Nonaqueous electrolyte for batteries and lithium secondary batteries

Abstract

A non-aqueous electrolyte for a battery is provided that can improve the capacity retention rate of the battery after storage. [Solution] A non-aqueous electrolyte solution for a battery contains additive A, which is a compound represented by formula (A), additive B, which is a compound represented by formula (B), and an electrolyte, which is a lithium salt other than additive B, wherein the content of additive B is 0.001% by mass to 10% by mass relative to the total amount of the non-aqueous electrolyte solution for a battery. 1 represents an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom. 2 represents a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom. JPEG2022126851000009.jpg31164

Description

[Technical field]

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

[0002] In recent years, lithium secondary batteries have been widely used in electronic devices such as mobile phones and notebook computers, as well as power sources for electric vehicles and power storage. In particular, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be installed in hybrid and electric vehicles. A lithium secondary battery includes, for example, a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a non-aqueous electrolyte for batteries containing a lithium salt and a non-aqueous solvent. The positive electrode active material used in the positive electrode is, for example, a lithium metal oxide such as LiCoO2, LiMnO2, LiNiO2, or LiFePO4. In addition, as a non-aqueous electrolyte for batteries, a solution in which a Li electrolyte such as LiPF6, LiBF4, LiN(SO2CF3)2, or LiN(SO2CF2CF3)2 is mixed with a mixed solvent (non-aqueous solvent) of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, or ethyl methyl carbonate is used. On the other hand, known negative electrode active materials used in the negative electrode include metallic lithium, metal compounds capable of absorbing and releasing lithium (such as simple metals, oxides, and alloys with lithium), and carbon materials. In particular, lithium secondary batteries that employ coke, artificial graphite, and natural graphite capable of absorbing and releasing lithium have been put to practical use.

[0003] 2. Description of the Related Art In order to improve the performance of a battery (such as a lithium secondary battery) that contains a nonaqueous electrolyte solution for a battery, various additives have been added to the nonaqueous electrolyte solution for a battery. For example, as a nonaqueous electrolyte for batteries that can improve low-temperature cycle characteristics and suppress the precipitation of metallic lithium after a low-temperature cycle, a nonaqueous electrolyte containing additive A, which is a five-membered cyclic sulfate ester compound having a specific structure, and additive B, which is a sulfonyl fluoride compound having a specific structure, is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-66481 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, there are cases where it is required to further improve the capacity retention rate after storage for batteries that contain a non-aqueous electrolyte solution that contains an additive that is a sulfonyl fluoride compound having a specific structure. Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte for a battery that can improve the capacity retention rate after storage of the battery, and a lithium secondary battery that uses this nonaqueous electrolyte for a battery. [Means for solving the problem]

[0006] Means for solving the above problems include the following aspects. <1> Additive A is a compound represented by formula (A); Additive B, which is a compound represented by formula (B); an electrolyte which is a lithium salt other than additive B; A non-aqueous electrolyte for a battery comprising:

[0007] [ka]

[0008] [In formula (A), R 1represents a hydrocarbon group having 1 to 6 carbon atoms, a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom. In formula (B), R 2 represents a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom.

[0009] <2> The content of the additive A is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for a battery. <1> The non-aqueous electrolyte for a battery according to claim 1. <3> The content of the additive B is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for a battery. <1> or <2> The non-aqueous electrolyte for a battery according to claim 1. <4> Further, the present invention contains an additive C which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. <1> ~ <3> 13. The nonaqueous electrolyte for a battery according to claim 12, <5> The content of the additive C is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for a battery. <4> The non-aqueous electrolyte for a battery according to claim 1.

[0010] <6> A positive electrode and a negative electrode containing at least one selected from the group consisting of metallic lithium, a lithium-containing alloy, a metal or alloy capable of being alloyed with lithium, an oxide capable of being doped / dedoped with lithium ions, a transition metal nitride capable of being doped / dedoped with lithium ions, and a carbon material capable of being doped / dedoped with lithium ions as a negative electrode active material; <1> ~ <5> and a non-aqueous electrolyte for a battery according to any one of the above items. A lithium secondary battery comprising: <7> <6> 2. A lithium secondary battery obtained by charging and discharging the lithium secondary battery described in claim 1. Effect of the Invention

[0011] According to the present disclosure, there are provided a nonaqueous electrolyte for a battery capable of improving the capacity retention rate of a battery after storage, and a lithium secondary battery using this nonaqueous electrolyte for a battery. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic perspective view showing an example of a laminated battery, which is an example of a lithium secondary battery according to the present disclosure. [Diagram 2] 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the laminated battery shown in FIG. 1. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, the amount of each component in a composition means, when a plurality of substances corresponding to each component are present in the composition, the total amount of the plurality of substances present in the composition, unless otherwise specified.

[0014] [Nonaqueous electrolyte for batteries] The nonaqueous electrolyte for a battery according to the present disclosure (hereinafter, also simply referred to as the “nonaqueous electrolyte”) contains an additive A which is a compound represented by formula (A), an additive B which is a compound represented by formula (B), and an electrolyte which is a lithium salt other than the additive B.

[0015] [ka]

[0016] In formula (A), R 1represents a hydrocarbon group having 1 to 6 carbon atoms, a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom. In formula (B), R 2 represents a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom.

[0017] The nonaqueous electrolyte of the present disclosure can improve the capacity retention rate of a battery after storage. Although the reason why such an effect is achieved is not clear, it is believed that the combination of Additive A and Additive B forms a coating with excellent durability on the surface of the battery electrode.

[0018] Hereinafter, each component of the nonaqueous electrolyte solution of the present disclosure will be described.

[0019] <Additive A> The nonaqueous electrolyte solution of the present disclosure contains Additive A, which is a compound represented by the following formula (A). The additive A may be one type or two or more types selected from the group consisting of compounds represented by the following formula (A).

[0020] [ka]

[0021] In formula (A), R 1 represents a hydrocarbon group having 1 to 6 carbon atoms, a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom.

[0022] R 1 The "hydrocarbon group having 1 to 6 carbon atoms" represented by the following formula represents an unsubstituted hydrocarbon group having 1 to 6 carbon atoms. R 1The "hydrocarbon group having 1 to 6 carbon atoms" represented by the following formula may be a straight-chain hydrocarbon group, a branched hydrocarbon group, or a cyclic hydrocarbon group. R 1 The "hydrocarbon group having 1 to 6 carbon atoms" represented by the following formula is preferably an alkyl group or an alkenyl group, and more preferably an alkyl group. R 1 The number of carbon atoms in the "hydrocarbon group having 1 to 6 carbon atoms" represented by the following formula is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

[0023] R 1 Examples of the "hydrocarbon group having 1 to 6 carbon atoms" represented by the formula (1) include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a 1-ethylpropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 2-methylbutyl group, a 3,3-dimethylbutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, and a tert-hexyl group; and alkenyl groups such as a vinyl group, a 1-propenyl group, an allyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a pentenyl group, a hexenyl group, an isopropenyl group, a 2-methyl-2-propenyl group, a 1-methyl-2-propenyl group, and a 2-methyl-1-propenyl group.

[0024] R 1 The "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the formula (I) is the same as the above-mentioned R 1 In particular, examples of the substituent include a group having a structure in which a "hydrocarbon group having 1 to 6 carbon atoms" (that is, an unsubstituted hydrocarbon group having 1 to 6 carbon atoms) represented by the following formula (I) is substituted with at least one fluorine atom.

[0025] R 1Examples of the "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the formula (1) include fluoroalkyl groups such as a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, a perfluoroisopropyl group, and a perfluoroisobutyl group; and fluoroalkenyl groups such as a 2-fluoroethenyl group, a 2,2-difluoroethenyl group, a 2-fluoro-2-propenyl group, a 3,3-difluoro-2-propenyl group, a 2,3-difluoro-2-propenyl group, a 3,3-difluoro-2-methyl-2-propenyl group, a 3-fluoro-2-butenyl group, a perfluorovinyl group, a perfluoropropenyl group, and a perfluorobutenyl group.

[0026] In formula (A), R 1 The hydrocarbon group portion in the structure of the "hydrocarbon oxy group having 1 to 6 carbon atoms" represented by the above R 1 This has the same meaning as the "hydrocarbon group having 1 to 6 carbon atoms" represented by the following formula: R 1 The "hydrocarbon oxy group having 1 to 6 carbon atoms" represented by the following formula is preferably an alkoxy group or an alkenyloxy group, and more preferably an alkoxy group.

[0027] R 1 Examples of the "hydrocarbon oxy group having 1 to 6 carbon atoms" represented by the formula (1) include alkoxy groups such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, a 2-butoxy group, a tert-butoxy group, a cyclopropyloxy group, and a cyclopentyloxy group; alkenyloxy groups such as an allyloxy group and a vinyloxy group; and the like.

[0028] In formula (A), R 1 The "hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the formula (I) is the same as the above-mentioned R 1In particular, examples of the substituent include a group having a structure in which a "hydrocarbon oxy group having 1 to 6 carbon atoms" (that is, an unsubstituted hydrocarbon oxy group having 1 to 6 carbon atoms) represented by the following formula (I) is substituted with at least one fluorine atom.

[0029] In formula (A), R 1 As the alkyl group, a hydrocarbon group having 1 to 6 carbon atoms (i.e., an unsubstituted hydrocarbon group having 1 to 6 carbon atoms) or a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom is preferable, a hydrocarbon group having 1 to 6 carbon atoms is more preferable, and an alkyl group having 1 to 6 carbon atoms is particularly preferable.

[0030] The compound represented by formula (A) is methanesulfonyl fluoride, ethanesulfonyl fluoride, propanesulfonyl fluoride, 2-propanesulfonyl fluoride, butanesulfonyl fluoride, 2-butanesulfonyl fluoride, hexanesulfonyl fluoride, trifluoromethanesulfonyl fluoride, perfluoroethanesulfonyl fluoride, perfluoropropanesulfonyl fluoride, perfluorobutanesulfonyl fluoride, ethenesulfonyl fluoride, 1-propene-1-sulfonyl fluoride, or 2-propene-1-sulfonyl fluoride is preferred; More preferred are methanesulfonyl fluoride, ethanesulfonyl fluoride, propanesulfonyl fluoride, 2-propanesulfonyl fluoride, butanesulfonyl fluoride, 2-butanesulfonyl fluoride, hexanesulfonyl fluoride, trifluoromethanesulfonyl fluoride, perfluoroethanesulfonyl fluoride, perfluoropropanesulfonyl fluoride, or perfluorobutanesulfonyl fluoride; More preferred are methanesulfonyl fluoride, ethanesulfonyl fluoride, propanesulfonyl fluoride, 2-propanesulfonyl fluoride, butanesulfonyl fluoride, 2-butanesulfonyl fluoride, and hexanesulfonyl fluoride; More preferably, methanesulfonyl fluoride, ethanesulfonyl fluoride, or propanesulfonyl fluoride is used. Methanesulfonyl fluoride is particularly preferred.

[0031] The content of additive A is preferably 0.001 mass% to 10 mass%, more preferably 0.01 mass% to 10 mass%, even more preferably 0.05 mass% to 5 mass%, even more preferably 0.1 mass% to 5 mass%, even more preferably 0.5 mass% to 5 mass%, even more preferably 0.5 mass% to 3 mass%, even more preferably 0.5 mass% to 2 mass%, and even more preferably 0.5 mass% to 1 mass%, based on the total amount of the non-aqueous electrolyte.

[0032] <Additive B> The nonaqueous electrolyte solution of the present disclosure contains Additive B, which is a compound represented by the following formula (B). The additive B may be one type or two or more types selected from the group consisting of compounds represented by the following formula (B).

[0033] [ka]

[0034] In formula (B), R 2 represents a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom.

[0035] In formula (B), R 2 The "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the formula (A) is R 1 This has the same meaning as "a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the following formula: In formula (B), R 2 The "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the formula (A) is R 1 This has the same meaning as "a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by the following formula:

[0036] In formula (B), R2 is preferably a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, more preferably an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom, still more preferably a perfluoroalkyl group having 1 to 6 carbon atoms, still more preferably a perfluoromethyl group (also known as a trifluoromethyl group) or a perfluoroethyl group (also known as a pentafluoroethyl group), and particularly preferably a perfluoromethyl group (also known as a trifluoromethyl group).

[0037] The compound represented by formula (B) preferably includes at least one selected from the group consisting of lithium trifluoromethanesulfonate and lithium pentafluoroethanesulfonate, and particularly preferably lithium trifluoromethanesulfonate.

[0038] The content of additive B is preferably 0.001 mass% to 10 mass%, more preferably 0.01 mass% to 10 mass%, even more preferably 0.05 mass% to 5 mass%, even more preferably 0.1 mass% to 5 mass%, even more preferably 0.5 mass% to 5 mass%, even more preferably 0.5 mass% to 3 mass%, even more preferably 0.5 mass% to 2 mass%, and even more preferably 0.5 mass% to 1 mass%, based on the total amount of the non-aqueous electrolyte.

[0039] <Electrolytes> The nonaqueous electrolyte solution of the present disclosure contains an electrolyte that is a lithium salt other than Additive B (hereinafter also referred to as a "specific lithium salt"). The specific lithium salt as the electrolyte may be of one type only, or of two or more types.

[0040] Specific examples of specific lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, Li2SiF6, and LiPF n [C k F (2k+1) ] (6-n) (n=an integer of 1 to 5, k=an integer of 1 to 8) and the like. Also usable are lithium salts represented by the following general formula:

[0041] LiC(SO2R 27 )(SO2R 28 )(SO2R 29 ), LiN(SO2OR 30 )(SO2OR 31 ), LiN(SO2R 32 )(SO2R 33 ) (where R 27 ~R 33 may be the same or different and are perfluoroalkyl groups having 1 to 8 carbon atoms.) These electrolytes may be used alone or in combination of two or more kinds.

[0042] The specific lithium salt preferably includes at least one of LiPF6 and LiBF4, and more preferably includes LiPF6. When the specific lithium salt contains LiPF6, the ratio of LiPF6 in the specific lithium salt is preferably 10 mass % to 100 mass %, more preferably 50 mass % to 100 mass %, and particularly preferably 70 mass % to 100 mass %.

[0043] The concentration of the electrolyte in the nonaqueous electrolyte solution is preferably 0.1 mol / L to 3 mol / L, and more preferably 0.5 mol / L to 2 mol / L.

[0044] <Additive C> The nonaqueous electrolyte solution of the present disclosure preferably contains additive C which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. When the nonaqueous electrolyte solution of the present disclosure contains the additive C, it is possible to reduce the resistance of the battery before and after storage. Furthermore, it is possible to suppress an increase in the battery resistance due to storage. Additive C preferably comprises lithium difluorophosphate.

[0045] The content of additive C, relative to the total amount of the nonaqueous electrolyte, is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 10% by mass, even more preferably 0.05% by mass to 5% by mass, even more preferably 0.1% by mass to 5% by mass, even more preferably 0.5% by mass to 5% by mass, even more preferably 0.5% by mass to 3% by mass, even more preferably 0.5% by mass to 2% by mass, and even more preferably 0.5% by mass to 1% by mass.

[0046] <Additive D> The nonaqueous electrolyte solution of the present disclosure may contain an additive D, which is a compound represented by the following formula (D). Additive D may be one type or two or more types selected from the group consisting of compounds represented by the following formula (D).

[0047] [ka]

[0048] In formula (D), Y 1 and Y 2 each independently represents a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

[0049] Examples of the compound represented by formula (D) include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, and dipropyl vinylene carbonate. Of these, vinylene carbonate is particularly preferred.

[0050] The content of additive D, relative to the total amount of the nonaqueous electrolyte, is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 10% by mass, even more preferably 0.05% by mass to 5% by mass, even more preferably 0.1% by mass to 5% by mass, even more preferably 0.5% by mass to 5% by mass, even more preferably 0.5% by mass to 3% by mass, even more preferably 0.5% by mass to 2% by mass, and even more preferably 0.5% by mass to 1% by mass.

[0051] <Other additives> The nonaqueous electrolyte solution of the present disclosure may contain additives other than Additive A, Additive B, Additive C, and Additive D (also referred to herein as "other additives"). When the nonaqueous electrolyte solution of the present disclosure contains other additives, the number of such additives contained may be only one type, or two or more types. The other additives are preferably at least one selected from the group consisting of fluorophosphate compounds (excluding lithium monofluorophosphate and lithium difluorophosphate), carbonate compounds having a carbon-carbon unsaturated bond (excluding additive D), carbonate compounds having a fluorine atom, and cyclic sultone compounds.

[0052] (Fluorophosphate compounds) Examples of the fluorophosphate compound (excluding lithium monofluorophosphate and lithium difluorophosphate) include difluorophosphate, monofluorophosphate, methyl difluorophosphate, ethyl difluorophosphate, dimethyl fluorophosphate, diethyl fluorophosphate, etc. Among these, lithium difluorophosphate and lithium monofluorophosphate are preferred.

[0053] (Carbonate compounds having carbon-carbon unsaturated bonds) Examples of carbonate compounds having a carbon-carbon unsaturated bond (excluding Additive D) include chain carbonates such as methyl vinyl carbonate, ethyl vinyl carbonate, divinyl carbonate, methyl propynyl carbonate, ethyl propynyl carbonate, dipropynyl carbonate, methyl phenyl carbonate, ethyl phenyl carbonate, and diphenyl carbonate; and cyclic carbonates such as vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, ethynyl ethylene carbonate, 4,4-diethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, propynyl ethylene carbonate, 4,4-dipropynyl ethylene carbonate, and 4,5-dipropynyl ethylene carbonate. Of these, methyl phenyl carbonate, ethyl phenyl carbonate, diphenyl carbonate, vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, and 4,5-divinyl ethylene carbonate are preferred, and vinyl ethylene carbonate is more preferred.

[0054] (Carbonate compound having a fluorine atom) Examples of carbonate compounds having fluorine atoms include chain carbonates such as methyl trifluoromethyl carbonate, ethyl trifluoromethyl carbonate, bis(trifluoromethyl)carbonate, methyl(2,2,2-trifluoroethyl)carbonate, ethyl(2,2,2-trifluoroethyl)carbonate, and bis(2,2,2-trifluoroethyl)carbonate; and cyclic carbonates such as 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, and 4-trifluoromethylethylene carbonate. Among these, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate are preferred.

[0055] (Cyclic sultone compounds) Examples of the cyclic sultone compound include sultones such as 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1-methyl-1,3-propene sultone, 2-methyl-1,3-propene sultone, and 3-methyl-1,3-propene sultone. Of these, 1,3-propane sultone and 1,3-propene sultone are preferred.

[0056] When the non-aqueous electrolyte solution of the present disclosure contains other additives, there are no particular limitations on the content thereof (the total content when there are two or more types), but from the viewpoint of more effectively achieving the effects of the present disclosure, the content thereof is preferably 0.001% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, even more preferably 0.1% by mass to 4% by mass, even more preferably 0.1% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass, relative to the total amount of the non-aqueous electrolyte solution.

[0057] <Non-aqueous solvent> The non-aqueous electrolyte generally contains a non-aqueous solvent. As the non-aqueous solvent, various known solvents can be appropriately selected, but it is preferable to use at least one selected from a cyclic aprotic solvent and a chain aprotic solvent.

[0058] When it is desired to increase the flash point of the solvent in order to improve the safety of the battery, it is preferable to use a cyclic aprotic solvent as the non-aqueous solvent.

[0059] (cyclic aprotic solvents) As the cyclic aprotic solvent, a cyclic carbonate, a cyclic carboxylate, a cyclic sulfone, or a cyclic ether can be used.

[0060] The cyclic aprotic solvent may be used alone or in combination of two or more kinds. The mixing ratio of the cyclic aprotic solvent in the nonaqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass. By adjusting the ratio in this manner, the conductivity of the electrolyte, which is related to the charge / discharge characteristics of the battery, can be increased.

[0061] Specific examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. Among these, ethylene carbonate and propylene carbonate, which have high dielectric constants, are preferably used. In the case of a battery using graphite as the negative electrode active material, ethylene carbonate is more preferable. In addition, two or more of these cyclic carbonates may be mixed and used.

[0062] Specific examples of cyclic carboxylates include γ-butyrolactone, δ-valerolactone, and alkyl-substituted esters such as methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.

[0063] Cyclic carboxylates have low vapor pressure, low viscosity, and high dielectric constant, and can reduce the viscosity of the electrolyte without lowering the flash point of the electrolyte and the degree of dissociation of the electrolyte. Therefore, they have the characteristic of being able to increase the conductivity of the electrolyte, which is an index related to the discharge characteristics of the battery, without increasing the flammability of the electrolyte. Therefore, when aiming to increase the flash point of the solvent, it is preferable to use a cyclic carboxylate as the cyclic aprotic solvent. Among the cyclic carboxylates, γ-butyrolactone is the most preferable.

[0064] In addition, the cyclic carboxylate is preferably used in combination with another cyclic aprotic solvent, for example, a mixture of a cyclic carboxylate with a cyclic carbonate and / or a chain carbonate.

[0065] Examples of cyclic sulfones include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, dipropylsulfone, methylethylsulfone, and methylpropylsulfone. An example of a cyclic ether is dioxolane.

[0066] (chain aprotic solvent) As the chain aprotic solvent, chain carbonates, chain carboxylates, chain ethers, chain phosphates, and the like can be used.

[0067] The mixing ratio of the chain aprotic solvent in the nonaqueous solvent is preferably 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.

[0068] Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, ethyl pentyl carbonate, dipentyl carbonate, methyl heptyl carbonate, ethyl heptyl carbonate, diheptyl carbonate, methyl hexyl carbonate, ethyl hexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate, dioctyl carbonate, methyl trifluoroethyl carbonate, etc. Two or more of these chain carbonates may be mixed and used.

[0069] Specific examples of the chain carboxylate include methyl pivalate. A specific example of the chain ether is dimethoxyethane. Specific examples of chain phosphate esters include trimethyl phosphate.

[0070] (Solvent Combination) The non-aqueous solvent used in the non-aqueous electrolyte of the present disclosure may be one type or a mixture of multiple types. In addition, one or more types of cyclic aprotic solvents may be used alone, one or more types of chain aprotic solvents may be used alone, or a mixture of cyclic aprotic solvents and chain protic solvents may be used. When it is particularly intended to improve the load characteristics and low temperature characteristics of the battery, it is preferable to use a combination of a cyclic aprotic solvent and a chain aprotic solvent as the non-aqueous solvent.

[0071] In addition, from the viewpoint of electrochemical stability of the electrolyte, it is most preferable to use a cyclic carbonate for the cyclic aprotic solvent and a chain carbonate for the chain aprotic solvent. Also, the conductivity of the electrolyte, which is related to the charge-discharge characteristics of the battery, can be increased by combining a cyclic carboxylate with a cyclic carbonate and / or a chain carbonate.

[0072] Specific examples of combinations of cyclic carbonates and chain carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, propylene carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, and ethylene carbonate and dimethyl carbonate. and diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, and methyl ethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, and the like.

[0073] The mixing ratio of the cyclic carbonate and the chain carbonate is, in terms of mass ratio, 5:95 to 80:20, more preferably 10:90 to 70:30, and particularly preferably 15:85 to 55:45, of the cyclic carbonate:chain carbonate. By setting such a ratio, the increase in the viscosity of the electrolyte can be suppressed and the degree of dissociation of the electrolyte can be increased, so that the conductivity of the electrolyte, which is related to the charge / discharge characteristics of the battery, can be increased. In addition, the solubility of the electrolyte can be further increased. Therefore, the electrolyte can be made to have excellent electrical conductivity at room temperature or low temperature, so that the load characteristics of the battery at room temperature to low temperature can be improved.

[0074] Specific examples of combinations of a cyclic carboxylate and a cyclic carbonate and / or a chain carbonate include γ-butyrolactone and ethylene carbonate, γ-butyrolactone, ethylene carbonate and dimethyl carbonate, γ-butyrolactone, ethylene carbonate and methylethyl carbonate, γ-butyrolactone, ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone, propylene carbonate and dimethyl carbonate, and γ-butyrolactone, propylene carbonate and methyl ethyl carbonate, gamma-butyrolactone, propylene carbonate, and diethyl carbonate, gamma-butyrolactone, ethylene carbonate, and propylene carbonate, gamma-butyrolactone, ethylene carbonate, propylene carbonate, and dimethyl carbonate, gamma-butyrolactone, ethylene carbonate, propylene carbonate, and methyl ethyl carbonate, gamma-butyrolactone, ethylene carbonate, propylene carbonate, and diethyl carbonate, gamma-butyrolactone, ethylene carbonate, dimethyl carbonate, and methyl ethyl Carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate, and diethyl carbonate, γ-butyrolactone, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate, and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, and dimethyl carbonate γ-butyrolactone and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and sulfolane, γ-butyrolactone and ethylene carbonate and sulfolane, γ-butyrolactone and propylene carbonate and sulfolane, γ-butyrolactone and ethylene carbonate and propylene carbonate and sulfolane,Examples include γ-butyrolactone, sulfolane, and dimethyl carbonate.

[0075] (Other Solvents) The non-aqueous solvent may also be any other solvent than those mentioned above. Specific examples of the other solvents include amides such as dimethylformamide, chain carbamates such as methyl-N,N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, cyclic ureas such as N,N-dimethylimidazolidinone, boron compounds such as trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, and trimethylsilyl borate, and polyethylene glycol derivatives represented by the following general formula. HO(CH2CH2O) a H HO[CH2CH(CH3)O] b H CH3O(CH2CH2O) c H CH3O[CH2CH(CH3)O] d H CH3O(CH2CH2O) e CH3 CH3O[CH2CH(CH3)O] f CH3 C9H 19 PhO(CH2CH2O) g [CH(CH3)O] h CH3 (Ph is a phenyl group) CH3O[CH2CH(CH3)O] i CO[OCH(CH3)CH2] j OCH3 In the above formula, a to f are integers of 5 to 250, g to j are integers of 2 to 249, 5≦g+h≦250, and 5≦i+j≦250.

[0076] The nonaqueous electrolyte solution of the present disclosure is not only suitable as a nonaqueous electrolyte solution for lithium secondary batteries, but can also be used as a nonaqueous electrolyte solution for primary batteries, a nonaqueous electrolyte solution for electrochemical capacitors, electric double layer capacitors, and an electrolyte solution for aluminum electrolytic capacitors.

[0077] [Lithium secondary battery] The lithium secondary battery of the present disclosure includes a positive electrode, a negative electrode, and the nonaqueous electrolyte of the present disclosure.

[0078] (Negative electrode) The negative electrode may include a negative electrode active material and a negative electrode current collector. The negative electrode active material in the negative electrode can be at least one selected from the group consisting of metallic lithium, lithium-containing alloys, metals or alloys capable of being alloyed with lithium, oxides capable of being doped / dedoped with lithium ions, transition metal nitrides capable of being doped / dedoped with lithium ions, and carbon materials capable of being doped / dedoped with lithium ions (which may be used alone or a mixture containing two or more of these may be used). Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, tin alloys, etc. Lithium titanate may also be used. Among these, carbon materials capable of doping and dedoping lithium ions are preferred. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, etc. The carbon materials may be in any of the following forms: fibrous, spherical, potato-like, and flake-like.

[0079] Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500° C. or lower, and mesophase pitch carbon fiber (MCF). Examples of the graphite material include natural graphite and artificial graphite. Examples of the artificial graphite include graphitized MCMB and graphitized MCF. Examples of the graphite material that can be used include those containing boron. Examples of the graphite material that can be used include those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those mixed with amorphous carbon and graphite.

[0080] These carbon materials may be used alone or in combination of two or more kinds. As the carbon material, a carbon material having an interplanar spacing d(002) of the (002) plane measured by X-ray analysis of 0.340 nm or less is particularly preferable. Further, as the carbon material, graphite having a true density of 1.70 g / cm 3 or a highly crystalline carbon material having properties similar thereto is also preferable. When using the carbon material as described above, the energy density of the battery can be made higher.

[0081] There is no particular limitation on the material of the negative electrode current collector in the negative electrode, and known materials can be arbitrarily used. Specific examples of the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among them, copper is particularly preferable from the viewpoint of ease of processing.

[0082] (Positive electrode) The positive electrode may include a positive electrode active material and a positive electrode current collector. As the positive electrode active material in the positive electrode, transition metal oxides or transition metal sulfides such as MoS2, TiS2, MnO2, V2O5, LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNi X Co (1-X) O2 [0 < X < 1], Li having an α-NaFeO2 type crystal structure 1+α Me 1-α O2 (Me is a transition metal element containing Mn, Ni, and Co, 1.0 ≦ (1 + α) / (1 - α) ≦ 1.6), LiNi x Co y Mn z O2 [x + y + z = 1, 0 < x < 1, 0 < y < 1, 0 < z < 1] (for example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3Examples of the conductive polymer materials include a composite oxide of lithium and a transition metal, such as LiFePO4, LiMnPO4, etc., polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composite. Among these, a composite oxide of lithium and a transition metal is particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can also be used as the positive electrode. Also, a mixture of a composite oxide of lithium and a transition metal and a carbon material can also be used as the positive electrode. The positive electrode active material may be used alone or in combination of two or more. When the positive electrode active material has insufficient conductivity, it may be used together with a conductive assistant to form a positive electrode. Examples of the conductive assistant include carbon materials such as carbon black, amorphous whiskers, and graphite.

[0083] There is no particular limitation on the material of the positive electrode current collector in the positive electrode, and any known material can be used. Specific examples of the positive electrode current collector include metal materials such as aluminum, aluminum alloys, stainless steel, nickel, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and the like.

[0084] (Separator) The lithium secondary battery of the present disclosure preferably includes a separator between the negative electrode and the positive electrode. The separator is a membrane that electrically insulates the positive electrode from the negative electrode and is permeable to lithium ions, and examples of the separator include a porous membrane and a polymer electrolyte. As the porous membrane, a microporous polymer film is preferably used, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like. In particular, porous polyolefin is preferred, specifically, a porous polyethylene film, a porous polypropylene film, or a multi-layer film of a porous polyethylene film and a porous polypropylene film can be exemplified. The porous polyolefin film may be coated with another resin having excellent thermal stability. Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, and a polymer swollen with an electrolytic solution. The nonaqueous electrolyte solution of the present disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

[0085] (Battery composition) The lithium secondary battery of the present disclosure can have various known shapes, such as a cylindrical shape, a coin shape, a square shape, a laminate shape, a film shape, or any other shape, but the basic structure of the battery is the same regardless of the shape, and the design can be modified according to the purpose.

[0086] An example of the lithium secondary battery (nonaqueous electrolyte secondary battery) of the present disclosure is a laminated battery. FIG. 1 is a schematic perspective view showing an example of a laminated battery, which is an example of the lithium secondary battery of the present disclosure, and FIG. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body contained in the laminated battery shown in FIG. The laminated battery shown in Fig. 1 contains a nonaqueous electrolyte (not shown in Fig. 1) and a laminated electrode body (not shown in Fig. 1) and includes a laminated exterior body 1 whose periphery is sealed to seal the inside. As the laminated exterior body 1, for example, an aluminum laminated exterior body is used. 2, the laminated electrode body housed in the laminate exterior body 1 includes a laminate in which positive electrode plates 5 and negative electrode plates 6 are alternately stacked with separators 7 interposed therebetween, and a separator 8 surrounding the periphery of the laminate. The positive electrode plates 5, the negative electrode plates 6, the separators 7, and the separator 8 are impregnated with the nonaqueous electrolyte solution of the present disclosure. Each of the multiple positive electrode plates 5 in the laminated electrode body is electrically connected to a positive electrode terminal 2 via a positive electrode tab (not shown), and a part of this positive electrode terminal 2 protrudes outward from the peripheral edge of the laminated exterior body 1 (FIG. 1). The portion of the peripheral edge of the laminated exterior body 1 from which the positive electrode terminal 2 protrudes is sealed with an insulating seal 4. Similarly, each of the multiple negative electrode plates 6 in the laminated electrode body is electrically connected to a negative electrode terminal 3 via a negative electrode tab (not shown), and a portion of this negative electrode terminal 3 protrudes outward from the peripheral edge of the laminated exterior body 1 (FIG. 1). The portion of the peripheral edge of the laminated exterior body 1 from which the negative electrode terminal 3 protrudes is sealed with an insulating seal 4. In the laminated battery according to the above example, the number of positive electrode plates 5 is five and the number of negative electrode plates 6 is six, and the positive electrode plates 5 and the negative electrode plates 6 are laminated with separators 7 interposed therebetween in an arrangement in which the outermost layers on both sides are negative electrode plates 6. However, it goes without saying that the number and arrangement of positive and negative electrode plates in the laminated battery are not limited to this example, and various modifications may be made.

[0087] Another example of the lithium secondary battery of the present disclosure is a coin-type battery. FIG. 3 is a schematic perspective view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure. 3, a disk-shaped negative electrode 12, a separator 15 filled with a non-aqueous electrolyte, a disk-shaped positive electrode 11, and, if necessary, spacer plates 17, 18 made of stainless steel, aluminum, or the like are stacked in this order and housed between a positive electrode can 13 (hereinafter also referred to as a "battery can") and a sealing plate 14 (hereinafter also referred to as a "battery can lid"). The positive electrode can 13 and the sealing plate 14 are crimped and sealed with a gasket 16 interposed therebetween. In this example, the nonaqueous electrolyte of the present disclosure is used as the nonaqueous electrolyte injected into separator 15 .

[0088] The lithium secondary battery of the present disclosure may be a lithium secondary battery obtained by charging and discharging a lithium secondary battery (a lithium secondary battery before charging and discharging) including a negative electrode, a positive electrode, and the nonaqueous electrolyte solution of the present disclosure. That is, the lithium secondary battery of the present disclosure may be a lithium secondary battery (a charged and discharged lithium secondary battery) produced by first preparing a pre-charged lithium secondary battery including a negative electrode, a positive electrode, and the nonaqueous electrolyte solution of the present disclosure, and then charging and discharging this pre-charged lithium secondary battery at least once.

[0089] The lithium secondary battery of the present disclosure is not particularly limited in its application, and can be used in a variety of known applications, including notebook computers, mobile computers, mobile phones, headphone stereos, video movie players, liquid crystal televisions, handy cleaners, electronic organizers, calculators, radios, backup power sources, motors, automobiles, electric automobiles, motorcycles, electric motorcycles, bicycles, electric bicycles, lighting equipment, game consoles, watches, power tools, cameras, and the like, regardless of whether they are small portable devices or large devices. EXAMPLES

[0090] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples. In the following examples, the "amount added" refers to the content in the finally obtained non-aqueous electrolyte solution (that is, the amount relative to the total amount of the finally obtained non-aqueous electrolyte solution). Additionally, "wt%" means mass%.

[0091] Example 1 A coin-type battery (test battery), which is a lithium secondary battery, was fabricated by the following procedure. <Preparation of negative electrode> 20 parts by mass of artificial graphite, 80 parts by mass of natural graphite, 1 part by mass of carboxymethyl cellulose, and 2 parts by mass of SBR latex were kneaded with an aqueous solvent to prepare a paste-like negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to a negative electrode current collector made of a strip of copper foil having a thickness of 18 μm, dried, and then compressed by a roll press to obtain a sheet-like negative electrode consisting of a negative electrode current collector and a negative electrode active material layer. The coating density of the negative electrode active material layer at this time was 10 mg / cm. 2 and the packing density was 1.5 g / ml.

[0092] <Preparation of positive electrode> LiNi 0.5 Mn 0.3 Co 0.2 90 parts by mass of O2, 5 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride were kneaded using N-methylpyrrolidinone as a solvent to prepare a paste-like positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to a positive electrode current collector made of a strip of aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to obtain a sheet-like positive electrode consisting of the positive electrode current collector and the positive electrode active material. The coating density of the positive electrode active material layer at this time was 30 mg / cm. 2 and the packing density was 2.5 g / ml.

[0093] <Preparation of non-aqueous electrolyte> As a non-aqueous solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:35:35 to obtain a mixed solvent. In the resulting mixed solvent, LiPF6 as an electrolyte was dissolved so that the electrolyte concentration in the finally obtained non-aqueous electrolyte solution was 1 mol / L. For the solution obtained above, Additive A: methanesulfonyl fluoride (hereinafter, also referred to as "MSF") (addition amount: 0.5 mass%), Additive B: lithium trifluoromethanesulfonate (hereinafter also referred to as "TFMSLi") (addition amount 0.5 mass%) to obtain a non-aqueous electrolyte solution.

[0094] <Making a coin-type battery> The negative electrode and the positive electrode were punched into a disk shape with a diameter of 14 mm and 13 mm, respectively, to obtain coin-shaped electrodes (negative electrode and positive electrode). A microporous polyethylene film with a thickness of 20 μm was punched into a disk shape with a diameter of 17 mm to obtain a separator. The obtained coin-shaped negative electrode, separator and coin-shaped positive electrode were stacked in this order in a stainless steel battery can (size 2032), and 20 μl of the above nonaqueous electrolyte was poured in to impregnate the separator, positive electrode and negative electrode. Furthermore, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery was sealed by crimping the battery can lid with a polypropylene gasket interposed therebetween, producing a coin-type battery (hereinafter sometimes referred to as the "test battery") having the configuration shown in Figure 3, with a diameter of 20 mm and a height of 3.2 mm.

[0095] <Measurement of capacity retention rate after high temperature storage> The coin-type battery was charged to 4.25 V at a charge rate of 0.2 C in a thermostatic chamber at 25° C., and discharged to 2.85 V at a discharge rate of 0.2 C in the same thermostatic chamber at 25° C. The discharge capacity at the time of discharge was measured, and this discharge capacity was defined as the discharge capacity [mAh] before high-temperature storage. The coin-type battery whose discharge capacity [mAh] before high-temperature storage was measured was charged to 4.25 V at a charge rate of 0.2 C in a thermostatic chamber at 25°C, after which the temperature of the thermostatic chamber was raised to 60°C and the coin-type battery was stored in the thermostatic chamber at 60°C for 5 days (high-temperature storage). After the high-temperature storage, the temperature of the thermostatic chamber was returned to 25°C, and the coin-type battery was discharged to 2.85V at a discharge rate of 2C in the thermostatic chamber at 25°C. The discharge capacity at the time of discharge was measured, and this discharge capacity was defined as the discharge capacity after high-temperature storage [mAh]. From these results, the "capacity retention rate [%] after high-temperature storage" was calculated using the following formula. The results are shown in Table 1.

[0096] Capacity retention rate after high temperature storage [%] = (discharge capacity after high temperature storage [mAh] / discharge capacity before high temperature storage [mAh]) × 100 [%]

[0097] Comparative Example 1 The non-aqueous electrolyte solution was prepared in the same manner as in Example 1, except that Additive A was not added and the amount of Additive B added was changed to 1.0 mass %. The results are shown in Table 1.

[0098] Comparative Example 2 The non-aqueous electrolyte solution was prepared in the same manner as in Example 1, except that Additive B was not added and the amount of Additive A added was changed to 1.0 mass %. The results are shown in Table 1.

[0099] [Table 1]

[0100] As shown in Table 1, Example 1, which used a non-aqueous electrolyte solution containing both Additive A and Additive B, had a superior capacity retention rate after high-temperature storage compared to Comparative Examples 1 and 2, which used non-aqueous electrolyte solutions not containing either Additive A or Additive B. More specifically, in Example 1, by replacing 0.5 wt% of Additive B (1.0 wt%) with Additive A in the nonaqueous electrolyte of Comparative Example 1, which did not contain Additive A, the capacity retention rate after high-temperature storage was improved. In addition, in Example 1, by replacing 0.5 wt% of Additive A (1.0 wt%) with Additive B compared to the nonaqueous electrolyte of Comparative Example 2 not containing Additive B, the capacity retention rate after high-temperature storage was improved.

[0101] Example 2 The same procedure as in Example 1 was carried out, except that in preparing the non-aqueous electrolyte solution, lithium difluorophosphate (hereinafter, also referred to as "LiDFP") (addition amount 0.5 mass %) was further added as additive C. Table 2 shows the results of the capacity retention rate after high-temperature storage. For comparison, Table 2 also shows the capacity retention rate after high-temperature storage in Example 1 described above.

[0102] The coin batteries of Examples 1 and 2 were measured for DC resistance before storage (-20°C), DC resistance after storage (-20°C), and the increase rate (%) of DC resistance due to storage. The results are shown in Table 2.

[0103] <DC resistance before storage (-20℃)> The coin battery was charged and discharged three times at a constant voltage of 4.2V, then charged to a constant voltage of 3.9V, and then cooled to -20°C in a thermostatic chamber. The coin battery cooled to -20°C was discharged at a constant current of 0.2mA at -20°C, and the DC resistance [Ω] of the coin battery was measured by measuring the potential drop for 10 seconds from the start of discharge. The measured value was taken as the DC resistance (-20°C) (Ω) before storage.

[0104] <DC resistance after storage (-20℃)> The coin-type battery whose DC resistance (-20°C) before storage was measured was charged at a constant voltage of 4.25 V, and the charged coin-type battery was stored in a thermostatic chamber at 60°C for 5 days. After storage for 5 days, the coin battery was charged to a constant voltage of 3.9V, and then cooled to -20°C in a thermostatic chamber. The coin battery cooled to -20°C was discharged at a constant current of 0.2mA at -20°C, and the DC resistance [Ω] of the coin battery was measured by measuring the potential drop for 10 seconds from the start of discharge. The measured value was taken as the DC resistance (-20°C) (Ω) after storage.

[0105] <Increase in DC resistance due to storage (%)> Based on the DC resistance before storage (-20°C) and the DC resistance after storage (-20°C), the increase rate (%) of DC resistance due to storage was calculated using the following formula.

[0106] Increase rate of DC resistance due to storage (%) = ((DC resistance after storage (-20°C) - DC resistance before storage (-20°C)) / DC resistance before storage (-20°C)) x 100

[0107] [Table 2]

[0108] As shown in Table 2, the nonaqueous electrolyte solution of Example 2, in which Additive C was further added to the nonaqueous electrolyte solution of Example 1, was able to significantly reduce the DC resistance before and after high-temperature storage, as well as the increase in DC resistance due to high-temperature storage, without causing an almost any decrease in the capacity retention rate after high-temperature storage. [Explanation of symbols]

[0109] 1 Laminate exterior body 2 Positive terminal 3 Negative terminal 4 Insulation seal 5 Positive plate 6 Negative plate 7, 8 Separator 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gasket 17, 18 Spacer plate

Claims

1. Additive A, which is a compound represented by formula (A); Additive B, which is a compound represented by formula (B); an electrolyte which is a lithium salt other than additive B; Contains The content of the additive B is 0.001% by mass to 5% by mass based on the total amount of the nonaqueous electrolyte for a battery. Non-aqueous electrolyte for batteries. 【Chemistry 1】 [In formula (A), R １ represents an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom. In formula (B), R ２ represents a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbonoxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a fluorine atom.

2. 2. The non-aqueous electrolyte solution for a battery according to claim 1, wherein the content of the additive A is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte solution for a battery.

3. 3. The nonaqueous electrolyte for a battery according to claim 1, further comprising an additive C which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate.

4. 4. The non-aqueous electrolyte solution for a battery according to claim 3, wherein the content of the additive C is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte solution for a battery.

5. A positive electrode and a negative electrode containing at least one selected from the group consisting of metallic lithium, a lithium-containing alloy, a metal or alloy capable of being alloyed with lithium, an oxide capable of being doped / dedoped with lithium ions, a transition metal nitride capable of being doped / dedoped with lithium ions, and a carbon material capable of being doped / dedoped with lithium ions as a negative electrode active material; The nonaqueous electrolyte for a battery according to any one of claims 1 to 4, A lithium secondary battery comprising:

6. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 5.

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