ion secondary battery

Abstract

To provide a nonaqueous electrolyte for a lithium ion secondary battery in which an increase in resistance during high-temperature storage is suppressed and low-temperature characteristics after high-temperature storage are improved, and a lithium ion secondary battery using the same.SOLUTION: A non-aqueous electrolytic solution for a lithium ion secondary battery containing a compound represented by the following formula (1) and a non-aqueous solvent, further containing at least one selected from the group consisting of a chloroalkane having 3 or more carbon atoms and a chlorocycloalkane having 3 or more carbon atoms: LiN (R1SO2) (R2SO2) (1) In the formula (1), R1 and R2 each independently represent a fluoro atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms. ] SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a nonaqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery. [Background technology]

[0002] Lithium ion secondary batteries are widely used as power sources for electronic devices such as smartphones and personal computers, and for automobiles, etc. Lithium ion secondary batteries are adopted that have battery properties such as storage durability, safety, and charge / discharge characteristics that are suitable for the intended use.

[0003] In order to improve battery characteristics, various additives for electrolytes have been investigated. For example, Patent Document 1 proposes adding amidosulfuric acid as an additive to an electrolyte containing a specific fluorine-containing lithium sulfonylimide salt as an electrolyte. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 241161 Summary of the Invention [Problem to be solved by the invention]

[0005] Lithium ion secondary batteries are required to have various battery characteristics depending on their applications. For example, it is desirable for the batteries to have battery characteristics such as suppression of resistance increase during storage at high temperatures (e.g., 80°C, same below) and improvement of low-temperature battery characteristics after high-temperature storage.

[0006] Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte solution for a lithium ion secondary battery that suppresses an increase in resistance during high-temperature storage and improves low-temperature characteristics after high-temperature storage, and a lithium ion secondary battery using the same. [Means for solving the problem]

[0007] The present disclosure provides, for example, the lithium ion secondary batteries described in the following [1] to

[10] . [1] A non-aqueous electrolyte solution for a lithium ion secondary battery, comprising a compound represented by the following formula (1) and a non-aqueous solvent: The non-aqueous electrolyte solution further comprises at least one selected from the group consisting of chloroalkanes having 3 or more carbon atoms and chlorocycloalkanes having 3 or more carbon atoms. LiN(R 1 SO2)(R 2 SO2)···(1) [In formula (1), R 1 and R 2 each independently represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.] [2] The nonaqueous electrolyte solution according to [1], wherein the chloroalkane has 3 or more and 8 or less carbon atoms. [3] The nonaqueous electrolyte solution according to [1], wherein the chlorocycloalkane has 3 or more and 8 or less carbon atoms. [4] The nonaqueous electrolyte solution according to any one of [1] to [3], wherein the total content of at least one selected from the group consisting of the chloroalkanes and the chlorocycloalkanes is 0.002 parts by mass to 1 part by mass per 100 parts by mass of the compound represented by formula (1). [5] The nonaqueous electrolyte solution according to any one of [1] to [3], wherein the total content of at least one selected from the group consisting of the chloroalkanes and the chlorocycloalkanes is 0.002 parts by mass to 0.4 parts by mass per 100 parts by mass of the compound represented by formula (1). [6] The non-aqueous electrolyte solution according to any one of [1] to [5], wherein the non-aqueous solvent comprises at least one selected from the group consisting of cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, lactone solvents, ester solvents, and nitrile solvents. [7] The non-aqueous electrolyte solution according to any one of [1] to [5], wherein the non-aqueous solvent comprises at least one solvent selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated chain carbonate solvents. [8] A lithium ion secondary battery comprising the nonaqueous electrolyte solution according to any one of [1] to [7]. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a nonaqueous electrolyte solution for a lithium ion secondary battery that suppresses an increase in resistance during high-temperature storage and improves low-temperature characteristics after high-temperature storage, and a lithium ion secondary battery using the same. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. When a numerical range is indicated as X to Y, it means X or more and Y or less. For example, "1 to 6 carbon atoms" means that the number of carbon atoms is 1 or more and 6 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 for lithium-ion secondary batteries> One embodiment of the present disclosure is a nonaqueous electrolyte solution for a lithium ion secondary battery (hereinafter also simply referred to as "nonaqueous electrolyte solution") comprising a compound represented by formula (1) described below and a nonaqueous solvent, and further comprising at least one selected from the group consisting of chloroalkanes having 3 or more carbon atoms and chlorocycloalkanes having 3 or more carbon atoms.

[0011] <Compound represented by formula (1)> The non-aqueous electrolyte solution according to this embodiment contains a compound represented by the following formula (1). LiN(R 1 SO2)(R 2 SO2) …(1)

[0012] In formula (1), R 1 and R 2each independently represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms. A fluoroalkyl group is a group having a structure in which one or more hydrogen atoms in a saturated chain aliphatic hydrocarbon group are substituted with fluorine atoms.

[0013] The number of carbon atoms in the alkyl group and the fluoroalkyl group may be 1 to 5, 1 to 4, 1 to 3, 1 to 2, or 1. The number of fluorine atoms in the fluoroalkyl 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 fluoroalkyl group may be a perfluoroalkyl group having 1 to 6 carbon atoms.

[0014] 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.

[0015] The non-aqueous electrolyte may contain only one type of compound represented by formula (1), or may contain two or more types.

[0016] The content of the compound represented by formula (1) in the non-aqueous electrolyte may be, for example, in terms of molar concentration, 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. Although it is not necessary to explain again, when the non-aqueous electrolyte contains two or more compounds represented by formula (1), the content referred to here means the total content of all compounds represented by formula (1) contained in the non-aqueous electrolyte.

[0017] <Non-aqueous solvent> The non-aqueous solvent in the non-aqueous electrolyte is an organic solvent other than water, and any known solvent used in lithium ion secondary batteries can be used as the non-aqueous solvent.Specific examples of non-aqueous solvents include cyclic carbonate (non-fluorinated saturated cyclic carbonate) solvents such as ethylene carbonate, propylene carbonate, 2,3-dimethylethylene carbonate, 1,2-butylene carbonate, and erythrityl carbonate; chain carbonate (non-fluorinated saturated chain carbonate) solvents such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, and methyl phenyl carbonate; methyl propionate, ethyl propionate, butyl propionate, isopropyl propionate, and propionate. Carboxylic acid ester (chain ester) solvents such as propyl acetate, ethyl acetate, methyl acetate, propyl acetate, and isopropyl acetate; chain ether solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, and triethylene glycol dimethyl ether; cyclic ether solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, 1,4-dioxane, and 1,3-dioxolane; fluorine-containing cyclic carbonate solvents such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and trifluoropropylene carbonate; aromatic carboxylic acid ester solvents such as methyl benzoate and ethyl benzoate; lactone solvents such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; phosphate ester solvents such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, and triethyl phosphate; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, Examples of suitable solvents include nitrile solvents such as nitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, and isobutyronitrile; sulfur compound solvents such as dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane; aromatic nitrile solvents such as benzonitrile and tolunitrile; and nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, and 3-methyl-2-oxazolidinone.

[0018] Among these, the non-aqueous solvent may contain at least one selected from the group consisting of cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, lactone solvents, ester solvents, and nitrile solvents, or may contain at least one selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated chain carbonate solvents.

[0019] <Chloroalkanes with 3 or more carbon atoms and chlorocycloalkanes with 3 or more carbon atoms> The non-aqueous electrolyte solution according to this embodiment contains at least one selected from the group consisting of chloroalkanes having 3 or more carbon atoms and chlorocycloalkanes having 3 or more carbon atoms.

[0020] Of the chloroalkanes having 3 or more carbon atoms and the chlorocycloalkanes having 3 or more carbon atoms, the nonaqueous electrolyte may contain only the chloroalkanes having 3 or more carbon atoms, or may contain only the chlorocycloalkanes having 3 or more carbon atoms, or may contain both the chloroalkanes having 3 or more carbon atoms and the chlorocycloalkanes having 3 or more carbon atoms.

[0021] Chloroalkanes are compounds with a molecular structure in which one or more hydrogen atoms in a saturated chain aliphatic hydrocarbon are replaced with chlorine atoms. The saturated chain aliphatic hydrocarbon may be either a linear aliphatic hydrocarbon group or a branched aliphatic hydrocarbon group.

[0022] The number of carbon atoms in the chloroalkane may be 3 or more and 12 or less, 3 or more and 10 or less, or 3 or more and 8 or less.

[0023] The number of chlorine atoms in the chloroalkane may be 1 or more and 5 or less, 1 or more and 3 or less, or 1 or more and 2 or less.

[0024] Specific examples of chloroalkanes include 1-chloropropane, 2-chloropropane, 1-chlorobutane, 1,2-dichlorobutane, 1,4-dichlorobutane, 1-chloropentane, 1,3-dichloropentane, 1,3,5-trichloropentane, 1-chlorohexane, 1,4-dichlorohexane, 1-chlorononane, 1,9-dichlorononane, 1-chlorodecane, and 1,3,10-trichlorodecane.

[0025] Chlorocycloalkanes are compounds with a molecular structure in which one or more hydrogen atoms in a saturated cyclic aliphatic hydrocarbon are replaced with chlorine atoms.

[0026] The chlorocycloalkane may have 3 or more and 12 or less carbon atoms, 3 or more and 10 or less carbon atoms, or 3 or more and 8 or less carbon atoms.

[0027] The number of chlorine atoms in the chlorocycloalkane may be 1 or more and 5 or less, 1 or more and 3 or less, or 1 or more and 2 or less.

[0028] Specific examples of chlorocycloalkanes include chlorocyclohexane, 1,2-dichlorocyclohexane, 1,3-dichlorocyclohexane, and 1,4-dichlorocyclohexane.

[0029] The total content of at least one selected from the group consisting of chloroalkanes and chlorocycloalkanes in the non-aqueous electrolyte may be 0.002 parts by mass to 1 part by mass, 0.002 parts by mass to 0.8 parts by mass, 0.002 parts by mass to 0.6 parts by mass, or 0.002 parts by mass to 0.4 parts by mass, relative to 100 parts by mass of the compound represented by formula (1).

[0030] <Fluorine-containing lithium salt> The non-aqueous electrolyte preferably further contains, in addition to the compound represented by formula (1), a fluorine-containing lithium salt other than the compound represented by formula (1).

[0031] The fluorine-containing lithium salt is a salt composed of an anion having a fluorine atom and a lithium ion. Specific examples of the fluorine-containing lithium salt include at least one selected from the group consisting of LiPF, LiBF, LiPO, FSOLi, lithium difluorooxalatoborate (LiBF(CO), LiDFOB), lithium difluorooxalatophosphate (LiPF(CO), LiDFOP), (SOCFCFSO)NLi, (SOCFCFCFSO)NLi, LiFSO(CHSO)N, LiFSO(CFSO)N, LiFSO(CHSO)N, and LiAsF. (SOCFCFSO)NLi and (SOCFCFCFSO)NLi are salts composed of a cyclic sulfonimide anion and a lithium ion.

[0032] Among these, the fluorine-containing lithium salt may be at least one selected from the group consisting of LiPF6, LiBF4, LiPO2F2, FSO3Li, LiBF2(C2O4), and LiPF2(C2O4), or may be LiPF6.

[0033] The non-aqueous electrolyte may contain only one type of fluorine-containing lithium salt, or may contain two or more types.

[0034] The content of the fluorine-containing lithium salt in the non-aqueous electrolyte may be, for example, in terms of molar concentration, 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. Although it is not necessary to explain again, when the non-aqueous electrolyte contains two or more kinds of fluorine-containing lithium salts, the content referred to here means the total content of all the fluorine-containing lithium salts contained in the non-aqueous electrolyte.

[0035] When the non-aqueous electrolyte solution further contains a fluorine-containing lithium salt other than the compound represented by formula (1) in addition to the compound represented by formula (1), the total content of the compound represented by formula (1) and the fluorine-containing lithium salt other than the compound represented by formula (1) may be, for example, in terms of molar concentration, 0.01 mol / L or more and 10.0 mol / L or less, 0.05 mol / L or more and 4.00 mol / L or less, 0.10 mol / L or more and 2.00 mol / L or less, 0.15 mol / L or more and 1.20 mol / L or less, 0.20 mol / L or more and 1.00 mol / L or less, or 0.40 mol / L or more and 0.80 mol / L or less.

[0036] <Other ingredients> The non-aqueous electrolyte may further contain other components in addition to the components described above. For example, the non-aqueous electrolyte may further contain at least one selected from the group consisting of unsaturated cyclic carbonates, nitrile compounds, ester compounds, and fluorine-containing lithium salts.

[0037] The unsaturated cyclic carbonate may be, for example, at least one selected from the group consisting of vinylene carbonate (VC), methyl vinylene carbonate, ethyl vinylene carbonate, 2-vinyl ethylene carbonate, and phenyl ethylene carbonate. For example, the unsaturated cyclic carbonate may be vinylene carbonate.

[0038] The nitrile compound is a compound having a cyano group in the molecule, and may be, for example, at least one selected from the group consisting of a mononitrile compound having one cyano group in the molecule, a dinitrile compound having two cyano groups in the molecule, and a trinitrile compound having three or more cyano groups in the molecule, or may be at least one selected from the group consisting of a dinitrile compound and a trinitrile compound.

[0039] The mononitrile compound may be, for example, at least one selected from the group consisting of 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.

[0040] Examples of dinitrile compounds include succinonitrile, malononitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2,3,3-trimethylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3,3-trimethyl ... ,2,3,3-Tetramethylsuccinonitrile, 2,3-Diethyl-2,3-dimethylsuccinonitrile, 2,2-Diethyl-3,3-dimethylsuccinonitrile, Bicyclohexyl-1,1-dicarbonitrile, Bicyclohexyl-2,2-dicarbonitrile, Bicyclohexyl-3,3-dicarbonitrile, 2,5-Dimethyl-2,5-hexanedicarbonitrile, 2,3-Diisobutyl-2,3-dimethylsuccinonitrile, 2,2-Diisobutyl-3,3-dimethylsuccinonitrile, 2-Methylglutaro Nitriles, 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-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyano It may be at least one selected from the group consisting of benzene, 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, or it may be at least one selected from the group consisting of succinonitrile, malononitrile, glutaronitrile, adiponitrile, pimelonitrile, and suberonitrile, or it may be succinonitrile.

[0041] The trinitrile compound may be, for example, at least one selected from the group consisting of 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.

[0042] 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 -OC(=O)-O- in the molecule. The carbonate ester compound may be a compound having two divalent groups represented by -OC(=O)-O- in the molecule. For example, the ester compound is represented by the following formula (2): [ka] [In formula (2), R 11 and R 12 R 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.

[0043] As described above, the non-aqueous electrolyte may further contain at least one selected from the group consisting of vinylene carbonate, 1,3-propane sultone, succinonitrile, and dimethyl 2,5-dioxahexanedioate. The non-aqueous electrolyte may also contain components 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; heptane sulfonates, etc. Examples of suitable sulfonates include saturated hydrocarbon compounds such as ethane, octane, and cycloheptane; sulfamic acid (amidosulfuric acid, H3NSO3); sulfamic acid salts (for example, alkali metal salts such as lithium salt, sodium salt, and potassium salt; alkaline earth metal salts such as calcium salt, strontium salt, and barium salt; other metal salts such as manganese salt, copper salt, zinc salt, iron salt, cobalt salt, and nickel salt; ammonium salt; guanidine salt; and fluorosulfonic acid compounds such as sodium fluorosulfonate (NaFSO3), potassium fluorosulfonate (KFSO3), and magnesium fluorosulfonate (Mg(FSO3)2).

[0044] When the non-aqueous electrolyte solution further contains at least one compound selected from the group consisting of unsaturated cyclic carbonates, nitrile compounds, and ester compounds, the total content of these components may be 0.1 to 10 mass %, or 0.3 to 5 mass %.

[0045] Alternatively, the non-aqueous electrolyte may contain at least one selected from the group consisting of carbon dioxide, carbon monoxide, bicarbonate ions, and carbonate ions.

[0046] When the non-aqueous electrolyte solution contains at least one selected from the group consisting of carbon dioxide, carbon monoxide, bicarbonate ions, and carbonate ions, the total content of the at least one selected from the group consisting of carbon dioxide, carbon monoxide, bicarbonate ions, and carbonate ions, when dissolved, 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 solubility amount at 25°C or less.

[0047] The method for producing a non-aqueous electrolyte solution is not particularly limited. A method for producing a non-aqueous electrolyte solution in which the compound represented by formula (1) is lithium bis(fluorosulfonyl)imide will be described. For example, a lithium bis(fluorosulfonyl)imide powder may be obtained by the method described in International Publication No. 2011 / 149095 or Japanese Patent Application Laid-Open No. 2014-201453, and then this may be dissolved in a non-aqueous solvent together with at least one selected from the group consisting of chloroalkanes having 3 or more carbon atoms and chlorocycloalkanes having 3 or more carbon atoms. Alternatively, a non-aqueous solvent containing lithium bis(fluorosulfonyl)imide may be obtained by the method described in International Publication No. 2016 / 052752 or Japanese Patent Application Laid-Open No. 2017 / 204302, and then at least one selected from the group consisting of chloroalkanes having 3 or more carbon atoms and chlorocycloalkanes having 3 or more carbon atoms may be dissolved in the non-aqueous solvent.

[0048] <Lithium-ion secondary battery> Another aspect of the present disclosure is a lithium-ion secondary battery including a nonaqueous electrolyte solution according to an embodiment of the present disclosure, 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.

[0049] <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.

[0050] The positive electrode of the lithium ion secondary battery according to one embodiment 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) LiMPO4…(B)

[0051] In formula (A), 0.2≦v≦1.2, 0.3≦x≦0.9, 0 <y≦0.3、0<z≦0.4、x+y+z=1、-0.2≦w≦0.2である。

[0052] 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.

[0053] In formula (A), w is preferably −0.1 or more and 0.1 or less, and more preferably 0.

[0054] The positive electrode active material represented by formula (A) is LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2 is preferred, LiNi 0.5 Co 0.2 Mn 0.3 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2 is more preferred.

[0055] 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).

[0056] The positive electrode active material represented by formula (B) may be LiFePO4, LiNiPO4, LiMnPO4, or LiCoPO4.

[0057] The content of the positive electrode active material in the positive electrode composite layer is preferably 75 to 99 mass %, and more preferably 85 to 95 mass %, from the viewpoint of improving the output characteristics and electrical characteristics of the lithium ion secondary battery according to this embodiment.

[0058] 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.

[0059] The content of the conductive additive in the positive electrode mixture layer is preferably 0.5 to 20 mass %, more preferably 1 to 5 mass %, from the viewpoint of improving the output characteristics and electrical characteristics of the lithium ion secondary battery according to this embodiment.

[0060] 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.

[0061] The content of the binder in the positive electrode mixture layer is preferably 0.5 to 20 mass %, and more preferably 1 to 5 mass %.

[0062] The positive electrode mixture layer may further contain other components as necessary, such as 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; preservatives, etc.

[0063] The content of the other components in the positive electrode may be 0 to 15% by mass, or 0 to 10% by mass.

[0064] Examples of the positive electrode current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum, with aluminum being preferred.

[0065] 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.

[0066] 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.

[0067] <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.

[0068] The negative electrode composite 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, and lithium alloys such as lithium-aluminum alloys, and preferably contains graphite.

[0069] The content of the negative electrode active material in the negative electrode mixture layer is preferably 80 to 99 mass %, and more preferably 90 to 98 mass %.

[0070] 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 to 10 mass %, more preferably 1 to 5 mass %.

[0071] 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 to 10 mass %, more preferably 1 to 5 mass %.

[0072] 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.

[0073] The negative electrode current collector may be the same as the positive electrode current collector, and is preferably made of copper.

[0074] 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.

[0075] <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.

[0076] <Battery exterior materials> 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.

[0077] 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. [Example]

[0078] The present disclosure will be described in more detail below using examples, but the present disclosure is not limited to the following examples.

[0079] Test Example 1: Fabrication and Evaluation of Lithium-Ion Secondary Battery Comprising NCM523 Positive Electrode / OMAC-R Negative Electrode Cell In Test Example 1, a lithium-ion secondary battery was fabricated and evaluated, including a cell fabricated from a positive electrode (NCM523 positive electrode) containing nickel, cobalt, and manganese in a molar ratio of 5:2:3 and a negative electrode (OMAC-R negative electrode) based on graphite (OMAC-R).

[0080] (Preparation of positive electrode) As a ternary positive electrode active material, "NCM523" (LiNi 0.5 Co 0.2 Mn 0.3 O2 (Beijing Dangsheng Co., Ltd.), acetylene black (Denka, Denka Black), graphite (Nippon Graphite, SP270), and polyvinylidene fluoride (PVdF, #1120, commercially available) were weighed in a mass ratio of 100:3:3:3 and dispersed in N-methyl-2-pyrrolidone (NMP, commercially available) to prepare a slurry. The prepared slurry was coated on one side of aluminum foil (coating weight 19.5 mg / cm). 2 ) and dried, followed by roll pressing to prepare a positive electrode.

[0081] (Preparation of negative electrode) An aqueous slurry was prepared with a mass ratio of graphite (OMAC-R, manufactured by Osaka Gas Chemicals Co., Ltd.): carbon fiber (VGCF, manufactured by Showa Denko K.K.): styrene butadiene rubber (SBR, commercially available): carboxymethyl cellulose (CMC, commercially available) = 100:2:1:1. The aqueous slurry was coated on one side of copper foil (coating weight 9.8 mg / cm). 2 ) and dried, and then roll pressed to prepare a negative electrode.

[0082] (Preparation of Electrolyte) The electrolyte solution was prepared by dissolving LiFSI (manufactured by Nippon Shokubai Co., Ltd.), LiPF6 (manufactured by Kishida Chemical Co., Ltd.), and a chloroalkane or chlorocycloalkane in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 (EC / EMC = 3 / 7 (vol / vol)) to give the concentrations shown in Table 1. In Table 1, the content (parts by mass) of the chloroalkane or chlorocycloalkane is the content when the content of LiFSI is taken as 100 parts by mass.

[0083] (Battery construction) The positive electrode has an effective area of ​​12 cm 2 The negative electrode was cut to a thickness of 13.44 cm, and the polarity lead was welded using an ultrasonic welder. 2 The battery was cut with a 3000 Ω cutter, and the polarity lead was ultrasonically welded. These 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 create an unfilled cell. 700 μL of electrolyte was poured into one of the unsealed parts to create a 30 mAh laminated battery. The laminated battery was charged at a constant current of 3 mA for 3 hours, then one side was opened and vacuum sealed again to degas the battery. After degassing, the laminated battery was stored at 25°C for 48 hours and then charged and discharged under the following conditioning conditions to complete the evaluation. <Conditioning conditions> 1st cycle: 3mA, constant current constant voltage charge at 4.2V, terminated at 0.3mA ⇒ Discharge: Discharge at 6mA, terminate at 2.75V. 2nd cycle: 15mA, constant current / constant voltage charge at 4.2V, terminated at 0.6mA ⇒ Discharge: Discharge at 6mA, terminate at 2.75V. 3rd cycle: 15mA, constant current / constant voltage charge at 4.2V, terminated at 0.6mA ⇒ Discharge: Discharge at 30mA, terminate at 2.75V. 4th cycle: 15mA, constant current / constant voltage charge at 4.2V, terminated at 0.6mA ⇒ Discharge: Discharge at 60mA, terminate at 2.75V.

[0084] (Battery high temperature storage test) The laminated battery for evaluation was charged to a full charge state by constant current and constant voltage charging at 4.2 V, 30 mA, and 0.6 mA termination. The fully charged laminated battery was then stored at 80°C for 28 days. After storage, the laminated batteries were discharged at a constant current of 6 mA at 25°C with a cutoff of 2.75 V. The discharged laminated batteries were then charged at a constant current of 30 mA (1 C), 4.2 V, and 0.6 mA to a fully charged state, and the DCR was measured at 25°C. For the DCR measurement, the batteries were discharged at 6 mA (0.2 C) for 10 seconds after waiting 30 minutes. After a 30-minute wait, the batteries were discharged at 30 mA (1 C) for 10 seconds. Finally, after a 30-minute wait, the batteries were discharged at 90 mA (3 C) for 10 seconds. An IV line was created based on the relationship between the difference in voltage immediately before and 10 seconds after discharge at each discharge current and the current, and the DCR was calculated as the slope of the line. The results are shown in Table 1. After measuring the DCR, the laminated battery was fully charged under the same charging conditions. After charging, the battery was stored at 0°C for 3 hours, and then discharged at a constant current of 1C (30mA) at 0°C with a cutoff voltage of 2.75V to determine the discharge capacity (mAh / g) after high-temperature storage. The results are shown in Table 1. Table 1 shows the improvement (%) in DCR and discharge capacity relative to a laminated battery using an electrolyte solution of the same composition except that it did not contain chloroalkanes or chlorocycloalkanes. Because a decrease in DCR is desirable, the decrease in DCR was evaluated as the improvement. Because an increase in discharge capacity is desirable, the increase in discharge capacity was evaluated as the improvement. For example, the improvement in DCR and discharge capacity of Example 1 is the improvement in DCR and discharge capacity relative to a laminated battery of Comparative Example 1 using an electrolyte solution of the same composition except that it did not contain 1-chloropropane.

[0085] [Table 1] JPEG2026022061000003.jpg146149

[0086] As is clear from Table 1, in the examples in which a chloroalkane having 3 or more carbon atoms or a chlorocycloalkane having 3 or more carbon atoms was added as an additive to the nonaqueous electrolyte, the DCR after storage at 80°C was reduced and the discharge capacity at 0°C was improved. The reason for this phenomenon is not entirely clear, but the inventors speculate that the chloroalkanes or chlorocycloalkanes oxidized at the positive electrode polymerize and act as a positive electrode protective film, thereby suppressing deterioration of the positive electrode due to high-temperature storage. As is clear from Table 1, the improvement effect is particularly large in Examples in which the chloroalkane or chlorocycloalkane has 3 to 8 carbon atoms and Examples in which the amount of chloroalkane or chlorocycloalkane added is 0.002 to 0.2 parts by mass. On the other hand, in the comparative examples in which a chloroalkane having two or fewer carbon atoms (dichloromethane, dichloroethane) or a chloroaryl compound (dichlorobenzene) was used as an additive, no improvement was obtained. Although the reason for this phenomenon is not entirely clear, it is believed that even when a chloroalkane having two or fewer carbon atoms is oxidatively decomposed at the positive electrode to form a polymer, the resulting film has a small molecular weight and is easily dissolved in the electrolyte, so it does not function as a protective film. It is believed that when a chloroaryl compound is oxidatively decomposed at the positive electrode, the film becomes too thick and becomes a resistive film, so no improvement was obtained.

[0087] Test Example 2: Fabrication and Evaluation of Lithium-Ion Secondary Battery Comprising NCM811 Positive Electrode / OMAC-R Negative Electrode Cell In Test Example 2, a lithium-ion secondary battery was fabricated and evaluated, including a cell fabricated from a positive electrode (NCM811 positive electrode) containing nickel, cobalt, and manganese in a molar ratio of 8:1:1 and a negative electrode (OMAC-R negative electrode) based on graphite (OMAC-R).

[0088] (Preparation of positive electrode) As a ternary positive electrode active material, "NCM811" (LiNi 0.8 Co 0.1 Mn 0.1O2 (Beijing Dangsheng Co., Ltd.), acetylene black (Denka, Denka Black), graphite (Nippon Graphite, SP270), and polyvinylidene fluoride (PVdF, #1120, commercially available) were weighed in a mass ratio of 100:3:3:3 and dispersed in N-methyl-2-pyrrolidone (NMP, commercially available) to prepare a slurry. The prepared slurry was coated on one side of aluminum foil (coating weight 19.5 mg / cm). 2 ) and dried, followed by roll pressing to prepare a positive electrode.

[0089] (Preparation of negative electrode) An aqueous slurry was prepared with a mass ratio of graphite (OMAC-R, manufactured by Osaka Gas Chemicals Co., Ltd.): carbon fiber (VGCF, manufactured by Showa Denko K.K.): styrene butadiene rubber (SBR, commercially available): carboxymethyl cellulose (CMC, commercially available) = 100:2:1:1. The aqueous slurry was coated on one side of copper foil (coating weight 9.8 mg / cm). 2 ) and dried, and then roll pressed to prepare a negative electrode.

[0090] (Preparation of Electrolyte) The electrolyte solution was prepared by dissolving LiFSI (manufactured by Nippon Shokubai Co., Ltd.), LiPF6 (manufactured by Kishida Chemical Co., Ltd.), and a chloroalkane or chlorocycloalkane in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 (EC / EMC = 3 / 7 (vol / vol)) to give the concentrations shown in Table 2. In Table 2, the content (parts by mass) of the chloroalkane or chlorocycloalkane is the content when the content of LiFSI is taken as 100 parts by mass.

[0091] (Battery construction) The positive electrode has an effective area of ​​12 cm 2 The negative electrode was cut to a thickness of 13.44 cm, and the polarity lead was welded using an ultrasonic welder. 2 The battery was cut with a 3000 Ω cutter, and the polarity lead was ultrasonically welded. These 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 create an unfilled cell. 700 μL of electrolyte was poured into one of the unsealed parts to create a 30 mAh laminated battery. The laminated battery was charged at a constant current of 3 mA for 3 hours, then one piece was opened and vacuum sealed again to degas the battery. After degassing, the laminated battery was stored at 25°C for 48 hours and then charged and discharged under the following conditioning conditions to complete the evaluation. <Conditioning conditions> 1st cycle: 3mA, constant current constant voltage charge at 4.2V, terminated at 0.3mA ⇒ Discharge: Discharge at 6mA, terminate at 2.75V. 2nd cycle: 15mA, constant current / constant voltage charge at 4.2V, terminated at 0.6mA ⇒ Discharge: Discharge at 6mA, terminate at 2.75V. 3rd cycle: 15mA, constant current / constant voltage charge at 4.2V, terminated at 0.6mA ⇒ Discharge: Discharge at 30mA, terminate at 2.75V. 4th cycle: 15mA, constant current / constant voltage charge at 4.2V, terminated at 0.6mA ⇒ Discharge: Discharge at 60mA, terminate at 2.75V.

[0092] (Battery high temperature storage test) The laminated battery for evaluation was charged to a full charge state by constant current and constant voltage charging at 4.2 V, 30 mA, and 0.6 mA termination. The fully charged laminated battery was then stored at 80°C for 28 days. After storage, the laminated batteries were discharged at a constant current of 6 mA at 25°C with a cutoff of 2.75 V. The discharged laminated batteries were then charged at a constant current of 30 mA (1 C), 4.2 V, and 0.6 mA to a full charge state, and the DCR was measured at 25°C. For the DCR measurement, the batteries were waited 30 minutes after full charge and then discharged at 6 mA (0.2 C) for 10 seconds. After a 30-minute wait, the batteries were discharged at 30 mA (1 C) for 10 seconds. Finally, after a 30-minute wait, the batteries were discharged at 90 mA (3 C) for 10 seconds. An IV line was created based on the relationship between the difference in voltage immediately before and 10 seconds after discharge at each discharge current and the current, and the DCR was calculated as the slope. The results are shown in Table 2. After measuring the DCR, the laminated battery was fully charged under the same charging conditions. After charging, it was stored at 0°C for 3 hours, and then discharged at a constant current of 1C (30mA) at 0°C with a cutoff of 2.75V to determine the discharge capacity after high-temperature storage. The results are shown in Table 2. As in Table 1 above, Table 2 also shows the improvement (%) in DCR and discharge capacity relative to a laminated battery using an electrolyte solution of the same composition except that it did not contain chloroalkanes or chlorocycloalkanes.

[0093] [Table 2] JPEG2026022061000005.jpg146149

[0094] As is clear from Table 2, in the examples in which a chloroalkane having 3 or more carbon atoms or a chlorocycloalkane having 3 or more carbon atoms was added as an additive to the nonaqueous electrolyte, the DCR after storage at 80°C was reduced and the discharge capacity at 0°C was improved. The reason for this phenomenon is not entirely clear, but the inventors speculate that the chloroalkanes or chlorocycloalkanes oxidized at the positive electrode polymerize and act as a positive electrode protective film, thereby suppressing deterioration of the positive electrode due to high-temperature storage. As is clear from Table 2, the improvement effect is particularly large in Examples in which the chloroalkane or chlorocycloalkane has 3 to 8 carbon atoms and Examples in which the amount of chloroalkane or chlorocycloalkane added is 0.002 to 0.2 parts by mass. On the other hand, in the comparative examples in which chloroalkanes with two or fewer carbon atoms (dichloromethane, dichloroethane) or chloroaryls (dichlorobenzene) were used as additives, no improvement was observed. Although the reason for this phenomenon is not entirely clear, it is believed that even when chloroalkanes with two or fewer carbon atoms are oxidatively decomposed at the positive electrode to form a polymer, the resulting film has a small molecular weight and is easily dissolved in the electrolyte, so it does not function as a protective film. It is believed that when chloroaryl compounds are oxidatively decomposed at the positive electrode, the film becomes too thick and becomes a resistive film, so no improvement was observed.

[0095] Test Example 3: Preparation and Evaluation of Lithium-Ion Secondary Battery Including LFP Positive Electrode / Gr Negative Electrode Cell In Test Example 3, a lithium ion secondary battery including a cell made from a positive electrode containing lithium iron phosphate (LFP positive electrode) and a negative electrode based on graphite (Gr negative electrode) was fabricated and evaluated.

[0096] (Preparation of positive electrode) Commercially available LiFePO4, acetylene black (Denka), and PVdF (Kureha, product number KF Polymer 7208, solid content 8%) were weighed in a solid content ratio of 100:9:6 and dispersed in NMP as a solvent to prepare a slurry. The prepared slurry was applied to aluminum foil at a coating weight of 20.2 mg / cm. 2 The mixture was dried on a hot plate at 130°C, and then dried for 12 hours in a vacuum drying oven set at 130°C. The dried material was pressed with a roll press to prepare a positive electrode with a composite density of 1.9 g / cc.

[0097] (Preparation of negative electrode) An aqueous slurry was prepared with a mass ratio of graphite (OMAC-R, manufactured by Osaka Gas Chemicals Co., Ltd.): graphite (SFG-15, manufactured by Imerys Co., Ltd.): carbon fiber (VGCF, manufactured by Showa Denko K.K.): styrene butadiene rubber (SBR, commercially available): carboxymethyl cellulose (CMC, commercially available) = 85:15:2:1:1. The aqueous slurry was coated on one side of copper foil (coating weight 8.8 mg / cm). 2 ) and dried, and then roll pressed to prepare a negative electrode.

[0098] (Preparation of Electrolyte) The electrolyte solution was prepared by dissolving LiFSI (manufactured by Nippon Shokubai Co., Ltd.), LiPF6 (manufactured by Kishida Chemical Co., Ltd.), and a chloroalkane or chlorocycloalkane in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 (EC / EMC = 3 / 7 (vol / vol)) to give the concentrations shown in Table 3. In Table 3, the content (parts by mass) of the chloroalkane or chlorocycloalkane is the content when the content of LiFSI is taken as 100 parts by mass.

[0099] (Battery construction) The positive electrode has an effective area of ​​12 cm 2 The negative electrode was cut to a thickness of 13.44 cm, and the polarity lead was welded using an ultrasonic welder. 2 The battery was cut with a 25-μm thick polyethylene separator between them, and the polarity lead was ultrasonically welded. An unfilled cell was fabricated by sealing the three sides with a laminate exterior. 500 μL of electrolyte was poured into one of the unsealed parts, resulting in a 25 mAh laminated battery. The laminated battery was charged at a constant current of 2.5 mA for 3 hours, then one piece was opened and vacuum sealed again to degas the battery. After degassing, the battery was stored at 25°C for 48 hours and then charged under the following conditioning conditions to complete the laminated battery for evaluation. <Conditioning conditions> 1st cycle: Charging: 2.5mA, constant current constant voltage charging at 3.6V, termination at 0.25mA ⇒ Discharge: Discharge at 5mA, terminate at 2.0V. 2nd cycle: 12.5mA, constant current / constant voltage charge at 3.6V, terminated at 0.5mA ⇒ Discharge: Discharge at 5mA, terminate at 2.0V. 3rd cycle: 12.5mA, constant current / constant voltage charge at 3.6V, terminated at 0.5mA ⇒ Discharge: Discharge at 25mA, terminate at 2.0V. 4th cycle: 12.5mA, constant current / constant voltage charge at 3.6V, terminated at 0.5mA ⇒ Discharge: Discharge at 50mA, terminate at 2.0V.

[0100] (Battery high temperature storage test) The laminated battery for evaluation was charged to a full charge state by constant current and constant voltage charging at 3.6 V, 25 mA, and 0.5 mA termination. The fully charged laminated battery was then stored at 80°C for 28 days. After storage, the laminated batteries were discharged at a constant current of 5 mA at 25°C with a cutoff of 2.0 V. The discharged laminated batteries were then charged at a constant current of 25 mA (1 C), 3.6 V, and 0.5 mA to a full charge state, and the DCR was measured at 25°C. For the DCR measurement, the batteries were waited 30 minutes after full charge and then discharged at 5 mA (0.2 C) for 10 seconds. After a 30-minute wait, the batteries were discharged at 25 mA (1 C) for 10 seconds. Finally, after a 30-minute wait, the batteries were discharged at 50 mA (3 C) for 10 seconds. An IV line was created based on the relationship between the difference in voltage immediately before and 10 seconds after discharge at each discharge current and the current, and the DCR was calculated as the slope. The results are shown in Table 3. After measuring the DCR, the laminated battery was fully charged under the same charging conditions. After charging, it was stored at 0°C for 3 hours, and then discharged at 0°C at 1C (25mA) with a cutoff voltage of 2.0V to determine the discharge capacity after high-temperature storage. The results are shown in Table 3. As in Table 1 above, Table 3 also shows the improvement (%) in DCR and discharge capacity relative to a laminated battery using an electrolyte solution of the same composition except that it did not contain chloroalkanes or chlorocycloalkanes.

[0101] [Table 3] JPEG2026022061000007.jpg133149

[0102] As is clear from Table 3, in the examples in which a chloroalkane having 3 or more carbon atoms or a chlorocycloalkane having 3 or more carbon atoms was added as an additive to the non-aqueous electrolyte, the DCR after storage at 80°C was reduced and the discharge capacity at 0°C was improved. The reason for this phenomenon is not entirely clear, but the inventors speculate that the chloroalkanes or chlorocycloalkanes oxidized at the positive electrode polymerize and act as a positive electrode protective film, thereby suppressing deterioration of the positive electrode due to high-temperature storage. As is clear from Table 3, the improvement effect is particularly large in Examples in which the chloroalkane or chlorocycloalkane has 3 to 8 carbon atoms and Examples in which the amount of chloroalkane or chlorocycloalkane added is 0.002 to 0.2 parts by mass. On the other hand, in the comparative examples in which a chloroalkane having two or fewer carbon atoms (dichloromethane, dichloroethane) or a chloroaryl compound (dichlorobenzene) was used as an additive, no improvement was obtained. Although the reason for this phenomenon is not entirely clear, it is believed that even when a chloroalkane having two or fewer carbon atoms is oxidatively decomposed at the positive electrode to form a polymer, the resulting film has a small molecular weight and is easily dissolved in the electrolyte, so it does not function as a protective film. It is believed that when a chloroaryl compound is oxidatively decomposed at the positive electrode, the film becomes too thick and becomes a resistive film, so no improvement was obtained.

[0103] [Reference test example: electrolyte storage stability test] The ionic conductivity of the electrolyte was measured using a Toa DKK electrical conductivity meter (CM-25R) according to the following method. A chloroalkane shown in Table 4 was added to a 1M / L LiFSI solution with an EC / MEC ratio of 3 / 7 (volume ratio) in an amount of 0.3 parts by mass per 100 parts by mass of LiFSI to prepare the electrolyte. The electrolyte was placed in a PP vial, and a CM-25R electrode and thermocouple were placed inside. The vial was then cooled in a -20°C thermostatic chamber. The electrical conductivity was read when the electrolyte temperature reached -20°C, and this was taken as the ionic conductivity at -20°C. The results are shown in Table 4.

[0104] [Table 4]

[0105] As is clear from Table 4, in the examples in which a chloroalkane having three or more carbon atoms was added, ionic conduction at −20° C. was improved. The reason for this phenomenon is not entirely clear, but the inventors speculate that in non-aqueous electrolytes containing chloroalkanes, the additive interacts appropriately with Li ions, increasing the dissociation of LiFSI, thereby improving ionic conduction at −20° C.

Claims

1. A non-aqueous electrolyte solution for a lithium ion secondary battery, comprising a compound represented by the following formula (1) and a non-aqueous solvent: The non-aqueous electrolyte solution further comprises at least one selected from the group consisting of chloroalkanes having 3 or more carbon atoms and chlorocycloalkanes having 3 or more carbon atoms. LiN(R １ SO ２ )(R ２ SO ２ )・・・(1) [In formula (1), R １ and R ２ each independently represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.

2. 2. The nonaqueous electrolyte according to claim 1, wherein the chloroalkane has 3 or more and 8 or less carbon atoms.

3. 2. The nonaqueous electrolyte according to claim 1, wherein the chlorocycloalkane has 3 or more and 8 or less carbon atoms.

4. 3. The nonaqueous electrolyte solution according to claim 1, wherein the total content of at least one selected from the group consisting of the chloroalkane and the chlorocycloalkane is 0.002 parts by mass to 1 part by mass relative to 100 parts by mass of the compound represented by formula (1).

5. 3. The nonaqueous electrolyte solution according to claim 1, wherein the total content of at least one selected from the group consisting of the chloroalkane and the chlorocycloalkane is 0.002 parts by mass to 0.4 parts by mass relative to 100 parts by mass of the compound represented by formula (1).

6. 3. The nonaqueous electrolyte solution according to claim 1, wherein the nonaqueous solvent comprises at least one selected from the group consisting of cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, lactone solvents, ester solvents, and nitrile solvents.

7. 3. The non-aqueous electrolyte solution according to claim 1, wherein the non-aqueous solvent comprises at least one solvent selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated chain carbonate solvents.

8. A lithium ion secondary battery comprising the nonaqueous electrolyte solution according to claim 1 or 2.

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