Electrolyte solution, method for producing electrolyte solution, battery, method for producing battery, and vehicle

Abstract

Provided is an electrolyte solution which contains a bis(fluorosulfonyl) imide salt, a hexafluorophosphate, a compound that contains an anion represented by general formula (1), and a nonaqueous solvent, wherein: the ratio of the mass of the hexafluorophosphate to the mass of the bis(fluorosulfonyl) imide salt in the electrolyte solution is 0.45 or less; and the content of the compound that contains an anion represented by general formula (1) is 0.03 mass% or more in 100 mass% of the electrolyte solution.　General formula (1): R1SO3 - (R1 represents a halogen atom.)

Description

Electrolyte, method for manufacturing electrolyte, battery, method for manufacturing battery, and vehicle

[0001] The present invention relates to an electrolyte, a method for manufacturing an electrolyte, a battery, a method for manufacturing a battery, and a vehicle.

[0002] Non-aqueous electrolyte batteries such as lithium secondary batteries are being put to practical use in a wide range of applications, from so-called consumer power sources for mobile phones, laptops, etc. to on-board power sources for driving automobiles, etc. However, in recent years, there has been an increasing demand for higher performance for non-aqueous electrolyte batteries, and in particular, improvements in various battery characteristics such as high capacity, low-temperature usage characteristics, high-temperature storage characteristics, cycle characteristics, and safety during overcharge have been desired. To date, as a means for improving the input / output characteristics of non-aqueous electrolyte secondary batteries, many technologies have been investigated for various battery components, including active materials for positive and negative electrodes and non-aqueous electrolytes. Patent Document 1 discloses a method for producing a non-aqueous electrolyte battery having a specific formula (1): M(FSO ３ ) ｘ A non-aqueous electrolyte solution containing at least one fluorosulfonate represented by the formula: ６ In addition to the above fluorosulfonate and LiPF ６ Patent Document 2 describes that by setting the ratio of X to SO within a specific range, a nonaqueous electrolyte solution can be realized that can provide a nonaqueous electrolyte secondary battery with improved initial charge capacity and input / output characteristics. ２ -Y-SO ２ -Z and SO ３It is described that input / output characteristics can be improved when a non-aqueous electrolyte solution contains one or more compounds selected from group (A) consisting of cyclic compounds having a structure and a fluorosulfonate salt (B) having a specific structure, the content of the compound belonging to group (A) in the non-aqueous electrolyte solution is within a specific range, and the ratio of the mass content of the specific fluorosulfonate salt to the content is 1 or less. Patent Document 3 describes that a lithium bis(fluorosulfonyl)imide composition containing 90 mass% or more of lithium bis(fluorosulfonyl)imide and a specific amount of LiFSO3 improves discharge characteristics at high temperatures, input / output characteristics at low temperatures, and rate characteristics at room temperature. However, Patent Documents 1 to 3 have problems such as insufficient thermal stability of the battery and large self-discharge of the battery.

[0003] International Publication No. 2011 / 099585 Japanese Patent Application Laid-Open No. 2023-130374 Japanese Patent Application Laid-Open No. 2018-35059

[0004] An object of the present invention is to provide a non-aqueous electrolyte solution that can solve the above problems and simultaneously improve the thermal stability of a battery and suppress self-discharge of the battery.

[0005] In view of the above circumstances, the present inventors have conducted extensive research and have found that when a non-aqueous electrolyte solution contains a hexafluorophosphate salt, a bis(fluorosulfonyl)imide salt, and a specific sulfonate anion-containing compound in a specific ratio, the thermal stability of the battery is improved and a non-aqueous electrolyte battery in which self-discharge of the battery is suppressed can be obtained, thereby completing the present invention.

[0006] That is, the gist of the present invention resides in the following: [1] An electrolytic solution containing a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, a compound containing an anion represented by the following general formula (1), and a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 0.45 or less, and the content of the compound containing the anion represented by the general formula (1) is 0.03 mass% or more in 100 mass% of the electrolytic solution. １ SO ３ － (1) (R １represents a halogen atom.) [2] An electrolytic solution comprising a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, a compound containing an anion represented by the following general formula (2), and a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 1 or less, and the content of the compound containing the anion represented by the general formula (2) is 0.01 mass% or more in 100 mass% of the electrolytic solution. R ２ SO ３ － (2) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.) [3] The electrolytic solution according to [1] or [2], wherein the concentration of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 8% by mass or more. [4] The electrolytic solution according to any one of [1] to [3], wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 0.01 or more. [5] The electrolytic solution according to any one of [1] to [4], wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 0.2 or less. [6] The electrolytic solution according to any one of [1] to [5], wherein the ratio of the mass of the compound containing the anion represented by general formula (1) to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 3.7 or less. [7] The electrolyte solution according to any one of [1] to [6], wherein the ratio of the mass of the compound containing the anion represented by the general formula (1) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.0001 or more. [8] The bis(fluorosulfonyl)imide salt is LiN(FSO ２ ) ２ and the hexafluorophosphate is LiPF ６ The electrolyte solution according to any one of [1] to [7], wherein the compound containing the anion represented by the general formula (1) is a compound represented by the following general formula (1-1): １ SO３ (1-1) (R １ represents a halogen atom.) [9] The electrolytic solution according to any one of [1] to [8], further comprising at least one compound (A) selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, organic compounds having an isocyanate group, organic compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, cyclic compounds having an ether bond, fluorine-free carboxylic acid esters, carboxylic acid anhydrides, triple bond-containing compounds, phosphazene compounds, cyclic acetal compounds, boron anion-containing compounds, oxalato complex anion-containing compounds, and phosphate anion-containing compounds having a P═O bond and a P—F bond (excluding the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by the general formula (1)).

[10] The electrolyte solution according to [9], wherein the compound (A) contains at least one compound selected from the group consisting of the oxalato complex anion-containing compound, a phosphate anion-containing compound having a P═O bond and a P—F bond, a cyclic carbonate having a carbon-carbon unsaturated bond, and a fluorine-containing cyclic carbonate.

[11] The electrolyte solution according to [2] to [5], wherein the ratio of the mass of the compound containing the anion represented by the general formula (2) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 3.7 or less.

[12] The electrolyte solution according to any one of [2] to [5] and

[11] , wherein the ratio of the mass of the compound containing the anion represented by the general formula (2) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.0001 or more.

[13] The bis(fluorosulfonyl)imide salt is LiN(FSO ２ ) ２ and the hexafluorophosphate is LiPF ６ The electrolyte solution according to any one of [2] to [5],

[11] and

[12] , wherein the compound containing the anion represented by the general formula (2) is a compound represented by the following general formula (2-1): ２ SO３ (2-1) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.

[14] The electrolytic solution further contains at least one compound (A) selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, organic compounds having an isocyanate group, organic compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, cyclic compounds having an ether bond, fluorine-free carboxylic acid esters, carboxylic acid anhydrides, triple bond-containing compounds, phosphazene compounds, cyclic acetal compounds, boron anion-containing compounds, oxalato complex anion-containing compounds, and phosphate anion-containing compounds having a P═O bond and a P—F bond (excluding the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by the general formula (2)).

[13] The electrolytic solution according to any one of [2] to [5],

[11] ,

[12] , and

[13] .

[15] The electrolytic solution according to

[14] , wherein the compound (A) contains at least one compound selected from the group consisting of the oxalato complex anion-containing compound, a phosphate anion-containing compound having a P═O bond and a P—F bond, a cyclic carbonate having a carbon-carbon unsaturated bond, and a fluorine-containing cyclic carbonate.

[16] A method for producing an electrolytic solution, comprising a step of dissolving a bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and a compound containing an anion represented by the following general formula (1) in a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 0.45 or less, and the content of the compound containing the anion represented by general formula (1) is 0.03 mass% or more in 100 mass% of the electrolytic solution. １ SO ３ － (1) (R １represents a halogen atom.)

[17] A method for producing an electrolytic solution, comprising a step of dissolving a bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and a compound containing an anion represented by the following general formula (2) in a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 1 or less, and the content of the compound containing the anion represented by the general formula (2) is 0.01 mass% or more in 100 mass% of the electrolytic solution. ２ SO ３ － (2) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.)

[18] A battery comprising a positive electrode, a negative electrode, and the electrolyte solution according to any one of [1] to

[15] .

[19] The battery according to

[18] , wherein the positive electrode contains a compound represented by the following composition formula (3): Li １＋ｘ MO ２ (3) (In the composition formula (3), x is −0.1≦x≦0.5, and M contains an element including at least one transition metal.)

[20] The battery according to

[19] , wherein the content of Ni in M ​​is 55 mol % or more.

[21] The battery according to

[18] , wherein the positive electrode contains a compound represented by the following composition formula (4): LiMn １－ｙ Fe ｙ P.O. ４ (4) (In the composition formula (4), y is 0<y≦1.)

[22] A method for manufacturing a battery, comprising the steps of housing a positive electrode and a negative electrode in an exterior body and injecting the electrolyte solution according to any one of [1] to

[15] into the exterior body.

[23] A vehicle, comprising the battery according to any one of

[18] to

[21] .

[0007] According to the present invention, it is possible to provide a nonaqueous electrolyte solution that can improve the thermal stability of a battery and simultaneously suppress self-discharge of the battery, and also to provide a nonaqueous electrolyte battery that includes the nonaqueous electrolyte solution.

[0008] The inventors speculate as to why the nonaqueous electrolyte solution having the configuration of the present invention exhibits such excellent effects as follows. Because hexafluorophosphate anions are unstable at high temperatures, they are prone to decomposition and heat generation when the battery is heated to high temperatures. However, they are effective in protecting the aluminum current collector from leaching. On the other hand, bis(fluorosulfonyl)imide anions are highly thermally stable compounds, but the coatings they form on the electrodes are unstable and leaching, presumably resulting in battery self-discharge. The present inventors discovered that by mixing bis(fluorosulfonyl)imide salt with hexafluorophosphate salt in a specific ratio or greater and further containing a specific sulfonate anion-containing compound, a nonaqueous electrolyte solution can be constructed that simultaneously improves the battery's thermal stability (suppresses heat generation in high-temperature environments) and suppresses self-discharge. The inventors speculate that this is because increasing the ratio of bis(fluorosulfonyl)imide anions enhances thermal stability, the specific sulfonate anions stabilize the coating on the electrode surface, and the three anions react in a balanced manner with aluminum to form a coating with low solubility on the electrode surface. As a result, it is presumed that the thermal stability of the battery is improved and self-discharge of the battery can be suppressed.

[0009] The following describes in detail the embodiments of the present invention. However, the following description is an example (typical example) of the embodiment of the present invention, and the present invention is not limited to these details. Furthermore, the present invention can be implemented with any modifications within the scope of the gist of the present invention.

[0010] [1. First Electrolyte Solution] [1-1. Hexafluorophosphate, Bis(fluorosulfonyl)imide Salt, and Compound Containing an Anion Represented by General Formula (1)] A nonaqueous electrolyte solution according to one embodiment of the present invention (hereinafter, may be referred to as the "first electrolyte solution") is a nonaqueous electrolyte solution containing hexafluorophosphate, bis(fluorosulfonyl)imide salt, and a compound containing an anion represented by the following general formula (1), characterized in that the ratio of the mass of hexafluorophosphate to the mass of bis(fluorosulfonyl)imide salt in the nonaqueous electrolyte solution is 0.45 or less, and the content of the compound containing the anion represented by general formula (1) is 0.03 mass% or more in 100 mass% of the electrolyte solution. １ SO ３ － (1) (R １ represents a halogen atom.) Each component will be explained below.

[0011] Hexafluorophosphate salts are salts of hexafluorophosphate anions and counter cations. Bis(fluorosulfonyl)imide salts are salts of bis(fluorosulfonyl)imide anions and counter cations. The cations constituting the hexafluorophosphate salts and bis(fluorosulfonyl)imide salts are preferably alkali metal cations such as lithium, sodium, and potassium, and more preferably lithium cations.

[0012] In the general formula (1), R １ represents a halogen atom. The halogen atom is preferably a fluorine atom. In general formula (1), R １ When R is a fluorine atom, self-discharge and heat generation in the battery tend to be more effectively suppressed. １ SO ３ The counter cation is preferably an alkali metal cation such as lithium, sodium, or potassium, and more preferably a lithium cation.

[0013] The concentration of hexafluorophosphate in the non-aqueous electrolyte is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, and most preferably 2% by mass or more, relative to the total amount of the non-aqueous electrolyte, and is usually 18% by mass or less, preferably 16% by mass or less, more preferably 14% by mass or less, even more preferably 11% by mass or less, still more preferably 9% by mass or less, particularly preferably 7% by mass or less, particularly preferably 6% by mass or less, and most preferably 5% by mass or less. When the concentration of hexafluorophosphate in the non-aqueous electrolyte is within the above range, self-discharge of the battery tends to be suppressed. The concentration of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte solution is usually 3.5% by mass or more, preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 8% by mass or more, particularly preferably 9% by mass or more, and most preferably 10% by mass or more, and is usually 25% by mass or less, preferably 22% by mass or less, more preferably 20% by mass or less, particularly preferably 17% by mass or less, and most preferably 15% by mass or less, relative to the total amount of the non-aqueous electrolyte solution. When the concentration of the bis(fluorosulfonyl)imide salt is within the above range, the thermal stability of the battery tends to be improved. The concentration of the compound containing the anion represented by general formula (1) in the non-aqueous electrolyte is 0.03% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and most preferably 0.5% by mass or more, based on the total amount of the non-aqueous electrolyte. It is usually 10% by mass or less, preferably 5% by mass or less, more preferably 4% by mass or less, particularly preferably 3% by mass or less, and most preferably 2.5% by mass or less. When the concentration of the compound containing the anion represented by general formula (1) in the non-aqueous electrolyte is within the above range, the self-discharge and heat generation of the battery tend to be suppressed. In the non-aqueous electrolyte, the mass ratio of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt is 0.45 or less, preferably 0.40 or less, more preferably 0.35 or less, even more preferably 0.30 or less, particularly preferably 0.25 or less, and most preferably 0.2 or less.Also, it is usually 0.01 or more, preferably 0.04 or more, more preferably 0.06 or more, particularly preferably 0.1 or more, and most preferably 0.13 or more. When the mass ratio of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte is within the above range, self-discharge and heat generation of the battery tend to be suppressed. The mass ratio of the compound containing the anion represented by general formula (1) to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte is not particularly limited, but is usually 3.7 or less, preferably 2.6 or less, more preferably 1.6 or less, even more preferably 0.8 or less, particularly preferably 0.4 or less, and most preferably 0.3 or less. Also, it is usually 0.0001 or more, preferably 0.0005 or more, more preferably 0.001 or more, particularly preferably 0.002 or more, and most preferably 0.003 or more. When the ratio of the mass of the compound containing the anion represented by general formula (1) to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte solution is within the above range, self-discharge and heat generation in the battery tend to be suppressed. The identification and content of the compound in the non-aqueous electrolyte solution are measured using ion chromatography or magnetic resonance (NMR) spectroscopy.

[0014] In the first electrolyte, the bis(fluorosulfonyl)imide salt is LiN(FSO ２ ) ２ and the hexafluorophosphate is preferably LiPF ６ The compound containing the anion represented by general formula (1) is preferably a compound represented by the following general formula (1-1): １ SO ３ (1-1) (R in general formula (1-1) １ represents R in general formula (1). １ The same applies to the preferred ones.)

[0015] In the first electrolyte, LiN(FSO ２ ) ２ , LiPF ６and the mass of the compound represented by general formula (1-1), and the mass ratio thereof, are preferably within the ranges described above for the mass of the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by general formula (1), and the mass ratio thereof.

[0016] [1-2. Other Electrolytes] <Lithium Salts> In the non-aqueous electrolyte solution, other electrolytes than the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by general formula (1) are usually lithium salts. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used, and specific examples thereof include the following. For example, lithium fluoroborate salt, lithium fluorophosphate salt, lithium tungstate salt, lithium carboxylate salt, lithium imide salt, lithium methide salt, lithium oxalate salt, and fluorine-containing organic lithium salt are mentioned. Among them, LiBF is an example of the lithium fluoroborate salt. ４ Lithium fluorophosphate salt: Li ２ P.O. ３ F, LiPO ２ F ２ LiN(FSO) as a lithium imide salt ２ ) (CF ３ SO ２ ), LiN(CF ３ SO ２ ) ２ , LiN(C ２ F ５ SO ２ ) ２ , lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide; as lithium methide salts, LiC(FSO ２ ) ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３As the lithium oxalato salt, lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, lithium tris(oxalato)phosphate, etc. are more preferred because they have the effect of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, etc. The above electrolyte salts may be used alone or in combination of two or more. The total content of the electrolyte in the non-aqueous electrolyte solution (the total content of the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, the compound containing the anion represented by general formula (1), and other electrolytes) is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and is usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, relative to the total amount of the non-aqueous electrolyte solution. When the electrolyte content is within the above range, the electrical conductivity is appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[0017] [1-3. Nonaqueous Solvent] The first electrolytic solution, like a general nonaqueous electrolytic solution, usually contains, as its main component, a nonaqueous solvent that dissolves the above-mentioned electrolyte. There are no particular limitations on the nonaqueous solvent used as long as it dissolves the above-mentioned electrolyte, and known organic solvents can be used. Examples of organic solvents include, but are not limited to, saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, cyclic carboxylic acid esters, ether-based compounds, and sulfone-based compounds. One organic solvent can be used alone, or two or more organic solvents can be used in combination. There are no particular limitations on the combination of two or more organic solvents, but examples include saturated cyclic carbonates and chain carbonates, saturated cyclic carbonates and chain carboxylic acid esters, cyclic carboxylic acid esters or chain carbonates, and saturated cyclic carbonates, chain carbonates, and chain carboxylic acid esters. Among these, saturated cyclic carbonates and chain carbonates, and saturated cyclic carbonates, chain carbonates, and chain carboxylic acid esters are preferred.

[0018] [1-3-1. Saturated Cyclic Carbonate] Examples of saturated cyclic carbonates include those having an alkylene group containing 2 to 4 carbon atoms. From the viewpoint of improving battery characteristics due to the improved degree of lithium ion dissociation, saturated cyclic carbonates containing 2 to 3 carbon atoms are preferably used. Specific examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, etc. Among these, ethylene carbonate or propylene carbonate is preferred, and ethylene carbonate, which is less susceptible to oxidation and reduction, is more preferred. One saturated cyclic carbonate may be used alone, or two or more may be used in any combination and ratio. The content of the saturated 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. However, it is typically 3% by volume or more, preferably 5% by volume or more, relative to the total amount of nonaqueous solvent in the nonaqueous electrolyte solution, and typically 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting the content of the saturated cyclic carbonate within this range, it is possible to avoid a decrease in electrical conductivity due to a decrease in the dielectric constant of the nonaqueous electrolyte, and it is easy to set the large current discharge characteristics and cycle characteristics of the nonaqueous electrolyte secondary battery within a good range, and the oxidation / reduction resistance of the nonaqueous electrolyte is improved, and the stability with respect to the negative electrode and the stability during high-temperature storage tend to be improved. Note that, in this embodiment, "volume %" means the volume at 25°C and 1 atmosphere.

[0019] [1-3-2. Chain Carbonate] As the chain carbonate, for example, one having 3 to 7 carbon atoms is used, and in order to adjust the viscosity of the electrolyte solution within an appropriate range, a chain carbonate having 3 to 5 carbon atoms is preferably used. Specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate. Dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferred. Chain carbonates containing fluorine atoms (hereinafter sometimes abbreviated as "fluorinated chain carbonate") can also be suitably used. The number of fluorine atoms contained in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, the multiple fluorine atoms may be bonded to the same carbon or different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives such as fluoromethyl methyl carbonate; fluorinated ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate; and fluorinated diethyl carbonate derivatives such as ethyl-(2-fluoroethyl) carbonate. One type of chain carbonate may be used alone, or two or more types may be used in any combination and ratio. The content of the chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, and more preferably 25% by volume or more, relative to the total amount of the nonaqueous solvent in the nonaqueous electrolyte solution, and is usually 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting the content of the chain carbonate within the above range, the viscosity of the nonaqueous electrolyte solution can be set within an appropriate range, a decrease in ionic conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be set within a favorable range.

[0020] Furthermore, by combining a specific chain carbonate with ethylene carbonate at a specific content, battery performance can be significantly improved. For example, when dimethyl carbonate and ethyl methyl carbonate are selected as the specific chain carbonate, the content of ethylene carbonate is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the present invention, but it is usually 15% by volume or more, preferably 20% by volume or more, and usually 45% by volume or less, preferably 40% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. The content of dimethyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. The content of ethyl methyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. By setting the content within the above range, high temperature stability is excellent and gas generation tends to be suppressed.

[0021] [1-3-3. Chain Carboxylic Acid Ester] Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. Among these, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate are preferred in terms of improving battery characteristics. Chain carboxylic acid esters in which some of the hydrogen atoms in the above-mentioned compounds have been substituted with fluorine (e.g., methyl trifluoroacetate, ethyl trifluoroacetate, etc.) can also be used. The content of the chain carboxylic acid ester is typically 1% by volume or more, preferably 5% by volume or more, and more preferably 15% by volume or more, based on the total amount of nonaqueous solvent in the nonaqueous electrolyte. This range improves the electrical conductivity of the nonaqueous electrolyte and facilitates the improvement of the high-current discharge characteristics of nonaqueous electrolyte batteries. Furthermore, the content of the chain carboxylic acid ester is typically 70% by volume or less, preferably 50% by volume or less, and more preferably 40% by volume or less. By setting the upper limit in this manner, the viscosity of the nonaqueous electrolyte solution can be kept within an appropriate range, a decrease in electrical conductivity can be avoided, an increase in negative electrode resistance can be suppressed, and the large current discharge characteristics of the nonaqueous electrolyte secondary battery can be made to fall within a favorable range.

[0022] [1-3-4. Cyclic Carboxylic Acid Ester] Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Among these, γ-butyrolactone is more preferred. Cyclic carboxylic acid esters in which some of the hydrogen atoms in the above-mentioned compounds are substituted with fluorine can also be used. The content of the cyclic carboxylic acid ester is typically 1 vol% or more, preferably 5 vol% or more, and more preferably 15 vol% or more, based on the total amount of nonaqueous solvent in the nonaqueous electrolyte. This range improves the electrical conductivity of the nonaqueous electrolyte and facilitates the enhancement of the high-current discharge characteristics of nonaqueous electrolyte secondary batteries. Furthermore, the content of the cyclic carboxylic acid ester is typically 70 vol% or less, preferably 50 vol% or less, and more preferably 40 vol% or less. By setting the upper limit in this manner, the viscosity of the nonaqueous electrolyte can be kept within an appropriate range, a decrease in electrical conductivity can be avoided, an increase in negative electrode resistance can be suppressed, and the high-current discharge characteristics of nonaqueous electrolyte secondary batteries can be easily maintained within a favorable range.

[0023] [1-3-5. Ether Compounds] Preferred ether compounds are chain ethers having 3 to 10 carbon atoms, such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether, and cyclic ethers having 3 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane. Some of the hydrogen atoms in the above-mentioned ether compounds may be substituted with fluorine. Among these, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are preferred as linear ethers having 3 to 10 carbon atoms, as they have a high solvation ability for lithium ions, improve ionic dissociation, have low viscosity, and provide high ionic conductivity. Tetrahydrofuran, 1,3-dioxane, and 1,4-dioxane are preferred as cyclic ethers having 3 to 6 carbon atoms, as they provide high ionic conductivity. The content of the ether-based compound is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention. However, the content is typically 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and typically 30% by volume or less, preferably 25% by volume or less, and more preferably 20% by volume or less, relative to the total amount of nonaqueous solvent in the nonaqueous electrolyte solution. If the content of the ether-based compound is within the above range, it is easy to ensure the effect of improving the degree of lithium ion dissociation by the ether-based compound and improving ionic conductivity due to the reduced viscosity of the nonaqueous electrolyte solution. Furthermore, when the negative electrode active material is a carbonaceous material, the phenomenon of chain ethers being co-inserted with lithium ions can be suppressed, and therefore the input / output characteristics and charge / discharge rate characteristics can be kept within appropriate ranges.

[0024] [1-3-6. Sulfone Compound] The sulfone compound is not particularly limited and may be a cyclic sulfone or a chain sulfone. In the case of a cyclic sulfone, the carbon number is usually 3 to 6, preferably 3 to 5, and in the case of a chain sulfone, the carbon number is usually 2 to 6, preferably 2 to 5. The number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2. Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoints of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred. Preferred sulfolanes are sulfolane and sulfolane derivatives. Preferred sulfolane derivatives are those in which one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with a fluorine atom, an alkyl group, or a fluorine-substituted alkyl group. Among these, 2-methyl sulfolane, 3-methyl sulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,3-difluorosulfolane, 2-trifluoromethyl sulfolane, 3-trifluoromethyl sulfolane, and the like are preferred in terms of high ionic conductivity and high input / output. Examples of chain sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, and pentafluoroethyl methyl sulfone. Of these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in terms of improving the high-temperature storage stability of the electrolyte. The content of the sulfone-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention according to the present embodiment. However, it is usually 0.3 vol% or more, preferably 0.5 vol% or more, more preferably 1 vol% or more, and usually 40 vol% or less, preferably 35 vol% or less, more preferably 30 vol% or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte solution.When the content of the sulfone-based compound is within the above range, an electrolyte solution having excellent high-temperature storage stability tends to be obtained.

[0025] [1-4. Auxiliary Agent] The first electrolytic solution may contain various auxiliary agents within the range that does not significantly impair the effects of the present invention. Any conventionally known auxiliary agent can be used as the auxiliary agent. Note that one auxiliary agent may be used alone, or two or more auxiliary agents may be used in any combination and ratio. Examples of the auxiliary agent that may be contained in the non-aqueous electrolyte solution include cyclic carbonates having carbon-carbon unsaturated bonds, fluorine-containing cyclic carbonates, organic compounds having an isocyanate group, organic compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, fluorine-free carboxylic acid esters, cyclic compounds having an ether bond, carboxylic acid anhydrides, triple bond-containing compounds, phosphazene compounds, cyclic acetal compounds, borate anion-containing compounds, phosphate anion-containing compounds having a P=O bond and a P-F bond, and at least one compound (A) selected from the group consisting of oxalate complex anion-containing compounds (however, bis(fluorosulfonyl)imide salts, hexafluorophosphate salts, and compounds represented by the general formula (1-1)) can be exemplified. Specific examples of these include compounds described in WO 2015 / 111676 and the like. Compound (A) is a cyclic carbonate having a carbon-carbon unsaturated bond, a fluorine-containing cyclic carbonate, an organic compound having an isocyanate group, an organic compound having an isocyanuric acid skeleton, a sulfur-containing organic compound, a phosphorus-containing organic compound, an organic compound having a cyano group, a silicon-containing compound, an aromatic compound, a cyclic compound having an ether bond, a fluorine-free carboxylic acid ester, a carboxylic acid anhydride, a triple bond-containing compound, a phosphazene compound, a cyclic acetal compound, a boron anion-containing compound, an oxalate complex anion-containing compound, and at least one compound selected from the group consisting of a phosphate anion-containing compound having a P═O bond and a P—F bond (however, bis(fluorosulfonyl)imide salt, hexafluorophosphate salt, and a compound containing an anion represented by general formula (1) are excluded).Among these, at least one anion-containing compound selected from a phosphate anion-containing compound having a P—F bond and a P═O bond, and an oxalate complex anion-containing compound (hereinafter also referred to as a "specific anion-containing compound"), a cyclic carbonate having a carbon-carbon unsaturated bond, and at least one carbonate compound selected from a fluorine-containing cyclic carbonate (hereinafter also referred to as a "specific carbonate compound") are preferred, and at least one anion-containing compound selected from a phosphate anion-containing compound having a P—F bond and a P═O bond, and an oxalate complex anion-containing compound are particularly preferred from the viewpoint of suppressing an increase in the internal resistance of the battery. The content of the auxiliary agent is not particularly limited and may be any as long as it does not significantly impair the effects of the present invention, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably less than 1% by mass, based on the total amount of the non-aqueous electrolyte solution.

[0026] Cyclic compounds having an ether bond can be used as auxiliary agents in non-aqueous electrolyte solutions, and some of them can also be used as non-aqueous solvents as described in "1-3. Non-aqueous solvents." When used as auxiliary agents, cyclic compounds having an ether bond are used in an amount of less than 4 mass %. Borate anion-containing compounds, oxalate complex anion-containing compounds, monofluorophosphate anion-containing compounds, and difluorophosphate anion-containing compounds can be used as auxiliary agents in non-aqueous electrolyte solutions, and some of them can also be used as electrolytes as described in "1-2. Electrolytes." When used as auxiliary agents, these compounds are used in an amount of less than 8 mass %.

[0027] [1-4-1. Specific Anion-Containing Compound] The specific anion-containing compound is usually an acid or a salt. The specific anion-containing compound is preferably a salt, and the counter cation is preferably an alkali metal cation such as lithium, sodium, or potassium, and more preferably a lithium cation. At least one anion-containing compound selected from phosphate anion-containing compounds having a P—F bond and a P═O bond and oxalate complex anion-containing compounds can be used alone or in combination of two or more in any ratio. Among these, phosphate anion-containing compounds having a P—F bond and a P═O bond are preferred from the viewpoint of suppressing the amount of gas generation after high-temperature storage.

[0028] [1-4-1-1. Phosphate anion-containing compound having a P—F bond and a P═O bond] Examples of phosphate anion-containing compounds having a F—P bond and a P═O bond include PO ３ F ２ － monofluorophosphate anions such as PO ２ F ２ － Among these, compounds containing difluorophosphate anions are preferred from the viewpoint of the balance between the output characteristics of the battery and the protection of the electrode interface.

[0029] [1-4-1-2. Oxalato Complex Anion-Containing Compound] The oxalato complex anion-containing compound is not particularly limited as long as it contains an anion having an oxalato complex in the molecule. The oxalato complex anion-containing compound is a compound containing an anion of an acid in which oxalic acid is coordinated or bonded to a central atom to form a complex. Examples of the oxalato complex anion-containing compound include a boron oxalato complex anion in which oxalic acid is coordinated or bonded to a boron atom, and a phosphorus oxalato complex anion in which oxalic acid is coordinated or bonded to a phosphorus atom. Examples of the boron oxalato complex anion include a bis(oxalato)borate anion and a difluorooxalatoborate anion. Examples of the phosphorus oxalato complex anion include a tetrafluorooxalatophosphate anion, a difluorobis(oxalato)phosphate anion, and a tris(oxalato)phosphate anion. Among these, from the viewpoint of forming a stable composite coating on the surface of the electrode, compounds containing boron oxalato complex anions are preferred, and compounds containing bis(oxalato)borate anions are more preferred.

[0030] (Content of specific anion-containing compound) When the non-aqueous electrolyte solution contains a specific anion-containing compound, the content of the specific anion-containing compound (total amount when two or more types are contained) in the total amount of the non-aqueous electrolyte solution is preferably 0.001 mass% or more, more preferably 0.01 mass% or more, even more preferably 0.1 mass% or more, and is preferably 5 mass% or less, more preferably 4 mass% or less, and even more preferably 3 mass% or less. If the content of the specific anion-containing compound is within the above range, the battery characteristics, particularly the DCR retention rate after high-temperature storage, can be significantly improved, and the amount of gas generation after high-temperature storage can be significantly suppressed. Although the reason for this is unclear, it is thought that when the content of the specific anion-containing compound is within the above mass ratio range, side reactions of the components of the non-aqueous electrolyte solution on the electrode surface can be minimized. The identification and content measurement of the specific anion-containing compound are performed by nuclear magnetic resonance (NMR) spectroscopy.

[0031] (Mass ratio of specific anion-containing compound to compound containing an anion represented by general formula (1)) The mass ratio of the content of the specific anion-containing compound (total amount when two or more types are used) to the content of the compound containing an anion represented by general formula (1) (specific anion-containing compound [g] / compound containing an anion represented by general formula (1) [g]) is usually 0.01 or more, preferably 0.05 or more, more preferably 0.3 or more, and usually 100 or less, preferably 10 or less, more preferably 5 or less, and even more preferably 4 or less. The mass ratio of the content of the specific anion-containing compound to the content of the compound represented by general formula (1-1) (specific anion-containing compound [g] / compound represented by general formula (1-1) [g]) is also preferably within the same range as above. If the mass ratio is within the above range, the battery characteristics, particularly the resistance retention rate after high-temperature storage, can be significantly improved, and the amount of gas generation after high-temperature storage can be significantly suppressed. The reason for this is unclear, but it is thought that by containing the compound containing the anion represented by general formula (1) and the specific anion-containing compound within the above mass ratio range, side reactions of the components of the non-aqueous electrolyte solution on the electrode surface can be minimized.

[0032] (Mass ratio of specific anion-containing compound to electrolyte) When the non-aqueous electrolyte solution contains a specific anion-containing compound, the mass ratio of the content of the specific anion-containing compound (total amount when two or more types are used) to the content of the electrolyte (specific anion-containing compound [g] / electrolyte [g]) is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, even more preferably 0.025 or more, and is usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, even more preferably 0.35 or less. If the mass ratio is within the above range, the battery characteristics, particularly the resistance retention rate after high-temperature storage, can be significantly improved, and the amount of gas generation after high-temperature storage can be significantly suppressed. Although the reason for this is unclear, it is thought that by containing the specific anion-containing compound and electrolyte within the above mass ratio range, side reactions of the electrolyte in the battery system can be minimized.

[0033] [1-4-2. Specific Carbonate Compound] The nonaqueous electrolyte preferably contains at least one carbonate compound selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond and cyclic carbonates having a fluorine atom. Among these, it is preferable to contain a cyclic carbonate having a carbon-carbon unsaturated bond, and it is more preferable to contain vinylene carbonate. These compounds can be used alone or in combination of two or more compounds in any ratio. It is preferable to combine an unsaturated cyclic carbonate with a fluorinated cyclic carbonate, and it is more preferable to combine vinylene carbonate with a fluorinated cyclic carbonate or an unsaturated cyclic carbonate with monofluoroethylene carbonate, and it is even more preferable to combine vinylene carbonate with monofluoroethylene carbonate.

[0034] (Content of specific carbonate compound) The content of the specific carbonate compound (total amount when two or more types are used) in the total amount of the non-aqueous electrolyte is usually 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. It is also usually 10% by mass or less, preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. If the content of the specific carbonate compound is within the above range, the battery characteristics, particularly durability, can be improved. While the reason for this is unclear, it is believed that the inclusion of the carbonate compound at this ratio forms a coating on the electrode, minimizing side reactions of the components of the non-aqueous electrolyte. The identification and content measurement of the specific carbonate compound are performed by nuclear magnetic resonance (NMR) spectroscopy.

[0035] (Mass ratio of specific carbonate compound to compound containing an anion represented by general formula (1)) The mass ratio of the content of the specific carbonate compound (total amount when two or more types are used) to the content of the compound containing an anion represented by general formula (1) (specific carbonate compound [g] / compound containing an anion represented by general formula (1) [g]) is usually 0.01 or more, preferably 0.05 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is usually 100 or less, preferably 10 or less, more preferably 5 or less, and even more preferably 4 or less. The mass ratio of the content of the specific carbonate compound to the content of the compound represented by general formula (1-1) (specific carbonate compound [g] / compound represented by general formula (1-1) [g]) is also preferably within the same range as above. If the mass ratio is within the above range, the battery characteristics, particularly durability, can be improved. The reason for this is unclear, but it is thought that by containing the specific carbonate compound within the above mass ratio range, a coating is formed on the electrode, minimizing side reactions of the components of the non-aqueous electrolyte solution.

[0036] (Mass ratio of specific carbonate compound to electrolyte) In the non-aqueous electrolyte solution, the mass ratio of the content of the specific carbonate compound (total amount when two or more types are used) to the content of the electrolyte (specific carbonate compound [g] / electrolyte [g]) is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and even more preferably 0.025 or more, and is usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. If the mass ratio is within the above range, the battery characteristics, particularly durability, can be improved. Although the reason for this is unclear, it is thought that by containing the carbonate compound and the electrolyte within the above mass ratio range, a coating is formed on the electrode, minimizing side reactions of the electrolyte in the battery system.

[0037] [1-4-2-1. Cyclic Carbonates Having Carbon-Carbon Unsaturated Bonds] Cyclic carbonates having carbon-carbon unsaturated bonds (hereinafter also referred to as "unsaturated cyclic carbonates") are not particularly limited as long as they are cyclic carbonates having a carbon-carbon double bond or a carbon-carbon triple bond. Cyclic carbonates having an aromatic ring are also included in the unsaturated cyclic carbonates. Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring, a carbon-carbon double bond, or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, and catechol carbonates. Among these, vinylene carbonates and ethylene carbonates substituted with a substituent having an aromatic ring, a carbon-carbon double bond, or a carbon-carbon triple bond are preferred. Examples of vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-vinyl vinylene carbonate, allyl vinylene carbonate, and 4,5-diallyl vinylene carbonate. Examples of ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ethylene carbonate, 4-allyl-5-ethynyl ethylene carbonate, phenyl ethylene carbonate, 4,5-diphenyl ethylene carbonate, 4-phenyl-5-vinyl ethylene carbonate, 4-allyl-5-phenyl ethylene carbonate, allyl ethylene carbonate, 4,5-diallyl ethylene carbonate, and 4-methyl-5-allyl ethylene carbonate.Among these, vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate are preferred because they form a more stable composite coating on the electrode, and one or more selected from vinylene carbonate and vinylethylene carbonate are more preferred, with vinylene carbonate being even more preferred. The unsaturated cyclic carbonates can be used alone or in combination of two or more in any ratio.

[0038] [1-4-2-2. Cyclic Carbonates Having Fluorine Atoms] The cyclic carbonates having fluorine atoms are not particularly limited as long as they have a cyclic carbonate structure and contain fluorine atoms. Examples of cyclic carbonates having fluorine atoms include fluorinated cyclic carbonates having an alkylene group with 2 to 6 carbon atoms, and derivatives thereof, such as fluorinated ethylene carbonate (fluoroethylene carbonate) and derivatives thereof, and ethylene carbonate having a fluorine-containing group. Examples of derivatives of fluorinated ethylene carbonate include fluorinated ethylene carbonate substituted with an alkyl group (for example, an alkyl group with 1 to 4 carbon atoms). Among these, fluoroethylene carbonate having 1 to 8 fluorine atoms and derivatives thereof are preferred. Examples of fluoroethylene carbonate and derivatives thereof having 1 to 8 fluorine atoms, and ethylene carbonate having a fluorine-containing group 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. Among these, from the viewpoint of imparting high ionic conductivity to the electrolyte and facilitating the formation of a stable interface protective coating, one or more selected from monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate are preferred. The fluorine atom-containing cyclic carbonates can be used alone or in combination of two or more in any ratio.

[0039] [1-5. Method for Producing Electrolyte Solution] The first electrolytic solution can be produced by dissolving a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, a compound containing an anion represented by general formula (1), and other components used as needed in a non-aqueous solvent at a specific mass ratio. The present invention also relates to a method for producing such an electrolytic solution. That is, one embodiment of the present invention relates to a method for producing a first electrolytic solution, which includes a step of dissolving a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, and a compound containing an anion represented by general formula (1) in a non-aqueous solvent, characterized in that the mass ratio of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 0.45 or less, and the content of the compound containing an anion represented by general formula (1) is 0.03 mass% or more in 100 mass% of the electrolytic solution. The method for mixing the components and the order of addition are not particularly limited, and known methods can be used. For example, the first electrolytic solution can be prepared by adding the components to a non-aqueous solvent under an inert gas atmosphere and mixing them.

[0040] [2. Second Electrolyte Solution] [2-1. Hexafluorophosphate, Bis(fluorosulfonyl)imide Salt, and Compound Containing an Anion Represented by General Formula (2)] A nonaqueous electrolyte solution according to one embodiment of the present invention (hereinafter, may be referred to as the "second electrolyte solution") is a nonaqueous electrolyte solution containing hexafluorophosphate, bis(fluorosulfonyl)imide salt, and a compound containing an anion represented by the following general formula (2), characterized in that the ratio of the mass of hexafluorophosphate to the mass of bis(fluorosulfonyl)imide salt in the nonaqueous electrolyte solution is 1 or less, and the content of the compound containing the anion represented by general formula (2) is 0.01 mass% or more in 100 mass% of the electrolyte solution. ２ SO ３ － (2) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.

[0041] Hexafluorophosphate salts are salts of hexafluorophosphate anions and counter cations. Bis(fluorosulfonyl)imide salts are salts of bis(fluorosulfonyl)imide anions and counter cations. The cations constituting the hexafluorophosphate salts and bis(fluorosulfonyl)imide salts are preferably alkali metal cations such as lithium, sodium, and potassium, and more preferably lithium cations.

[0042] In the general formula (2), R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom. ２ is preferably an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom, more preferably an aliphatic saturated alkoxy group having 1 to 3 carbon atoms, and particularly preferably an aliphatic saturated alkoxy group having 1 to 2 carbon atoms. The halogen atom is preferably a fluorine atom. The alkoxy group is preferably an ethoxy group or a methoxy group. In general formula (2), R ２ When R has the above-described preferred structure, self-discharge and heat generation in the battery tend to be more effectively suppressed. ２ SO ３ The counter cation is preferably an alkali metal cation such as lithium, sodium, or potassium, and more preferably a lithium cation.

[0043] The concentration of hexafluorophosphate in the non-aqueous electrolyte is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, and most preferably 2% by mass or more, relative to the total amount of the non-aqueous electrolyte, and is usually 18% by mass or less, preferably 16% by mass or less, more preferably 14% by mass or less, even more preferably 11% by mass or less, still more preferably 9% by mass or less, particularly preferably 7% by mass or less, particularly preferably 6% by mass or less, and most preferably 5% by mass or less. When the concentration of hexafluorophosphate in the non-aqueous electrolyte is within the above range, self-discharge of the battery tends to be suppressed. The concentration of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte solution is usually 3.5% by mass or more, preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 8% by mass or more, particularly preferably 9% by mass or more, and most preferably 10% by mass or more, and is usually 25% by mass or less, preferably 22% by mass or less, more preferably 20% by mass or less, particularly preferably 17% by mass or less, and most preferably 15% by mass or less, relative to the total amount of the non-aqueous electrolyte solution. When the concentration of the bis(fluorosulfonyl)imide salt is within the above range, the thermal stability of the battery tends to be improved. The concentration of the compound containing the anion represented by general formula (2) in the non-aqueous electrolyte solution is 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and most preferably 0.5% by mass or more, based on the total amount of the non-aqueous electrolyte solution, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 4% by mass or less, particularly preferably 3% by mass or less, and most preferably 2.5% by mass or less. When the concentration of the compound containing the anion represented by general formula (2) in the non-aqueous electrolyte solution is within the above range, self-discharge and heat generation of the battery tend to be suppressed.The mass ratio of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte solution is 1 or less, specifically 0.80 or less, more specifically 0.60 or less, and even more specifically 0.50 or less, preferably 0.45 or less, more preferably 0.40 or less, even more preferably 0.35 or less, especially preferably 0.30 or less, particularly preferably 0.25 or less, and most preferably 0.20 or less. It is also usually 0.01 or more, preferably 0.04 or more, more preferably 0.06 or more, particularly preferably 0.1 or more, and most preferably 0.13 or more. When the mass ratio of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte solution is within the above range, the self-discharge and heat generation of the battery tend to be suppressed. The mass ratio of the compound containing the anion represented by general formula (2) to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte is not particularly limited, but is usually 3.7 or less, preferably 2.6 or less, more preferably 1.6 or less, even more preferably 0.8 or less, particularly preferably 0.4 or less, and most preferably 0.3 or less. It is also usually 0.0001 or more, preferably 0.0005 or more, more preferably 0.001 or more, particularly preferably 0.002 or more, and most preferably 0.003 or more. When the mass ratio of the compound containing the anion represented by general formula (2) to the mass of the bis(fluorosulfonyl)imide salt in the non-aqueous electrolyte is within the above range, self-discharge and heat generation in the battery tend to be suppressed. The above compounds in the non-aqueous electrolyte are identified and their content measured using ion chromatography or magnetic resonance (NMR) spectroscopy.

[0044] In the second electrolyte, the bis(fluorosulfonyl)imide salt is LiN(FSO ２ ) ２ and the hexafluorophosphate is preferably LiPF ６ The compound containing the anion represented by general formula (2) is preferably a compound represented by the following general formula (2-1): ２ SO３ (2-1) (R in general formula (2-1) ２ is R in general formula (2). ２ The same applies to the preferred ones.)

[0045] In the second electrolyte, LiN(FSO ２ ) ２ , LiPF ６ and the mass of the compound represented by general formula (2-1), and the mass ratio thereof, are preferably within the ranges described above for the mass of the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by general formula (2), and the mass ratio thereof.

[0046] [2-2. Other Electrolytes] <Lithium Salt> In the non-aqueous electrolyte solution, a lithium salt is typically used as the other electrolyte other than the bis(fluorosulfonyl)imide salt, hexafluorophosphate salt, and compound containing an anion represented by general formula (2). The lithium salt is not particularly limited as long as it is known to be used for this application, and any lithium salt can be used. The lithium salt may be used alone or in combination of two or more. Specific examples are the same as those described above for the first electrolyte solution, and preferred examples are also the same. The total content of the electrolytes in the non-aqueous electrolyte solution (the total content of the bis(fluorosulfonyl)imide salt, hexafluorophosphate salt, compound containing an anion represented by general formula (2), and other electrolytes) is not particularly limited, but is typically 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and typically 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, based on the total amount of the non-aqueous electrolyte solution. When the content of the electrolyte is within the above range, the electrical conductivity becomes appropriate for the battery operation, and sufficient output characteristics tend to be obtained.

[0047] [2-3. Non-aqueous solvent] The second electrolytic solution, like a general non-aqueous electrolytic solution, usually contains a non-aqueous solvent that dissolves the above-mentioned electrolyte as its main component. The non-aqueous solvent used is not particularly limited as long as it dissolves the above-mentioned electrolyte, and known organic solvents can be used. The organic solvent can be used alone or in combination of two or more. Specific examples thereof are the same as those described above for the first electrolytic solution, and preferred examples are also the same. Specific examples of combinations of two or more non-aqueous solvents are the same as those described above for the first electrolytic solution, and preferred examples are also the same. The preferred range of the content of each non-aqueous solvent is also the same as the range described above for the first electrolytic solution.

[0048] [2-4. Auxiliary Agent] The second electrolytic solution may contain various auxiliary agents within the range that does not significantly impair the effects of the present invention. Any conventionally known auxiliary agent can be used as the auxiliary agent. Note that one auxiliary agent may be used alone, or two or more auxiliary agents may be used in any combination and ratio. Examples of the auxiliary agent that may be contained in the non-aqueous electrolyte solution include cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, organic compounds having an isocyanate group, organic compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, fluorine-free carboxylic acid esters, cyclic compounds having an ether bond, carboxylic acid anhydrides, triple bond-containing compounds, phosphazene compounds, cyclic acetal compounds, borate anion-containing compounds, phosphate anion-containing compounds having a P=O bond and a P-F bond, and at least one compound (A) selected from the group consisting of oxalate complex anion-containing compounds (however, bis(fluorosulfonyl)imide salts, hexafluorophosphate salts, and compounds represented by the general formula (2-1)) can be exemplified. Specific examples of these include the specific examples described above in the first electrolyte solution, for example, compounds described in WO 2015 / 111676 and the like. Compound (A) is a cyclic carbonate having a carbon-carbon unsaturated bond, a fluorine-containing cyclic carbonate, an organic compound having an isocyanate group, an organic compound having an isocyanuric acid skeleton, a sulfur-containing organic compound, a phosphorus-containing organic compound, an organic compound having a cyano group, a silicon-containing compound, an aromatic compound, a cyclic compound having an ether bond, a fluorine-free carboxylic acid ester, a carboxylic acid anhydride, a triple bond-containing compound, a phosphazene compound, a cyclic acetal compound, a boron anion-containing compound, an oxalate complex anion-containing compound, and at least one compound selected from the group consisting of a phosphate anion-containing compound having a P═O bond and a P—F bond (however, bis(fluorosulfonyl)imide salt, hexafluorophosphate salt, and a compound containing an anion represented by general formula (2) are excluded).Among these, at least one anion-containing compound selected from a phosphate anion-containing compound having a P—F bond and a P═O bond, and an oxalate complex anion-containing compound (hereinafter also referred to as a “specific anion-containing compound”), and / or a cyclic carbonate having a carbon-carbon unsaturated bond, and at least one carbonate compound selected from a fluorine-containing cyclic carbonate (hereinafter also referred to as a “specific carbonate compound”) are preferred. The content of the auxiliary agent is not particularly limited and may be any as long as it does not significantly impair the effects of the present invention, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably less than 1% by mass, relative to the total amount of the non-aqueous electrolyte solution. The preferred ranges of the content of each auxiliary agent and the preferred ranges of the content of each auxiliary agent are the same as those described above for the first electrolyte solution.

[0049] (Mass ratio of specific anion-containing compound to compound containing an anion represented by general formula (2)) The mass ratio of the content of the specific anion-containing compound (total amount when two or more types are used) to the content of the compound containing an anion represented by general formula (2) (specific anion-containing compound [g] / compound containing an anion represented by general formula (2) [g]) is usually 0.01 or more, preferably 0.05 or more, more preferably 0.3 or more, and usually 100 or less, preferably 10 or less, more preferably 5 or less, and even more preferably 4 or less. The mass ratio of the content of the specific anion-containing compound to the content of the compound represented by general formula (2-1) (specific anion-containing compound [g] / compound represented by general formula (2-1) [g]) is also preferably within the same range as above. If the mass ratio is within the above range, the battery characteristics, particularly the resistance retention rate after high-temperature storage, can be significantly improved, and the amount of gas generation after high-temperature storage can be significantly suppressed. The reason for this is unclear, but it is thought that by containing the compound containing the anion represented by general formula (2) and the specific anion-containing compound within the above mass ratio range, side reactions of the components of the nonaqueous electrolyte solution on the electrode surface can be minimized.

[0050] (Mass ratio of specific carbonate compound to compound containing an anion represented by general formula (2)) The mass ratio of the content of the specific carbonate compound (total amount when two or more types are used) to the content of the compound containing an anion represented by general formula (2) (specific carbonate compound [g] / compound containing an anion represented by general formula (2) [g]) is usually 0.01 or more, preferably 0.05 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is usually 100 or less, preferably 10 or less, more preferably 5 or less, and even more preferably 4 or less. The mass ratio of the content of the specific carbonate compound to the content of the compound represented by general formula (2-1) (specific carbonate compound [g] / compound represented by general formula (2-1) [g]) is also preferably within the same range as above. If the mass ratio is within the above range, the battery characteristics, particularly durability, can be improved. The reason for this is unclear, but it is thought that by containing the specific carbonate compound within the above mass ratio range, a coating is formed on the electrode, minimizing side reactions of the components of the non-aqueous electrolyte solution.

[0051] [2-5. Method for Producing Electrolyte Solution] The second electrolytic solution can be produced by dissolving a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, a compound containing an anion represented by general formula (2), and other components used as needed in a non-aqueous solvent at a specific mass ratio. The present invention also relates to a method for producing such an electrolytic solution. That is, one embodiment of the present invention relates to a method for producing an electrolytic solution, which includes a step of dissolving a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, and a compound containing an anion represented by general formula (2) in a non-aqueous solvent, characterized in that the mass ratio of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 1 or less, and the content of the compound containing an anion represented by general formula (2) is 0.01 mass% or more in 100 mass% of the electrolytic solution. The method for mixing the components and the order of addition are not particularly limited, and known methods can be used. For example, the second electrolytic solution can be prepared by adding the components to a non-aqueous solvent under an inert gas atmosphere and mixing them.

[0052] [3. Battery] A battery (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 including a nonaqueous electrolyte.

[0053] [3-1. Nonaqueous Electrolyte] The nonaqueous electrolyte is the first or second electrolyte described above. Note that other nonaqueous electrolytes may be mixed with the nonaqueous electrolyte described above within the scope of the present invention.

[0054] [3-2. Positive Electrode] The positive electrode has a positive electrode active material on at least a portion of the surface of a current collector.

[0055] [3-2-1. Positive Electrode Active Material] The positive electrode active material (lithium transition metal compound) used in the positive electrode will be described below.

[0056] [3-2-1-1. Lithium transition metal compounds] Lithium transition metal compounds are compounds having a structure that can extract and insert lithium ions, and examples thereof include sulfides, phosphate compounds, silicate compounds, borate compounds, and lithium transition metal composite oxides. Among these, phosphate compounds and lithium transition metal composite oxides are preferred, and lithium transition metal composite oxides are more preferred. Examples of lithium transition metal composite oxides include those having a spinel structure that allows three-dimensional diffusion and those belonging to a layered structure that allows two-dimensional diffusion of lithium ions. Those having a spinel structure are generally represented by the following composition formula: Li ｘ’ M' ２ O ４ (In the above composition formula, x' is 1≦x'≦1.5, and M' contains at least one transition metal element.) Specifically, LiMn ２ O ４ , LiCoMnO ４ , LiNi ０．５ Mn １．５ O ４ , LiCoVO ４Those having a layered structure are generally represented by the following composition formula (3): Li １＋ｘ MO ２ ... (3) (In composition formula (3), x is -0.1≦x≦0.5, and M contains at least one transition metal element.) In composition formula (3), M is preferably at least one element selected from the group consisting of Ni, Co, Mn, Al, Mg, Zr, Fe, Ti, V, Cr, La, Ce, Mo, Sc, Y, and Er, and preferably contains at least Ni. The Ni content in M ​​is preferably 30 mol% or more, more preferably 45 mol% or more, even more preferably 55 mol% or more, particularly preferably 65 mol% or more, and most preferably 75 mol% or more. Specifically, LiCoO ２ , LiNiO ２ , LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , Li １．０５ Ni ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６１ Mn ０．１９ Co ０．２０ O ２ , LiNi ０．８３ Mn ０．０６ Co ０．１１ O ２ , Li １．０５ Ni ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．８ Co０．１ Mn ０．１ O ２ , Li [L ｉ１／３ Mn ２／３ ]O ２ Among these, from the viewpoint of improving the battery capacity, a lithium transition metal composite oxide having a layered structure is preferred, and a transition metal composite oxide represented by the following composition formula (3-1) is more preferred. Li ａ１ Ni ｂ１ M ｃ１ O ２ ... (3-1) (In composition formula (3-1), a1, b1, and c1 represent values ​​satisfying 0.90≦a1≦1.10, 0.30≦b1≦0.98, and 0.01≦c1≦0.5, respectively. M represents at least one element selected from the group consisting of Co, Mn, Al, Mg, Zr, Fe, Ti, V, Cr, La, Ce, Mo, Sc, Y, and Er.) In composition formula (3-1), b1 preferably satisfies 0.4≦b1, more preferably 0.5≦b1, and particularly preferably 0.6≦b1. Furthermore, in composition formula (3-1), it is preferable that 0.50≦b1+c1, more preferably 0.50≦b1+c1≦1, and even more preferably b1+c1=1. In particular, from the viewpoint of the structural stability of the lithium transition metal composite oxide, a transition metal oxide represented by the following composition formula (3-2) is preferred. Li ａ２ Ni ｂ２ Co ｃ２ M ｄ２ O ２... (3-2) (In the composition formula (3-2), a2, b2, and c2 are numerical values ​​that satisfy 0.90≦a2≦1.10, 0.50≦b2≦0.98, and 0.01≦c2<0.50, respectively, and satisfy 0.01≦d2<0.50. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, V, Cr, La, Ce, Mo, Sc, Y, and Er.) In the composition formula (3-2), M preferably contains Mn or Al, and more preferably contains Mn. This is because the structural stability of the lithium transition metal oxide is increased and structural deterioration during repeated charge and discharge is suppressed. In addition, in the composition formula (3-2), it is preferable that b2+c2+d2=1. Suitable specific examples of the lithium transition metal oxide represented by the composition formula (3-2) include, for example, LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , Li １．０５ Ni ０．５０ Co ０．２０ Mn ０．３０ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．６１ Mn ０．１９ Co ０．２０ O ２ , LiNi ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．８３ Mn ０．０６ Co ０．１１ O ２ etc.

[0057] Phosphate compounds are generally represented by the following formula: Li ｘ "M" ｙ "P.O. ４(In the above composition formula, 0.8≦x″≦1.5, 0.9≦y″≦1.1, and M″ contains at least one transition metal element.) Examples of M″ include Fe, Ni, Co, and Mn. Specifically, the phosphate compound is preferably a compound represented by the following composition formula (4): LiMn １－ｙ Fe ｙ P.O. ４ (4) (In the composition formula (4), y is 0<y≦1.) Suitable specific examples of the phosphate compound represented by the composition formula (4) include LiFePO ４ , LiMn ０．６ Fe ０．４ P.O. ４ etc.

[0058] [3-2-1-2. Introduction of a Foreign Element] Furthermore, an element (foreign element) other than the elements included in the above composition formula may be introduced into the lithium transition metal composite oxide.

[0059] [3-2-1-3. Surface Coating] The surface of the positive electrode active material may be coated with a substance (surface-attached substance) having a different composition from the positive electrode active material. Examples of surface-attached substances include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. These surface-attached substances can be attached to the surface of the positive electrode active material, for example, by dissolving or suspending them in a solvent, impregnating the positive electrode active material, and drying. The amount of the surface-attached substance is preferably 1 μmol / g or more, and preferably 10 μmol / g or more, and typically 1 mmol / g or less, relative to the positive electrode active material. In this specification, the positive electrode active material coated with the surface-attached substance is also referred to as a "positive electrode active material."

[0060] [3-2-1-4. Blends] These positive electrode active materials may be used singly or in any combination of two or more in any ratio.

[0061] [3-2-2. Positive Electrode Configuration and Manufacturing Method] The configuration and manufacturing method of the positive electrode are described below. In this embodiment, a positive electrode using a positive electrode active material can be manufactured by a conventional method. That is, a positive electrode can be obtained by a coating method in which a positive electrode active material, a binder, and, if necessary, a conductive material and a thickener are mixed in a dry state to form a sheet and then pressed onto a positive electrode current collector, or by dissolving or dispersing these materials in a liquid medium such as an aqueous solvent or an organic solvent to form a slurry, which is then applied to a positive electrode current collector and dried to form a positive electrode active material layer on the current collector. Alternatively, for example, the above-described positive electrode active material may be roll-formed into a sheet electrode, or may be compression-molded into a pellet electrode. Below, a case in which a slurry is sequentially applied to a positive electrode current collector and then dried will be described.

[0062] [3-2-2-1. Active Material Content] The content of the positive electrode active material in the positive electrode active material layer is usually 80% by mass or more and 99.5% by mass or less.

[0063] [3-2-2-2. Conductive Material] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon-based materials such as amorphous carbon such as needle coke. One conductive material may be used alone, or two or more conductive materials may be used in any combination and ratio. The conductive material is typically used so that it is contained in the positive electrode active material layer in an amount of 0.01% by mass to 50% by mass.

[0064] [3-2-2-3. Binder] The binder used in the production of the positive electrode active material layer is not particularly limited, for example, when forming the positive electrode active material layer by a coating method, as long as it is a material that can be dissolved or dispersed in a liquid medium for the slurry. However, from the viewpoint of weather resistance, chemical resistance, heat resistance, flame retardancy, etc., fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, etc.; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, etc. are preferred. In addition, mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. of the above polymers can also be used. Note that one type of binder may be used alone, or two or more types may be used in any combination and ratio. Furthermore, when a resin is used as a binder, the weight-average molecular weight of the resin is optional as long as it does not significantly impair the effects of the present invention, but is usually 10,000 or more, preferably 50,000 or more, and particularly preferably 100,000 or more, and is usually 3,000,000 or less, preferably 950,000 or less, and particularly preferably 900,000 or less. A molecular weight within this range improves the strength of the electrode, allowing for convenient electrode formation. The proportion of the binder in the positive electrode active material layer is usually 0.1% by mass or more and 80% by mass or less.

[0065] [3-2-2-4. Current Collector] The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Among these, aluminum is preferred. Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punched metal, and foamed metal. Of these, metal foil or metal thin film is preferred. The metal thin film may be formed into a mesh shape as appropriate. When the shape of the positive electrode current collector is a plate or film, the thickness of the current collector is optional, but is usually 1 μm or more and 1 mm or less.

[0066] [3-2-2-5. Thickness of Positive Electrode Plate] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the positive electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the positive electrode plate is usually 10 μm or more and 500 μm or less on one side of the current collector.

[0067] [3-2-2-6. Electrode Density] The positive electrode active material layer obtained by coating and drying is preferably compacted by a hand press, a roller press, or the like in order to increase the packing density of the positive electrode active material. The density of the positive electrode active material layer present on the current collector is usually 1.5 g / cm ３ 4.5g / cm or more ３ The following is the result.

[0068] [3-2-2-7. Surface Coating of Positive Electrode Plate] The positive electrode plate may have a substance of a different composition from that of the positive electrode plate attached to its surface, and the substance may be the same as the surface-attached substance that may be attached to the surface of the positive electrode active material.

[0069] [3-3. Negative Electrode] The negative electrode has a negative electrode active material on at least a portion of the surface of a current collector.

[0070] [3-3-1. Negative Electrode Active Material] The negative electrode active material used in the negative electrode is not particularly limited as long as it is capable of electrochemically absorbing and releasing metal ions. Specific examples include carbon-based materials, materials containing metal elements and / or metalloid elements capable of alloying with Li, lithium-containing metal composite oxide materials, alkali metals, and mixtures thereof. Among these, carbon-based materials, materials containing metal elements and / or metalloid elements capable of alloying with Li, and mixtures of materials containing metal elements and / or metalloid elements capable of alloying with Li and carbon-based materials are preferred because of their excellent cycle characteristics and safety, as well as their excellent continuous charge characteristics. These materials may be used alone or in any combination of two or more.

[0071] [3-3-1-1. Carbon-Based Materials] Examples of carbon-based materials include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Of these, natural graphite is preferred. One type of carbon-based material may be used alone, or two or more types may be used in any combination and ratio. Examples of natural graphite include scaly graphite, flake graphite, and / or graphite particles obtained by subjecting these graphites to treatments such as spheroidization and densification. Among these, spherical or ellipsoidal graphite particles that have been subjected to a spheroidization treatment are particularly preferred from the viewpoint of particle packing properties or charge / discharge rate characteristics. The average particle diameter (d50) of the graphite particles is typically 1 μm or more and 100 μm or less.

[0072] [3-3-1-2. Physical Properties of Carbon-Based Materials] Carbon-based materials used as negative electrode active materials preferably satisfy at least one of the characteristics, such as physical properties and shape, shown in the following items (1) to (4), and particularly preferably satisfy several of them simultaneously. (1) X-ray Diffraction Parameters The d value (interlayer distance) of the lattice plane (002 plane) of a carbon-based material determined by X-ray diffraction using the Gakushin method is typically 0.335 nm or more and 0.360 nm or less. The crystallite size (Lc) of a carbon-based material determined by X-ray diffraction using the Gakushin method is typically 1.0 nm or more. (2) Volume-Based Average Particle Size The volume-based average particle size of a carbon-based material is the volume-based average particle size (median diameter) determined by laser diffraction / scattering, and is typically 1 μm or more and 100 μm or less. (3) Raman R value and Raman half-width The Raman R value of a carbon-based material is a value measured using an argon ion laser Raman spectroscopy, and is usually 0.01 or more and 1.5 or less. －１ The Raman half-width in the vicinity is not particularly limited, but is usually 10 cm －１ Above, 100cm －１ (4) BET specific surface area The BET specific surface area of ​​a carbon-based material is the value of the specific surface area measured using the BET method, and is usually 0.1 m ２ ・g －１ Over 100m ２ ・g －１The negative electrode active material may contain two or more carbon-based materials with different properties. The properties referred to here mean X-ray diffraction parameters, volume-based average particle size, Raman R value, Raman half-width, and BET specific surface area. Preferred examples include a volume-based particle size distribution that is not symmetrical about the median diameter, two or more carbon-based materials with different Raman R values, and two or more carbon-based materials with different X-ray parameters.

[0073] [3-3-1-3. Material Containing a Metal Element and / or a Metalloid Element That Can Be Alloyed with Li] Any conventionally known material containing a metal element and / or a metalloid element that can be alloyed with Li can be used. However, from the viewpoint of capacity and cycle life, a simple substance or a compound of a metal and / or metalloid element, which may be coated with carbon and is selected from the group consisting of Sb, Si, Sn, Al, As, and Zn, is preferred. Furthermore, when a material containing a metal element and / or a metalloid element that can be alloyed with Li contains two or more elements, the material may be an alloy material made of an alloy of these metals. Furthermore, examples of materials containing a metal element and / or a metalloid element that can be alloyed with Li include oxides, nitrides, carbides, etc. These may contain two or more types of metal element and / or metalloid element that can be alloyed with Li. Among these, metal Si (hereinafter sometimes referred to as Si) or a Si-containing inorganic compound is preferred in terms of increasing capacity. In addition, the material of the metal element and / or metalloid element that can be alloyed with Li may already be alloyed with Li during the production of the negative electrode, which will be described later. In this specification, Si or Si-containing inorganic compounds are collectively referred to as Si compounds. Specific examples of Si compounds include SiO ｘ (0≦x≦2) and the like. Specific examples of metal compounds alloyed with Li include Li ｙ Si (0<y≦4.4), Li ２ SiO ２＋ｚ (0<z≦2) and the like. Examples of Si compounds include Si oxides (SiO ｘ１, 0<x1≦2) is preferred because it has a larger theoretical capacity than graphite, and amorphous Si or nano-sized Si crystals are preferred because they allow alkali ions such as lithium ions to easily enter and exit, making it possible to obtain a high capacity. When the material containing a metal element and / or a metalloid element that can be alloyed with Li is in the form of particles, the average particle diameter (d50) is usually 0.01 μm or more and 10 μm or less from the viewpoint of cycle life.

[0074] [3-3-1-4. Mixture of Particles of a Material Containing a Metal Element and / or a Metalloid Element That Can Be Alloyed with Li and Graphite Particles] The mixture of particles of a material containing a metal element and / or a metalloid element that can be alloyed with Li and graphite particles used as the negative electrode active material may be a mixture in which the particles of the material containing a metal element and / or a metalloid element that can be alloyed with Li and the graphite particles are mixed in the state of particles of independent materials, or may be a composite in which particles of a material containing a metal element and / or a metalloid element that can be alloyed with Li are present on the surface or inside of graphite particles. The content of the particles of the material containing a metal element and / or a metalloid element that can be alloyed with Li relative to the total content of the particles of the material containing a metal element and / or a metalloid element that can be alloyed with Li and the graphite particles is typically 1% by mass or more and 99% by mass or less.

[0075] [3-3-1-5. Lithium-Containing Metal Composite Oxide Material] The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. However, from the viewpoint of high current density charge / discharge characteristics, a lithium-containing metal composite oxide material containing titanium is preferred, a composite oxide of lithium and titanium (hereinafter sometimes abbreviated as "lithium titanium composite oxide") is more preferred, and a lithium titanium composite oxide having a spinel structure is particularly preferred because it significantly reduces output resistance. Furthermore, the lithium and / or titanium in the lithium titanium composite oxide may be substituted with another metal element, for example, at least one element selected from the group consisting of Al, Ga, Cu, and Zn. As the lithium titanium composite oxide, Li ４／３ Ti ５／３ O ４ , Li１ Ti ２ O ４ and Li ４／５ Ti １１／５ O ４ Furthermore, examples of lithium-titanium composite oxides in which part of lithium and / or titanium is substituted with other elements include Li ４／３ Ti ４／３ Al １／３ O ４ is preferred.

[0076] [3-3-2. Negative Electrode Configuration and Manufacturing Method] The negative 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 negative electrode can be manufactured by adding a binder, a liquid medium such as an aqueous solvent or an organic solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to the negative electrode active material to form a slurry, which is then applied to a current collector, dried, and pressed to form a negative electrode active material layer.

[0077] [3-3-2-1. Active Material Content] The content of the negative electrode active material in the negative electrode active material layer is usually 80% by mass or more and 99.5% by mass or less.

[0078] [3-3-2-2. Electrode Density] The negative electrode active material layer obtained by coating and drying is preferably compacted by a hand press, a roller press, or the like in order to increase the packing density of the negative electrode active material. The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the negative electrode active material layer present on the current collector is usually 1 g cm －３ Above, 2.2g・cm －３ The following is the result.

[0079] [3-3-2-3. Thickener] A thickener is typically used to adjust the viscosity of the slurry. While the thickener is not particularly limited, specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, and salts thereof. These may be used alone or in any combination and ratio of two or more. When a thickener is used, the ratio of the thickener to the negative electrode active material is typically 0.1% by mass or more and 5% by mass or less.

[0080] [3-3-2-4. Binder] The binder used to bind the negative electrode active material is not particularly limited as long as it is stable in the nonaqueous electrolyte solution and the liquid medium used in electrode production. Specific examples include rubbery polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; and fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and tetrafluoroethylene-ethylene copolymer. These may be used alone, or two or more may be used in any combination and ratio. The ratio of the binder to the negative electrode active material is usually 0.1% by mass or more and 20% by mass or less. In particular, when the binder contains a rubbery polymer such as SBR as a major component, the ratio of the binder to the negative electrode active material is preferably 0.1% by mass or more and 5% by mass or less. When the binder contains a fluorine-based polymer such as polyvinylidene fluoride as a main component, the ratio of the binder to the negative electrode active material is preferably 1% by mass or more and 15% by mass or less.

[0081] [3-3-2-5. Current Collector] Any known current collector can be used as the current collector that holds the negative electrode active material. Examples of negative electrode current collectors include metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel, with copper being particularly preferred from the standpoints of ease of processing and cost. Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punched metal, and foamed metal. Of these, metal foil or metal thin film is preferred. Metal foil and metal thin film may be appropriately formed into a mesh shape. When the negative electrode current collector is in the shape of a plate or film, the thickness of the current collector is optional, but is typically 1 μm or more and 1 mm or less.

[0082] [3-3-2-6. Thickness of Negative Electrode Plate] The thickness of the negative electrode (also referred to as "negative electrode plate") is designed to match the positive electrode to be used and is not particularly limited, but the thickness of the negative electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the negative electrode material is usually 15 μm or more and 300 μm or less.

[0083] [3-3-2-7. Surface Coating of Negative Electrode Plate] The negative electrode plate may have a substance (surface-attached substance) attached to its surface, the substance having a different composition from the negative electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[0084] [3-4. Separator] A separator is usually interposed between the positive electrode and the negative electrode to prevent short-circuiting. In this case, the non-aqueous electrolyte is usually impregnated into the separator. There are no particular restrictions on the material or shape of the separator, and any known separator can be used as long as it does not significantly impair the effects of the present invention.

[0085] [3-5. Battery Design] [3-5-1. 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. The ratio of the volume of the electrode group to the internal volume of the battery is usually 40% or more and 90% or less.

[0086] [3-5-2. Current Collection Structure] When the electrode group has the aforementioned laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to a terminal is preferably used. A structure in which multiple terminals are provided within the electrode to reduce resistance is also preferably used. When the electrode group has the aforementioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive and negative electrodes and bundling them to a terminal.

[0087] [3-5-3. Protective Element] Examples of protective elements that can be used include a PTC (Positive Temperature Coefficient) element whose resistance increases with heat generation due to excessive current, a thermal fuse, a thermistor, and a valve (current cutoff valve) that cuts off the current flowing in the circuit due to a sudden increase in the internal pressure or temperature of the battery during abnormal heat generation. It is preferable to select the above protective element so that it will not operate under normal use at high current, and it is more preferable to design it so that abnormal heat generation or thermal runaway does not occur even without a protective element.

[0088] [3-5-4. Exterior Body] A non-aqueous electrolyte secondary battery is typically constructed by housing the above-mentioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc., in an exterior body (exterior case). There are no limitations on this exterior body, and any known exterior body can be used as long as it does not significantly impair the effects of the present invention. The material of the exterior case is not particularly limited as long as it is a substance stable with respect to the non-aqueous electrolyte used, but from the perspective of weight reduction, aluminum or aluminum alloy metal or laminate film is preferably used. Examples of exterior cases using the above metals include those that have a sealed, airtight structure formed by welding the metals together by laser welding, resistance welding, or ultrasonic welding, and those that have a crimped structure using the above metals via a resin gasket.

[0089] [3-5-5. Shape] The shape of the exterior case is also arbitrary, and may be, for example, cylindrical, rectangular, laminated, coin-shaped, large, or the like.

[0090] [3-6. Battery Manufacturing Method] A battery according to one embodiment of the present invention can be manufactured by housing a positive electrode, a negative electrode, and other materials used as needed in an outer casing, and then injecting the above-described electrolyte solution of the present invention into the outer casing. The present invention also relates to a method for manufacturing such a battery. That is, the battery manufacturing method according to one embodiment of the present invention includes the steps of housing a positive electrode and a negative electrode in an outer casing, and injecting the above-described electrolyte solution of the present invention into the outer casing.

[0091] [4. Applications] The electrolyte and battery according to one embodiment of the present invention can be used in a wide range of applications, from so-called consumer power sources for laptops and the like to on-board power sources for driving automobiles and the like. In particular, the electrolyte of the present invention can simultaneously improve the thermal stability of the battery and suppress self-discharge of the battery, and therefore can be suitably used as an on-board power source for driving vehicles and the like. That is, the present invention suitably provides a vehicle including the battery according to one embodiment of the present invention.

[0092] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0093] Examples A-1 to A-14 and Comparative Examples A-1 to A-3 [Preparation of Non-Aqueous Electrolyte] In a dry argon atmosphere, a mixture of ethylene carbonate and dimethyl carbonate (volume ratio 3:7) was dissolved in LiPF 6 as a hexafluorophosphate. ６ , LiN(FSO) as a bis(fluorosulfonyl)imide salt ２ ) ２ (hereinafter, sometimes referred to as "LiFSI"), LiFSO as a compound containing an anion represented by general formula (1) ３ , and other compounds listed in Table 1 (LiBOB (lithium bis(oxalato)borate), LiPO ２ F ２ , VC (vinylene carbonate)) was dissolved in the non-aqueous electrolyte solution to give the concentration shown in Table 1. In Tables 1 to 3, "compound (1)" means a compound containing an anion represented by general formula (1).

[0094] [Preparation of non-aqueous electrochemical cell] Aluminum foil was used as the positive electrode (12 cm ２ ), a negative electrode (13.4 cm) in which lithium foil was pressed onto copper foil ２ ), and a polyolefin separator were laminated in the order of negative electrode, separator, and positive electrode. The battery element thus obtained was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution was poured into the film, followed by sealing to prepare a sheet-shaped nonaqueous electrochemical cell. <Evaluation of Nonaqueous Electrochemical Cell>

[0095] [Self-discharge] A sheet-shaped non-aqueous electrochemical cell was placed in a thermostatic chamber at 25°C and subjected to 4 V application for 24 hours. The charge capacity after constant voltage charging at 4.3 V for 24 hours was recorded as "self-discharge." The smaller the self-discharge, the better. Table 1 shows the self-discharge of the examples and comparative examples (relative values ​​with Comparative Example A-1 set to 100).

[0096]

[0097] As is clear from Table 1, non-aqueous electrolyte secondary batteries comprising non-aqueous electrolyte solutions (Examples A-1 to A-14) containing hexafluorophosphate, bis(fluorosulfonyl)imide salt, and a compound containing an anion represented by the general formula (1) in a specific content, have suppressed self-discharge compared to non-aqueous electrolyte solutions in which the ratio represented by hexafluorophosphate / bis(fluorosulfonyl)imide salt exceeds a specific ratio (Comparative Example A-1), non-aqueous electrolyte solutions not containing hexafluorophosphate (Comparative Example A-2), and non-aqueous electrolyte solutions not containing a compound containing an anion represented by the general formula (1) (Comparative Example A-3).

[0098] Examples B-1 to B-7 and Comparative Examples B-1 to B-3 [Preparation of non-aqueous electrolyte solution] In a dry argon atmosphere, a mixture of ethylene carbonate and dimethyl carbonate (volume ratio 3:7) was dissolved in LiPF 6 as a hexafluorophosphate. ６ , LiFSI as a bis(fluorosulfonyl)imide salt, and LiFSO as a compound containing an anion represented by general formula (1) ３ was dissolved in the nonaqueous electrolyte solution to give the concentration shown in Table 2. Using this nonaqueous electrolyte solution, a nonaqueous electrolyte secondary battery was fabricated by the following method and evaluated.

[0099] [Preparation of Positive Electrode] LiNi was used as the positive electrode active material. ０．６１ Mn ０．１９ Co ０．２０ O ２ 90 parts by mass of the above, 7 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone to form a slurry. The obtained slurry was uniformly applied to an aluminum foil with a thickness of 15 μm, dried, and then roll-pressed to form a positive electrode. The density of the positive electrode active material layer was 3.4 g / cm. ３ It was.

[0100] [Fabrication of Negative Electrode] 49 parts by mass of graphite powder was mixed with 50 parts by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) as a thickener and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) as a binder using 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.

[0101] [Production of Non-Aqueous Electrolyte Secondary Battery] The above-mentioned positive electrode, negative electrode, and polyolefin separator were stacked in the order of negative electrode, separator, and positive electrode. The resulting battery element was wrapped in an aluminum laminate film, and the above-mentioned non-aqueous electrolyte solution was injected and then vacuum-sealed to produce a sheet-shaped non-aqueous electrolyte secondary battery. Non-aqueous electrolyte secondary batteries were produced using the non-aqueous electrolyte solutions listed in Table 2, and these were designated as the non-aqueous electrolyte secondary batteries of Examples B-1 to B-7 and Comparative Examples B-1 to B-3.

[0102] [Evaluation of Voltage Drop] In a thermostatic bath at 25°C, a sheet-shaped nonaqueous electrolyte secondary battery was charged at a constant current of 0.05C (the current value at which the rated capacity based on the discharge capacity at a one-hour rate is discharged in one hour is defined as 1C; the same applies below) to 3.7V, then charged at a constant current and constant voltage of 0.2C to a voltage of 4.25V, and then discharged at a constant current of 0.2C to 2.8V. Furthermore, the battery was charged at a constant current and constant voltage of 0.2C to 4.1V, and the voltage drop after storing at 60°C for 24 hours was evaluated. Table 2 shows the voltage drop of the examples and comparative examples (relative values ​​assuming that Comparative Example B-1 is 100).

[0103]

[0104] As is clear from Table 2, the nonaqueous electrolyte secondary batteries (Examples B-1 to B-7) containing specific amounts of hexafluorophosphate, bis(fluorosulfonyl)imide salt, and a compound containing an anion represented by general formula (1) suppress the voltage drop due to self-discharge compared to nonaqueous electrolytes not containing hexafluorophosphate (Comparative Examples B-1 to B-2) and nonaqueous electrolytes in which the ratio of hexafluorophosphate / bis(fluorosulfonyl)imide salt exceeds a specific ratio (Comparative Example B-3).

[0105] Examples C-1 to C-5 Preparation of Non-Aqueous Electrolyte Solution In a dry argon atmosphere, a mixture of ethylene carbonate and dimethyl carbonate (volume ratio 3:7) was dissolved in LiPF 6 as a hexafluorophosphate. ６ , LiFSI as a bis(fluorosulfonyl)imide salt, LiFSO as a compound containing an anion represented by general formula (1) ３ , and other compounds listed in Table 3 (VC (vinylene carbonate), LiBOB (lithium bis(oxalato)borate), LiPO ２ F ２ , ) were dissolved in the nonaqueous electrolyte solution to give the concentrations shown in Table 3. Using this nonaqueous electrolyte solution, a nonaqueous electrolyte secondary battery was fabricated by the following method and evaluated.

[0106] [Preparation of Positive Electrode] LiMn ０．６ Fe ０．４ P.O. ４ 90 parts by mass of the above, 5 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone to form a slurry. The obtained slurry was uniformly applied to an aluminum foil with a thickness of 15 μm, dried, and then roll-pressed to form a positive electrode. The density of the positive electrode active material layer was 1.8 g / cm. ３ It was.

[0107] [Fabrication of Negative Electrode] 97.5 parts by mass of graphite powder, 0.7 parts by mass of sodium carboxymethyl cellulose as a thickener, and 1.8 parts by mass of styrene-butadiene rubber as a binder were mixed in water to form a slurry. The resulting slurry was uniformly coated on a 10 μm-thick copper foil, dried, and roll-pressed to form a negative electrode.

[0108] [Production of Non-Aqueous Electrolyte Secondary Battery] The above-mentioned positive electrode, negative electrode, and polyolefin separator were stacked in the order of negative electrode, separator, and positive electrode. The resulting battery element was wrapped in an aluminum laminate film, and the above-mentioned non-aqueous electrolyte solution was injected and then vacuum-sealed to produce a sheet-shaped non-aqueous electrolyte secondary battery. Non-aqueous electrolyte secondary batteries were produced using the non-aqueous electrolyte solutions listed in Table 3, and were designated as the non-aqueous electrolyte secondary batteries of Examples C-1 to C-5.

[0109] [Evaluation of Voltage Drop] In a thermostatic bath at 25 ° C., a sheet-shaped non-aqueous electrolyte secondary battery was charged at a constant current of 0.05 C (the current value at which the rated capacity based on the discharge capacity at a 1-hour rate is discharged in 1 hour is defined as 1 C; the same applies below) for 10 hours, then discharged at a constant current of 0.2 C to 2.5 V, then charged at a constant current and constant voltage to a voltage of 4.2 V, and stored at 60 ° C. for 24 hours. Next, the battery was discharged at a constant current of 0.2 C to 2.5 V, and then charged at a constant current and constant voltage to a voltage of 4.2 V, which was repeated twice, and then stored at 60 ° C. for 72 hours. Furthermore, the battery was charged at a constant current and constant voltage of 0.2 C to 4.1 V, and the voltage drop after storing at 60 ° C. for 72 hours was evaluated. Table 3 shows the voltage drop of the examples (relative values ​​assuming that Example C-2 is 100).

[0110]

[0111] As is clear from Table 3, the nonaqueous electrolyte secondary battery (Examples C-1 to C-2) includes a nonaqueous electrolyte containing a specific content of a compound containing a hexafluorophosphate salt, a bis(fluorosulfonyl)imide salt, and an anion represented by general formula (1). The nonaqueous electrolyte (Examples C-3 to C-5) further includes a specific compound added thereto, and the voltage drop due to self-discharge is suppressed.

[0112] <Examples D-1 to D-2, Comparative Examples D-1 to D-2> [Preparation of Positive Electrode] LiNi was used as the positive electrode active material. ０．８３Mn ０．０６ Co ０．１１ O ２ 90 parts by mass of the above, 7 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone to form a slurry. The obtained slurry was uniformly applied to an aluminum foil with a thickness of 15 μm, dried, and then roll-pressed to form a positive electrode. The density of the positive electrode active material layer was 3.0 g / cm. ３ It was.

[0113] [Production of Non-Aqueous Electrolyte Secondary Battery] Except for using the above positive electrode, a sheet-shaped non-aqueous electrolyte secondary battery was produced in the same manner as in Example B. The above non-aqueous electrolyte secondary batteries were produced using the non-aqueous electrolytes listed in Table 4, and were designated as the non-aqueous electrolyte secondary batteries of Examples D-1 and D-2 and Comparative Examples D-1 and D-2.

[0114] [Evaluation of Heat Generation Amount] In a thermostatic bath at 25°C, a sheet-shaped nonaqueous electrolyte secondary battery was charged at a constant current of 0.05C to 3.7V, then charged at a constant current and constant voltage of 0.2C to a voltage of 4.3V, and then discharged at a constant current of 0.2C to 2.8V. Furthermore, the battery was charged at a constant current and constant voltage of 0.2C to 4.1V, stored at 60°C for 24 hours, and then discharged at a constant current of 0.2C to 2.8V. After charging at a constant current and constant voltage of 0.2C to 4.3V, the negative electrode was removed from the battery and placed in a measurement cell together with the electrolyte for measurement using a Calbe calorimeter. The measurement was performed by increasing the temperature at a rate of 1K / min, and the heat generation amount between 80°C and 200°C was measured. Table 4 shows the heat generation amounts (relative values ​​assuming Comparative Example D-1 as 100) of the Examples and Comparative Examples. It can be determined that the smaller the heat generation amount, the more improved the thermal stability of the battery.

[0115]

[0116] As is clear from Table 4, the nonaqueous electrolyte secondary battery (Examples D-1 to D-2) containing a specific content of hexafluorophosphate, bis(fluorosulfonyl)imide salt, and a compound containing an anion represented by general formula (1) suppresses the amount of heat generated compared to the nonaqueous electrolyte (Comparative Examples D-1 to D-2) in which the ratio represented by hexafluorophosphate / bis(fluorosulfonyl)imide salt exceeds a specific ratio.

[0117] Examples E-1 to E-4 and Comparative Examples E-1 to E-4 [Preparation of non-aqueous electrolyte solution] In a dry argon atmosphere, a mixture of ethylene carbonate and dimethyl carbonate (volume ratio 3:7) was added with LiPF 6 as a hexafluorophosphate. ６ , LiFSI as a bis(fluorosulfonyl)imide salt, LiCH as a compound containing an anion represented by general formula (2) ３ OSO ３ , LiC ２ H ５ OSO ３ was dissolved in the non-aqueous electrolyte solution to give the concentration shown in Table 1. In Tables 5 to 7, "compound (2)" means a compound containing an anion represented by general formula (2).

[0118] [Preparation of non-aqueous electrochemical cell, evaluation of self-discharge] A sheet-shaped non-aqueous electrochemical cell was prepared in the same manner as in Example A, except that the above-mentioned non-aqueous electrolyte solution was used. Using the obtained sheet-shaped non-aqueous electrochemical cell, evaluation of self-discharge was carried out in the same manner as in Example A. Table 5 shows the self-discharge of the examples and comparative examples (relative values ​​assuming that Comparative Example E-1 is 100).

[0119]

[0120] As is clear from Table 5, the nonaqueous electrolyte secondary battery (Examples E-1 to E-4) containing a specific content of a compound containing hexafluorophosphate, bis(fluorosulfonyl)imide salt, and an anion represented by the general formula (2) suppresses self-discharge compared to the nonaqueous electrolyte (Comparative Examples E-1 to E-2) that does not contain a compound containing an anion represented by the general formula (2) and the nonaqueous electrolyte (Comparative Examples E-3 to E-4) that does not contain hexafluorophosphate.

[0121] Examples F-1 to F-5 Preparation of Non-Aqueous Electrolyte Solution In a dry argon atmosphere, a mixture of ethylene carbonate and dimethyl carbonate (volume ratio 3:7) was dissolved in LiPF 6 as a hexafluorophosphate. ６ , LiFSI as a bis(fluorosulfonyl)imide salt, LiCH as a compound containing an anion represented by general formula (2) ３ OSO ３ , and other compounds listed in Table 6 (VC (vinylene carbonate), LiBOB (lithium bis(oxalato)borate), LiPO ２ F ２ , ) were dissolved in the non-aqueous electrolyte solution to give the concentrations shown in Table 6.

[0122] [Production of non-aqueous electrolyte secondary battery, evaluation of voltage drop] A sheet-shaped non-aqueous electrochemical cell was produced in the same manner as in Example C, except that the above non-aqueous electrolyte was used. Using the obtained sheet-shaped non-aqueous electrochemical cell, the voltage drop was evaluated in the same manner as in Example C. Table 6 shows the voltage drop self-discharge of the examples (relative values ​​with Example F-2 set to 100).

[0123]

[0124] As is clear from Table 6, the nonaqueous electrolyte secondary battery (Examples F-1 to F-2) includes a nonaqueous electrolyte containing a specific content of a compound containing a hexafluorophosphate salt, a bis(fluorosulfonyl)imide salt, and an anion represented by general formula (2). The nonaqueous electrolyte (Examples F-3 to F-5) further includes a specific compound added thereto. The voltage drop due to self-discharge is suppressed.

[0125] Examples G-1 to G-2, Comparative Examples G-1 to G-4 [Preparation of Non-Aqueous Electrolyte Solution] Non-aqueous electrolyte solutions shown in Table 7 were prepared in the same manner as in Example F.

[0126] [Production of Non-Aqueous Electrolyte Secondary Battery and Evaluation of Heat Generation Amount] A sheet-shaped non-aqueous electrolyte secondary battery was produced in the same manner as in Example D, except that the above non-aqueous electrolyte was used. Using the obtained sheet-shaped non-aqueous electrolyte secondary battery, the heat generation amount was evaluated in the same manner as in Example D. Table 7 shows the heat generation amounts (relative values ​​with Comparative Example G-1 set to 100) of the Examples and Comparative Examples.

[0127]

[0128] As is clear from Table 7, non-aqueous electrolyte secondary batteries comprising a non-aqueous electrolyte solution (Examples G-1 to G-2) containing a specific content of a compound containing hexafluorophosphate, bis(fluorosulfonyl)imide salt, and an anion represented by the general formula (2) have a non-aqueous electrolyte solution that does not contain a compound containing an anion represented by the general formula (2) (Comparative Examples G-1 to G-2), and a non-aqueous electrolyte solution in which the ratio of hexafluorophosphate / bis(fluorosulfonyl)imide salt is greater than a specific ratio (Comparative Examples G-2 to G-4). The amount of heat generated is suppressed.

Claims

1. An electrolytic solution comprising a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, a compound containing an anion represented by the following general formula (1), and a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 0.45 or less, and the content of the compound containing the anion represented by general formula (1) is 0.03 mass% or more in 100 mass% of the electrolytic solution. １ SO ３ － (1) (R １ represents a halogen atom.) 2. An electrolytic solution comprising a bis(fluorosulfonyl)imide salt, a hexafluorophosphate salt, a compound containing an anion represented by the following general formula (2), and a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolytic solution is 1 or less, and the content of the compound containing the anion represented by the general formula (2) is 0.01 mass% or more in 100 mass% of the electrolytic solution. ２ SO ３ － (2) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.

3. The electrolyte solution according to claim 1 or 2, wherein the concentration of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 8 mass % or more.

4. The electrolyte solution according to any one of claims 1 to 3, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.01 or more.

5. The electrolyte solution according to any one of claims 1 to 4, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.2 or less.

6. The electrolyte solution according to claim 1, wherein the ratio of the mass of the compound containing the anion represented by general formula (1) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 3.7 or less.

7. The electrolyte solution according to claim 1 or 6, wherein the ratio of the mass of the compound containing the anion represented by general formula (1) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.0001 or more.

8. The bis(fluorosulfonyl)imide salt is LiN(FSO ２ ) ２ and the hexafluorophosphate is LiPF ６ The electrolyte solution according to any one of claims 1, 6 and 7, wherein the compound containing the anion represented by general formula (1) is a compound represented by the following general formula (1-1): LiR １ SO ３ (1-1) (R １ represents a halogen atom.) 9. The electrolyte solution according to any one of claims 1, 6, 7, and 8, further comprising at least one compound (A) selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, organic compounds having an isocyanate group, organic compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, cyclic compounds having an ether bond, fluorine-free carboxylic acid esters, carboxylic acid anhydrides, triple bond-containing compounds, phosphazene compounds, cyclic acetal compounds, boron anion-containing compounds, oxalate complex anion-containing compounds, and phosphate anion-containing compounds having a P=O bond and a P-F bond (excluding the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by general formula (1)).

10. The electrolyte solution according to claim 9, wherein the compound (A) comprises at least one compound selected from the group consisting of the oxalato complex anion-containing compound, a phosphate anion-containing compound having a P═O bond and a P—F bond, a cyclic carbonate having a carbon-carbon unsaturated bond, and a fluorine-containing cyclic carbonate.

11. The electrolyte solution according to claim 2, wherein the ratio of the mass of the compound containing the anion represented by general formula (2) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 3.7 or less.

12. The electrolyte solution according to claim 2 or 11, wherein the ratio of the mass of the compound containing the anion represented by general formula (2) to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.0001 or more.

13. The bis(fluorosulfonyl)imide salt is LiN(FSO ２ ) ２ and the hexafluorophosphate is LiPF ６ The electrolyte solution according to any one of claims 2, 11, and 12, wherein the compound containing the anion represented by the general formula (2) is a compound represented by the following general formula (2-1): ２ SO ３ (2-1) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.

14. The electrolyte solution according to any one of claims 2, 11, 12, and 13, further comprising at least one compound (A) selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, organic compounds having an isocyanate group, organic compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, cyclic compounds having an ether bond, fluorine-free carboxylic acid esters, carboxylic acid anhydrides, triple bond-containing compounds, phosphazene compounds, cyclic acetal compounds, boron anion-containing compounds, oxalato complex anion-containing compounds, and phosphate anion-containing compounds having a P=O bond and a P-F bond (excluding the bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and the compound containing the anion represented by general formula (2)).

15. The electrolyte solution according to claim 14, wherein the compound (A) comprises at least one compound selected from the group consisting of the oxalato complex anion-containing compound, a phosphate anion-containing compound having a P═O bond and a P—F bond, a cyclic carbonate having a carbon-carbon unsaturated bond, and a fluorine-containing cyclic carbonate.

16. A method for producing an electrolyte solution, comprising a step of dissolving a bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and a compound containing an anion represented by the following general formula (1) in a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 0.45 or less, and the content of the compound containing the anion represented by general formula (1) is 0.03 mass% or more in 100 mass% of the electrolyte solution. １ SO ３ － (1) (R １ represents a halogen atom.) 17. A method for producing an electrolyte solution, comprising a step of dissolving a bis(fluorosulfonyl)imide salt, the hexafluorophosphate salt, and a compound containing an anion represented by the following general formula (2) in a non-aqueous solvent, wherein the ratio of the mass of the hexafluorophosphate salt to the mass of the bis(fluorosulfonyl)imide salt in the electrolyte solution is 1 or less, and the content of the compound containing the anion represented by general formula (2) is 0.01 mass% or more in 100 mass% of the electrolyte solution. ２ SO ３ － (2) (R ２ represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, or an alkoxy group having 1 to 3 carbon atoms which may be substituted with a halogen atom.

18. A battery comprising a positive electrode, a negative electrode, and the electrolyte solution according to any one of claims 1 to 15.

19. The battery according to claim 18, wherein the positive electrode contains a compound represented by the following composition formula (3): Li １＋ｘ MO ２ (3) (In the composition formula (3), x is −0.1≦x≦0.5, and M includes an element including at least one transition metal.) 20. The battery according to claim 19, wherein the content of Ni in M ​​is 55 mol % or more.

21. The battery according to claim 18, wherein the positive electrode contains a compound represented by the following composition formula (4): LiMn １－ｙ Fe ｙ P.O. ４ (4) (In the composition formula (4), y is 0<y≦1.) 22. A method for manufacturing a battery, comprising the steps of housing a positive electrode and a negative electrode in an exterior body and injecting the electrolyte solution according to any one of claims 1 to 15 into the exterior body.

23. A vehicle comprising a battery according to any one of claims 18 to 21.

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