Non-aqueous electrolyte solution and non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte solution

Abstract

To provide a non-aqueous electrolyte solution capable of suppressing the amount of gas generated during high-temperature storage and improving the resistance retention rate.SOLUTION: A non-aqueous electrolyte solution includes a compound represented by a formula (I) and a fluorinated cyclic carbonate and / or an unsaturated cyclic carbonate.(In the formula, R1 is H, a halogen atom, a silyl group, an acyl group, a sulfonyl group, a sulfonyloxy group, or a phosphate group, and R2 and R5 are independently halogen atoms or hydrocarbon groups, and R3 and R4 are independently H, halogen atoms, or hydrocarbon groups).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte solution and a non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte solution. [Background technology]

[0002] Lithium nonaqueous electrolyte secondary batteries, which use a lithium-containing transition metal oxide as a positive electrode and a nonaqueous solvent as an electrolyte, can achieve high energy density and are therefore used in a wide range of applications, from small power sources for mobile phones, laptop computers, etc. to large power sources for automobiles, railways, and load leveling. However, in recent years, there has been an increasing demand for higher performance in nonaqueous electrolyte secondary batteries, and there is a strong demand for improvements in various characteristics.

[0003] For example, Patent Document 1 discloses an electrolyte solution containing a specific heterocyclic compound having a silyl group and a fluorinated cyclic carbonate as additives, which is capable of suppressing deterioration due to charge / discharge cycles and swelling of the battery.

[0004] Patent Document 2 discloses a nonaqueous electrolyte solution containing a specific aromatic compound, and discloses that a nonaqueous electrolyte secondary battery including the electrolyte solution has improved capacity retention during charge-discharge cycles and reduced increase in battery thickness.

[0005] Non-Patent Document 1 discloses that the amount of carbon dioxide generated increases in a secondary battery that contains a non-aqueous electrolyte solution that contains monofluoroethylene carbonate as a fluorinated cyclic carbonate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Publication No. 2019 / 0326637 [Patent Document 2] U.S. Patent Publication No. 2004 / 0185347 [Non-patent literature]

[0007] [Non-Patent Document 1] ACS Energy Letters, Volume 2, Issue 10, 2228-2233, 2017. Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, non-aqueous electrolyte secondary batteries have been required to meet increasingly higher performance requirements, particularly for battery-equipped automobiles, and there has been a strong demand for suppressing the amount of gas generated during battery storage. In particular, the addition of fluorinated cyclic carbonates and / or unsaturated cyclic carbonates can improve battery performance such as cycle characteristics, and therefore, for example, monofluoroethylene carbonate is used as an additive in non-aqueous electrolyte secondary batteries. However, as described in Non-Patent Document 1, it is known that the addition of a fluorinated cyclic carbonate increases the amount of carbon dioxide generated in the battery, causing the battery to expand. The non-aqueous electrolyte secondary battery described in Patent Document 1 is still insufficient in terms of the efficiency of suppressing battery swelling during high-temperature storage. Furthermore, Patent Document 2 does not describe the gas suppression efficiency when a fluorinated cyclic carbonate is used in the non-aqueous electrolyte secondary battery.

[0009] An object of the present invention is to solve the above-mentioned problems in nonaqueous electrolyte secondary batteries, to provide a nonaqueous electrolyte that can suppress the amount of gas generation by adsorbing carbon dioxide generated inside the battery, and in addition, can improve the resistance retention rate. [Means for solving the problem]

[0010] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by adding a specific nitrogen-containing aromatic compound and a fluorinated cyclic carbonate and / or an unsaturated cyclic carbonate to a non-aqueous electrolyte solution, and have arrived at the present invention.

[0011] That is, the gist of the present invention lies in the following. [1] A non-aqueous electrolyte solution comprising a compound represented by formula (I) and a fluorinated cyclic carbonate and / or an unsaturated cyclic carbonate. [ka] (In formula (I), R 1 is a hydrogen atom, a halogen atom, a silyl group, an acyl group, a sulfonyl group, a sulfonyloxy group, or a phosphate group, and R 2 and R 5 are each independently a halogen atom or a hydrocarbon group, and R 3 and R 4 are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group, and R 2 and R 3 , R 3 and R 4 , and R 4 and R 5 At least one of the combinations selected from the following is bonded to each other to form a ring, and the ring is an aromatic ring which may have a heteroatom. [2] In the formula (I), R 1 is a hydrogen atom, a silyl group, a sulfonyl group, or a sulfonyloxy group. [3] In the formula (I), R 2 and R 5 are each independently at least one selected from the group consisting of an alkyl group, an alkenyl group, and an aryl group. [4] The nonaqueous electrolyte solution according to any one of [1] to [3], wherein in formula (I), the aromatic ring optionally having a heteroatom is a ring selected from the group consisting of a benzene ring, a naphthalene ring, a pyrrole ring, a thiophene ring, and a furan ring. [5] The nonaqueous electrolyte solution according to any one of [1] to [4], wherein the fluorinated cyclic carbonate is monofluoroethylene carbonate and / or difluoroethylene carbonate. [6] The nonaqueous electrolyte solution according to any one of [1] to [5], wherein the unsaturated cyclic carbonate is vinylene carbonate, vinyl ethylene carbonate, and / or ethynyl ethylene carbonate. [7] The non-aqueous electrolyte solution according to any one of [1] to [6], wherein the compound represented by formula (I) is contained in the non-aqueous electrolyte solution in an amount of 0.01 to 10% by mass. [8] The non-aqueous electrolyte solution according to any one of [1] to [7], wherein the fluorinated cyclic carbonate and / or unsaturated cyclic carbonate is contained in an amount of 0.01 to 10 mass % in the non-aqueous electrolyte solution. [9] A nonaqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; and the nonaqueous electrolyte solution according to any one of [1] to [8]. [Effects of the Invention]

[0012] The present invention provides a nonaqueous electrolyte solution that can suppress gas generation during high-temperature storage and improve resistance retention during storage, and also provides a nonaqueous electrolyte secondary battery that includes the nonaqueous electrolyte solution. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes in detail the embodiments of the present invention. However, the following description is merely an example (typical example) of the present invention, and the present invention is not limited to the contents thereof as long as it does not depart from the gist of the claims.

[0014] [1.Non-aqueous electrolyte] The non-aqueous electrolyte solution of the present invention contains a compound represented by formula (I) and a fluorinated cyclic carbonate and / or an unsaturated cyclic carbonate. [ka] In formula (I), R 1 is a hydrogen atom, a halogen atom, a silyl group, an acyl group, a sulfonyl group, a sulfonyloxy group, or a phosphate group, and R2 and R 5 are each independently a halogen atom or a hydrocarbon group, and R 3 and R 4 are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group, and R 2 and R 3 , R 3 and R 4 , R 4 and R 5 At least one of the combinations selected from the above is bonded to each other to form a ring, and the ring is an aromatic ring which may have a heteroatom.

[0015] The nonaqueous electrolyte solution having the configuration of the present invention is preferable in that it can suppress the amount of gas generation during high-temperature storage and improve the resistance retention rate during storage. The inventors speculate that the reason for such excellent effects is as follows. That is, the suppression of gas generation during high-temperature storage is believed to be due to the reaction of carbon dioxide gas generated from the fluorinated cyclic carbonate and / or unsaturated cyclic carbonate in the nonaqueous electrolyte secondary battery with the lithium amide salt derived from the compound of formula (I). 1 From the viewpoint of the efficiency of lithium amide formation by elimination of R 1 It is considered undesirable for is to be a hydrocarbon group.

[0016] Furthermore, the nonaqueous electrolyte solution described in Patent Document 1 contains a specific heterocyclic compound having a silyl group. However, since the carbon atom adjacent to the nitrogen atom has high reactivity, if the compound has a hydrogen atom with a small steric bulk, a side reaction occurs within the battery, and it is thought that the amount of gas generated during storage cannot be efficiently improved. On the other hand, it is believed that by including a nitrogen-containing aromatic compound in the non-aqueous electrolyte solution, in which the carbon atom adjacent to the nitrogen atom, which is a highly active site, is protected by a substituent other than hydrogen, as in the present application, the progression of the above-mentioned side reactions can be suppressed, the generation of storage gas can be efficiently suppressed to a higher level than before, and the resistance retention rate can also be improved. Each component will be described below.

[0017] [1-1. Compound represented by formula (I)] [ka] R in formula (I) 1 is a hydrogen atom, a halogen atom, a silyl group, an acyl group, a sulfonyl group, a sulfonyloxy group, or a phosphate group. Among these, a hydrogen atom, a silyl group, a sulfonyl group, or a sulfonyloxy group is preferred in terms of suppressing the amount of gas generated during high-temperature storage, and a hydrogen atom is more preferred. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a fluorine atom is preferred in terms of stability in the electrolyte solution. Examples of the silyl group include a trialkylsilyl group, a triarylsilyl group, a trialkenylsilyl group, and a trialiquinylsilyl group. Of these, a trialkylsilyl group is preferred, and a trimethylsilyl group, a triethylsilyl group, and a triisopropylsilyl group are particularly preferred in terms of leaving ability.

[0018] Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a benzoyl group, and a benzoyl group. Among these, an acetyl group is preferred from the viewpoint of leaving ability. Examples of the sulfonyl group include a mesyl group, a tosyl group, a nosyl group, and a trifluoromethanesulfonyl group. Among these, a mesyl group is preferred from the viewpoint of leaving ability. Examples of the sulfonyloxy group include a mesyloxy group, a tosyloxy group, a nosyloxy group, and a trifluoromethanesulfonyloxy group. Among these, a mesyloxy group is preferred because of the ease of synthesis of the compound. Examples of the phosphate group include a methyl phosphate group, an ethyl phosphate group, and a phenyl phosphate group. Among these, the methyl phosphate group is preferred from the viewpoint of the stability of the compound in an electrolyte solution.

[0019] R in formula (I) 2 and R 5 are each independently a halogen atom or a hydrocarbon group, and among these, a hydrocarbon group is preferred. Halogen atoms are R1 This is the same as that specified in The hydrocarbon group is an alkyl group, an alkenyl group, an alkynyl group, or an aryl group. Among these, an alkyl group, an alkenyl group, and an aryl group are more preferred, and an aryl group is even more preferred. The hydrocarbon group may further have a substituent such as a fluorine atom. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, an n-pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. Of these, an alkyl group having 1 to 6 carbon atoms is preferred in terms of solubility in an electrolyte solution.

[0020] Examples of the alkenyl group include a vinyl group, an allyl group, a methallyl group, a 2-butenyl group, a 3-methyl-2-butenyl group, a 3-butenyl group, a 4-pentenyl group, a 5-hexenyl group, a 6-heptenyl group, and a 7-octenyl group, etc. Among these, an alkenyl group having 1 to 6 carbon atoms is preferred in terms of solubility in an electrolyte solution. Examples of the alkynyl group include an ethynyl group, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynyl group, a 5-hexynyl group, a 6-heptynyl group, and a 7-octynyl group. Of these, an alkynyl group having 1 to 6 carbon atoms is preferred in terms of solubility in an electrolyte solution. Examples of the aryl group include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 2-thienyl group, a 3-thienyl group, a 2-furyl group, a 3-furyl group, a 2-pyrrolyl group, a 3-pyrrolyl group, and a benzyl group. Of these, an aryl group having 6 to 12 carbon atoms is preferred, and a phenyl group, a 1-naphthyl group, and a 2-naphthyl group are more preferred in terms of solubility in an electrolyte, and a phenyl group is even more preferred.

[0021] R in formula (I) 3 and R 4 are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group. where R 3 and R 4 The halogen atoms and hydrocarbon groups in R 2 and R 5This is the same as that specified in R in formula (I) 2 and R 3 , R 3 and R 4 , and R 4 and R 5 At least one of the combinations selected from the above is bonded to each other to form a ring, and the ring is an aromatic ring which may have a heteroatom. Among them, R 2 and R 3 , or R 4 and R 5 In terms of stability in an electrolyte, it is preferable that the groups bond to each other to form a ring in the above formula (1).

[0022] Examples of aromatic rings that may have heteroatoms include benzene rings, naphthalene rings, pyrrole rings, thiophene rings, furan rings, imidazole rings, thiazole rings, carbazole rings, porphyrin rings, and pyridine rings. Among these, benzene rings, naphthalene rings, pyrrole rings, thiophene rings, and furan rings are preferred in terms of stability to the electrolyte, more preferably benzene rings and naphthalene rings, and even more preferably benzene rings. The aromatic rings that may have heteroatoms may have a substituent such as a fluorine atom.

[0023] Specific examples of the compound represented by formula (I) include the following compounds. [ka] [ka] [ka] [ka] [ka] [ka] [ka]

[0024] Among these, the following compounds are preferred: [ka] [ka] [ka] [ka]

[0025] More preferably, the following compounds are preferred: [ka] [ka]

[0026] More preferably, the following compounds are preferred: [ka]

[0027] The following compounds are particularly preferred: [ka]

[0028] The compound represented by formula (I) is not particularly limited, but is preferably contained in the non-aqueous electrolyte solution in an amount of 0.01 to 10 mass %, more preferably 0.01 to 6 mass %, and particularly preferably 0.05 to 4 mass %.

[0029] [1-2. Fluorinated cyclic carbonates] The fluorinated cyclic carbonate of the present invention is not limited as long as it is a cyclic carbonate having at least one fluorine atom, and specifically includes cyclic carbonates having a fluorine atom in the cyclic carbonate skeleton, such as monofluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, and tetrafluoroethylene carbonate, cyclic carbonates having a fluorinated alkyl group in the substituent, such as trifluoromethyl carbonate and pentafluoroethyl carbonate, and cyclic carbonates having a fluorinated alkyl group in the substituent and a fluorine atom in the cyclic carbonate skeleton, such as fluorotrifluoromethyl carbonate and fluoropentafluoroethyl carbonate.Among these, cyclic carbonates having a fluorine atom in the cyclic carbonate skeleton are preferred, and monofluoroethylene carbonate and / or difluoroethylene carbonate are particularly preferred in terms of the effect of the present invention of suppressing the amount of carbon dioxide generated. There are no particular restrictions on the fluorinated cyclic carbonate, but it is preferable that the non-aqueous electrolyte solution contain 0.01 to 10 mass %, more preferably 0.05 to 8 mass %, and particularly preferably 0.1 to 6 mass %.

[0030] [1-3. Unsaturated cyclic carbonates] The unsaturated cyclic carbonate of the present invention is not limited as long as it is a cyclic carbonate having at least one carbon-carbon unsaturated bond, but specific examples include saturated cyclic carbonates having a carbon-carbon unsaturated bond such as an alkynyl group in a substituent, such as vinyl ethylene carbonate, ethynyl ethylene carbonate, and allyl ethylene carbonate; cyclic carbonates having a carbon-carbon unsaturated bond in a cyclic carbonate skeleton, such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, monofluoro vinylene carbonate, and difluoro vinylene carbonate; and cyclic carbonates having a carbon-carbon unsaturated bond such as an alkynyl group in a substituent and a carbon-carbon unsaturated bond in a cyclic carbonate skeleton, such as vinyl vinylene carbonate, allyl vinylene carbonate, and ethynyl vinylene carbonate. Among these, cyclic carbonates having a carbon-carbon unsaturated bond in the cyclic carbonate skeleton are preferred, and vinylene carbonate, methylvinylene carbonate, Vinyl carbonate and ethylvinylene carbonate are particularly preferred in terms of the effect of the present invention of suppressing the amount of carbon dioxide generated. There are no particular restrictions on the unsaturated cyclic carbonate, but it is preferable that the non-aqueous electrolyte solution contain 0.01 to 10 mass %, more preferably 0.05 to 8 mass %, and particularly preferably 0.1 to 6 mass %.

[0031] [1-4. Electrolytes] [1-4-1. Lithium salts] As the electrolyte in the non-aqueous electrolytic solution, a lithium salt is usually used. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used, and specific examples thereof include the following:

[0032] Examples of the lithium salts include lithium fluoroborates, lithium fluorophosphates, lithium tungstates, lithium carboxylates, lithium sulfonates, lithium imide salts, lithium methide salts, lithium oxalate salts, and fluorine-containing organic lithium salts.

[0033] Among them, lithium fluoroborates include LiBF4; lithium fluorophosphates include LiPF 6、 Li2PO3F, LiPO2F2; lithium sulfonate salts such as LiFSO3 and CH3SO3Li; lithium imide salts such as LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, and lithium cyclic 1,3-perfluoropropanedisulfonylimide; lithium methide salts such as LiC(FSO2)3, LiC(CF3SO2)3, and LiC(C2F5SO2)3; and lithium oxalate salts such as lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate are more preferred because they have the effect of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, and cycle characteristics. More preferred are LiPF6, LiN(FSO2)2, lithium bis(oxalato)borate and LiFSO3, and particularly preferred is LiPF6. The above electrolyte salts may be used alone or in combination of two or more.

[0034] The combination of two or more electrolyte salts is not particularly limited, but includes LiPF6 and LiN(FSO2)2, LiPF6 and LiBF4, LiPF6 and LiN(CF3SO2)2, LiBF4 and LiN(FSO2)2, LiBF4 and LiPF6 and LiN(FSO2)2. Of these, LiPF6 and LiN(FSO2)2, LiPF6 and LiBF4, LiBF4, LiPF6 and LiN(FSO2)2 are preferred.

[0035] The total concentration of these electrolytes in the non-aqueous electrolyte solution is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and is usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, based on the total amount of the non-aqueous electrolyte solution. When the total concentration of the electrolytes is within the above range, the electrical conductivity becomes appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[0036] [1-5. Solvent] The non-aqueous electrolyte solution, like a general non-aqueous electrolyte solution, usually contains a non-aqueous solvent that dissolves the above-mentioned electrolyte as its main component. The non-aqueous solvent to be used is not particularly limited as long as it dissolves the above-mentioned electrolyte, and known organic solvents can be used. Examples of the organic solvent include saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, and cyclic carboxylic acid esters. Examples of the organic solvent include, but are not limited to, ether compounds, sulfone compounds, etc. The organic solvent may be used alone or in combination of two or more. The combination of two or more organic solvents is not particularly limited, and examples thereof include saturated cyclic carbonate and chain carbonate, saturated cyclic carbonate and chain carboxylic acid ester, cyclic carboxylic acid ester and chain carbonate, and saturated cyclic carbonate, chain carbonate and chain carboxylic acid ester. Among these, saturated cyclic carbonate and chain carbonate, and saturated cyclic carbonate, chain carbonate and chain carboxylic acid ester are preferred.

[0037] [1-5-1. Saturated cyclic carbonates] Examples of saturated cyclic carbonates include those having an alkylene group having 2 to 4 carbon atoms, and saturated cyclic carbonates having 2 to 3 carbon atoms are preferably used from the viewpoint of improving battery characteristics resulting from an improved degree of lithium ion dissociation.

[0038] Specific examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and / or propylene carbonate are preferred, and ethylene carbonate, which is less susceptible to oxidation and reduction, is more preferred. The saturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

[0039] The content of the saturated cyclic carbonate is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is usually 3% by volume or more, preferably 5% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less, relative to the total amount of nonaqueous solvent in the nonaqueous electrolyte. By setting the content within this range, a decrease in electrical conductivity resulting from a decrease in the dielectric constant of the nonaqueous electrolyte can be avoided, the large-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the nonaqueous electrolyte secondary battery tend to be in good ranges, and the oxidation / reduction resistance of the nonaqueous electrolyte and stability during high-temperature storage tend to be improved. In this embodiment, the volume % refers to the volume at 25° C. and 1 atmosphere.

[0040] [1-5-2. Chain carbonate] As the chain carbonate, for example, one having 3 to 7 carbon atoms is used, and in order to adjust the viscosity of the electrolyte solution within an appropriate range, a chain carbonate having 3 to 5 carbon atoms is preferably used.

[0041] Specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate. Dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferred.

[0042] Furthermore, chain carbonates having fluorine atoms (hereinafter sometimes abbreviated as "fluorinated chain carbonate") can also be suitably used. The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, and preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, the multiple fluorine atoms may be bonded to the same carbon or different carbons. Examples of fluorinated chain carbonates include fluorinated dimethyl carbonate derivatives such as fluoromethyl methyl carbonate; fluorinated ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate; and fluorinated diethyl carbonate derivatives such as ethyl-(2-fluoroethyl) carbonate.

[0043] The chain carbonate may be used alone or in any combination and ratio of two or more kinds. They may be used in combination at the same rate.

[0044] The content of the chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less, relative to the total amount of nonaqueous solvent in the nonaqueous electrolyte. By setting the content of the chain carbonate within the above range, the viscosity of the nonaqueous electrolyte can be set within an appropriate range, a decrease in ionic conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be easily set within a good range.

[0045] Furthermore, by combining a specific chain carbonate with ethylene carbonate in a specific content, the battery performance can be significantly improved.

[0046] For example, when dimethyl carbonate and ethyl methyl carbonate are selected as specific chain carbonates, the content of ethylene carbonate is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the present invention, but is usually 15% by volume or more, preferably 20% by volume or more, and usually 45% by volume or less, preferably 40% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. The content of dimethyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. The content of ethyl methyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. By setting the content within the above range, high temperature stability is excellent and gas generation tends to be suppressed.

[0047] [1-5-3. Chain carboxylic acid esters] Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. Among these, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate are preferred from the viewpoint of improving battery characteristics. Chain carboxylic acid esters in which some of the hydrogen atoms of the above-mentioned compounds are substituted with fluorine atoms (e.g., methyl trifluoroacetate, ethyl trifluoroacetate, etc.) can also be suitably used.

[0048] The amount of the chain carboxylic acid ester is typically 1% by volume or more, preferably 5% by volume or more, and more preferably 15% by volume or more, based on the total amount of the nonaqueous solvent. This range improves the electrical conductivity of the nonaqueous electrolyte and facilitates the enhancement of the large-current discharge characteristics of the nonaqueous electrolyte battery. Furthermore, the amount of the chain carboxylic acid ester is typically 70% by volume or less, preferably 50% by volume or less, and more preferably 40% by volume or less. By setting the upper limit in this manner, the viscosity of the nonaqueous electrolyte can be kept within an appropriate range, a decrease in electrical conductivity can be avoided, an increase in negative electrode resistance can be suppressed, and the large-current discharge characteristics of the nonaqueous electrolyte secondary battery can be easily maintained within a favorable range.

[0049] [1-5-4. Cyclic carboxylic acid esters] Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Among these, γ-butyrolactone is more preferred. Cyclic carboxylic acid esters in which some of the hydrogen atoms in the above-mentioned compounds are substituted with fluorine atoms can also be used preferably.

[0050] The amount of the cyclic carboxylic acid ester is usually 1% by volume or more, preferably 5% by volume or more, and more preferably 15% by volume or more, based on the total amount of the non-aqueous solvent. Within this range, the electrical conductivity of the non-aqueous electrolyte is improved, and the large-current discharge characteristics of the non-aqueous electrolyte battery are easily improved. Furthermore, the amount of the cyclic carboxylic acid ester is usually 70% by volume or less, preferably 50% by volume or less, and more preferably 40% by volume or less. By setting the upper limit in this way, the viscosity of the non-aqueous electrolyte is kept within an appropriate range, a decrease in electrical conductivity is avoided, and an increase in negative electrode resistance is prevented. This makes it easier to keep the large current discharge characteristics of the non-aqueous electrolyte secondary battery within a favorable range.

[0051] [1-5-5. Ether compounds] Preferred ether compounds include chain ethers having 3 to 10 carbon atoms, such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether, and cyclic ethers having 3 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane. Some of the hydrogen atoms in the above-mentioned ether compounds may be substituted with fluorine atoms. Among these, as the chain ethers having 3 to 10 carbon atoms, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are preferred because they have a high solvation ability for lithium ions, improve ionic dissociation, have low viscosity, and provide high ionic conductivity, and as the cyclic ethers having 3 to 6 carbon atoms, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, and the like are preferred because they provide high ionic conductivity.

[0052] The content of the ether-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention. However, it is usually 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and usually 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less, based on the total amount of nonaqueous solvent in the nonaqueous electrolyte. If the content of the ether-based compound is within the above range, it is easy to ensure the effects of improving the degree of lithium ion dissociation by the ether-based compound and improving ionic conductivity due to the reduced viscosity of the nonaqueous electrolyte. Furthermore, when the negative electrode active material is a carbon-based material, the phenomenon of chain ethers being co-inserted with lithium ions can be suppressed, thereby allowing the input / output characteristics and charge / discharge rate characteristics to be within appropriate ranges.

[0053] [1-5-6. Sulfone compounds] The sulfone compound is not particularly limited and may be a cyclic sulfone or a chain sulfone. In the case of a cyclic sulfone, the carbon number is usually 3 to 6, preferably 3 to 5, and in the case of a chain sulfone, the carbon number is usually 2 to 6, preferably 2 to 5. In addition, the number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2.

[0054] Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones, and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoints of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0055] Preferred sulfolanes are sulfolane and sulfolane derivatives, and preferred sulfolane derivatives are those in which one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with a fluorine atom, an alkyl group, or a fluorine-substituted alkyl group.

[0056] Among these, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,3-difluorosulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, and the like are preferred because they have high ionic conductivity and high input / output.

[0057] Examples of the chain sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, and methyl methyl sulfone. Among them, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in terms of improving the high-temperature storage stability of the electrolyte solution.

[0058] The content of the sulfone compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is usually 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and usually 40% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, based on the total amount of solvent in the nonaqueous electrolyte solution. If the content of the sulfone compound is within the above range, an electrolyte solution with excellent high-temperature storage stability tends to be obtained.

[0059] [1-6. Auxiliaries] The non-aqueous electrolyte solution of the present invention may contain various auxiliary agents within the range that does not significantly impair the effects of the present invention. As the auxiliary agent, any conventionally known agent can be used. In addition, one auxiliary agent may be used alone, or two or more auxiliary agents may be used in any combination and ratio.

[0060] Examples of auxiliary agents that may be contained in the non-aqueous electrolyte solution include cyclic carbonates having a carbon-carbon unsaturated bond, compounds having an isocyanate group, compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, fluorine-free carboxylic acid esters, cyclic compounds having an ether bond, carboxylic acid anhydrides, borates, oxalates, monofluorophosphates, difluorophosphates, fluorosulfonates, etc. Examples include compounds described in International Publication No. 2015 / 111676.

[0061] The content of the auxiliary agent is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably less than 1% by mass, relative to the total amount of the nonaqueous electrolyte solution.

[0062] Cyclic compounds having an ether bond can be used as auxiliary agents in non-aqueous electrolyte solutions, and some of them can also be used as non-aqueous solvents as described in 1-5. When used as auxiliary agents, cyclic compounds having an ether bond are used in an amount of less than 4% by mass. Borates, oxalates, monofluorophosphates, difluorophosphates, and fluorosulfonates can be used as auxiliary agents in non-aqueous electrolyte solutions, and some of them can also be used as electrolytes as described in 1-4. When used as auxiliary agents, these compounds are used in an amount of less than 3% by mass.

[0063] [2. Non-aqueous electrolyte secondary battery] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention is a nonaqueous electrolyte battery including a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions, and a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions, and contains a nonaqueous electrolyte.

[0064] [2-1. Non-aqueous electrolyte] The nonaqueous electrolyte solution used is the nonaqueous electrolyte solution described above. Note that, within the scope of the present invention, other nonaqueous electrolyte solutions may be mixed with the nonaqueous electrolyte solution described above.

[0065] [2-2. Negative electrode] The negative electrode has a negative electrode active material on at least a portion of the surface of a current collector. [2-2-1. Negative electrode active material] The negative electrode active material used in the negative electrode is not particularly limited as long as it is capable of electrochemically absorbing and releasing metal ions. Specific examples include carbon-based materials, materials containing metal elements and / or metalloid elements that can be alloyed with Li, lithium-containing metal composite oxide materials, and mixtures thereof. Among these, it is preferable to use carbon-based materials, materials containing metal elements and / or metalloid elements that can be alloyed with Li, or mixtures of graphite particles and materials containing metal elements and / or metalloid elements that can be alloyed with Li, in view of their excellent cycle characteristics and safety, as well as their excellent continuous charge characteristics. These materials may be used alone or in any combination of two or more.

[0066] [2-2-2. Carbon-based materials] Examples of carbonaceous materials include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Of these, natural graphite is preferred. One type of carbonaceous material may be used alone, or two or more types may be used in any combination and ratio. Examples of natural graphite include scaly graphite, scaly graphite, and / or graphite particles obtained by subjecting such graphite to treatment such as spheroidization or densification. Among these, spherical or ellipsoidal graphite particles that have been subjected to spheroidization treatment are particularly preferred from the viewpoint of particle packing properties or charge / discharge rate characteristics. The average particle size (d50) of the graphite particles is usually 1 μm or more and 100 μm or less.

[0067] [2-2-3. Physical properties of carbon-based materials] The carbonaceous material as the negative electrode active material preferably satisfies at least one of the characteristics such as physical properties and shape shown in the following items (1) to (4), and it is particularly preferable that it simultaneously satisfies several items. (1) X-ray diffraction parameters The d value (interlayer distance) of the lattice plane (002 plane) of carbon-based materials determined by X-ray diffraction using the Gakushin method is usually 0.335 nm or more and 0.360 nm or less. In addition, the crystallite size (Lc) of carbon-based materials determined by X-ray diffraction using the Gakushin method is 1.0 nm or more. (2) Volume-based average particle size The volume-based average particle size of the carbon-based material is the volume-based average particle size (median diameter) determined by a laser diffraction / scattering method, and is usually 1 μm or more and 100 μm or less. (3) Raman R value, Raman half-width The Raman R value of a carbon-based material is a value measured using argon ion laser Raman spectroscopy, and is usually 0.01 or more and 1.5 or less. In addition, the 1580 cm -1 The Raman half-width in the vicinity is not particularly limited, but is usually 10 cm -1 More than 100cm -1 The following is the result. (4)BET specific surface area The BET specific surface area of ​​a carbon-based material is the value of the specific surface area measured using the BET method, and is usually 0.1 m 2 ·g -1 Over 100m 2 ·g -1 The following is the result. The negative electrode active material may contain two or more carbonaceous materials with different properties, where the properties refer to one or more characteristics selected from the group consisting of X-ray diffraction parameters, volume-based average particle size, Raman R value, Raman half-width, and BET specific surface area. Preferred examples include a case where the volume-based particle size distribution is not symmetrical about the median diameter, a case where two or more carbon-based materials with different Raman R values ​​are contained, and a case where X-ray parameters are different.

[0068] [2-2-4. Materials containing metallic and / or semi-metallic elements that can be alloyed with Li] Any conventionally known material containing a metal element and / or a metalloid element that can be alloyed with Li can be used. However, from the viewpoint of capacity and cycle life, for example, Sb, Si, Sn It is preferably a material containing a metal element and / or a metalloid element selected from the group consisting of Al, As, and Zn. Further, when the material contains two or more kinds of metal elements and / or metalloid elements capable of alloying with Li, the material may be a material composed of an alloy of these metal elements and / or metalloid elements.

[0069] Examples of the material containing a metal element and / or a metalloid element capable of alloying with Li include metal oxides, metal nitrides, metal carbides, Si-containing inorganic compounds, etc. The compound may contain two or more kinds of materials containing a metal element and / or a metalloid element capable of alloying with Li. Among them, metallic Si (hereinafter sometimes referred to as Si) or a Si-containing inorganic compound is preferable in terms of increasing the capacity.

[0070] Further, the material containing a metal element and / or a metalloid element capable of alloying with Li may already be alloyed with Li during the production of the negative electrode described later, and Si or a Si-containing inorganic compound is preferable in terms of increasing the capacity. In this specification, Si or a Si-containing inorganic compound is collectively referred to as a Si compound. Specific examples of the Si compound include SiO x (0≦x≦2), etc. Specific examples of the material containing a metal element and / or a metalloid element capable of alloying with Li include Li y Si(where 0<y≦4.4), Li 2z SiO 2+z (where 0<z≦2), etc. As the Si compound, silicon oxide (SiO x、 where 0<x≦2) is preferable in that its theoretical capacity is larger than that of graphite, or amorphous Si or nano-sized Si crystals are preferable in that alkali ions such as lithium ions can easily enter and exit, making it possible to obtain a high capacity.

[0071] [2-2-5. Mixture of metal particles capable of alloying with Li and graphite particles] The mixture of graphite particles and a material containing a metal element and / or a metalloid element that can be alloyed with Li, which is used as the negative electrode active material, may be a mixture in which the material containing a metal element and / or a metalloid element that can be alloyed with Li and the graphite particles are mixed in the form of particles that are independent of each other, or may be a composite in which the material containing a metal element and / or a metalloid element that can be alloyed with Li is present on the surface or inside of graphite particles. The content of the material containing a metal element and / or a metalloid element that can be alloyed with Li relative to the total of the material containing a metal element and / or a metalloid element that can be alloyed with Li and the graphite particles is typically 1 mass% or more and 99 mass% or less.

[0072] [2-2-6. Lithium-containing metal composite oxide materials] The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. However, from the viewpoint of high current density charge / discharge characteristics, a lithium-containing metal composite oxide material containing titanium is preferred, a composite oxide of lithium and titanium (hereinafter sometimes abbreviated as "lithium titanium composite oxide") is more preferred, and a lithium titanium composite oxide having a spinel structure is particularly preferred because it significantly reduces output resistance.

[0073] Furthermore, the lithium and / or titanium of the lithium titanium composite oxide may be substituted with another metal element, for example, at least one element selected from the group consisting of Al, Ga, Cu, and Zn. As a lithium titanium composite oxide, Li 4 / 3 Ti 5 / 3 O4, Li1Ti2O4 and Li 4 / 5 Ti 11 / 5 O4 is preferred. In addition, examples of lithium titanium composite oxides in which part of lithium and / or titanium is substituted with other elements include Li 4 / 3 Ti 4 / 3 Al 1 / 3 O4 is preferred.

[0074] [2-2-7. Negative electrode structure and manufacturing method] The negative electrode may be produced by any known method as long as it does not significantly impair the effects of the present invention. For example, the negative electrode active material can be prepared by adding a binder, a liquid medium such as an aqueous solvent or an organic solvent, and, if necessary, a thickener, a conductive material, a filler, and the like to the negative electrode active material to form a slurry, which is then applied to a current collector, dried, and pressed to form a negative electrode active material layer.

[0075] [2-2-7-1. Current collector] Any known current collector can be used to support the negative electrode active material. Examples of the negative electrode current collector include metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel, but copper is particularly preferred from the standpoints of ease of processing and cost. The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Of these, a metal foil or a metal thin film is preferred. The metal thin film may be formed into a mesh shape as appropriate. When the negative electrode current collector is in the form of a plate or film, the thickness of the current collector is not limited, but is usually 1 μm or more and 1 mm or less.

[0076] [2-2-7-2. Binder] The binder for binding the negative electrode active material is not particularly limited as long as it is a material that is stable to the non-aqueous electrolyte solution and the solvent used in producing the electrode. Specific examples include rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber, as well as fluorine-containing polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and polytetrafluoroethylene-ethylene copolymers. These may be used alone or in any combination and ratio of two or more. The ratio of the binder to the negative electrode active material is usually 0.1 mass % or more and 20 mass % or less. In particular, when a rubber-like polymer such as SBR is contained as a main component, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more and 5% by mass or less. Also, when a fluorine-based polymer such as polyvinylidene fluoride is contained as a main component, the ratio of the binder to the negative electrode active material is usually 1% by mass or more and 15% by mass or less.

[0077] [2-2-7-3. Thickener] Thickeners are usually used to adjust the viscosity of the slurry. Examples of thickeners include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, etc. These may be used alone or in any combination and ratio of two or more. Furthermore, when a thickener is used, the ratio of the thickener to the negative electrode active material is usually 0.1 mass % or more and 5 mass % or less.

[0078] [2-2-8. Electrode density] There are no particular restrictions on the electrode structure when the negative electrode active material is made into an electrode, but the density of the negative electrode active material on the current collector is usually 1 g cm -3 More than 2.2g cm -3 The following is the result.

[0079] [2-2-9. Thickness of negative electrode plate] The thickness of the negative electrode plate is designed to match the positive electrode plate to be used and is not particularly limited, but the thickness of the negative electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the negative electrode plate is usually 15 μm or more and 300 μm or less.

[0080] [2-2-10. Surface coating of negative electrode plate] Furthermore, a substance having a different composition from the negative electrode active material may be attached to the surface of the negative electrode plate (surface-attached substance). Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[0081] [2-3. Positive electrode] The positive electrode refers to a current collector having a positive electrode active material on at least a portion of its surface. [2-3-1. Positive electrode active material] The positive electrode active material (lithium transition metal compound) used in the positive electrode will be described below.

[0082] [2-3-1-1. Lithium transition metal compounds] The lithium transition metal compound is a compound having a structure capable of desorbing and inserting lithium ions, and examples thereof include sulfides, phosphate compounds, silicate compounds, borate compounds, lithium transition metal composite oxides, etc. Among these, lithium transition metal composite oxides are preferred.

[0083] Lithium transition metal composite oxides include those with a spinel structure that allows three-dimensional diffusion and those with a layered structure that allows two-dimensional diffusion of lithium ions. Those with a spinel structure are generally expressed as LixM2O4 (M is one or more transition metals, x is usually 1 or more and 1.5 or less), and specific examples include LiMn2O4, LiCoMnO4, and LiNi 0.5 Mn 1.5 O4, LiCoVO4, etc. Those with a layered structure are generally expressed as LixMO2 (M is one or more transition metals, x is usually 1 or more and 1.5 or less). Specifically, LiCoO2, LiNiO2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.05 Ni 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0084] Among these, lithium transition metal composite oxides having a layered structure are preferred, and transition metal composite oxides represented by the following composition formula (1) are more preferred. Li a1 Ni b1 Co c1 M d1 O2···(1) (In formula (1), a1, b1, c1, and d1 represent numerical values ​​of 0.90≦a1≦1.10, 0.30≦b1≦0.98, 0.01≦c1≦0.50, and 0.0≦d1≦0.50, respectively, and satisfy 0.50≦b1+c1 and b1+c1+d1=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.) In formula (1), it is preferable that the value d1 is 0.1≦d1≦0.50.

[0085] In particular, a transition metal composite oxide represented by the following composition formula (2) is preferred. Li a2 Ni b2 Co c2 M d2 O2···(2) (In formula (2), a2, b2, c2, and d2 are numerical values ​​that satisfy 0.90≦a2≦1.10, 0.50≦b2≦0.98, 0.01≦c2<0.50, and 0.01≦d2<0.50, respectively, and b2+c2+d2=1 is satisfied. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.)

[0086] A preferred specific example of the lithium transition metal composite oxide represented by formula (2) is LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.5 Mn 0.3 Co 0.2O2, Li 1.05 Ni 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0087] In each composition formula, M preferably contains Mn or Al, and more preferably Mn, which increases the structural stability of the lithium transition metal composite oxide and suppresses structural deterioration during repeated charge and discharge.

[0088] [2-3-1-2. Introduction of different elements] Furthermore, elements other than those included in the above composition formula may be incorporated into the lithium transition metal composite oxide.

[0089] [2-3-1-3. Surface coating] The positive electrode active material may have a surface-attached substance (surface-attached substance) having a different composition from the positive electrode active material attached to its surface. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent, adding them to the positive electrode active material by impregnation, and drying them. The amount of the surface-adhering substance is preferably 1 μmol / g or more, more preferably 10 μmol / g or more, and is usually 1 mmol / g or less, relative to the positive electrode active material. In this specification, a positive electrode active material having the above-mentioned surface-adhering substance attached to its surface is also referred to as a "positive electrode active material."

[0090] [2-3-1-4. Blend] These positive electrode active materials may be used alone or in any combination of two or more in any ratio.

[0091] [2-3-2. Positive electrode structure and manufacturing method] The configuration and manufacturing method of the positive electrode are described below. In this embodiment, the positive electrode using the positive electrode active material can be manufactured by a conventional method. That is, the positive electrode active material and a binder, and optionally a conductive material and a thickener, are mixed in a dry state to form a sheet, which is then pressed onto the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium such as an aqueous solvent or an organic solvent to form a slurry, which is then applied to the positive electrode current collector and dried to form a positive electrode active material layer on the current collector, thereby obtaining a positive electrode. In addition, for example, the above-mentioned positive electrode active material may be roll-formed into a sheet electrode, or may be compression-molded into a pellet electrode. Hereinafter, the case where the slurry is sequentially applied to the positive electrode current collector and then dried will be described.

[0092] [2-3-2-1. Active material content] The content of the positive electrode active material in the positive electrode active material layer is usually 80% by mass or more and 99.5% by mass or less.

[0093] [2-3-2-2. Density of the positive electrode active material layer] The positive electrode active material layer obtained by coating and drying is preferably compacted by a hand press, a roller press, or the like to increase the packing density of the positive electrode active material. The density of the positive electrode active material layer is usually 1.5 g / cm. 3 More than 4.5g / cm 3 The following is the result.

[0094] [2-3-2-3.Conductive materials] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon-based materials such as amorphous carbon such as needle coke. One conductive material may be used alone, or two or more may be used in any combination and ratio. The conductive material is typically used so that it is contained in the positive electrode active material layer in an amount of 0.01 mass % or more and 50 mass % or less.

[0095] [2-3-2-4. Binder] When the positive electrode active material layer is formed by, for example, a coating method, the binder used in producing the positive electrode active material layer is not particularly limited as long as it is a material that can be dissolved or dispersed in a liquid medium for the slurry. However, in view of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like, fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide are preferred. Also usable are mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. The binder may be used alone or in any combination and ratio of two or more types. Furthermore, when a resin is used as a binder, the weight-average molecular weight of the resin is optional as long as it does not significantly impair the effects of the present invention, but is usually from 10,000 to 3,000,000. When the molecular weight is in this range, the strength of the electrode is improved, and the electrode can be suitably formed. The proportion of the binder in the positive electrode active material layer is usually 0.1 mass % or more and 80 mass % or less.

[0096] [2-3-2-5. Solvent] The solvent for forming the slurry is not particularly limited in type as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed, and either an aqueous solvent or an organic solvent may be used.

[0097] [2-3-2-6. Current collector] The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Among these, aluminum is preferred. The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Of these, a metal thin film is preferred. The metal thin film may be suitably formed into a mesh shape.

[0098] When the current collector of the positive electrode is in the form of a plate or film, the thickness of the current collector is optional, but is usually 1 μm or more and 1 mm or less.

[0099] [2-3-2-7. Thickness of the positive electrode plate] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the positive electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the positive electrode plate is usually 10 μm or more and 500 μm or less on one side of the current collector.

[0100] [2-3-2-8. Surface coating of positive electrode plate] In addition, the positive electrode plate may have a substance of a different composition attached to its surface, and the substance may be the same as the surface-attached substance that may be attached to the surface of the positive electrode active material.

[0101] [2-4. Separator] A separator is usually placed between the positive electrode and the negative electrode to prevent short circuits, and in this case, the non-aqueous electrolyte is usually impregnated into the separator before use. The separator is not particularly limited in material or shape, and any known material may be used as long as it does not significantly impair the effects of the present invention. Among these, it is preferable to use a material that is stable against a non-aqueous electrolyte solution, such as a resin, glass fiber, or inorganic material, and that is in the form of a porous sheet or nonwoven fabric having excellent liquid retention.

[0102] [2-4-1. Materials] The separator may be made of, for example, a glass filter or polyolefin, preferably polyolefin, and particularly preferably polyethylene or polypropylene. These materials may be used alone or in any combination of two or more in any ratio.These materials may also be used in a laminated state.

[0103] [2-4-2. Thickness] The thickness of the separator is not limited, but is usually 1 μm or more and 50 μm or less.

[0104] [2-4-3. Porosity] When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is not limited, but is usually 20% or more and 90% or less.

[0105] [2-4-4.Form] As for the form, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. In the thin film form, a film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above independent thin film form, a separator may be used in which a composite porous layer containing the above inorganic particles is formed on the surface layer of the positive electrode and / or negative electrode using a resin binder.

[0106] [2-4-5. Air permeability] The characteristics of a separator in a nonaqueous electrolyte secondary battery can be understood by its Gurley value. The Gurley value indicates the difficulty of air passing through the film in the thickness direction, and is expressed as the number of seconds required for 100 ml of air to pass through the film. The Gurley value of a separator is arbitrary, but is usually 10 to 1000 seconds / 100 ml.

[0107] [2-5.Battery design] [2-5-1. Electrode group] The electrode group may have either a laminated structure of the positive electrode plate and the negative electrode plate sandwiched between the separator, or a structure of the positive electrode plate and the negative electrode plate spirally wound with the separator sandwiched between them. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% or more and 90% or less.

[0108] [2-5-2. Current collection structure] When the electrode group has the aforementioned laminated structure, a structure in which the metal core portions of the electrode layers are bundled and welded to a terminal is preferably used. It is also preferable to provide multiple terminals within the electrode to reduce resistance. When the electrode group has the aforementioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive and negative electrodes and bundling them to a terminal.

[0109] [2-5-3.Protection elements] The protective element may be a PTC (Positive Temperature Coefficient) element whose resistance increases as heat is generated by excessive current, a thermal fuse, a thermistor, or a valve (current cutoff valve) that cuts off the current flowing in the circuit due to a sudden rise in the internal pressure or temperature of the battery when abnormal heat is generated. It is preferable to select the above protective element so that it will not operate under normal use at high current, and it is even more preferable to design it so that abnormal heat generation or thermal runaway does not occur even without the protective element.

[0110] [2-5-4. Exterior body] A non-aqueous electrolyte secondary battery is usually constructed by housing the above-mentioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc. in an exterior body (exterior case). There are no limitations on this exterior body, and any known exterior body can be used as long as it does not significantly impair the effects of the present invention. The material of the exterior case is not particularly limited as long as it is stable against the non-aqueous electrolyte solution used, but from the viewpoint of weight reduction, metal such as aluminum or an aluminum alloy, or a laminate film is preferably used. Examples of exterior cases using the above metals include those in which metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed, airtight structure, and those in which the above metals are used via a resin gasket to form a crimped structure.

[0111] [2-5-5. Shape] The shape of the exterior case may also be arbitrary, and may be, for example, cylindrical, rectangular, laminated, coin-shaped, large, or the like. [Example]

[0112] Next, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The compounds used in this example are shown below. Compound 4 can be synthesized by a known method (Organometalics, Volume 36, Issue 4, 767-776, 2017). [ka]

[0113] [Evaluation of non-aqueous electrolyte secondary batteries] The non-aqueous electrolyte secondary batteries prepared in the examples were evaluated as follows. ·Initial charge / discharge In a thermostatic bath at 25°C, a sheet-shaped non-aqueous electrolyte secondary battery was charged at a constant current of 0.025C (the current value at which the rated capacity based on the discharge capacity at a 1-hour rate is discharged in 1 hour is defined as 1C; the same applies below) to 3.6V, then charged at a constant current / constant voltage of 0.167C to a voltage of 4.2V, and then discharged at a constant current of 0.167C to 2.5V. Furthermore, the non-aqueous electrolyte secondary battery was stabilized by charging at a constant current and constant voltage of 0.167 C up to 4.1 V and then storing at 60°C for 12 hours. The battery was discharged at a constant current and then charged at a constant voltage of 0.167 C to a voltage of 4.2 V. Thereafter, the battery was discharged at a constant current of 0.167 C to 2.5 V, and the discharge capacity at this time was defined as the initial capacity (A). Thereafter, constant current-constant voltage charging was carried out at 0.167 C at 25°C up to a voltage of 3.7 V. This was then discharged at 0.5 C, 1.0 C, and 1.5 C at 25°C, and the voltage was measured after 10 seconds. From this current-voltage line, the internal resistance (R 1A Next, constant current-constant voltage charging was performed at 0.2 C up to a voltage of 4.2 V, and the initial charge-discharge was completed.

[0114] -Evaluation of remaining capacity and resistance retention rates The nonaqueous electrolyte secondary battery after the initial charge and discharge was left at 60°C for 14 days. This nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C and subjected to constant current discharge at 0.2C down to 2.5V. The discharge capacity was recorded as the capacity after storage (B), and the ratio of the difference between the initial capacity (A) and the capacity after storage (B) ((AB) / A x 100) was recorded as the remaining capacity retention rate. The remaining capacity retention rates in Table 3 are shown with Comparative Example 3-1 normalized to 100. Thereafter, a constant current-constant voltage charge was performed at 0.167C down to a voltage of 3.7V. This battery was discharged at 0.5C, 1.0C, and 1.5C at 25°C, and the voltage was measured 10 seconds after the discharge. From this current-voltage line, the internal resistance (R 1B The resistance retention rate was calculated based on the initial internal resistance (R 1A ) and the internal resistance after storage (R 1B ) ratio ((R 1B ) / (R 1A )) was defined as the resistance retention rate. The resistance retention rates in Tables 1 and 2 were listed by normalizing Comparative Example 1-1 and Comparative Example 2-1, respectively, to 100. It can be said that a larger remaining capacity retention rate is preferable, and a smaller resistance retention rate is preferable.

[0115] ·Storage gas evaluation The nonaqueous electrolyte secondary battery after the initial charge / discharge was left at 60°C for 14 days. Before and after leaving the battery, the nonaqueous electrolyte secondary battery was immersed in an ethanol bath at room temperature to measure its volume, and the change in volume during leaving the battery was recorded as "storage gas." The less storage gas there is, the better.

[0116] [Examples 1-1 to 1-4, Comparative Example 1-1] [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> Under a dry argon atmosphere, thoroughly dried LiPF was dissolved in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:4:3) to prepare a nonaqueous electrolyte solution at 1.0 mol / L (as the concentration in the nonaqueous electrolyte solution). Additives 1 and 2 listed in Table 1 were dissolved in the nonaqueous electrolyte solution as a reference. Using this nonaqueous electrolyte, a nonaqueous electrolyte secondary battery was fabricated and evaluated in the following manner. <Preparation of positive electrode> Li as the positive electrode active material 1.05 Ni 0.34 Mn 0.33 Co 0.33 O2(Ni / M 3 85 parts by mass of cellulose acetate (molar ratio = 0.34), 10 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone to form a slurry. This slurry was uniformly applied to a 15 μm thick aluminum foil, dried, and then roll-pressed to form a positive electrode. The plate density of the positive electrode was 2.6 g / cm. 3 It was.

[0117] <Preparation of negative electrode> 49 parts by mass of graphite powder was mixed with 50 parts by mass of an aqueous dispersion of sodium carboxymethyl cellulose (concentration of sodium carboxymethyl cellulose: 1% by mass) as a thickener and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 49% by mass) as a binder, and mixed in a disperser to form a slurry. The obtained slurry was uniformly applied to a copper foil with a thickness of 10 μm, dried, and roll-pressed. The negative electrode was formed by welding.

[0118] <Production of non-aqueous electrolyte secondary battery> The positive electrode, negative electrode, and polyolefin separator were stacked in this order, and the resulting battery element was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution was poured into the battery, followed by vacuum sealing to prepare a sheet-shaped nonaqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery thus obtained was evaluated for storage gas and resistance retention rate as described above, and the results are shown in Table 1. MFEC stands for monofluoroethylene carbonate.

[0119] [Table 1]

[0120] As is clear from Table 1, when comparing Example 1-1 with Comparative Example 1-1, it can be seen that adding Compound 1 when using MFEC reduces the amount of gas generation during storage in the present example. Furthermore, Example 1-2 revealed that increasing the amount of compound 1 further suppresses gas generation during storage and improves the resistance retention rate during high-temperature storage. Furthermore, Examples 1-3 and 1-4 show that Compound 2 and Compound 4 also reduce the amount of gas generation during storage and improve the resistance retention rate.

[0121] [Examples 2-1 to 2-2, Comparative Example 2-1] [Fabrication of non-aqueous electrolyte secondary battery] A sheet-shaped nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that Additive 1 and Additive 2 were added as shown in Table 2. The resulting nonaqueous electrolyte secondary battery was evaluated for storage gas and resistance retention as described above. The results are shown in Table 2. VC stands for vinylene carbonate.

[0122] [Table 2]

[0123] As is clear from Table 2, when Examples 2-1 and 2-2 are compared with Comparative Example 2-1, it can be seen that the addition of VC also reduces the amount of gas generated during storage, as with the addition of MFEC described above, and improves the resistance retention rate. From the above results, it is presumed that Compounds 1, 2, and 4 efficiently capture the carbon dioxide generated when MFEC and VC are added.

[0124] [Examples 3-1 to 3-3, Comparative Example 3-1] [Fabrication of non-aqueous electrolyte secondary battery] A sheet-shaped nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that Additive 1 and Additive 2 were added as shown in Table 3. The resulting nonaqueous electrolyte secondary battery was evaluated for storage gas and remaining capacity retention as described above. The results are shown in Table 3.

[0125] [Table 3]

[0126] As is clear from Table 3, when Examples 3-1, 3-2, and 3-3 are compared with Comparative Example 3-1, it is found that the amount of gas stored is efficiently reduced and the remaining capacity retention rate during storage is improved in the Examples. This is presumably because, as in Compound 1, Compound 2, and Compound 4, the nitrogen-containing aromatic compound has a substituent other than a hydrogen atom on the carbon atom (position 2) adjacent to the nitrogen atom, which is a highly reactive site, and thus side reactions are more efficiently suppressed than in Compound 3, which has a hydrogen atom at position 2.

Claims

1. A non-aqueous electrolyte solution for a battery, comprising a compound represented by formula (I) and a fluorinated cyclic carbonate and / or an unsaturated cyclic carbonate, The compound represented by formula (I) is contained in a non-aqueous electrolyte solution in an amount of 0.01 to 10% by mass, The non-aqueous electrolyte solution for a battery contains the fluorinated cyclic carbonate and / or the unsaturated cyclic carbonate in an amount of 0.01 to 10 mass %. 【Chemical 1】 (In formula (I), R １ is a hydrogen atom, a halogen atom, a silyl group, an acyl group, a sulfonyl group, a sulfonyloxy group, or a phosphate group, and R ２ and R ５ are each independently a halogen atom or a hydrocarbon group, and R ３ and R ４ are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group, and R ２ and R ３ , R ３ and R ４ , and R ４ and R ５ At least one of the combinations selected from the following is bonded to each other to form a ring, and the ring is an aromatic ring which may have a heteroatom.

2. In the formula (I), R １ The nonaqueous electrolyte solution for a battery according to claim 1 , wherein is a hydrogen atom, a silyl group, a sulfonyl group, or a sulfonyloxy group.

3. In the formula (I), R ２ and R ５ 3. The nonaqueous electrolyte solution for a battery according to claim 1, wherein each of the groups independently represents at least one selected from the group consisting of an alkyl group, an alkenyl group, and an aryl group.

4. 4. The nonaqueous electrolyte solution for a battery according to claim 1, wherein in formula (I), the aromatic ring optionally having a heteroatom is a ring selected from the group consisting of a benzene ring, a naphthalene ring, a pyrrole ring, a thiophene ring, and a furan ring.

5. 5. The nonaqueous electrolyte solution for a battery according to claim 1, wherein the fluorinated cyclic carbonate is monofluoroethylene carbonate and / or difluoroethylene carbonate.

6. 6. The nonaqueous electrolyte solution for a battery according to claim 1, wherein the unsaturated cyclic carbonate is vinylene carbonate, vinyl ethylene carbonate, and / or ethynyl ethylene carbonate.

7. 7. A nonaqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; and the nonaqueous electrolyte solution for batteries according to claim 1.

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