Nonaqueous electrolyte secondary battery

Abstract

To provide a nonaqueous electrolyte secondary battery, which is high in a capacity-keeping rate after high-temperature storage, which is held down in a stored gas amount after high-temperature storage, which is low in resistance after high-temperature storage, lower in metal elution from a positive electrode, and lower in an amount of heat generation at a high temperature.SOLUTION: A nonaqueous electrolyte secondary battery comprises; a positive electrode having a positive electrode active material capable of occluding and releasing metal ions; a negative electrode having a negative electrode active material capable of occluding and releasing metal ions; and a nonaqueous electrolyte solution. In the nonaqueous electrolyte secondary battery, the positive electrode active material contains a lithium transition metal-based compound; the positive electrode active material contains at least Ni, Mn, and Co; a mole ratio of Mn / (Ni+Mn+Co) is greater than 0 and equal to or smaller than 0.32; a mole ratio of Ni / (Ni+Mn+Co) is equal to or larger than 0.55; the positive electrode has electrode plate density equal to or greater than 3.0 g / cm3; and the nonaqueous electrolyte solution contains monofluorophosphate and / or difluorophosphate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. [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 describes that by using a nonaqueous electrolyte secondary battery that uses an electrolyte containing monofluorophosphate, difluorophosphate, or the like, it is possible to obtain a nonaqueous electrolyte secondary battery that has a high capacity, a long life, and a high output even when made into a large battery.

[0004] Patent Document 2 describes that when a non-aqueous electrolyte secondary battery is used as a power source for a hybrid vehicle or an electric vehicle, output characteristics and cycle characteristics are extremely important, and therefore, by reducing the disorder in the crystals of the primary particles of a lithium transition metal compound, the resistance inside the crystals can be reduced, and a positive electrode active material for a non-aqueous electrolyte secondary battery with good cycle characteristics and long life can be stably provided. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2007 / 055087 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-242288 Summary of the Invention [Problem to be solved by the invention]

[0006] However, despite the recent demand for improved performance of nonaqueous electrolyte secondary batteries, the above-mentioned conventional technologies have yet to achieve a high level of performance that combines various performance characteristics of nonaqueous electrolyte secondary batteries. For example, the nonaqueous electrolyte secondary battery of Patent Document 1 requires further improvements in battery capacity and safety, while the nonaqueous electrolyte secondary battery of Patent Document 2 requires improvements in high-temperature life and safety due to its low capacity retention rate after high-temperature storage and high amounts of stored gas and metal elution after high-temperature storage. In particular, large batteries for automobiles are exposed to high temperatures due to heat from the motor, solar heat, and other environmental factors. Therefore, there has been a demand for nonaqueous electrolyte secondary batteries that have excellent high-temperature characteristics (e.g., high capacity retention rate after high-temperature storage and low amount of stored gas after high-temperature storage) and high safety (e.g., low resistance after high-temperature storage, low metal elution from the positive electrode, and low heat generation at high temperatures).

[0007] An object of the present invention is to provide a nonaqueous electrolyte secondary battery that has a high capacity retention rate after high-temperature storage, a small amount of stored gas after high-temperature storage, low resistance after high-temperature storage, little metal elution from the positive electrode, and a small amount of heat generation at high temperatures. [Means for solving the problem]

[0008] As a result of extensive research to solve the above problems, the present inventors have found that by using a specific positive electrode and a nonaqueous electrolyte containing a specific compound to form a nonaqueous electrolyte secondary battery, it is possible to obtain a nonaqueous electrolyte secondary battery that has a high capacity retention rate after high-temperature storage, a small amount of storage gas after high-temperature storage, low resistance after high-temperature storage, little metal elution from the positive electrode, and a small amount of heat generation at high temperatures. This discovery led to the present invention.

[0009] That is, the gist of the present invention is as follows. [1] 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 a non-aqueous electrolyte, The positive electrode active material includes a lithium transition metal compound, the positive electrode active material includes at least Ni, Mn, and Co, the Mn / (Ni+Mn+Co) molar ratio is greater than 0 and not greater than 0.32, the Ni / (Ni+Mn+Co) molar ratio is 0.45 or greater, and the positive electrode plate density is 3.0 g / cm 3 The nonaqueous electrolyte secondary battery as described above, wherein the nonaqueous electrolyte contains a monofluorophosphate and / or a difluorophosphate. [2] The nonaqueous electrolyte secondary battery according to [1], wherein the positive electrode active material contains a lithium transition metal compound represented by the following formula (I): Li 1+x MO2···(I) (In the above formula (I), x is equal to or greater than −0.05 and equal to or less than 0.06, and M is composed of at least Ni, Mn, and Co.) [3] The nonaqueous electrolyte secondary battery according to [2], wherein x is 0.028 or less. [4] The nonaqueous electrolyte secondary battery according to any one of [1] to [3], wherein the Mn / (Ni+Mn+Co) molar ratio is 0.28 or less. [5] The nonaqueous electrolyte secondary battery according to any one of [1] to [4], wherein the Ni / (Ni+Mn+Co) molar ratio is 0.55 or more. [6] The positive electrode has a plate density of 3.2 g / cm 3 The nonaqueous electrolyte secondary battery according to any one of [1] to [5] above. [7] The nonaqueous electrolyte secondary battery according to any one of [1] to [6], wherein the positive electrode active material further contains a sulfate. [8] The nonaqueous electrolyte secondary battery according to [7], wherein the amount of the sulfate contained in the positive electrode active material is 15 μmol / g or more. [9] The nonaqueous electrolyte secondary battery according to any one of [1] to [8], wherein the lithium transition metal compound has an average Ni valence of 2.1 or more in an uncharged state.

[10] The nonaqueous electrolyte secondary battery according to any one of [1] to [9], wherein the aqueous solution of the lithium transition metal compound has a pH of 11 or more at a liquid temperature of 25°C.

[11] The nonaqueous electrolyte secondary battery according to any one of [1] to

[10] , wherein the positive electrode active material contains 10 μmol / g or more of carbonate.

[12] The tap density of the lithium transition metal compound is 1.8 g / cm 3 The non-aqueous electrolyte secondary battery according to any one of [1] to

[11] above. [Effects of the Invention]

[0010] According to the present invention, a nonaqueous electrolyte secondary battery can be obtained which has a high capacity retention rate after high-temperature storage, a small amount of stored gas after high-temperature storage, a low resistance after high-temperature storage, little metal elution from the positive electrode, and a small amount of heat generation at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] An embodiment of the present invention relates to a non-aqueous electrolyte secondary battery, which includes 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 a non-aqueous electrolyte. Each component will be described below.

[0013] [1. Non-aqueous electrolyte] The nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery of the present invention contains an electrolyte and a nonaqueous solvent that dissolves the electrolyte, similar to general nonaqueous electrolytes, and is mainly characterized by containing a monofluorophosphate and / or a difluorophosphate.

[0014] [1-1. Monofluorophosphate, difluorophosphate] The monofluorophosphate and difluorophosphate are not particularly limited as long as they are salts having at least one monofluorophosphate or difluorophosphate structure in the molecule. The use of an electrolyte containing one or more selected from monofluorophosphates and difluorophosphates can improve the durability of nonaqueous electrolyte secondary batteries. Furthermore, by applying the electrolyte to a nonaqueous secondary battery having a specific positive electrode, described below, a nonaqueous electrolyte secondary battery can be obtained that has a high capacity retention rate after high-temperature storage, a small amount of storage gas after high-temperature storage, low resistance after high-temperature storage, little metal elution from the positive electrode, and a small amount of heat generation at high temperatures.

[0015] The counter cation in the monofluorophosphate and difluorophosphate is not particularly limited, and may be lithium, sodium, potassium, magnesium, calcium, NR 121 R 122 R 123 R 124 (In the formula, R 121 ~R 124 are independently a hydrogen atom or an organic group having 1 to 12 carbon atoms. 121 ~R 124 The organic group having 1 to 12 carbon atoms represented by is not particularly limited, and examples thereof include an alkyl group which may be substituted with a fluorine atom, a cycloalkyl group which may be substituted with a halogen atom or an alkyl group, an aryl group which may be substituted with a halogen atom or an alkyl group, and a nitrogen atom-containing heterocyclic group which may have a substituent. 121 ~R 124 are each preferably a hydrogen atom, an alkyl group, a cycloalkyl group, or a nitrogen atom-containing heterocyclic group, etc. As the counter cation, lithium, sodium, and potassium are preferred, and lithium is particularly preferred.

[0016] Examples of monofluorophosphates and difluorophosphates include lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate, with lithium monofluorophosphate and lithium difluorophosphate being preferred, and lithium difluorophosphate being more preferred.

[0017] The total content of the monofluorophosphate and difluorophosphate, as a concentration in the nonaqueous electrolyte, is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, and most preferably 0.5% by mass or more. Also, it is preferably 8% by mass or less, more preferably 4% by mass or less, particularly preferably 2% by mass or less, and most preferably 1.5% by mass or less. When the total content of the monofluorophosphate and difluorophosphate is within this range, a nonaqueous electrolyte secondary battery has a large capacity after high-temperature storage and is suppressed in terms of battery swelling and metal elution, resulting in excellent high-temperature life and safety, and avoiding an increase in the manufacturing cost of the nonaqueous electrolyte secondary battery. The monofluorophosphates and difluorophosphates may be used alone or in any combination of two or more in any ratio. In the present invention, the monofluorophosphates and difluorophosphates include those produced in the electrolyte and the battery.

[0018] [1-2. Electrolytes] There is no limitation on the electrolyte used in the non-aqueous electrolyte solution, and any known electrolyte that can be used as an electrolyte in a non-aqueous electrolyte secondary battery can be used. When a non-aqueous electrolyte solution is used in a lithium secondary battery, a lithium salt is usually used as the electrolyte.

[0019] Specific examples of electrolytes include: inorganic lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2; Fluorine-containing organic lithium salts such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,3-hexafluoropropanedisulfonylimide, lithium cyclic 1,2-tetrafluoroethanedisulfonylimide, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2; dicarboxylic acid-containing complex lithium salts such as lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate; etc.

[0020] Among these, from the viewpoints of solubility and degree of dissociation in non-aqueous solvents, electrical conductivity, and the resulting battery characteristics, LiPF6, LiBF4, LiSO3F, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate are preferred, with LiPF6 and LiBF4 being particularly preferred. In the present invention, LiBF4, LiSO3F, lithium difluorooxalatoborate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate include those produced in the electrolyte and the battery.

[0021] The electrolyte may be used alone or in any combination and ratio of two or more. Combining two specific inorganic lithium salts or combining an inorganic lithium salt with a fluorine-containing organic lithium salt is particularly preferred, as it suppresses gas generation during trickle charging and deterioration after high-temperature storage. Combining LiPF6 with LiBF4, or combining an inorganic lithium salt such as LiPF6 or LiBF4 with a fluorine-containing organic lithium salt such as LiCF3SO3, LiN(CF3SO2)2, or LiN(C2F5SO2)2, is particularly preferred.

[0022] Furthermore, when LiPF6 and LiBF4 are used in combination, it is preferable that LiBF4 be contained in a ratio of 0.01 mass% or more and 50 mass% or less relative to the total electrolyte. The above ratio is more preferably 0.05 mass% or more, and particularly preferably 0.1 mass% or more. On the other hand, the upper limit is more preferably 20 mass% or less, even more preferably 10 mass% or less, particularly preferably 5 mass% or less, and most preferably 3 mass% or less. By having the ratio in the above range, it becomes easier to achieve the desired effect, and the low dissociation degree of LiBF4 prevents the resistance of the electrolyte from increasing.

[0023] On the other hand, inorganic lithium salts such as LiPF6 and LiBF4, inorganic lithium salts such as LiSO3F and LiN(FSO2)2, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,3-hexafluoropropanedisulfonylimide, lithium cyclic 1,2-tetrafluoroethanedisulfonylimide, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2 When inorganic lithium salts are used in combination with fluorine-containing organic lithium salts such as LiBF(CF), LiBF(C), LiBF(CF), LiBF(CFSO), and LiBF(C)FSO), or dicarboxylic acid-containing complex lithium salts such as lithium bis(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorooxalatoborate, lithium tri(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate, the proportion of inorganic lithium salts in the entire electrolyte is usually 70% by mass or more, preferably 80% by mass or more, and more preferably 85% by mass or more. Also, it is usually 99% by mass or less, and preferably 95% by mass or less.

[0024] The concentration of the electrolyte in the nonaqueous electrolyte solution may be any concentration as long as it does not impair the effects of the present invention, but is usually 0.5 mol / L or more, preferably 0.6 mol / L or more, and more preferably 0.8 mol / L or more. It is also usually 3 mol / L or less, preferably 2 mol / L or less, more preferably 1.8 mol / L or less, and even more preferably 1.6 mol / L or less. By having the electrolyte concentration within the above range, the electrical conductivity of the nonaqueous electrolyte solution becomes sufficient, and a decrease in electrical conductivity due to an increase in viscosity, i.e., a decrease in the performance of the nonaqueous electrolyte secondary battery, is suppressed.

[0025] [1-3. Nonaqueous solvents] The non-aqueous solvent contained in the non-aqueous electrolyte solution can be appropriately selected from those known as solvents for non-aqueous electrolyte solutions. Examples of commonly used non-aqueous solvents include cyclic carbonates, chain carbonates, chain and cyclic carboxylic acid esters, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0026] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. The number of carbon atoms in cyclic carbonates is usually 3 or more and 6 or less. Among these, ethylene carbonate and propylene carbonate are preferred because they have a high dielectric constant, which makes it easy for the electrolyte to dissolve therein, and they provide good cycle characteristics when used in a non-aqueous electrolyte secondary battery.

[0027] Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, di-n-propyl carbonate, etc. The number of carbon atoms in the alkyl group constituting the chain carbonate is preferably 1 to 5, and particularly preferably 1 to 4. Among these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred from the viewpoint of improving battery characteristics. Further, examples of the chain carbonate include chain carbonates in which part of the hydrogen atoms of an alkyl group is substituted with fluorine atoms. Examples of the chain carbonate substituted with fluorine atoms include bis(fluoromethyl)carbonate, bis(difluoromethyl)carbonate, bis(trifluoromethyl)carbonate, bis(2-fluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, bis(2,2,2-trifluoroethyl)carbonate, 2-fluoroethylmethylcarbonate, 2,2-difluoroethylmethylcarbonate, and 2,2,2-trifluoroethylmethylcarbonate.

[0028] Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, ethyl pivalate, and the like, as well as chain carboxylic acid esters in which part of the hydrogen atoms in these compounds have been substituted with fluorine. Examples of the carboxylic acid ester include methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate. Among these, 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 are preferred in terms of improving battery characteristics.

[0029] Examples of the cyclic carboxylic acid ester include γ-butyrolactone, γ-valerolactone, and cyclic carboxylic acid esters in which some of the hydrogen atoms in these compounds have been substituted with fluorine atoms. Among these, γ-butyrolactone is more preferable.

[0030] Examples of chain ethers include dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, 1,2-ethoxymethoxyethane, and chain ethers in which some of the hydrogen atoms in these compounds have been substituted with fluorine atoms. Examples of the chain ether substituted with fluorine include bis(trifluoroethoxy)ethane, ethoxytrifluoroethoxyethane, methoxytrifluoroethoxyethane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethyl-pentane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-ethoxy-4-trifluoromethyl-pentane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-propoxy-4-trifluoromethyl-pentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 2,2-difluoroethyl-2,2,3,3-tetrafluoropropyl ether. Among these, 1,2-dimethoxyethane and 1,2-diethoxyethane are more preferred.

[0031] Examples of phosphorus-containing organic solvents include trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphine oxide, triethylphosphine oxide, triphenylphosphine oxide, and phosphorus-containing organic solvents in which some of the hydrogen atoms in these compounds have been substituted with fluorine. Examples of phosphorus-containing organic solvents substituted with fluorine include tris(2,2,2-trifluoroethyl)phosphate and tris(2,2,3,3,3-pentafluoropropyl)phosphate.

[0032] Examples of sulfur-containing organic solvents include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, dibutyl sulfate, and the like, as well as sulfur-containing organic solvents in which part of the hydrogen atoms in these compounds have been substituted with fluorine.

[0033] Examples of the aromatic fluorine-containing solvent include fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and benzotrifluoride.

[0034] Among the above non-aqueous solvents, it is preferable to use cyclic carbonates such as ethylene carbonate and / or propylene carbonate, and it is further preferable to use these in combination with a chain carbonate, since this allows the electrolyte to have both high conductivity and low viscosity.

[0035] The nonaqueous solvent may be used alone, or two or more may be used in any combination and ratio. When two or more types are used in combination, for example, when a cyclic carbonate and a chain carbonate are used in combination, the preferred content of the chain carbonate in the nonaqueous solvent is usually 20% by volume or more, preferably 40% by volume or more, and usually 95% by volume or less, preferably 90% by volume or less. On the other hand, the preferred content of the cyclic carbonate in the nonaqueous solvent is usually 5% by volume or more, preferably 10% by volume or more, and usually 80% by volume or less, preferably 60% by volume or less. By having the proportion of the chain carbonate in the above range, an increase in the viscosity of the nonaqueous electrolyte solution is suppressed, and a decrease in the electrical conductivity of the nonaqueous electrolyte solution due to a decrease in the degree of dissociation of the lithium salt as the electrolyte is suppressed. In this specification, the volume of the nonaqueous solvent is measured at 25°C, but for a solid at 25°C, such as ethylene carbonate, the measured value at the melting point is used.

[0036] [1-4. Other additives] Various additives may be contained within the range that does not significantly impair the effects of the present invention. Any conventionally known additives may be used as the additive. The additives may be used alone or in any combination and ratio of two or more.

[0037] Examples of conventionally known additives that can be added to non-aqueous electrolyte solutions include cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, compounds having an isocyanato group (isocyanate group), 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 a plurality of ether bonds, compounds having an isocyanuric acid skeleton, borates, oxalates, and fluorosulfonates. Each additive will be described below, but some of these may include those already mentioned above.

[0038] [1-4-1. Cyclic carbonates having carbon-carbon unsaturated bonds] The cyclic carbonate having a carbon-carbon unsaturated bond (hereinafter sometimes referred to as "unsaturated cyclic carbonate") is not particularly limited, and any unsaturated carbonate can be used as long as it is a cyclic carbonate having a carbon-carbon double bond or a carbon-carbon triple bond. Note that cyclic carbonates having an aromatic ring are also included in the unsaturated cyclic carbonate.

[0039] Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, and catechol carbonates.

[0040] Among these, particularly preferred unsaturated cyclic carbonates for use in combination include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, vinyl vinylene carbonate, 4,5-vinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, allyl ethylene carbonate, 4,5-diallyl ethylene carbonate, 4-methyl-5-allyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, and 4-vinyl-5-ethynyl ethylene carbonate. Furthermore, vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate are preferred because they form a more stable interface protective film, with vinylene carbonate and vinylethylene carbonate being more preferred, and vinylene carbonate being even more preferred.

[0041] The molecular weight of the unsaturated cyclic carbonate is not particularly limited and may be any as long as it does not significantly impair the effects of the present invention. The molecular weight is preferably 80 or more, more preferably 85 or more, and is preferably 250 or less, more preferably 150 or less. Within this range, the solubility of the unsaturated cyclic carbonate in the nonaqueous electrolyte solution is easily ensured, and the effects of the present invention are easily exhibited.

[0042] The method for producing the unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production. The unsaturated cyclic carbonate may be used alone or in any combination and ratio of two or more. The amount of the unsaturated cyclic carbonate is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention. The amount of the unsaturated cyclic carbonate may be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, based on 100% by mass of the non-aqueous electrolyte solution. The content can be 10% by mass or less, preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less. Within this range, the nonaqueous electrolyte secondary battery is likely to exhibit a sufficient effect of improving cycle characteristics, and also exhibits good high-temperature storage characteristics, little gas generation, and a good discharge capacity retention rate.

[0043] [1-4-2. Fluorine-containing cyclic carbonates] Examples of fluorine-containing cyclic carbonates include fluorinated cyclic carbonates having an alkylene group usually containing 2 to 6 carbon atoms, and derivatives thereof, such as fluorinated ethylene carbonate (hereinafter sometimes referred to as "fluorinated ethylene carbonate") and derivatives thereof. Derivatives of fluorinated ethylene carbonate include fluorinated ethylene carbonate substituted with an alkyl group having 1 to 4 carbon atoms. Among these, fluorinated ethylene carbonate having 1 to 8 fluorine atoms and derivatives thereof are preferred.

[0044] By adding a fluorine-containing cyclic carbonate, the high-temperature storage characteristics and cycle characteristics of a battery using this electrolyte can be improved. Examples of fluorinated ethylene carbonate having 1 to 8 fluorines and derivatives thereof include monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4-(fluoromethyl)-ethylene carbonate, 4-(difluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylene carbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate, 4-(fluoromethyl)-5-fluoroethylene carbonate, 4-fluoro-4,5-dimethylethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, and 4,4-difluoro-5,5-dimethylethylene carbonate.

[0045] Among these, monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate are preferred because they impart high ionic conductivity to the electrolyte and facilitate the formation of a stable interface protective film. The fluorinated cyclic carbonate may be used alone or in any combination and ratio of two or more. The amount of the fluorinated cyclic carbonate (total amount when two or more types are used) is preferably 0.001 mass% or more, more preferably 0.01 mass% or more, even more preferably 0.1 mass% or more, still more preferably 0.5 mass% or more, particularly preferably 1 mass% or more, and most preferably 1.2 mass% or more, based on 100 mass% of the electrolyte solution. The amount of the fluorinated cyclic carbonate used as the non-aqueous solvent is preferably 1% by volume or more, more preferably 5% by volume or more, even more preferably 10% by volume or more, and is preferably 50% by volume or less, more preferably 35% by volume or less, even more preferably 25% by volume or less, based on 100% by volume of the non-aqueous solvent. By using the content as described above, it is possible to obtain sufficient effects of improving high-temperature storage characteristics and cycle characteristics, and also to suppress unnecessary gas generation.

[0046] [1-4-3. Compounds containing an isocyanato group] The non-aqueous electrolyte solution may contain a compound having an isocyanato group (isocyanate group), which may hereinafter be referred to as an "isocyanate compound." The isocyanate compound is not particularly limited as long as it is an organic compound having at least one isocyanate group in the molecule, but the number of isocyanate groups in one molecule is preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and even more preferably 1 or more and 2 or less.

[0047] The isocyanate compound is preferably a linear or branched alkylene group, a cycloalkylene group, a structure in which a cycloalkylene group and an alkylene group are linked together, an aromatic hydrocarbon group, a structure in which an aromatic hydrocarbon group and an alkylene group are linked together, an ether structure (-O-), a structure in which an ether structure (-O-) and an alkylene group are linked together, a carbonyl group (-C(=O)-), a structure in which a carbonyl group and an alkylene group are linked together, a sulfonyl group (-S(=O)-), a structure in which a sulfonyl group and an alkylene group are linked together, The preferred isocyanate compound is a compound having an isocyanate group bonded to a compound having a structure such as a cycloalkylene group, a structure in which a cycloalkylene group and an alkylene group are linked, an aromatic hydrocarbon group, or a structure in which an aromatic hydrocarbon group and an alkylene group are linked, and more preferably a compound having an isocyanate group bonded to a structure in which a cycloalkylene group and an alkylene group are linked. The preferred isocyanate compound is a compound having an isocyanate group bonded to a structure in which a cycloalkylene group and an alkylene group are linked. The molecular weight of the isocyanate compound is not particularly limited. The molecular weight is preferably 80 or more, more preferably 115 or more, even more preferably 170 or more, and 300 or less, more preferably 230 or less. Within this range, the solubility of the isocyanate compound in the non-aqueous electrolyte solution is easily ensured, and the effects of the present invention are easily achieved. The method for producing the isocyanate compound is not particularly limited, and any known method can be selected for production. Commercially available products may also be used.

[0048] The isocyanate compounds include: Examples of compounds having one isocyanate group include alkyl isocyanates such as methyl isocyanate, ethyl isocyanate, propyl isocyanate, isopropyl isocyanate, butyl isocyanate, and tertiary butyl isocyanate, cycloalkyl isocyanates such as cyclohexyl isocyanate, unsaturated isocyanates such as allyl isocyanate and propargyl isocyanate, and aromatic isocyanates such as phenyl isocyanate, trifluoromethylphenyl isocyanate, and p-toluenesulfonyl isocyanate;

[0049] Compounds with two isocyanato groups include monomethylene diisocyanate, dimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, 1,4-diisocyanato-2-butene, toluene diisocyanate, xylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methylisocyanate), and bicyclo[2.2.1]heptane. -2,6-diylbis(methyl isocyanate), isophorone diisocyanate, carbonyl diisocyanate, 1,4-diisocyanatobutane-1,4-dione, trimethylhexamethylene diisocyanate, and other compounds;

[0050] Compounds having three isocyanate groups include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylene diisocyanate, 1,3,5-triisocyanatomethylbenzene, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and trimer compounds derived from compounds having at least two isocyanate groups in the molecule (for example, biuret, isocyanurate, adduct, and difunctional modified polyisocyanates); etc.

[0051] Among these, compounds such as t-butyl isocyanate, cyclohexyl isocyanate, p-toluenesulfonyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), isophorone diisocyanate, and trimethylhexamethylene diisocyanate are preferred from the viewpoint of improving storage properties, and cyclohexyl isocyanate, p-toluenesulfonyl isocyanate, hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), isophorone diisocyanate, and trimethylhexamethylene diisocyanate are preferred. More preferred are 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), isophorone diisocyanate, and trimethylhexamethylene diisocyanate, and even more preferred are cyclohexyl isocyanate, p-toluenesulfonyl isocyanate, hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), and bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate).

[0052] The isocyanate compound may be used alone or as a mixture of two or more kinds in any combination and ratio. The amount of the isocyanate compound (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the electrolytic solution. Within this range, it is easy to control output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc.

[0053] [1-4-4. Sulfur-containing organic compounds] The sulfur-containing organic compound is not particularly limited as long as it is an organic compound having at least one sulfur atom in the molecule, but is preferably an organic compound having an S=O group in the molecule, and examples thereof include chain sulfonate esters, cyclic sulfonate esters, chain sulfate esters, cyclic sulfate esters, chain sulfite esters, and cyclic sulfite esters. However, those corresponding to fluorosulfonates are not sulfur-containing organic compounds described later, but are included in the fluorosulfonates that are electrolytes described later. Among these, chain sulfonate esters, cyclic sulfonate esters, chain sulfate esters, cyclic sulfate esters, chain sulfite esters and cyclic sulfite esters are preferred, and compounds having an S(=O)2 group are more preferred.

[0054] Chain sulfonate esters and cyclic sulfonate esters are more preferred, and cyclic sulfonate esters are more preferred. Specific examples of chain sulfonate esters, cyclic sulfonate esters, chain sulfate esters, cyclic sulfate esters, chain sulfite esters, and cyclic sulfite esters are shown below.

[0055] <Chain sulfonic acid ester> Fluorosulfonic acid esters such as methyl fluorosulfonate and ethyl fluorosulfonate. methanesulfonate esters such as methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl 2-(methanesulfonyloxy)propionate, ethyl 2-(methanesulfonyloxy)propionate, and ethyl methanesulfonyloxyacetate; Alkenylsulfonate esters such as methyl vinylsulfonate, ethyl vinylsulfonate, allyl vinylsulfonate, propargyl vinylsulfonate, methyl allylsulfonate, ethyl allylsulfonate, allyl allylsulfonate, propargyl allylsulfonate, and 1,2-bis(vinylsulfonyloxy)ethane. Alkyl disulfonate esters such as methoxycarbonylmethyl methanedisulfonate, ethoxycarbonylmethyl methanedisulfonate, methoxycarbonylmethyl 1,2-ethanedisulfonate, ethoxycarbonylmethyl 1,2-ethanedisulfonate, methoxycarbonylmethyl 1,3-propanedisulfonate, ethoxycarbonylmethyl 1,3-propanedisulfonate, and 1-methoxycarbonylethyl 1,3-propanedisulfonate.

[0056] <Cyclic sulfonate ester> Sultone compounds such as 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone, 1,4-butane sultone, and 1,5-pentane sultone. Disulfonate compounds such as methylenemethane disulfonate and ethylenemethane disulfonate. Nitrogen-containing compounds such as 1,2,3-oxathiazolidine-2,2-dioxide. Phosphorus-containing compounds such as 1,2,3-oxathiaphoslan-2,2-dioxide.

[0057] <Chain sulfate ester> Dialkyl sulfate compounds such as dimethyl sulfate, ethyl methyl sulfate and diethyl sulfate.

[0058] <Cyclic sulfate ester> Alkylene sulfate compounds such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butylene sulfate, 1,3-butylene sulfate, 1,4-butylene sulfate, 1,2-pentylene sulfate, 1,3-pentylene sulfate, 1,4-pentylene sulfate, and 1,5-pentylene sulfate.

[0059] <Chain sulfite ester> Dialkyl sulfite compounds such as dimethyl sulfite, ethyl methyl sulfite and diethyl sulfite.

[0060] <Cyclic sulfite ester> Alkylene sulfite compounds such as 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butylene sulfite, 1,3-butylene sulfite, 1,4-butylene sulfite, 1,2-pentylene sulfite, 1,3-pentylene sulfite, 1,4-pentylene sulfite, and 1,5-pentylene sulfite.

[0061] Among these, methyl 2-(methanesulfonyloxy)propionate, ethyl 2-(methanesulfonyloxy)propionate, 2-propynyl 2-(methanesulfonyloxy)propionate, 1-methoxycarbonylethyl propanedisulfonate, 1-ethoxycarbonylethyl propanedisulfonate, 1-methoxycarbonylethyl butanedisulfonate, 1-ethoxycarbonylethyl butanedisulfonate, 1,3-propanesultone, 1-propene-1,3-sultone, 1,4-butanesultone, 1,2-ethylene sulfate, 1,2-ethylene In terms of improving the initial efficiency, 1-methoxycarbonylethyl propanedisulfonate, 1-ethoxycarbonylethyl propanedisulfonate, 1-methoxycarbonylethyl butanedisulfonate, 1-ethoxycarbonylethyl butanedisulfonate, 1,3-propanesultone, 1-propene-1,3-sultone, 1,2-ethylene sulfate, and 1,2-ethylene sulfite are more preferred, and 1,3-propanesultone and 1-propene-1,3-sultone are even more preferred.

[0062] The sulfur-containing organic compound may be used alone or as a mixture of two or more kinds in any combination and ratio. The content of the sulfur-containing organic compound (total amount when two or more types are used) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, particularly preferably 0.6% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, particularly preferably 1.5% by mass or less, and most preferably 1.0% by mass or less. When the content is within this range, it is easy to control the output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc. of the battery.

[0063] [1-4-5. Phosphorus-containing organic compounds] The phosphorus-containing organic compound is not particularly limited as long as it is an organic compound having at least one phosphorus atom in the molecule. A battery using a nonaqueous electrolyte solution containing the phosphorus-containing organic compound can improve durability.

[0064] The phosphorus-containing organic compound is preferably a phosphate ester, a phosphonate ester, a phosphinate ester, or a phosphite ester, more preferably a phosphate ester or a phosphonate ester, and even more preferably a phosphonate ester. These esters may have a substituent.

[0065] Specific examples of phosphorus-containing organic compounds include: Diethyl vinyl phosphate, allyl diethyl phosphate, propargyl diethyl phosphate, trivinyl phosphate, triallyl phosphate, tripropargyl phosphate, diallyl ethyl phosphate, dipropargyl ethyl phosphate, 2-acryloyloxyethyl diethyl phosphate, tris(2-acryloyloxyethyl)phosphate, trimethyl phosphonoformate, methyl diethyl phosphonoformate, methyl dipropyl phosphonoformate, methyl dibutyl phosphonoformate, triethyl phosphonoformate, ethyl dimethyl phosphonoformate, ethyl dipropyl phosphonoformate, ethyl dibutyl phosphonoformate, tripropyl phosphonoformate, propyl dimethyl phosphonoformate, propyl Diethyl phosphonoformate, propyl dibutyl phosphonoformate, tributyl Phosphonoformate, butyl dimethylphosphonoformate, butyl diethylphosphonoformate, butyl dipropylphosphonoformate, methyl bis(2,2,2-trifluoroethyl)phosphonoformate, ethyl bis(2,2,2-trifluoroethyl)phosphonoformate, propyl bis(2,2,2-trifluoroethyl)phosphonoformate, butyl bis(2,2,2-trifluoroethyl)phosphonoformate, trimethyl phosphonoacetate, methyl diethylphosphonoacetate, methyl dipropylphosphonoacetate, methyl dibutylphosphonoacetate, triethyl phosphonoacetate, ethyl dimethylphosphonoacetate, ethyl dipropylphosphonoacetate, ethyl dibutylphosphonoacetate, tripropyl phosphonoacetate, propyl dimethylphosphonoacetate, propyl diethylphosphonoacetate, propyl dibutylphosphonoacetate, tributyl Phosphonoacetate, butyl dimethylphosphonoacetate, butyl diethylphosphonoacetate, butyl dipropylphosphonoacetate, methyl bis(2,2,2-trifluoroethyl)phosphonoacetate, ethyl bis(2,2,2-trifluoroethyl)phosphonoacetate, propyl bis(2,2,2-trifluoroethyl)phosphonoacetate, butyl bis(2,2,2-trifluoroethyl)phosphonoacetate, allyl dimethylphosphonoacetate, allyl diethylphosphonoacetate, 2-propynyl dimethylphosphonoacetate, 2-propynyl diethylphosphonoacetate, trimethyl 3-phosphonopropionate, methyl 3-(diethylphosphono)propionate, methyl 3-(dipropylphosphono)propionate, methyl 3-(dibutylphosphono)propionate, triethyl 3-phosphonopropionate, ethyl 3-(dimethylphosphono)propionate, ethyl 3-(dipropylphosphono)propionate, ethyl 3-(dibutylphosphono)propionate, tripropyl 3-phosphonopropionate, propyl 3-(dimethylphosphono)propionate, propyl 3-(diethylphosphono)propionate, propyl 3-(Dibutylphosphono)propionate, Tributyl 3-phosphonopropionate, Butyl 3-(dimethylphosphono)propionate, Butyl 3-(diethylphosphono)propionate, Butyl 3-(dipropylphosphono)propionate, Methyl 3-(bis(2,2,2-trifluoroethyl)phosphono)propionate, Ethyl 3-(bis(2,2,2-trifluoroethyl)phosphono)propionate, Propyl 3-(bis(2,2,2-trifluoroethyl)phosphono)propionate, Butyl 3-(bis(2,2,2-trifluoroethyl)phosphono)propionate, Trimethyl 4-phosphonobutyrate, Methyl 4-(diethylphosphono)butyrate, Methyl 4-(dipropylphosphono)butyrate, Methyl 4-(dibutylphosphono)butyrate, Triethyl 4-phosphonobutyrate, Ethyl Examples include 4-(dimethylphosphono)butyrate, ethyl 4-(dipropylphosphono)butyrate, ethyl 4-(dibutylphosphono)butyrate, tripropyl 4-phosphonobutyrate, propyl 4-(dimethylphosphono)butyrate, propyl 4-(diethylphosphono)butyrate, propyl 4-(dibutylphosphono)butyrate, tributyl 4-phosphonobutyrate, butyl 4-(dimethylphosphono)butyrate, butyl 4-(diethylphosphono)butyrate, and butyl 4-(dipropylphosphono)butyrate.

[0066] The phosphorus-containing organic compound may be used alone or as a mixture of two or more kinds in any combination and ratio. The content of the phosphorus-containing organic compound (total amount when there are two or more kinds) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.4% by mass or more, particularly preferably 0.6% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, particularly preferably 1.2% by mass or less, and most preferably 0.9% by mass or less. Within this range, output characteristics, load characteristics, low temperature It is easy to control characteristics, cycle characteristics, high-temperature storage characteristics, etc.

[0067] [1-4-6. Organic compounds containing a cyano group] Examples of organic compounds having a cyano group include pentanenitrile, octanenitrile, decanenitrile, dodecanenitrile, crotononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, glutaronitrile, and 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, 1,2,3-tricyanopropane, 1,3,5-tricyanopentane, 1,4,7-tricyanoheptane, 1,2,4-tricyanobutane, 1,2,5-tricyanopentane, 1,2,6-tricyanohexane, 1,3,6-tricyanohexane, and 1,2,7-tricyanoheptane.

[0068] The organic compound having a cyano group may be contained in a concentration of 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, relative to 100% by mass of the electrolyte solution, and may be contained in a concentration of 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, particularly preferably 2% by mass or less. Within this range, it is easy to control output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc. The organic compound having a cyano group may be used alone or in any combination and ratio of two or more kinds.

[0069] [1-4-7. Silicon-containing compounds] The silicon-containing compound is not particularly limited as long as it has at least one silicon atom in the molecule. By using an electrolyte containing a silicon-containing compound, the durability of a non-aqueous electrolyte secondary battery can be improved. The silicon-containing compound is preferably a compound represented by formula (2-6). [ka]

[0070] In formula (2-6), R 61 , R 62 and R 63 are independently a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 10 carbon atoms, X 61 is an organic group containing at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, and silicon atoms. R 61 , R 62 and R 63 is preferably a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a sec-butyl group, an i-butyl group, a tert-butyl group, or a phenyl group, and more preferably a methyl group.

[0071] X 61is an organic group containing at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, and silicon atoms, and is preferably an organic group containing at least an oxygen atom or a silicon atom. Here, the organic group refers to a group composed of one or more atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, silicon atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Examples of the organic group include alkyl groups, alkenyl groups, alkynyl groups, aryl groups, alkoxy groups, CN groups, isocyanato groups, fluoro groups, alkylsulfonic acid groups, and trialkylsilyl groups. Note that a portion of the monovalent organic group is substituted with a fluorine atom. The number of carbon atoms in the organic group may be 1 or more, preferably 3 or more, more preferably 5 or more, and may be 15 or less, preferably 12 or less, more preferably 8 or less.

[0072] Of these, alkylsulfonic acid groups, trialkylsilyl groups, boric acid groups, phosphoric acid groups and phosphorous acid groups are preferred. Examples of silicon-containing compounds include: boric acid compounds such as tris(trimethylsilyl) borate, tris(trimethoxysilyl) borate, tris(triethylsilyl) borate, tris(triethoxysilyl) borate, tris(dimethylvinylsilyl) borate, and tris(diethylvinylsilyl) borate; phosphate compounds such as tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(tripropylsilyl) phosphate, tris(triphenylsilyl) phosphate, tris(trimethoxysilyl) phosphate, tris(triethoxysilyl) phosphate, tris(triphenoxysilyl) phosphate, tris(dimethylvinylsilyl) phosphate, and tris(diethylvinylsilyl) phosphate; Phosphite compounds such as tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(tripropylsilyl) phosphite, tris(triphenylsilyl) phosphite, tris(trimethoxysilyl) phosphite, tris(triethoxysilyl) phosphite, tris(triphenoxysilyl) phosphite, tris(dimethylvinylsilyl) phosphite and tris(diethylvinylsilyl) phosphite; Sulfonic acid compounds such as trimethylsilyl methanesulfonate and trimethylsilyl tetrafluoromethanesulfonate; Disilane compounds such as hexamethyldisilane, hexaethyldisilane, 1,1,2,2-tetramethyldisilane, 1,1,2,2-tetraethyldisilane, 1,2-diphenyltetramethyldisilane, and 1,1,2,2-tetraphenyldisilane; etc.

[0073] Of these, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, trimethylsilyl methanesulfonate, trimethylsilyl tetrafluoromethanesulfonate, hexamethyldisilane, hexaethyldisilane, 1,2-diphenyltetramethyldisilane, and 1,1,2,2-tetraphenyldisilane are preferred, and tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and hexamethyldisilane are more preferred.

[0074] These silicon-containing compounds may be used alone or in any combination of two or more in any ratio. The silicon-containing compound (total amount when two or more kinds are used) can be 0.001% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, in 100% by mass of the electrolyte, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less. Within this range, it is easy to control the output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc.

[0075] [1-4-8. Aromatic compounds] The aromatic compound is not particularly limited as long as it is an organic compound having at least one aromatic ring in the molecule.

[0076] Examples of aromatic compounds include the following: Fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, benzotrifluoride, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphen Nyl carbonate, methyl phenyl carbonate, 2-phenylethyl acetate, 3-phenylpropyl acetate, methyl phenylacetate, ethyl phenylacetate, 2-phenylethyl phenylacetate, 3-phenylpropyl phenylacetate, methyl 3-phenylpropionate, ethyl 3-phenylpropionate, 2-phenylethyl 3-phenylpropionate, 3-phenylpropyl 3-phenylpropionate, methyl phenylsulfonate, 2-tert-butylphenylmethylsulfonate, 4-tert-butylphenylmethylsulfonate, cyclohexylphenylmethylsulfonate sulfonate, trimethylphenylsilane, tris(2-tert-butylphenyl)phosphate, tris(4-tert-butylphenyl)phosphate, tris(2-cyclohexylphenyl)phosphate, tris(4-cyclohexylphenyl)phosphate, diethylphenylphosphonate, diethylbenzylphosphonate, diethyl-(4-fluorobenzyl)phosphonate, 2-fluorophenylacetate, 4-fluorophenylacetate, 2,4-difluoroanisole, 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene. Of these, preferred are fluorobenzene, benzotrifluoride, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl carbonate, methylphenyl carbonate, 2-phenylethyl phenylacetate, 4-tert-butylphenyl methylsulfonate, cyclohexylphenyl methylsulfonate, tris(2-tert-butylphenyl)phosphate, tris(4-tert-butylphenyl)phosphate, tris(4-cyclohexylphenyl)phosphate, 2,4-difluoroanisole, and 2-fluorotoluene.

[0077] In addition to the above, 1-phenyl-1,3,3-trimethylindan, 2,3-dihydro-1,3-dimethyl-1-(2-methyl-2-phenylpropyl)-3-phenyl-1H-indan, 1-phenyl-1,3,3-trimethylindan, 2,3-dihydro-1,3-dimethyl-1-(2-methyl-2-phenylpropyl)-3-phenyl-1H-indan, 2,2-diphenylbutane, 3,3-diphenylpentane, 3,3-diphenylhexane, 4,4-diphenylheptane, 5,5-diphenyloctane, 6,6-diphenylnonane, 1,1-diphenyl-1,1-ditert-butyl-methane, 1,1-diphenylcyclohexane, 1,1-diphenylcyclopentane, 1,1-diphenyl-4-methylcyclohexane. 1,3-bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindane, 2,2-diphenylbutane, 3,3-diphenylpentane, 1,1-diphenyl-1,1-ditert-butyl-methane, 1,1-diphenylcyclohexane, 1,1-diphenylcyclopentane, 1,1-diphenyl-4-methylcyclohexane, 1,3-bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindane, 2,2-diphenylbutane, 1,1-diphenylcyclohexane, 1,1-diphenyl-4-methylcyclohexane, 1,3- Examples include bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindane, 1,1-diphenylcyclohexane, 1,1-diphenyl-4-methylcyclohexane, 1,3-bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindane, 1,1-diphenylcyclohexane, 1,3-bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindane, and the like.

[0078] The aromatic compounds may be used alone or in combination of two or more. The amount of aromatic compounds (total amount when two or more types are used) in the total amount (100 mass%) of the non-aqueous electrolyte solution is 0.001 mass% or more. The content may be 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2.5% by mass or less. By doing so, the effects of the present invention are easily exhibited and an increase in the resistance of the battery can be prevented.

[0079] [1-4-9. Fluorine-free carboxylic acid esters] The fluorine-free carboxylic acid ester can also be used as a solvent as described above. The fluorine-free carboxylic acid ester is not particularly limited as long as it is a carboxylic acid ester that does not have a fluorine atom in the molecule.

[0080] Examples of the fluorine-free chain carboxylic acid ester include the following. Methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, n-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, n-butyl butyrate, methyl valerate, ethyl valerate, n-propyl valerate, n-butyl valerate, methyl pivalate, ethyl pivalate, n-propyl pivalate, n-butyl pivalate. Among these, from the viewpoint of improving ionic conductivity by reducing the viscosity of the electrolyte, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, and n-butyl propionate are more preferred, methyl propionate, ethyl propionate, n-propyl propionate, and n-butyl propionate are even more preferred, and ethyl propionate and n-propyl propionate are particularly preferred.

[0081] The non-fluorine-containing carboxylic acid ester may be used alone or in any combination of two or more kinds in any ratio. The amount of the fluorine-free carboxylic acid ester (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 0.6% by mass or more, based on 100% by mass of the electrolyte solution. It can also be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. When the fluorine-free carboxylic acid ester is used as the non-aqueous solvent, the amount of the fluorine-free carboxylic acid ester is preferably 1% by volume or more, more preferably 5% by volume or more, even more preferably 10% by volume or more, even more preferably 20% by volume or more, based on 100% by volume of the non-aqueous solvent. It can also be contained in an amount of 50% by volume or less, more preferably 45% by volume or less, even more preferably 40% by volume or less. Within these ranges, an increase in negative electrode resistance is suppressed, and output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics can be easily controlled.

[0082] [1-4-10. Cyclic compounds with multiple ether bonds] The cyclic compound having multiple ether bonds is not particularly limited as long as it has multiple ether bonds in the molecule. The cyclic compound having multiple ether bonds contributes to improving the high-temperature storage characteristics of the battery, and can improve the durability characteristics of the non-aqueous electrolyte secondary battery.

[0083] Examples of cyclic compounds having a plurality of ether bonds include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and methyltetrahydropyran. The cyclic compound having multiple ether bonds may be used alone or in any combination and ratio of two or more. The amount of the cyclic compound having multiple ether bonds (total amount when two or more types are used) in 100% by mass of the electrolytic solution may be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, and may be 10% by mass or less, preferably 5% by mass or less. % by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. When the above range is satisfied, it is easy to control the output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc.

[0084] [1-4-11. Electrolyte additives] Among the additives, the following can be exemplified as additives that function as electrolytes (borates, oxalates, and fluorosulfonates). Of these salts, lithium salts are particularly preferred. The total content of borate, oxalate, and fluorosulfonate in the non-aqueous electrolyte solution is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, and is preferably 20% by mass or less, particularly preferably 10% by mass or less.

[0085] [1-4-11-1. Borates] The borate is not particularly limited as long as it is a salt having at least one boron atom in the molecule. However, those corresponding to oxalates are not borates but are included in the oxalates described below. In the battery of the present invention, the durability characteristics can be improved.

[0086] Counter cations in borates include lithium, sodium, potassium, magnesium, calcium, rubidium, cesium, and barium, with lithium being preferred. As the borate, a lithium salt is preferred, and a lithium borate salt can also be suitably used. Examples include LiBF4, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2. Among them, LiBF4 is more preferred because it has the effect of improving the initial charge-discharge efficiency and high-temperature cycle characteristics.

[0087] The borate salts may be used alone or in any combination of two or more in any ratio. The amount of borate (total amount when two or more types are used) can be 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 0.4% by mass or more, and can be 10.0% by mass or less, preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less, particularly preferably 1.0% by mass or less. Within this range, side reactions in the battery negative electrode are suppressed, and resistance is less likely to increase.

[0088] [1-4-11-2. Oxalate] The oxalate is not particularly limited as long as it is a compound having at least one oxalic acid structure in the molecule, and can improve the durability of the battery of the present invention. The oxalate is preferably a metal salt represented by formula (9), which has an oxalato complex as the anion. [ka]

[0089] In formula (9), M 1 is an element selected from the group consisting of Groups 1 and 2 of the periodic table and aluminum (Al), and M 2 is an element selected from the group consisting of transition metals, groups 13, 14, and 15 of the periodic table, and R 91is a group selected from the group consisting of halogen, alkyl groups having from 1 to 11 carbon atoms, and halogen-substituted alkyl groups having from 1 to 11 carbon atoms, a and b are positive integers, c is 0 or a positive integer, and d is an integer of 1 to 3. M 1 In terms of battery characteristics when an electrolyte solution containing an oxalate is used in a lithium secondary battery, lithium, sodium, potassium, magnesium, and calcium are preferred, with lithium being particularly preferred.

[0090] M 2 In terms of electrochemical stability when used in a lithium secondary battery, boron and phosphorus are particularly preferred. R 91 Examples of the alkyl group include fluorine, chlorine, a methyl group, a trifluoromethyl group, an ethyl group, a pentafluoroethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, and a tert-butyl group, and fluorine and a trifluoromethyl group are preferred.

[0091] Examples of the metal salt represented by formula (9) include the following. lithium oxalatoborate salts such as lithium difluorooxalatoborate and lithium bis(oxalato)borate; Lithium oxalatophosphate salts such as lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate; Of these, lithium bis(oxalato)borate and lithium difluorobis(oxalato)phosphate are preferred, with lithium bis(oxalato)borate being more preferred.

[0092] The oxalate may be used alone or in any combination of two or more in any ratio. The amount of oxalate (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, particularly preferably 1% by mass or less. Within this range, it is easy to control the output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc. of the secondary battery.

[0093] [1-4-11-3. Fluorosulfonate] The fluorosulfonate salt is not particularly limited as long as it has at least one fluorosulfonic acid structure in the molecule, and can improve the durability of the battery of the present invention.

[0094] The counter cation in the fluorosulfonate salt is not particularly limited, and may be lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, barium, or NR 131 R 132 R 133 R 134 (In the formula, R 131 ~R 134 are each independently a hydrogen atom or an organic group having 1 to 12 carbon atoms. Preferred counter cations are lithium, sodium and potassium, and of these, lithium is preferred.

[0095] Examples of fluorosulfonates include lithium fluorosulfonate, sodium fluorosulfonate, potassium fluorosulfonate, rubidium fluorosulfonate, and cesium fluorosulfonate, with lithium fluorosulfonate being preferred. Imide salts having a fluorosulfonic acid structure, such as lithium bis(fluorosulfonyl)imide, can also be used as fluorosulfonates.

[0096] The fluorosulfonates may be used alone or in any combination of two or more in any ratio. The content of fluorosulfonate (total amount when two or more types are used) can be 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 0.4% by mass or more, and can be 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, particularly preferably 1% by mass or less. Within this range, side reactions in the battery are reduced, and resistance is less likely to increase.

[0097] [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.

[0098] [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.

[0099] [2-2. Negative electrode] The negative electrode active material used in the negative electrode will be described below. There are no particular limitations on the negative electrode active material, as long as it is capable of electrochemically absorbing and releasing metal ions such as lithium ions. Specific examples include carbonaceous materials, alloy materials, and lithium-containing metal composite oxide materials. These may be used alone or in any combination of two or more.

[0100] <Negative electrode active material> Examples of the negative electrode active material include carbonaceous materials, alloy materials, and lithium-containing metal composite oxide materials. Examples of carbonaceous materials include (1) natural graphite, (2) artificial graphite, (3) amorphous carbon, (4) carbon-coated graphite, (5) graphite-coated graphite, and (6) resin-coated graphite.

[0101] (1) Examples of natural graphite include scaly graphite, scaly graphite, soil graphite, and / or graphite particles obtained by treating these graphites as raw materials with processes such as spheroidization and densification. Among these, spherical or ellipsoidal graphite that has been subjected to a spheroidization process is particularly preferred from the viewpoints of particle packing properties and charge / discharge rate characteristics.

[0102] (2) Examples of artificial graphite include those produced by graphitizing organic compounds such as coal tar pitch, coal-based heavy oil, atmospheric residual oil, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene silicide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin at temperatures typically above 2500°C and typically below 3200°C, followed by pulverization and / or classification as necessary. Silicon-containing compounds and boron-containing compounds can also be used as graphitization catalysts. Other examples include artificial graphite obtained by graphitizing mesocarbon microbeads separated during the heat treatment of pitch. Other examples include artificial graphite in the form of granulated particles composed of primary particles. Examples of such graphite particles include mesocarbon microbeads and graphite particles in which a plurality of flat particles are aggregated or bonded together so that their orientation planes are non-parallel, and which are obtained by mixing a graphitizable carbonaceous material powder such as coke with a graphitizable binder such as tar or pitch and a graphitization catalyst, graphitizing the mixture, and pulverizing the mixture as necessary.

[0103] (3) As for amorphous carbon, graphitizable carbon precursors such as tar and pitch are used as raw materials, Examples include amorphous carbon particles that have been heat-treated at least once in a temperature range where graphitization does not occur (400 to 2200°C), and amorphous carbon particles that have been heat-treated using a non-graphitizable carbon precursor such as a resin as a raw material.

[0104] (4) Examples of carbon-coated graphite include carbon-graphite composites in which natural graphite and / or artificial graphite are mixed with a carbon precursor, such as tar, pitch, or resin, and the resulting mixture is heat-treated at least once in the range of 400 to 2300°C, resulting in a core graphite, coated with amorphous carbon. The composite may be in the form of a coating on the entire or partial surface, or a composite of multiple primary particles using carbon derived from the carbon precursor as a binder. Carbon-graphite composites can also be obtained by reacting natural graphite and / or artificial graphite with a hydrocarbon gas, such as benzene, toluene, methane, propane, or aromatic volatiles, at high temperature to deposit carbon on the graphite surface (CVD).

[0105] (5) Examples of graphite-coated graphite include graphite-coated graphite in which natural graphite and / or artificial graphite is mixed with a carbon precursor of an easily graphitizable organic compound such as tar, pitch, or resin, and the mixture is heat-treated at least once in the range of about 2400 to 3200°C to obtain natural graphite and / or artificial graphite as core graphite, and the graphitized material coats the entire or part of the surface of the core graphite.

[0106] (6) Examples of resin-coated graphite include resin-coated graphite in which natural graphite and / or artificial graphite is mixed with resin or the like and dried at a temperature of less than 400°C to obtain natural graphite and / or artificial graphite as core graphite, and the core graphite is coated with resin or the like. The carbonaceous materials (1) to (6) above may be used singly or in any combination of two or more in any ratio.

[0107] The alloy-based material used as the negative electrode active material is not particularly limited, and may be any of lithium itself, elemental metals and alloys that form lithium alloys, or compounds such as oxides, carbides, nitrides, silicides, sulfides, or phosphides, as long as it is capable of absorbing and releasing lithium. The elemental metals and alloys that form lithium alloys are preferably materials containing metal or metalloid elements (i.e., excluding carbon) from Groups 13 and 14, and more preferably aluminum, silicon, and tin elemental metals and alloys or compounds containing these elements. These may be used alone, or two or more may be used in any combination and ratio.

[0108] <Physical properties of carbonaceous materials> When a carbonaceous material is used as the negative electrode active material, it is desirable that the material have the following physical properties.

[0109] (X-ray parameters) The d value (interlayer distance) of the lattice plane (002 plane) of the carbonaceous material determined by X-ray diffraction according to the Gakushin method is usually 0.335 nm or more and usually 0.360 nm or less, preferably 0.350 nm or less, and more preferably 0.345 nm or less. The crystallite size (Lc) of the carbonaceous material determined by X-ray diffraction according to the Gakushin method is preferably 1.0 nm or more, and more preferably 1.5 nm or more.

[0110] (Volume-based average particle size) The volume-based average particle size of the carbonaceous material is the volume-based average particle size (median diameter) determined by a laser diffraction / scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and particularly preferably 7 μm or more. Also, it is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and particularly preferably 25 μm or less. If the volume-based average particle size is below the above range, the irreversible capacity increases, which may result in a loss of initial battery capacity, whereas if it exceeds the above range, the coating surface tends to be non-uniform when an electrode is prepared by coating, which may be undesirable in the battery manufacturing process.

[0111] (BET specific surface area) The BET specific surface area of ​​a carbonaceous 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 0.7m 2 ·g -1 More than 1.0m is preferable. 2 ·g -1 More preferably, 1.5m or more 2 ·g -1 More than 100m is particularly preferable. 2 ·g -1 Less than or equal to 25m 2 ·g -1 Less than 15m is preferable 2 ·g -1 Less than 10m is more preferable. 2 ·g -1 The following are particularly preferred: If the BET specific surface area is below this range, when used as a negative electrode material, the lithium acceptance during charging tends to be poor, lithium tends to precipitate on the electrode surface, and stability may decrease. On the other hand, if the BET specific surface area is above this range, when used as a negative electrode material, the reactivity with a non-aqueous electrolyte increases, gas generation tends to increase, and it may be difficult to obtain a desirable battery.

[0112] <Negative electrode structure and manufacturing method> The electrode can be manufactured by any known method as long as it does not significantly impair the effects of the present invention. For example, the electrode can be formed by adding a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to the negative electrode active material to form a slurry, applying the slurry to a current collector, drying it, and then pressing it. When an alloy-based material is used, a method of forming a thin film layer (negative electrode active material layer) containing the above-mentioned negative electrode active material by a method such as vapor deposition, sputtering, or plating may also be used.

[0113] (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 present on the current collector must be 1 g cm-3 More than 1.2 g cm is preferable. -3 More than 1.3 g cm is more preferable. -3 More than 2.2 g cm is particularly preferable. -3 Preferably less than 2.1 g cm -3 Less than 2.0 g cm is preferable. -3 Less than 1.9 g cm is more preferable. -3 The following are particularly preferred: If the density of the negative electrode active material present on the current collector exceeds the above range, the negative electrode active material particles may be destroyed, resulting in an increase in the initial irreversible capacity and a deterioration in high current density charge / discharge characteristics due to a decrease in the permeability of the nonaqueous electrolyte solution near the current collector / negative electrode active material interface. If the density is below the above range, the conductivity between the negative electrode active materials may decrease, increasing the battery resistance and decreasing the capacity per unit volume.

[0114] [2-3. Positive electrode] <Cathode active material> In one embodiment of the present invention, the positive electrode active material used in the positive electrode comprises a lithium transition metal compound, which contains at least Ni, Mn, and Co, with the Mn / (Ni+Mn+Co) molar ratio being greater than 0 and not greater than 0.32, and the Ni / (Ni+Mn+Co) molar ratio being not less than 0.45. The lithium transition metal compound is described below. <Lithium transition metal compounds> A lithium transition metal compound is a compound having a structure that can extract and insert Li ions, and examples of the lithium transition metal compound used in the present invention include those represented by the following formula (I). In addition, those having a layered structure that allows two-dimensional diffusion of lithium ions are preferred. Here, the layered structure will be described in more detail. Representative crystal systems of those having a layered structure include those belonging to the α-NaFeO2 type, such as LiCoO2 and LiNiO2, which are hexagonal crystal systems and, due to their symmetry, belong to the space group

number

[0115] However, layered LiMeO2 is not limited to the layered R(-3)m structure. In addition, LiMnO2, also known as layered Mn, is a layered compound with an orthorhombic system and space group Pm2m, and Li2MnO3, also known as the 213 phase, is a compound with Li[Li 1 / 3 Mn 2 / 3 ]O2, and has a monoclinic space group C2 / m structure, but it also has a Li layer and [Li 1 / 3 Mn 2 / 3 ] layer and oxygen layer are stacked.

[0116] The lithium transition metal compound preferably contains a lithium transition metal compound represented by the following composition formula (I), and more preferably is a lithium transition metal compound represented by the following composition formula (I). Li 1+x MO2···(I) In formula (I), x is usually -0.20 or more and 0.50 or less. In particular, the lower limit of x is preferably -0.05 or more, more preferably -0.03 or more, particularly preferably -0.02 or more, and most preferably -0.01 or more. The upper limit of x can be 0.1 or less, preferably 0.06 or less, more preferably 0.028 or less, even more preferably 0.020 or less, particularly preferably 0.010 or less, and most preferably 0.005 or less. If x is within the above range, the gas generation suppression effect by combination with the monofluorophosphate and / or difluorophosphate contained in the electrolyte solution is easily exerted, and sufficient charge / discharge capacity can be obtained, which is preferable.

[0117] Furthermore, in formula (I), M is composed of at least Ni, Mn, and Co, and the Mn / (Ni+Mn+Co) molar ratio is greater than 0 and equal to or less than 0.32. The lower limit of the Mn / (Ni+Mn+Co) molar ratio is preferably 0.05 or more, more preferably 0.08 or more, even more preferably 0.10 or more, particularly preferably 0.12 or more, and most preferably 0.14 or more. The upper limit of the Mn / (Ni+Mn+Co) molar ratio is preferably 0.28 or less, more preferably 0.26 or less, even more preferably 0.25 or less, particularly preferably 0.24 or less, and most preferably 0.23 or less. If the Mn / (Ni+Mn+Co) molar ratio is within the above range, the ratio of Mn that is not involved in charging and discharging becomes sufficiently small, and the battery has a high capacity, which is preferable.

[0118] The lower limit of the Ni / (Ni+Mn+Co) molar ratio is 0.45 or more, preferably 0.50 or more, and more preferably 0.55 or more. The upper limit of the Ni / (Ni+Mn+Co) molar ratio is usually 0.95 or less, may be 0.85 or less, preferably 0.80 or less, more preferably 0.75 or less, even more preferably 0.70 or less, particularly preferably 0.68 or less, and most preferably 0.64 or less. If the Ni / (Ni+Mn+Co) molar ratio is within the above range, the proportion of Ni involved in charging and discharging becomes sufficiently large, and the battery has a high capacity, which is preferable.

[0119] Furthermore, the lower limit of the Co / (Ni+Mn+Co) molar ratio is not particularly limited, but is preferably 0.05 or more, more preferably 0.08 or more, even more preferably 0.10 or more, and particularly preferably 0.15 or more. The upper limit of the Co / (Ni+Mn+Co) molar ratio is not particularly limited, but is preferably 0.33 or less, more preferably 0.30 or less, even more preferably 0.28 or less, particularly preferably 0.26 or less, and most preferably 0.24 or less. If the Co / (Ni+Mn+Co) molar ratio is within the above range, the charge / discharge capacity becomes large, which is preferable.

[0120] In the above composition formula (I), the atomic ratio of oxygen is described as 2 for convenience, but some degree of non-stoichiometry is acceptable. Furthermore, x in the above formula (I) is the composition of the lithium transition metal compound charged during its production. Batteries on the market are usually aged after assembly. Therefore, the amount of Li in the positive electrode may be lost during charging and discharging. The lithium transition metal compound may contain a foreign element selected from one or more of B, Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Ru, Rh, Pd, Ag, In, Sb, Te, Ba, Ta, Mo, W, Re, Os, Ir, Pt, Au, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, N, F, S, Cl, Br, I, As, Ge, P, Pb, Sb, Si, and Sn. Among these, at least one element selected from the group consisting of Fe, Cu, W, Mo, Nb, V, Ta, Mg, Al, Ti, Zr, Zn, Ca, Be, B, Bi, Li, Na, and K is preferred. These foreign elements may be incorporated into the crystal structure of the lithium transition metal-based compound, or may not be incorporated into the crystal structure of the lithium transition metal-based compound and may be unevenly distributed as simple substances or compounds on the particle surfaces or grain boundaries.

[0121] (Physical properties of positive electrode active materials containing lithium transition metal compounds or lithium transition metal compounds) (1) Sulfates The positive electrode active material may contain a sulfate. The content of the sulfate that can be contained in the positive electrode active material is not particularly limited, but is preferably 15 μmol / g or more because the gas generation suppression effect of the monofluorophosphate and / or difluorophosphate is manifested. Furthermore, it is more preferably 20 μmol / g or more, even more preferably 25 μmol / g or more, particularly preferably 32 μmol / g or more, and most preferably 35 μmol / g or more. The upper limit is preferably 100 μmol / g or less, more preferably 80 μmol / g or less, even more preferably 60 μmol / g or less, particularly preferably 50 μmol / g or less, and most preferably 30 μmol / g or less, because gas generation due to side reactions becomes large.

[0122] The sulfate contained in the positive electrode active material can be measured by, for example, water extraction ion chromatography.

[0123] (2)Ni average valence The lithium transition metal compound contained in the positive electrode active material has an average Ni valence in an uncharged state that is not particularly limited, but is preferably 2.1 or higher, as this increases the Ni ratio and allows the battery to have a high capacity. It is more preferably 2.3 or higher, even more preferably 2.5 or higher, particularly preferably 2.55 or higher, and most preferably 2.6 or higher. The upper limit is preferably 3 or lower, more preferably 2.9 or lower, particularly preferably 2.8 or lower, and most preferably 2.7 or lower, as this reduces the structural stability of the active material.

[0124] Here, the Ni valence in the present invention will be described in detail. First, when the composition formula of the lithium transition metal compound is rewritten as the following composition formula (I'), M' is composed of Li, Ni and Mn, or Li, Ni, Mn and Co. LiM'O2···(I') In the above formula (I'), the atomic ratio of oxygen is described as 2 for convenience, but some degree of non-stoichiometry is acceptable. When non-stoichiometry exists, the atomic ratio of oxygen is usually in the range of 2±0.2, preferably in the range of 2±0.15, more preferably in the range of 2±0.12, even more preferably in the range of 2±0.10, and particularly preferably in the range of 2±0.05. Furthermore, it is particularly preferable that the lithium transition metal compound has an atomic structure in the M' site in the formula (I') shown below as formula (II). M'=Li z / (2+z) {(Ni (1+y) / 2 Mn (1-y) / 2 ) 1-x Co x} 2 / (2+z) (II)

[0125] Here, the chemical meaning of the Li composition (z and x) in the lithium nickel manganese cobalt composite oxide, which is a suitable composition for the lithium transition metal compound, will be explained in more detail below. As mentioned above, the layered structure is not necessarily limited to the R(-3)m structure, but it is preferable from the viewpoint of electrochemical performance that it be attributable to the R(-3)m structure. To determine x, y, and z in the composition formula of the lithium transition metal compound, each transition metal and Li are analyzed using an inductively coupled plasma atomic emission spectrometry (ICP-AES), and then surface impurity Li is analyzed using water extraction ion chromatography to determine the Li / Ni / Mn / Co ratio of the lithium transition metal compound.

[0126] From a structural point of view, it is thought that the Li associated with z is substituted into the same transition metal site. Here, due to the Li associated with z, the average valence of Ni becomes greater than divalent (trivalent Ni is generated) due to the principle of charge neutrality. Since z increases the average valence of Ni, it is an indicator of the Ni valence (proportion of Ni(III)). Furthermore, when calculating the Ni valence (m) associated with changes in z and z' from the above composition formula, assuming that the Co valence is trivalent and the Mn valence is tetravalent,

number

[0127] Furthermore, when the value of x is in the range of 0≦x≦0.1, that is, the amount of Co is small, not only is the cost reduced, but also the charge / discharge capacity, cycle characteristics, and safety are improved when the battery is used as a lithium secondary battery designed to be charged at a high charging potential.

[0128] (3) pH The pH of the aqueous solution of the lithium transition metal compound is not particularly limited, but is preferably 11 or higher at a liquid temperature of 25°C, since this allows the gas generation suppression effect to be fully exerted in combination with the monofluorophosphate and / or difluorophosphate contained in the electrolyte solution. The saturation index is more preferably 11.2 or higher, even more preferably 11.4 or higher, particularly preferably 11.6 or higher, and most preferably 11.8 or higher, at a liquid temperature of 25° C. In order to reduce gas generation due to side reactions, the upper limit is preferably 13 or lower, more preferably 12.7 or lower, particularly preferably 12.4 or lower, and most preferably 12 or lower, at a liquid temperature of 25° C. The pH of the lithium transition metal compound is measured by weighing 50 g of demineralized water into a beaker, adding 5 g of the sample while stirring, and monitoring the liquid temperature and pH value. The pH value and liquid temperature are measured 10 minutes after the addition, and the values ​​are used.

[0129] (4) Carbonates The positive electrode active material may contain a carbonate. The content of carbonate that can be contained in the positive electrode active material is not particularly limited, but is preferably 10 μmol / g or more because the gas generation suppression effect by combination with the monofluorophosphate and / or difluorophosphate contained in the electrolyte solution is easily achieved. Furthermore, the content is more preferably 20 μmol / g or more, even more preferably 40 μmol / g or more, particularly preferably 60 μmol / g or more, and most preferably 80 μmol / g or more. The upper limit is preferably 100 μmol / g or less, more preferably 98 μmol / g or less, particularly preferably 96 μmol / g or less, and most preferably 94 μmol / g or less, because gas generation due to side reactions is reduced.

[0130] The amount of carbonate contained in the lithium transition metal compound can be measured, for example, by water extraction ion chromatography.

[0131] (5) Tap density The lithium transition metal compound constituting the positive electrode active material is usually a powder, and its tap density is not particularly limited, but is preferably 1.8 g / cm 3 A density of 2 g / cm or more is preferable because the charge / discharge capacity of the battery is large. 3 More preferably, it is 2.1 g / cm or more. 3 More preferably, it is 2.2 g / cm or more. 3 It is particularly preferable that the concentration is 2.3 g / cm or more. 3 The most preferable value is 4.0 g / cm3 or more, since the output characteristics are sufficient. 3 Preferably, it is 3.8 g / cm or less. 3More preferably, it is 3.6 g / cm or less. 3 It is particularly preferable that the concentration is 3.4 g / cm or less. 3 Most preferably, the following:

[0132] By using a lithium transition metal compound with a high tap density, a high-density positive electrode can be formed. When the tap density of the lithium transition metal compound is within the above range, the amount of dispersion medium required for forming the positive electrode is appropriate, and the amounts of conductive material and binder are also appropriate. Therefore, there is no restriction on the filling rate of the lithium transition metal compound in the positive electrode, and the effect on battery capacity is reduced.

[0133] The tap density of lithium transition metal compounds is measured by passing them through a sieve with a mesh size of 300 μm. 3 After dropping a sample into the tapping cell to fill the cell volume, a powder density measuring device (e.g., Tap Denser manufactured by Seishin Enterprise Co., Ltd.) is used to perform tapping 200 times with a stroke length of 10 mm, and the density can be calculated from the volume and mass of the sample at that time. Alternatively, the density can be calculated simply by dropping the sample into a 10 mL measuring cylinder to fill it to capacity, then tapping it 200 times, and then calculating the density from the volume and mass of the sample.

[0134] (6) Surface coating The lithium transition metal compound may have a substance (hereinafter referred to as "surface-attached substance") of a different composition from the substance constituting the main lithium transition metal compound attached to its surface. Examples of surface-attached substances include aluminum oxide, silicon oxide, and oxide. Examples of the oxide include oxides such as titanium, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0135] These surface-attaching substances can be attached to the surface of the lithium transition metal compound by, for example, a method in which a surface-attaching substance precursor is dissolved or suspended in a solvent, impregnated into the lithium transition metal compound, and then dried, a method in which a surface-attaching substance precursor is dissolved or suspended in a solvent, impregnated into the lithium transition metal compound, and then reacted by heating, or a method in which the surface-attaching substance precursor is added to the lithium transition metal compound precursor and then calcined at the same time, etc. When carbon is attached, a method in which a carbonaceous material is mechanically attached later in the form of, for example, activated carbon, can also be used.

[0136] The mass of the surface-adhered substance adhering to the surface of the lithium transition metal compound is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the mass of the lithium transition metal compound, and is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-attached substance can suppress the oxidation reaction of the non-aqueous electrolyte on the surface of the lithium transition metal compound, thereby improving the battery life. Furthermore, when the amount of attachment is within the above range, this effect can be fully exerted, and the inflow and outflow of lithium ions is not hindered, and the resistance is less likely to increase.

[0137] (7) Shape The lithium transition metal compound may have any of the conventional shapes, such as a block, polyhedron, sphere, oval sphere, plate, needle, column, etc. Alternatively, the compound may be formed by agglomeration of primary particles to form secondary particles, and the secondary particles may have a spherical or oval sphere shape.

[0138] (8) Median diameter d50 The median diameter d50 of the lithium transition metal compound (the secondary particle diameter when primary particles are aggregated to form secondary particles) can be measured using a laser diffraction / scattering particle size distribution analyzer. The median diameter d50 is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, particularly preferably 3 μm or more, and preferably 30 μm or less, more preferably 20 μm or less, even more preferably 16 μm or less, particularly preferably 15 μm or less. When the median diameter d50 is within the above range, it becomes easier to obtain a high bulk density product, and further, because lithium diffusion within the particles does not take long, the battery characteristics are less likely to deteriorate. Furthermore, when producing a battery positive electrode, i.e., when the active material, conductive material, binder, etc. are slurried with a solvent and applied as a thin film, streaking and the like are less likely to occur.

[0139] In addition, by mixing two or more kinds of lithium transition metal compounds having different median diameters d50 in any ratio, the filling property during the preparation of the positive electrode can be further improved. The median diameter d50 of the lithium transition metal-based compound is measured using a 0.1 mass % aqueous solution of sodium hexametaphosphate as a dispersion medium, and a particle size distribution analyzer (for example, LA-920 manufactured by Horiba, Ltd.) is used, with the measurement refractive index set to 1.24 after ultrasonic dispersion of the lithium transition metal-based compound for 5 minutes.

[0140] (9) Average primary particle diameter When primary particles are aggregated to form secondary particles, the average primary particle size of the lithium transition metal compound is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.08 μm or more, particularly preferably 0.1 μm or more, and is preferably 3 μm or less, more preferably 2 μm or less, even more preferably 1 μm or less, and particularly preferably 0.6 μm or less. Within the above range, spherical secondary particles are easily formed, powder packing properties are appropriate, and a sufficient specific surface area can be secured, thereby suppressing a decrease in battery performance such as output characteristics. The average primary particle size of the lithium transition metal compound is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at 10,000x magnification, the longest intercept value of a horizontal line at the left and right boundary lines of the primary particle is determined for any 50 primary particles, and the average value is calculated.

[0141] (10)BET specific surface area The BET specific surface area of ​​the lithium transition metal compound is preferably 0.2 m or less as measured by the BET method. 2 ·g -1 More than 0.3m 2 ·g -1 More than 0.4m is preferable. 2 ·g -1 More preferably, it is 4.0 m or more. 2 ·g -1 Less than or equal to 2.5m 2 ·g -1 Less than 1.5m is preferable 2 ·g -1 The following is more preferable. When the BET specific surface area is within the above range, it is easy to prevent a decrease in battery performance. Furthermore, a sufficient tap density can be ensured, and the coating property during the formation of the positive electrode is good.

[0142] The BET specific surface area of ​​the lithium transition metal compound is measured using a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Okura Riken). Specifically, the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, and then measured by the nitrogen adsorption single-point BET method using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3. The specific surface area determined by this measurement is defined as the BET specific surface area of ​​the lithium transition metal compound in this invention.

[0143] (Method for producing a positive electrode active material containing a lithium transition metal compound) The method for producing a positive electrode active material containing a lithium transition metal compound is not particularly limited as long as it does not deviate from the gist of the present invention, but several methods can be mentioned, and a method generally used for producing inorganic compounds can be used. In particular, various methods can be considered for producing spherical or oval-spherical positive electrode active materials. One example is a method in which a transition metal raw material such as a transition metal nitrate or sulfate, and optionally raw materials of other elements, are dissolved or pulverized and dispersed in a solvent such as water, and the pH is adjusted while stirring to produce and recover a spherical precursor, which is then dried as necessary, and a Li source such as LiOH, Li2CO3, or LiNO3 is added and the mixture is fired at a high temperature to obtain the positive electrode active material.

[0144] Another example of such a method is to dissolve or pulverize and disperse a transition metal raw material such as a transition metal nitrate, sulfate, hydroxide, or oxide, and, if necessary, raw materials of other elements, in a solvent such as water, and then dry and mold the resulting mixture using a spray dryer or the like to form a spherical or ellipsoidal precursor, to which a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at a high temperature to obtain a positive electrode active material.

[0145] Yet another example of the method is to dissolve or pulverize and disperse a transition metal raw material such as a transition metal nitrate, sulfate, hydroxide, or oxide, a Li source such as LiOH, Li2CO3, or LiNO3, and, if necessary, raw materials of other elements, in a solvent such as water, and then dry and mold the resulting mixture using a spray dryer or the like to form a spherical or oval-spherical precursor, which is then calcined at a high temperature to obtain a positive electrode active material. In addition, in selecting a transition metal raw material, the sulfate content and carbonate content of the positive electrode active material described above can be set to desired values ​​by adjusting the amounts of sulfate and carbonate used, adjusting the firing temperature, whether or not washing is performed, etc.

[0146] The lithium transition metal compound used in the positive electrode active material may be one of the above compounds alone or a blend of two or more of them. The sulfides may be blended with titanium transition metal composite oxides. Examples of sulfides include compounds with two-dimensional layer structures such as TiS2 and MoS2, and compounds with the general formula Me xExamples of the 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 as LiMe2O4 (Me is at least one or more transition metals), and specifically include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4, etc. Those with a spinel structure are generally represented as LiMe2O4 (Me is at least one or more transition metals), and specifically include LiMn2O4, LiCoMnO4, LiNi 0.5 Mn 1.5 O4, LiCoVO4, etc. Those with a layered structure are specifically LiCoO2, LiNiO2, LiNi 1-x Co x O2, LiNi 1-x-y Co x Mn y O2, LiNi 0.5 Mn 0.5 O2, Li 1.2 Cr 0.4 Mn 0.4 O2, Li 1.2 Cr 0.4 Ti 0.4 O2, LiMnO2, etc.

[0147] <Configuration and manufacturing method of positive electrodes for lithium secondary batteries> The positive electrode for a lithium secondary battery is formed by forming a layer of a positive electrode active material containing the above-mentioned lithium transition metal compound and a binder on a current collector. The layer of the positive electrode active material is usually produced by dry-mixing a positive electrode active material containing a lithium transition metal compound, a binder, and optionally a conductive material, a thickener, and the like, into a sheet, which is then pressed onto the positive electrode current collector, or by dissolving or dispersing these materials in a liquid medium to form a slurry, which is then applied to the positive electrode current collector and dried.

[0148] The positive electrode current collector is typically made of a metal material such as aluminum, stainless steel, nickel plating, titanium, or tantalum, or a carbon material such as carbon cloth or carbon paper. The shape of the metal material may be a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, or a foamed metal; and the shape of the carbon material may be a carbon plate, a carbon thin film, or a carbon cylinder. The thin film may be formed in a mesh shape as appropriate.

[0149] The binder used in producing the layer of the positive electrode active material is not particularly limited, and in the case of a coating method, any material may be used as long as it is stable in the liquid medium used in producing the electrode. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers and their hydrogenated products; and EPDM (ethylene-propylene copolymer). Examples of suitable polymers include thermoplastic elastomers such as styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers, and their hydrogenated derivatives; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ionic conductivity for alkali metal ions (especially lithium ions). These substances may be used singly or in any combination of two or more in any ratio.

[0150] The proportion of the binder in the positive electrode active material layer is usually 0.1 mass % or more and 80 mass % or less. If the proportion of the binder is too low, the lithium transition metal compound cannot be sufficiently held, resulting in a lack of mechanical strength of the positive electrode, which may deteriorate battery performance such as cycle characteristics. On the other hand, if the proportion of the binder is too high, This may lead to a decrease in battery capacity and conductivity.

[0151] The positive electrode active material layer usually contains a conductive material to increase the conductivity. There are no particular limitations on the type of material, but 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 materials such as amorphous carbon such as needle coke. These substances may be used singly or in any combination of two or more in any ratio. The proportion of the conductive material in the positive electrode active material layer is usually 0.01 mass % or more and 50 mass % or less. If the proportion of the conductive material is too low, the conductivity may be insufficient, and conversely, if it is too high, the battery capacity may decrease.

[0152] The liquid medium for forming the slurry is not particularly limited as long as it can dissolve or disperse the cathode active material containing a lithium transition metal compound, the binder, and the conductive material and thickener used as needed. Either an aqueous or organic solvent can be used. Examples of aqueous solvents include water and alcohol. Examples of organic solvents include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane. When using an aqueous solvent, a dispersant is added along with the thickener, and a slurry is formed using a latex such as SBR. These solvents may be used alone or in any combination of two or more in any ratio.

[0153] The content of the lithium transition metal compound as the positive electrode material in the positive electrode active material layer is usually 10% by mass or more and 99.9% by mass or less. If the content of the lithium transition metal compound in the positive electrode active material layer is too high, the strength of the positive electrode tends to be insufficient, and if it is too low, the capacity may be insufficient.

[0154] The thickness of the positive electrode active material layer is usually about 10 to 200 μm. Here, the electrode plate density of the positive electrode according to the present invention is 3.0 g / cm 3 That's all. Also, 3.2g / cm 3 It is preferable that the concentration is 3.3 g / cm or more. 3 More preferably, it is 3.4 g / cm or more. 3 More preferably, it is 3.6 g / cm or more. 3 The upper limit is 4.2 g / cm because it is difficult for the input / output characteristics to deteriorate. 3 Preferably, it is 4.1 g / cm or less. 3 More preferably, it is 4.0 g / cm or less. 3 It is particularly preferable that the concentration is 3.9 g / cm or less. 3 Most preferably, the following: The positive electrode plate density can be increased to the above range by compressing the positive electrode active material layer after coating and drying using a roll press. The desired electrode plate density can be obtained by appropriately adjusting the pressure of the roll press.

[0155] [2-4. Separator] A separator is usually interposed 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.

[0156] There are no particular restrictions on the material or shape of the separator, and any known material can be used as long as it does not significantly impair the effects of the present invention. Among these, a material that is stable against a non-aqueous electrolyte solution is preferred. The material used is a resin, glass fiber, inorganic material, etc., and it is preferable to use a porous sheet or nonwoven fabric-like material having excellent liquid retention properties. Examples of materials that can be used for the resin or glass fiber separator include polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filters. Among these, glass filters and polyolefins are preferred, and polyolefins are even more preferred. These materials may be used alone or in any combination and ratio of two or more.

[0157] The thickness of the separator is not particularly limited, but is usually 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is thinner than the above range, the insulating properties and mechanical strength may be reduced, whereas if the separator is thicker than the above range, not only may the battery performance such as rate characteristics be reduced, but also the energy density of the nonaqueous electrolyte secondary battery as a whole may be reduced.

[0158] Furthermore, when a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is optional, but is usually 20% or more, preferably 35% or more, and more preferably 45% or more, and is usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too low, the membrane resistance increases, tending to deteriorate the rate characteristics, whereas if it is too high, the mechanical strength of the separator decreases, tending to deteriorate the insulating properties.

[0159] The average pore size of the separator can also be any value, but is usually 0.5 μm or less, preferably 0.2 μm or less. It is usually 0.05 μm or more. If the average pore size exceeds the above range, short circuits are more likely to occur. If the average pore size is below the above range, the membrane resistance increases, which may result in a decrease in rate characteristics.

[0160] On the other hand, inorganic materials include, for example, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate, and these are used in particulate or fibrous form.

[0161] The separator may be in the form of a thin film such as a nonwoven fabric, a woven fabric, or a microporous film. A thin 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-mentioned independent thin film, a separator may be used in which a composite porous layer containing the above-mentioned inorganic particles is formed on the surface layer of the positive electrode and / or negative electrode using a resin binder. For example, a porous layer may be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

[0162] The characteristics of a separator in a non-electrolyte secondary battery can be understood by its Gurley value. The Gurley value indicates the difficulty of air passing through the film thicknesswise. It is expressed as the number of seconds required for 100 ml of air to pass through the film. A smaller value indicates easier air permeability, while a larger value indicates less air permeability. In other words, a smaller value indicates better interconnectivity in the film thicknesswise, while a larger value indicates poorer interconnectivity in the film thicknesswise. Interconnectivity refers to the degree of connection of pores in the film thicknesswise. If the separator of the present invention has a low Gurley value, it can be used for various applications. For example, when used as a separator for a non-aqueous lithium secondary battery, a low Gurley value means easy lithium ion migration, which is preferable because it leads to excellent battery performance. The Gurley value of the separator is arbitrary, but is preferably 10 to 1,000 seconds / 100 ml, more preferably 15 to 800 seconds / 100 ml, and even more preferably 20 to 500 seconds / 100 ml. If the Gurley value is 1000 seconds / 100 ml or less, the electrical resistance is substantially low and is preferable as a separator.

[0163] [2-5.Battery design] <Electrode group> The electrode group may have either a laminated structure in which the positive electrode plate and the negative electrode plate are sandwiched between the separator, or a structure in which the positive electrode plate and the negative electrode plate are spirally wound with the separator sandwiched between them.

[0164] 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, preferably 50% or more, and usually 90% or less, preferably 80% or less. If the electrode group occupancy rate is below the above range, the battery capacity will be small, whereas if it exceeds the above range, the void space will be small, and the battery will become hot, causing the components to expand and the vapor pressure of the electrolyte liquid components to increase, resulting in an increase in internal pressure, which will degrade various battery characteristics such as repeated charge / discharge performance and high-temperature storage, and may even cause the gas release valve that releases internal pressure to the outside to operate.

[0165] <Protection element> The protective element may be a PTC (Positive Temperature Coefficient), whose resistance increases when abnormal heat is generated or excessive current flows, 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.

[0166] <Exterior body> The nonaqueous electrolyte secondary battery of the present invention is typically constructed by housing the above-described nonaqueous electrolyte, negative electrode, positive electrode, separator, etc., in an exterior body (exterior case). This exterior body is not particularly limited, and any known exterior body can be used as long as it does not significantly impair the effects of the present invention. Specifically, the exterior body may be made of any material, but typically, metals such as nickel-plated steel sheet, stainless steel, aluminum or its alloy, magnesium alloy, nickel, titanium, etc., or a laminate film of resin and aluminum foil 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. In the case of an outer case using the laminate film, a sealed and airtight structure is formed by heat-sealing resin layers, etc. In order to improve the sealing property, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed via a current collecting terminal to form a sealed structure, a bond is formed between metal and resin, so a resin having a polar group or a modified resin into which a polar group has been introduced is preferably used as the intervening resin.

[0167] The shape of the exterior body may also be arbitrary, and may be, for example, cylindrical, rectangular, laminated, coin-shaped, large, or the like.

[0168] <Battery voltage> The non-aqueous electrolyte secondary battery of the present invention is usually used at a battery voltage of 4.0 V or higher. The battery voltage is preferably 4.1 V or higher, more preferably 4.15 V or higher, and most preferably 4.2 V or higher. Increasing the battery voltage can increase the energy density of the battery. This is because it is possible to do so. On the other hand, increasing the battery voltage raises the potential of the positive electrode, causing the problem of increased side reactions on the positive electrode surface. While the use of the battery of the present invention can solve this problem, if the voltage is too high, the amount of side reactions on the positive electrode surface increases too much, deteriorating the battery characteristics. Therefore, the upper limit of the battery voltage is preferably 5 V or less, more preferably 4.8 V or less, and most preferably 4.6 V or less.

[0169] <Reasons why the present invention is effective> The reason why the present invention is effective is not yet clear, but is presumed to be as follows. To increase the capacity of automotive batteries, attempts have been made to use high-capacity lithium transition metal compounds as positive electrode active materials, which can be achieved, for example, by reducing the amount of Mn and increasing the amount of Ni. However, when such a positive electrode is used in a non-aqueous electrolyte secondary battery, problems have been found in that the capacity retention rate after high-temperature storage is low, the amount of storage gas and the amount of metal elution after high-temperature storage are increased, the resistance after high-temperature storage is high, and the amount of heat generated at high temperatures is large.

[0170] The inventors have investigated this issue and have hypothesized the following mechanism. In other words, when the Mn content is reduced and the Ni content is increased, the capacity increases, resulting in a decrease in the amount of Li within the lithium transition metal compound crystals during charging. In this case, oxygen atoms within the lithium transition metal compound crystals become unstable and activated. This increases the oxidizing power of the positive electrode and causes the surface crystalline structure to collapse and change to a rock salt structure. It is speculated that the lithium transition metal compound with increased oxidizing power decomposes the nonaqueous electrolyte in the battery, causing gas generation and metal elution, resulting in increased heat generation at high temperatures. It is also speculated that the collapse of the crystalline structure on the surface of the lithium transition metal compound causes a decrease in capacity and an increase in resistance after high-temperature storage.

[0171] In response to this, the inventors have discovered that by increasing the plate density of the positive electrode to a certain level or more and incorporating a specific phosphorus compound into the non-aqueous electrolyte solution, it is possible to suppress the destabilization of oxygen atoms in the crystals of the lithium transition metal compound, suppress the decrease in capacity retention rate after high-temperature storage, and the amount of gas generated and metal elution due to decomposition of the non-aqueous solvent in the non-aqueous electrolyte solution, thereby reducing the resistance after high-temperature storage and the amount of heat generated at high temperatures. Although the reason for this is not yet clear, it is presumed that the specific phosphorus compound of the present invention decomposes to form LiF, and this LiF appears on the surface of the lithium transition metal compound, whereby it reacts with the surface of the lithium transition metal compound, which has increased oxidizing power, thereby suppressing the destabilization of oxygen atoms in the crystal, suppressing a decrease in capacity retention rate after high-temperature storage and gas generation and metal elution due to decomposition of the electrolyte, lowering the resistance after high-temperature storage, and reducing the amount of heat generated at high temperatures. [Example]

[0172] 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 abbreviations for the compounds used in the examples are shown below. Compound 1: Lithium difluorophosphate

[0173] [Evaluation of non-aqueous electrolyte secondary batteries] ·Initial charge / discharge In a thermostatic bath at 25°C, a sheet-shaped non-aqueous electrolyte secondary battery was charged for 4 hours at 0.05C (the current value at which the rated capacity based on the hourly rate of discharge capacity is discharged in 1 hour is 1C; the same applies below), and then discharged at a constant current of 0.2C to 2.5V. Next, a charge-discharge cycle was performed in which one cycle consisted of a constant current-constant voltage charge at 0.2C to a predetermined voltage and a constant current discharge at 0.2C to 2.5V. I did two cycles. The battery was then charged at a constant current and constant voltage of 0.2 C to 4.0 V, and then stored at 45°C for 42 hours to stabilize it. It was then discharged at a constant current to 2.5 V at 25°C, and then charged at a constant current and constant voltage of 0.2 C to a predetermined voltage. It was then discharged at a constant current of 0.2 C to 2.5 V, and the discharge capacity at this point was recorded as the pre-storage capacity (A). It was then charged at a constant current and constant voltage of 0.2 C to a predetermined voltage. The predetermined voltage was typically 4.2 V, but could also be 4.3 V or 4.4 V.

[0174] Storage test The cell after the initial charge and discharge was stored at a high temperature of 85°C for 24 hours. After the battery was cooled sufficiently, it was immersed in an ethanol bath and its volume was measured. The amount of gas generated was calculated from the change in volume before and after the storage test. This was defined as the storage gas amount, and the percentage of the storage gas reduction amount due to the additive was defined as the "storage gas suppression rate" (e.g., storage gas suppression rate (%) of Example 1 = {(storage gas amount of Comparative Example 1 - storage gas amount of Example 1) / storage gas amount of Comparative Example 1} × 100). The discharge capacity of this cell, when discharged at a constant current of 0.2 C to 2.5 V in a constant temperature bath at 25°C, was defined as the post-storage capacity (B). The ratio of the post-storage capacity (B) to the pre-storage capacity (A) was defined as the "post-storage capacity remaining rate." It can be said that a larger residual capacity rate after storage is preferable, and a smaller storage gas amount is preferable because the battery swells less. Resistance after storage test After the storage test, the battery was charged at a constant current and constant voltage of 0.2 C up to 4.2 V, and then measured with an AC voltage of 10 mV (0.1 Hz). This was taken as the "resistance after storage," and the percentage of resistance reduction due to the additive was taken as the "resistance suppression rate." Metal elution amount after storage test The amount of metal elution was determined by quantifying the amount of metal deposited on the negative electrode. The amount of metal deposited on the negative electrode was determined by acid decomposition of the negative electrode and then analyzing the total amount of metal elution, i.e., Ni, Mn, and Co, using inductively coupled plasma (ICP) atomic emission spectroscopy. Here, the amount of metal elution reduction due to the additive was defined as the "metal elution suppression amount." ·Method for measuring calorific value After the initial charge and discharge, the cell was charged at a constant current and constant voltage of 0.2C up to 4.5V, after which the positive electrode was removed from the battery and placed in a measurement cell together with the electrolyte for measurement using a Calbe calorimeter. Measurements were performed by raising the temperature to 300°C at 1K / min, and the ratio of the total heat generation between 100°C and 300°C to the charge capacity up to 4.5V was defined as the "heat generation per unit capacity." The rate at which the heat generation was reduced by the additive was defined as the "heat generation suppression rate." How to measure tap density The tap density of the lithium transition metal compound was measured by dropping a sample into a 10 mL measuring cylinder to fill it to capacity, then tapping it 200 times, and calculating the density from the volume and mass of the sample at that time. -Measuring methods for sulfates and carbonates The sulfates and carbonates contained in the positive electrode active material were measured by water extraction ion chromatography. pH measurement method pH: 50 g of demineralized water was weighed into a beaker, and 5 g of the sample was added while stirring, followed by stirring for 30 minutes at 25° C. Thereafter, the pH value was measured while the liquid temperature was maintained at 25° C. ·Measuring method for Ni valence The ratio of each transition metal to Li was calculated by analyzing it using water extraction ion chromatography and inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0175] [Example] [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> Under a dry argon atmosphere, thoroughly dried LiPF was dissolved at 1 mol / L (as the concentration in the non-aqueous electrolyte) in a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7), and further thoroughly dried vinylene carbonate was dissolved at 2 mass% to prepare a non-aqueous electrolyte solution. Two types of non-aqueous electrolyte solutions were prepared: one in which Compound 1 was further dissolved at 1 mass% (as the concentration in the non-aqueous electrolyte) and one in which Compound 1 was not dissolved. Using this nonaqueous electrolyte, a nonaqueous electrolyte secondary battery was produced by the following method, and the following evaluations were carried out.

[0176] <Preparation of positive electrode> The lithium nickel manganese cobalt composite oxide used as the positive electrode active material is NMC622(Li 1.00 Ni 0.61 Mn 0.19 Co 0.20 O2:Mn / (Ni+Mn+Co) molar ratio = 0.19, Ni / (Ni+Mn+Co) molar ratio = 0.61, sulfate concentration = 38 μmol / g, carbonate concentration = 91 μmol / g, Ni average valence 2.63, aqueous solution pH 11.88, tap density 2.39 g / cm 3 ), NMC532(Li 1.05 Ni 0.52 Mn 0.29 Co 0.20 O2:Mn / (Ni + Mn + Co) molar ratio = 0.29, Ni / (Ni + Mn + Co) molar ratio = 0.52, sulfate concentration = 30 μmol / g, carbonate concentration = 16 μmol / g, Ni average valence 2.51, aqueous solution pH 11.75, tap density: 2.39 g / cm 3 ), or NMC111(Li 1.05 Ni 0.34 Mn 0.33 Co 0.33 O2:Mn / (Ni+Mn+Co) molar ratio = 0.33, Ni / (Ni+Mn+Co) molar ratio = 0.34, sulfate concentration = 14 μmol / g, carbonate concentration = 12 μmol / g, Ni average valence 2.15, aqueous solution pH 11.12, tap density: 1.55 g / cm 3) were used. 94 parts by mass of each positive electrode active material, 3 parts by mass of acetylene black as a conductive material, 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder, and 0.07 parts by mass of polyvinylpyrrolidone as a dispersant were mixed and slurried in N-methyl-2-pyrrolidone, which was uniformly applied to an aluminum foil with a thickness of 15 μm, dried, and then roll-pressed to form a positive electrode (hereinafter, this positive electrode may be referred to as positive electrode 1). The plate density of the positive electrode was adjusted to 2.4, 2.8, 3.0, 3.2, or 3.3 g / cm by setting the roll-press pressure to 0 to 13 kN / cm. 3 Positive electrodes with five different positive electrode densities were fabricated.

[0177] <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.

[0178] <Production of non-aqueous electrolyte secondary battery> The positive electrode, negative electrode, and polyolefin separator were stacked in this order: negative electrode, separator, positive electrode. The battery element thus obtained was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution described above was injected and then vacuum-sealed to produce a sheet-shaped nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 15 were produced using the combinations of three types of positive electrode active material compositions, five types of positive electrode plate densities, and two types of nonaqueous electrolyte solutions with or without Compound 1, as shown in Table 1.

[0179] [Table 1]

[0180] Table 2 shows the residual capacity rate after storage and the suppression rate of gas generation during storage. As is clear from Table 2, when Compound 1 is added to the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery including a positive electrode active material of a specific composition and having a specific electrode plate density, the residual capacity rate after storage is improved and the amount of gas generation during storage is suppressed. In other words, a nonaqueous electrolyte secondary battery with excellent high-temperature life is obtained. In Comparative Examples 6 and 8, the residual capacity rate was extremely low, reaching two significant digits of "0.0%."

[0181] [Table 2]

[0182] Table 3 shows the resistance after storage and the resistance suppression rate. As is clear from Table 3, the positive electrode active material with a specific composition When Compound 1 was added to the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery containing a material and having a positive electrode with a specific plate density, the resistance after storage was kept low. Because the internal resistance of the battery correlates with the amount of heat generated by the battery during charging, a nonaqueous electrolyte secondary battery with excellent safety and low heat generation during charging was obtained, even after high-temperature storage.

[0183] [Table 3]

[0184] Table 4 shows the heat generation amount per unit capacity and the heat generation suppression rate. As is clear from Table 4, when Compound 1 is added to the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery containing a positive electrode active material of a specific composition and having a positive electrode with a specific electrode plate density, the heat generation amount per unit capacity is suppressed to a low level. In other words, a high-capacity nonaqueous electrolyte secondary battery with low heat generation and excellent safety is obtained.

[0185] [Table 4]

[0186] The amount of metal elution suppression is shown in Table 5. As is clear from Table 5, when Compound 1 is added to the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery including a positive electrode active material of a specific composition and having a specific electrode plate density, the metal elution suppression effect is enhanced. In other words, a high-capacity nonaqueous electrolyte secondary battery with excellent safety and reduced metal elution from the positive electrode is obtained.

[0187] [Table 5]

[0188] Example 5 [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> Under a dry argon atmosphere, thoroughly dried LiPF was dissolved at 1 mol / L (as the concentration in the non-aqueous electrolyte) in a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7), and then thoroughly dried vinylene carbonate was dissolved at 2 mass % and Compound 1 at 1 mass % (as the concentration in the non-aqueous electrolyte) to prepare a non-aqueous electrolyte. Using this nonaqueous electrolyte, a nonaqueous electrolyte secondary battery was produced by the following method, and the following evaluations were carried out.

[0189] <Preparation of positive electrode> Lithium nickel manganese cobalt composite oxide (Li 1.00 Ni 0.61 Mn 0.19 Co 0.20 O2:Mn / (Ni+Mn+Co) molar ratio = 0.19, Ni / (Ni+Mn+Co) molar ratio = 0.61, sulfate concentration = 38 μmol / g, carbonate concentration = 91 μmol / g, Ni average valence 2.63, aqueous solution pH 11.88, tap density 2.39 g / cm 390 parts by mass of the cellulose acetate copolymer (C10), 7 parts by mass of acetylene black as a conductive material, 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder, and 0.07 parts by mass of polyvinylpyrrolidone as a dispersant were mixed in N-methyl-2-pyrrolidone to form a slurry, which was uniformly applied to an aluminum foil with a thickness of 15 μm, dried, and then roll-pressed to form a positive electrode (hereinafter, this positive electrode may be referred to as positive electrode 6). The electrode plate density of positive electrode 6 was 3.3 g / cm. 3 It was.

[0190] <Preparation of negative electrode> Negative electrodes of Examples 5 and 6 and Comparative Example 16 were prepared in the same manner as in Examples 1 to 4 and Comparative Examples 1 to 15.

[0191] <Production of non-aqueous electrolyte secondary battery> In the same manner as in Examples 1 to 4 and Comparative Examples 1 to 15, sheet-shaped nonaqueous electrolyte secondary batteries of Examples 5 and 6 and Comparative Example 16 were fabricated.

[0192] Comparative Example 16 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 5, except that Compound 1 was not added to the non-aqueous electrolyte. Table 6 shows the residual capacity rate after storage, the amount of gas stored, and the amount of metal eluted after the storage test for Example 6 and Comparative Example 16.

[0193] Example 6 The positive electrode active material is lithium nickel manganese cobalt composite oxide (Li 1.05 Ni 0.52 Mn 0.29 Co 0.20 O2:Mn / (Ni + Mn + Co) molar ratio = 0.29, Ni / (Ni + Mn + Co) molar ratio = 0.52, sulfate concentration = 30 μmol / g, carbonate concentration = 16 μmol / g, Ni average valence 2.51, aqueous solution pH 11.75, tap density: 2.39 g / cm 3 A positive electrode (hereinafter, this positive electrode may be referred to as positive electrode 7) was prepared in the same manner as in Example 5, except that a nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 5, except that the positive electrode was used. The electrode plate density of positive electrode 7 was 3.3 g / cm 3It was.

[0194] Comparative Example 17 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Comparative Example 16, except that the positive electrode 7 used in Example 6 above was used. Table 7 shows the remaining capacity rate after storage, the gas suppression rate after storage, and the amount of metal elution after the storage test for Example 6 and Comparative Example 17.

[0195] [Table 6]

[0196] [Table 7]

[0197] As is clear from Table 6, when Compound 1 is added to the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery having a positive electrode with a specific plate density and a positive electrode active material containing a specific composition and a specific amount of sulfate, the residual capacity after storage is improved, the amount of storage gas is suppressed, and the amount of metal elution is reduced. In other words, a nonaqueous electrolyte secondary battery with excellent high-temperature life and low heat generation at high temperatures is obtained. As is clear from Table 7, when Compound 1 is added to the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery having a positive electrode containing a sulfate, the residual capacity rate after storage is improved, the amount of storage gas is suppressed, and the amount of metal elution is reduced. In other words, a nonaqueous electrolyte secondary battery with excellent high-temperature life and low heat generation at high temperatures is obtained.

Claims

1. 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 a non-aqueous electrolyte, The positive electrode active material includes a lithium transition metal compound and a sulfate, the positive electrode active material includes at least Ni, Mn, and Co, the Mn / (Ni+Mn+Co) molar ratio is greater than 0 and less than or equal to 0.32, and the Ni / (Ni+Mn+Co) molar ratio is greater than or equal to 0.45, and the positive electrode plate density is 3.0 g / cm ３ The nonaqueous electrolyte secondary battery as described above, wherein the nonaqueous electrolyte contains a monofluorophosphate and / or a difluorophosphate.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material comprises a lithium transition metal compound represented by the following formula (I): Li １＋ｘ MO ２ ・・・(I) (In the above formula (I), x is −0.05 or more and 0.06 or less, and M is composed of at least Ni, Mn, and Co.)

3. 3. The nonaqueous electrolyte secondary battery according to claim 2, wherein x is 0.028 or less.

4. 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the Mn / (Ni+Mn+Co) molar ratio is 0.28 or less.

5. 5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the Ni / (Ni+Mn+Co) molar ratio is 0.55 or more.

6. The electrode density of the positive electrode is 3.2 g / cm ３ The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein

7. 7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the amount of the sulfate contained in the positive electrode active material is 15 μmol / g or more.

8. 8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal compound has an average Ni valence of 2.1 or more in an uncharged state.

9. 9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the aqueous solution of the lithium transition metal compound has a pH of 11 or higher at a solution temperature of 25°C.

10. 10. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains 10 μmol / g or more of carbonate.

11. The lithium transition metal compound has a tap density of 1.8 g / cm ３ The non-aqueous electrolyte secondary battery according to any one of claims 1 to 10, wherein

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