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

Abstract

To provide a nonaqueous electrolyte that may improve the battery capacity after a high-temperature preservation test.SOLUTION: The nonaqueous electrolyte contains a compound (A) represented by formula (I) or (II), and one or more salts (B) selected from the group consisting of phosphates having a P-F bond and sulfonates having an S-F bond. (In formula (I), R1, R2 and R3 are each independently a hydrogen atom, halogen atom or hydrocarbon group, where R1 and R2 may be bound to each other to form a cyclic structure; n is an integer from 0 to 4; and M1 is a monovalent cation. In formula (II), R4 is a hydrogen atom, halogen atom or hydrocarbon group; n is an integer from 0 to 4; and M2 is a monovalent cation.)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 electrochemical element characterized by having a negative electrode containing a specific negative electrode active material, a nonaqueous electrolyte solution containing an organic lithium sulfonate salt having a carbon-carbon double bond, and a specific separator, and discloses that the element has excellent safety during overcharging, excellent high-temperature storage properties, i.e., the ability to suppress battery swelling, and excellent low-temperature charging characteristics.

[0004] Patent Document 2 discloses an electrolyte solution containing a monomer having a sulfonic acid ion group, and discloses that a secondary battery using this electrolyte solution has an improved discharge capacity retention rate during charge-discharge cycles.

[0005] Patent Document 3 discloses a nonaqueous secondary battery including a positive electrode having a positive electrode composite layer containing a specific positive electrode active material and a nonaqueous electrolyte containing an organic lithium sulfonate salt having a carbon-carbon double bond, and discloses that the battery has improved discharge capacity, charge-discharge cycle characteristics, and safety. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-277723 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-42387 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-110943 Summary of the Invention [Problem to be solved by the invention]

[0007] 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 improved battery capacity after high-temperature storage. In particular, the addition of phosphates or sulfonates can improve battery performance such as capacity retention, and therefore, for example, lithium difluorophosphate is used as an additive in non-aqueous electrolyte secondary batteries. However, in the nonaqueous electrolyte secondary battery described in Patent Document 1, it is described that battery swelling can be suppressed by combining a specific separator with a nonaqueous electrolyte containing an organic lithium sulfonate salt having a carbon-carbon unsaturated bond, but there is no study or description of the battery capacity after high-temperature storage. Furthermore, in the nonaqueous electrolyte described in Patent Document 2, it is described that the discharge capacity retention rate during cycle testing can be improved, but there is no study or description of the battery capacity after high-temperature storage. Furthermore, in the nonaqueous secondary battery described in Patent Document 3, it is described that cycle characteristics can be improved by combining a specific positive electrode mixture layer with an electrolyte having a carbon-carbon double bond, but there is no description of the evaluation of battery characteristics when a phosphate or sulfonate is co-added.

[0008] An object of the present invention is to provide a non-aqueous electrolyte that can solve the above problems in non-aqueous electrolyte secondary batteries and improve the battery capacity after high-temperature storage. [Means for solving the problem]

[0009] 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 sulfonate having a specific carbon-carbon unsaturated bond and a specific phosphate or sulfonate to a non-aqueous electrolyte solution, and have arrived at the present invention.

[0010] That is, the gist of the present invention lies in the following. [1] A non-aqueous electrolyte solution comprising a compound (A) represented by formula (I) or formula (II), and one or more salts (B) selected from the group consisting of phosphates having a PF bond and sulfonates having an SF bond. [ka] (In formula (I), R 1 , R 2 and R 3 are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group, and R 1 and R 2 may be bonded to each other to form a cyclic structure; n is an integer of 0 to 4; M 1 is a monovalent cation. In formula (II), R 4 represents a hydrogen atom, a halogen atom, or a hydrocarbon group; n represents an integer of 0 to 4; M 2 is a monovalent cation.) [2] In the formula (I), R 1 , R 2 and R 3 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aralkyl group having 7 to 18 carbon atoms. [3] In the formula (II), R 4 is a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aralkyl group having 7 to 18 carbon atoms. [4] The nonaqueous electrolyte solution according to any one of [1] to [3], which contains 0.01% by mass or more and 10% by mass or less of the compound (A) represented by the formula (I) or (II). [5] The nonaqueous electrolyte solution according to any one of [1] to [4], containing 0.01% by mass or more and 10% by mass or less of the salt (B) selected from the group consisting of phosphates having a PF bond and sulfonates having an SF bond. [6] A non-aqueous 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 non-aqueous electrolyte solution according to any one of [1] to [5]. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a nonaqueous electrolyte solution that can improve battery capacity after high-temperature storage, and also to provide a nonaqueous electrolyte secondary battery that includes the nonaqueous electrolyte solution. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments of the present invention will be described in detail. The above is an example (typical example) of an embodiment of the present invention, and the present invention is not limited to these contents as long as it does not depart from the gist of the claims.

[0013] [1. Non-aqueous electrolyte] The nonaqueous electrolyte solution used in the nonaqueous electrolyte secondary battery according to the embodiment of the present invention, like a general nonaqueous electrolyte solution, contains an electrolyte and a nonaqueous solvent that dissolves the electrolyte, and contains at least one compound (A) represented by formula (I) or formula (II) (hereinafter, this may be referred to as a sulfonate salt having a carbon-carbon unsaturated bond), and one or more salts (B) (hereinafter, this may be referred to as a "phosphate or sulfonate salt having a fluorine atom") selected from the group consisting of phosphates having a P═O bond and a PF bond and sulfonates having an SF bond. [ka] (In formula (I), R 1 , R 2 and R 3 are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group, and R 1 , R 2 may be bonded to each other to form a cyclic structure; n is an integer of 0 to 4; M 1 is a monovalent cation. In formula (II), R 4 is a hydrogen atom, a halogen atom, or a hydrocarbon group; n is an integer of 0 to 4; M 2 is a monovalent cation.) The non-aqueous electrolyte solution according to the present invention is preferable in that it can improve the battery capacity after high-temperature storage. The inventors speculate that the reason for such excellent effects is as follows. It is believed that as the secondary battery is charged and discharged, the carbon-carbon unsaturated bond of compound (A) represented by formula (I) or formula (II) polymerizes on the electrode, and further reacts with phosphate having a PF bond or sulfonate having an SF bond (B), forming a hardly soluble and strong co-coating film on the electrode, thereby suppressing side reactions between the electrode active material and the solvent, etc. That is, it is believed that the present invention can efficiently improve the battery capacity after high-temperature storage to a higher level than before by including a sulfonate having a carbon-carbon unsaturated bond and a specific phosphate or specific sulfonate in a nonaqueous electrolyte solution. Each component will be described below.

[0014] [1-1. Compound (A) represented by formula (I) or formula (II) (sulfonate salt having a carbon-carbon unsaturated bond)] [1-1-1. Compounds represented by formula (I)] [ka] In formula (I), R 1 , R 2 and R 3 are each independently a hydrogen atom, a halogen atom or a hydrocarbon group, and are preferably a hydrogen atom or a hydrocarbon group. 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 hydrocarbon group include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, and an aralkyl group. Among these, an alkyl group, an alkenyl group, an aryl group, and an aralkyl group are particularly preferred. The hydrocarbon group may have a substituent such as a fluorine atom. The aryl group also includes a heteroaryl group in which any ring atom is substituted with a heteroatom. 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, etc. Among these, an alkyl group having 1 to 6 carbon atoms is preferred in terms of solubility in an electrolyte solution. 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 2 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, etc. Among these, an alkynyl group having 2 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. Among 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 particularly preferred in terms of solubility in an electrolyte solution. Examples of the aralkyl group include a phenylmethyl group (benzyl group), a phenylethyl group (phenethyl group), a phenylpropyl group, a phenylbutyl group, and a phenylisopropyl group. Of these, a benzyl group and a phenethyl group are preferred, and a benzyl group is particularly preferred in terms of stability in an electrolyte solution. R in formula (I) 1 and R 2 may be bonded to each other to form a cyclic structure. Examples of the cyclic structure include a cyclohexene ring, a cyclopentene ring, a benzene ring, a naphthalene ring, a pyrrole ring, a thiophene ring, a furan ring, an imidazole ring, a thiazole ring, a carbazole ring, and a pyridine ring. Among these, a cyclohexene ring, a benzene ring, a naphthalene ring, a pyrrole ring, a thiophene ring, and a furan ring are preferred in terms of stability to the electrolyte, and a cyclohexene ring, a benzene ring, and a naphthalene ring are more preferred. In addition, the atoms forming the cyclic structure may have a substituent such as a fluorine atom. M in formula (I) 1 is a monovalent cation, preferably a lithium ion, a sodium ion, ions, potassium ions, rubidium ions, and cesium ions. Among these, lithium ions, sodium ions, and potassium ions are preferred in terms of solubility in the electrolyte, and lithium ions and sodium ions are more preferred. n is an integer of 0 to 4, preferably an integer of 0 to 2, more preferably 0 or 1, in terms of solubility in the electrolyte.

[0015] Specific examples of the compound represented by formula (I) include the following compounds. [ka]

[0016] [ka]

[0017] [ka]

[0018] Among these, the following compounds are preferred: [ka]

[0019] [ka]

[0020] [ka]

[0021] More preferred are the following compounds: [ka]

[0022] [ka]

[0023] More preferred compounds include the following: [ka]

[0024] [ka]

[0025] Particularly preferred are the following compounds: [ka]

[0026] The content of the compound represented by formula (I) is not particularly limited, but the non-aqueous electrolyte solution contains the compound represented by formula (I) in an amount of preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, and particularly preferably 4% by mass or less. The compound represented by formula (I) may be used alone or in any combination and ratio of two or more. When the compound represented by formula (I) and the compound represented by formula (II) described below are used in combination, the total amount of the compound represented by formula (I) and the compound represented by formula (II), i.e., the total amount of the sulfonate salt (A) having a carbon-carbon unsaturated bond, may be within the above range, but it is preferable to use only the compound represented by formula (I). The identification and content of sulfonates having carbon-carbon unsaturated bonds are measured by nuclear magnetic resonance (NMR) spectroscopy.

[0027] [1-1-2. Compound represented by formula (II)] [ka]

[0028] R in formula (II) 4 is a hydrogen atom, a halogen atom, or a hydrocarbon group. 4 The halogen atom or hydrocarbon group in R 1 ~R 3 Examples of the alkyl group include those exemplified above, and are preferably a hydrogen atom, a halogen atom, an alkenyl group having 2 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aralkyl group having 7 to 18 carbon atoms, more preferably a hydrogen atom or a phenyl group, and even more preferably a hydrogen atom. M in formula (II) 2 is a monovalent cation, specifically, M 1 Examples of the ion include those exemplified in the above, and lithium ions, sodium ions, and potassium ions are preferred in terms of solubility in the electrolyte solution. n is an integer of 0 to 4, preferably an integer of 0 to 2, more preferably 0 or 1, in terms of solubility in the electrolyte.

[0029] Specific examples of the compound represented by formula (II) include the following compounds. [ka]

[0030] [ka]

[0031] Among these, the following compounds are preferred: [ka]

[0032] More preferred are the following compounds: [ka]

[0033] More preferred compounds include the following: [ka]

[0034] Particularly preferred are the following compounds: [ka]

[0035] The content of the compound represented by formula (II) in the non-aqueous electrolyte solution is not particularly limited, but the non-aqueous electrolyte solution contains the compound represented by formula (I) in an amount of preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, and particularly preferably 4% by mass or less. The compound represented by formula (II) may be used alone or in any combination and ratio of two or more. As described above, when the compound represented by formula (I) and the compound represented by formula (II) are used in combination, the total amount of the compound represented by formula (I) and the compound represented by formula (II), i.e., the total amount of the sulfonate salt (A) having a carbon-carbon unsaturated bond, should be set within the above range.

[0036] [1-2. Phosphates with Fluorine Atoms and Sulfonates with SF Bonds] [1-2-1. Phosphates with PF bonds (phosphates with fluorine atoms)] Specific examples of the phosphate salt having a P-F bond according to the present invention include lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, rubidium monofluorophosphate, cesium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, potassium difluorophosphate, rubidium difluorophosphate, cesium difluorophosphate, lithium monofluoromonomethylphosphate, sodium monofluoromonomethylphosphate, potassium monofluoromonomethylphosphate, rubidium monofluoromonomethylphosphate, and cesium monofluoromonomethylphosphate. Of these, lithium monofluorophosphate and lithium difluorophosphate are particularly preferred in terms of electrolyte stability. The content of the phosphate having a PF bond in the non-aqueous electrolyte is not particularly limited, but the non-aqueous electrolyte contains preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.1 mass% or more of the phosphate having a PF bond, and preferably 10 mass% or less, more preferably 8 mass% or less, and even more preferably 6 mass% or less. The identification and content of the phosphate having a PF bond are measured by nuclear magnetic resonance (NMR) spectroscopy.

[0037] [1-2-2. Sulfonates with SF bonds (sulfonates with fluorine atoms)] Specific examples of sulfonates having an SF bond of the present invention include lithium fluorosulfonate, sodium fluorosulfonate, potassium fluorosulfonate, rubidium fluorosulfonate, cesium fluorosulfonate, and lithium bisfluorosulfonylimide. Of these, lithium fluorosulfonate and lithium bisfluorosulfonylimide are particularly preferred in terms of electrolyte stability. The content of the sulfonate having an SF bond in the non-aqueous electrolyte solution is not particularly limited, but the non-aqueous electrolyte solution preferably contains 0.01 mass % or more, more preferably 0.05 mass % or more, and even more preferably 0.1 mass % or more of the sulfonate having an SF bond, and preferably contains 10 mass % or less, more preferably 8 mass % or less, and even more preferably 6 mass % or less.

[0038] That is, the content of the fluorine-containing phosphate or sulfonate (B) in the nonaqueous electrolyte solution is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. When the nonaqueous electrolyte solution contains two or more types of phosphates having a PF bond and sulfonates having an SF bond, the total amount of the phosphates having a PF bond and sulfonates having an SF bond, i.e., the total amount of salt (B), may be within the above-mentioned range.

[0039] [1-2. Electrolytes] <Lithium salt> 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:

[0040] Examples thereof 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.

[0041] Among these, the following are more preferred, as they have the effect of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, etc.: lithium fluoroborate salts such as LiBF; lithium fluorophosphate salts such as LiPF; lithium sulfonate salts such as CHSOLi; lithium imide salts such as LiN(FSO)(CFSO), LiN(CFSO), LiN(CFS0), lithium cyclic 1,2-perfluoroethanedisulfonylimide, and lithium cyclic 1,3-perfluoropropanedisulfonylimide; lithium methide salts such as LiC(FSO), LiC(CFSO), and LiC(CFS0); and lithium oxalate salts such as lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate. More preferred are LiPF6 and lithium bis(oxalato)borate, and particularly preferred is LiPF6. The above electrolytes may be used alone or in combination of two or more. However, when a lithium salt corresponding to "1-1. Compound (A) (sulfonate salt having a carbon-carbon unsaturated bond) represented by formula (I) or formula (II)" or "1-2. Phosphate salt having a fluorine atom and sulfonate salt having an S-F bond" is contained in a non-aqueous electrolyte solution, an electrolyte other than the lithium salt corresponding to "1-1. Compound (A) (sulfonate salt having a carbon-carbon unsaturated bond) represented by formula (I) or formula (II)" or "1-2. Phosphate salt having a fluorine atom and sulfonate salt having an S-F bond" must be contained. The combination of two or more electrolytes is not particularly limited, but examples thereof include a combination of LiPF6 and LiBF4, and a combination of LiPF6 and LiN(CF3SO2)2. Of these, the combination of LiPF6 and LiBF4 is preferred.

[0042] The total concentration of the electrolyte 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. If the total concentration of the electrolyte is within the above range, the electrical conductivity becomes appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[0043] [1-3. Non-aqueous solvents] Like common non-aqueous electrolytes, non-aqueous electrolytes usually contain a non-aqueous solvent as its main component, which dissolves the electrolyte. The non-aqueous solvent used is not particularly limited as long as it dissolves the electrolyte, and known organic solvents can be used. Examples of organic solvents include saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, cyclic carboxylic acid esters, ether-based compounds, and sulfone-based compounds, but are not particularly limited thereto. The organic solvents can 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 a saturated cyclic carbonate and a chain carboxylic acid ester, a cyclic carboxylic acid ester and a chain carbonate, and a saturated cyclic carbonate, a chain carbonate and a chain carboxylic acid ester. Among these, a saturated cyclic carbonate and a chain carbonate, and a saturated cyclic carbonate, a chain carbonate and a chain carboxylic acid ester are preferred.

[0044] [1-3-1. 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.

[0045] Specific examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate or propylene carbonate is 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.

[0046] 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.

[0047] [1-3-2. Chain carbonate] As the chain carbonate, one having 3 to 7 carbon atoms is usually 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.

[0048] 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.

[0049] 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 the fluorinated chain carbonate 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.

[0050] The chain carbonate may be used alone or in any combination of two or more kinds in any ratio.

[0051] 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.

[0052] Furthermore, by combining a specific chain carbonate with ethylene carbonate in a specific content, the battery performance can be significantly improved.

[0053] 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.

[0054] [1-3-3. Chain carboxylic acid esters] Examples of the chain carboxylic acid ester 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 for improving battery properties. Chain carboxylic acid esters in which some of the hydrogen atoms in the above-mentioned compounds have been substituted with fluorine atoms (for example, methyl trifluoroacetate, ethyl trifluoroacetate, etc.) can also be suitably used. 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.

[0055] [1-3-4. 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. The amount of the cyclic 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 cyclic carboxylic acid ester is typically 70% by volume or less, preferably 50% by volume or less, and more preferably 40% by volume or less, based on the total amount of the nonaqueous solvent. By setting the upper limit in this way, 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.

[0056] [1-3-5. 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 ether having 3 to 10 carbon atoms, dimethoxymethane, diethoxymethane, or ethoxymethoxymethane is preferred because it has a high solvation ability for lithium ions, improves ion dissociation, has low viscosity, and provides high ionic conductivity, and as the cyclic ether having 3 to 6 carbon atoms, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, or the like is preferred because it provides high ionic conductivity.

[0057] The content of the ether-based compound is not particularly limited and may be any amount 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 the non-aqueous solvent. When the content of the ether-based compound is within the above-mentioned preferred range, it is easy to ensure the effects of improving the degree of lithium ion dissociation of the ether and improving ionic conductivity due to reduced viscosity. Furthermore, when the negative electrode active material is a carbon-based material, the phenomenon of co-insertion of the chain ether with the lithium ion can be suppressed, thereby allowing the input / output characteristics and charge / discharge rate characteristics to be within appropriate ranges.

[0058] [1-3-6. 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 number of carbon atoms is usually 3 to 6, preferably 3 to 5. In the case of a chain sulfone, the carbon number is usually 2 to 6, and preferably 2 to 5. The number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Examples of the chain sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, pentafluoroethyl methyl sulfone, etc. Among these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in terms of improving the high-temperature storage stability of the electrolyte solution.

[0063] 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.

[0064] [1-4. 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.

[0065] Examples of auxiliary agents that may be contained in the non-aqueous electrolyte solution include cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, 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, etc. Examples include compounds described in International Publication No. 2015 / 111676. 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. Cyclic compounds having an ether bond can be used as auxiliary agents in non-aqueous electrolytes, and some can also be used as non-aqueous solvents as described in 1-3. When used as auxiliary agents, cyclic compounds having an ether bond are used in an amount of less than 4% by mass. Borates and oxalates can be used as auxiliary agents in non-aqueous electrolytes, and some can also be used as electrolytes as described in 1-2. When used as auxiliary agents, these compounds are used in an amount of less than 3% by mass.

[0066] [2. Non-aqueous electrolyte secondary battery] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention is a nonaqueous electrolyte secondary 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 containing a nonaqueous electrolyte.

[0067] [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.

[0068] [2-2. Negative electrode] The negative electrode is composed of a negative electrode active material layer containing a negative electrode active material and a binder, and 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 can electrochemically absorb and release 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, carbon-based materials are preferred because they have good cycle characteristics and safety, as well as excellent continuous charge characteristics. These materials may be used alone or in any combination of two or more.

[0069] [2-2-1-1. 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, flake 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.

[0070] [2-2-1-2. 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 of them. (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. Also, the crystallite size (Lc) of carbon-based materials determined by X-ray diffraction using the Gakushin method is usually 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 Raman R values ​​of carbon-based materials are measured using argon ion laser Raman spectroscopy. It is a value calculated by dividing the number of times ... 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 More than 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 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 having different Raman R values ​​are contained, and a case where two or more carbon-based materials having different X-ray parameters are contained.

[0071] [2-2-1-3. 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, but from the viewpoint of capacity and cycle life, it is preferable to use, for example, a simple substance or a compound of a metal and / or a metalloid element selected from the group consisting of Sb, Si, Sn, Al, As, and Zn. Furthermore, when the material containing a metal element and / or a metalloid element that can be alloyed with Li contains two or more elements, the material may be an alloy material made of an alloy of these metals. Examples of materials containing metal elements and / or metalloid elements that can be alloyed with Li include oxides, nitrides, carbides, etc. These may contain two or more metal elements and / or metalloid elements that can be alloyed with Li. Among these, metal Si (hereinafter sometimes referred to as Si) or Si-containing inorganic compounds are preferred in terms of achieving high capacity. Furthermore, the material of the metal element and / or metalloid element that can be alloyed with Li may already be alloyed with Li during the production of the negative electrode, which will be described later.

[0072] In this specification, Si or Si-containing inorganic compounds are collectively referred to as Si compounds. Specific examples of Si compounds include SiO x(0≦x≦2), etc. can be mentioned. As the metal compound alloyed with Li, specifically, Li y Si (0 < y ≦ 4.4), Li2SiO 2+z (0 < z ≦ 2), etc. can be mentioned. As the Si compound, Si oxide (SiO x1 , 0 < x1 ≦ 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, and a high capacity can be obtained. When the material containing a metal element and / or a semi-metal element that can be alloyed with Li is in the form of particles, its average particle diameter (d50) is usually 0.01 μm or more and 10 μm or less from the viewpoint of cycle life.

[0073] [2-2-1-4. Mixture of a material containing a metal element and / or a semi-metal element that can be alloyed with Li and a carbon-based material] The mixture of a material containing a metal element and / or a semi-metal element that can be alloyed with Li and a carbon-based material used as the negative electrode active material may be a mixture in which the material containing a metal element and / or a semi-metal element that can be alloyed with Li and the carbon-based material described above are mixed in a state of independent materials, or a composite in which the material containing a metal element and / or a semi-metal element that can be alloyed with Li exists on the surface or inside of the carbon-based material. The content ratio of the material containing a metal element and / or a semi-metal element that can be alloyed with Li to the total of the material containing a metal element and / or a semi-metal element that can be alloyed with Li and the carbon-based material is usually 1 mass% or more and 99 mass% or less.

[0074] [2-2-1-5. Lithium-containing metal composite oxide material] 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.

[0075] 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.

[0076] [2-2-1-6. Surface coating] The negative electrode active material may have a substance (surface-attached substance) attached to its surface, the substance having a different composition from the negative electrode active material. 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 negative electrode active material, for example, by dissolving or suspending them in a solvent, adding them to the negative electrode active material by impregnation, and then drying. 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, the term "negative electrode active material" also refers to a negative electrode active material having the surface-adhering substance attached to its surface.

[0077] [2-2-2. Negative electrode structure and manufacturing method] The negative electrode can 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 can be produced by adding a binder, a solvent such as an aqueous solvent or an organic solvent, and optionally a thickener, a conductive material, a filler, etc. 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. In this case, in order to increase the packing density of the negative electrode active material, it is preferable to compact it using a hand press, a roller press, etc.

[0078] [2-2-2-1. Active material content] The content of the negative electrode active material in the negative electrode active material layer is usually 80% by mass or more and 99.5% by mass or less.

[0079] [2-2-2-2. 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. 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.

[0080] [2-2-2-3. 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 rubbery polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; and fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and tetrafluoroethylene-ethylene copolymer. 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 the binder contains a rubber-like polymer such as SBR as a main component, the ratio of the binder to the negative electrode active material is preferably 0.1% by mass to 5% by mass, and when the binder contains a fluorine-based polymer such as polyvinylidene fluoride as a main component, the ratio of the binder to the negative electrode active material is preferably 1% by mass to 15% by mass.

[0081] [2-2-2-4. Solvent] The solvent for forming the slurry is not particularly limited as long as it is capable of dissolving or dispersing the negative electrode active material, the binder, and the thickener, conductive material, filler, and the like that are used as needed, and either an aqueous solvent or an organic solvent may be used.

[0082] [2-2-2-5. 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 foil or 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.

[0083] [2-2-2-6. Thickness and density of negative electrode active material layer] The thickness of the negative electrode active material layer is the thickness of the entire negative electrode minus the thickness of the current collector. Although there are no particular limitations, from the viewpoint of high capacity and high output, it is usually 15 μm or more and 300 μm or less. The density of the negative electrode active material layer is usually 0.8 g cm -3 More than 1.7g cm -3 The following is the result. The density of the negative electrode active material layer is measured by measuring the thickness and weight of the negative electrode active material layer.

[0084] [2-2-2-7. Surface coating of negative electrode plate] The negative electrode plate may have a surface to which a substance (surface-attached substance) having a different composition from the negative electrode active material is attached. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[0085] [2-3. Positive electrode] The positive electrode is composed of a positive electrode active material layer containing a positive electrode active material and a binder, and a current collector. [2-3-1. Positive electrode active material] The positive electrode active material used in the positive electrode is not particularly limited as long as it can electrochemically absorb and release metal ions. Specific examples include lithium transition metal compounds. These may be used alone or in any combination of two or more.

[0086] [2-3-1-1. Lithium transition metal compounds] Lithium transition metal compounds include sulfides, phosphate compounds, silicate compounds, and borate compounds. Among these, phosphate compounds and lithium transition metal composite oxides are preferred, and lithium transition metal composite oxides are more preferred. 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 represented by the following composition formula (1): Li x’ M'2O4···(1) (In formula (1), x' is 1≦x'≦1.5, and M' represents at least one transition metal element.) Specifically, LiMn2O4, LiCoMnO4, LiNi 0.5 Mn 1.5 Examples include O4 and LiCoVO4. Those having a layered structure are generally represented by the following composition formula (2). Li 1+x MO2···(2) (In formula (2), x is −0.1≦x≦0.5, and M represents at least one transition metal element.) 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 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0087] Among these, from the viewpoint of improving the battery capacity, a lithium transition metal composite oxide having a layered structure is preferred, and a transition metal composite oxide represented by the following composition formula (3) is more preferred. Li a1 Ni b1 M c1 O2···(3) (In formula (3), a1, b1, and c1 are numerical values ​​that satisfy 0.90≦a1≦1.10, 0.30≦b1≦0.98, and 0.01≦c1≦0.5, respectively, and satisfy 0.50≦b1+c1 and b1+c1=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.) In the composition formula (3), it is preferable that the value d1 satisfies 0.01≦d1≦0.50.

[0088] In particular, from the viewpoint of the structural stability of the lithium transition metal composite oxide, a transition metal oxide represented by the following composition formula (4) is preferred. Li a2 Ni b2 Co c2 M d2 O2···(4) (In formula (4), a2, b2, and c2 are numerical values ​​that satisfy 0.90≦a2≦1.10, 0.50≦b2≦0.98, and 0.01≦c2<0.50, respectively, and b2+c2=1 is satisfied. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.) A preferred example of the lithium transition metal oxide represented by the composition formula (4) is LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2. In each composition formula, M preferably contains Mn or Al, more preferably contains Mn, and further preferably is Mn or Al, because this increases the structural stability of the lithium transition metal oxide and suppresses structural deterioration during repeated charge and discharge.

[0089] [2-3-1-2. Introduction of different elements] Furthermore, elements (foreign elements) other than the elements contained in the above composition formula may be incorporated into the lithium transition metal composite oxide.

[0090] [2-3-1-3. Surface coating] The positive electrode active material may have a substance (surface-attached substance) attached to its surface, the substance having a different composition from the positive electrode active material. 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 surface-adhering substance attached to its surface is also referred to as a "positive electrode active material." [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, a positive electrode using a positive electrode active material can be manufactured by a conventional method. That is, a positive electrode can be obtained by a coating method in which a positive electrode active material, a binder, and, if necessary, a conductive material and a thickener are mixed in a dry state to form a sheet and then pressed onto a positive electrode current collector, or by dissolving or dispersing these materials in a solvent such as an aqueous solvent or an organic solvent to form a slurry, which is then applied to a positive electrode current collector and dried to form a positive electrode active material layer on the current collector. Furthermore, 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. In this case, in order to increase the packing density of the positive electrode active material, it is preferable to compact it using a hand press, roller press, or the like. 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.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 conductive materials 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% by mass to 50% by mass.

[0094] [2-3-2-3. 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 solvent for the slurry. However, in view of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like, preferred binders include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide. 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 may be any value as long as it does not significantly impair the effects of the present invention, but is usually between 10,000 and 3,000,000. When the thickness is within 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.

[0095] [2-3-2-4. 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.

[0096] [2-3-2-5. 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 foil or a metal thin film is preferred. The metal foil or the metal thin film may be formed into a mesh shape as appropriate. 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.

[0097] [2-3-2-6. Thickness and density of the positive electrode active material layer] The thickness of the positive electrode active material layer is the thickness obtained by subtracting the thickness of the current collector from the thickness of the entire positive electrode. Although there are no particular limitations, from the viewpoint of high capacity and high output, it is usually 10 μm or more and 500 μm or less on one side of the current collector. In addition, 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. The density of the positive electrode active material layer is measured by measuring the thickness and weight of the positive electrode active material layer.

[0098] [2-3-2-7. 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.

[0099] [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.

[0100] [2-4-1. Materials] The separator material is not particularly limited as long as it is stable against the non-aqueous electrolyte solution, but preferred examples include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates such as barium sulfate and calcium sulfate, inorganic materials such as glass filters made of glass fiber, and resins such as polyolefins, more preferably polyolefins, and particularly preferably polyethylene or polypropylene. These materials may be used alone or in any combination and ratio of two or more. The above materials may also be used in a laminated state.

[0101] [2-4-2.Form] The form is not particularly limited, but preferably, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. A thin film with a pore size of 0.01 to 1 μm and a thickness of 1 to 50 μm is preferably used. In addition to an independent thin film, a separator may be used in which a composite porous layer containing inorganic particles is formed on the surface of the positive electrode and / or negative electrode using a resin binder. The separator is preferably a microporous film or a nonwoven fabric because of its excellent liquid retention.

[0102] [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.

[0103] [2-4-4. Air permeability] The air permeability of a separator in a nonaqueous electrolyte secondary battery can be determined 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 can be any value, but is usually 10 to 1000 seconds / 100 mL.

[0104] [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% to 90%.

[0105] [2-5-2. Current collection structure] When the electrode group has the aforementioned laminated structure, a structure in which the metal core portions of each electrode layer are bundled and welded to a terminal is preferably used. A structure in which multiple terminals are provided within the electrode to reduce resistance is also preferably used. 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 electrode and negative electrode and bundling them to a terminal.

[0106] [2-5-3.Protection elements] The protective element may be a PTC (Positive Temperature Coefficient) element whose resistance increases with heat generation due to 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.

[0107] [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, metals such as aluminum or aluminum alloys, and laminate films are 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.

[0108] [2-5-5. Shape] The shape of the exterior case is also arbitrary, and may be, for example, cylindrical, rectangular, laminated, coin-shaped, large, or the like. [Example]

[0109] Next, specific embodiments of the present invention will be described in more detail with reference to examples. Therefore, it is not limited to this. The compounds used in the present examples and comparative examples are shown below.

[0110] [ka]

[0111] [Examples 1-1 to 1-2, 2-1 to 2-2, Comparative Examples 1-1 to 1-6, 2-1 to 2-6] [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> In a dry argon atmosphere, a nonaqueous electrolyte solution was prepared by dissolving thoroughly dried LiPF6 at 1.0 mol / L (12.3 mass%, as the concentration in the nonaqueous electrolyte solution) in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:4:3). Additives 1 and 2 were dissolved in the nonaqueous electrolyte solution as shown in Tables 1 and 2 to prepare the nonaqueous electrolyte solutions of Examples 1-1 to 1-2, 2-1 to 2-2, and Comparative Examples 1-2 to 1-6, and 2-2 to 2-6. The nonaqueous electrolyte solutions of Comparative Examples 1-1 and 2-1 were the standard electrolyte solutions.

[0112] <Preparation of positive electrode> Li as the positive electrode active material 1.05 Ni 0.34 Mn 0.33 Co 0.33 85 parts by mass of O2, 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.

[0113] <Preparation of negative electrode> 49 parts by weight of graphite powder was mixed with 50 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 49% by weight) as a binder, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was uniformly applied to a 10 μm-thick copper foil, dried, and roll-pressed to form a negative electrode.

[0114] <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 remaining capacity and recovered capacity of the obtained non-aqueous electrolyte secondary battery were evaluated as described above. The results are shown in Tables 1 and 2.

[0115] [Evaluation of non-aqueous electrolyte secondary batteries] The non-aqueous electrolyte secondary batteries prepared in the examples were evaluated as follows. -Evaluation of remaining capacity and recovery capacity after storage 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. The nonaqueous electrolyte secondary battery was then stabilized by constant current-constant voltage charging at 0.167 C to 4.1 V and then storing at 60°C for 12 hours. It was then discharged at a constant current to 2.5 V at 25°C, followed by constant current-constant voltage charging at 0.167 C to 4.2 V. It was then discharged at a constant current to 2.5 V at 0.167 C. It was then charged at a constant current-constant voltage to 4.2 V, completing the initial charge-discharge cycle. The nonaqueous electrolyte secondary battery after the initial charge-discharge cycle was left at 60°C for 14 days. After leaving the battery for 14 days, it was discharged at a constant current to 2.5 V at 25°C, and the discharge capacity at this time was recorded as the remaining capacity. It was then charged at a constant current-constant voltage to 4.2 V at 0.2 C. It was then discharged at a constant current to 2.5 V at 0.2 C, and the discharge capacity at this time was recorded as the recovered capacity. The results are shown in Tables 1 and 2. The remaining capacity and recovery capacity in Tables 1 and 2 are values ​​normalized by setting the values ​​of Comparative Example 1-1 and Comparative Example 2-1 to 100. It can be said that the larger the remaining capacity and recovery capacity, the more preferable it is.

[0116] [Table 1]

[0117] From Table 1, when comparing Examples 1-1 and 1-2 with Comparative Examples 1-1 to 1-3 and 1-6, it is clear that the sulfonate having an unsaturated bond and the phosphate having a PF bond are used in anhydrous It can be seen that the co-addition of Compound 2 to a nonaqueous electrolyte solution further improves the remaining capacity and recovered capacity of the nonaqueous electrolyte secondary battery. Furthermore, a comparison of Comparative Example 1-4 with Comparative Example 1-1 reveals that the use of a nonaqueous electrolyte solution containing Compound 2, a sulfonate salt having no unsaturated bonds, results in almost no change in the remaining capacity and recovered capacity of the nonaqueous secondary battery. Furthermore, Comparative Examples 1-3 to 1-5 reveal that the use of a nonaqueous electrolyte solution containing a sulfonate salt having no unsaturated bonds and a phosphate salt having a PF bond results in a lower remaining capacity and recovered capacity of the nonaqueous secondary battery than the use of a nonaqueous electrolyte solution containing only a phosphate salt having a PF bond. This demonstrates that the nonaqueous electrolyte solution of the present invention can specifically improve battery performance by co-adding a sulfonate salt having an unsaturated bond and a phosphate salt having a PF bond.

[0118] [Table 2]

[0119] Comparing Example 2-1 and Example 2-2 with Comparative Examples 2-1 to 2-3 and Comparative Example 2-6 in Table 2, it can be seen that the remaining capacity and recovered capacity of the nonaqueous electrolyte secondary battery are further improved by co-adding a sulfonate having an unsaturated bond and a sulfonate having an S—F bond to the nonaqueous electrolyte. Furthermore, a comparison of Comparative Example 2-4 with Comparative Example 2-1 reveals that the use of a sulfonate salt having no unsaturated bonds results in almost no difference in either the remaining capacity or the recovered capacity. On the other hand, Comparative Examples 2-3 to 2-5 reveal that the use of a nonaqueous electrolyte solution containing Compound 2, which is a sulfonate salt having no unsaturated bonds and a sulfonate salt having an SF bond, only results in the effect of adding the sulfonate salt having an SF bond. Furthermore, when a nonaqueous electrolyte solution containing a sulfonate salt having no unsaturated bonds and a sulfonate salt having an SF bond was used, the remaining capacity of the nonaqueous electrolyte secondary battery was found to be lower than when a nonaqueous electrolyte solution containing only a sulfonate salt having an SF bond was used. These results demonstrate that the nonaqueous electrolyte solution of the present invention can specifically improve battery performance by co-adding a sulfonate having an unsaturated bond and a sulfonate having an S—F bond.

Claims

1. The composition is characterized by comprising a compound (A) represented by formula (I) or formula (II), and one or more salts (B) selected from the group consisting of phosphates having a P—F bond and sulfonates having an S—F bond, The nonaqueous electrolyte solution, wherein the phosphate having a P—F bond is at least one selected from the group consisting of alkali metal monofluorophosphates and alkali metal difluorophosphates. 【Chemistry 1】 (In formula (I), R １ , R ２ and R ３ are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group, and R １ and R ２ may be bonded to each other to form a cyclic structure; n is an integer of 0 to 4; M １ is a monovalent cation. In formula (II), R ４ is a hydrogen atom, a halogen atom, or a hydrocarbon group; n is an integer of 0 to 4; M ２ is a monovalent cation.) 2. The non-aqueous electrolyte solution according to claim 1, wherein the phosphate having a P-F bond is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate.

3. The nonaqueous electrolyte solution according to claim 1, wherein the salt (B) selected from the group consisting of a phosphate having a P-F bond and a sulfonate having an S-F bond is a sulfonate having an S-F bond.

4. In the formula (I), R １ , R ２ and R ３ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aralkyl group having 7 to 18 carbon atoms.

5. In the formula (II), R ４ is a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aralkyl group having 7 to 18 carbon atoms.

6. The nonaqueous electrolyte solution according to any one of claims 1 to 5, containing 0.01 mass% or more and 10 mass% or less of the compound (A) represented by formula (I) or formula (II).

7. The nonaqueous electrolyte solution according to any one of claims 1 to 6, comprising 0.01% by mass or more and 10% by mass or less of the salt (B) selected from the group consisting of phosphates having a P-F bond and sulfonates having an S-F bond.

8. A non-aqueous 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 non-aqueous electrolyte solution according to any one of claims 1 to 7.

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