Non-aqueous secondary battery

Abstract

To provide a non-aqueous secondary battery that can be stably driven in a high-temperature environment even when a highly polar and reductively decomposable solvent is used in an electrolytic solution.SOLUTION: A non-aqueous secondary battery 100 includes: a positive electrode; a negative electrode; and a non-aqueous electrolytic solution. The non-aqueous electrolytic solution includes a lithium salt and a non-aqueous solvent. The lithium salt contains an inorganic lithium salt, and the inorganic lithium salt contains, as the inorganic lithium salt, 0.3 mol or more of lithium hexafluorophosphate per 1 L of the non-aqueous electrolytic solution. The non-aqueous solvent contains a nitrile compound represented by R-CN (in the formula, R represents a hydrocarbon group having 1 to 4 carbon atoms or a halogenated hydrocarbon group having 1 to 4 carbon atoms) in a proportion of 5 to 90% by volume with respect to the total amount of the non-aqueous solvent, and a compound composed of an inorganic component is contained in an amount of 10.0 to 50.0% by mass with respect to the compound composed of an organic component excluding lithium carbonate on the surface of the negative electrode active material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous secondary battery. [Background technology]

[0002] The applications of lithium-ion batteries are changing with the global trend toward electrification of automobiles. In particular, automotive batteries often use acetonitrile, an electrolyte with a low melting point and viscosity, to ensure stable operation even in low-temperature environments. Research into this type of electrolyte has been extensive. In addition, additives that form a coating on the anode to prevent easily reduced solvents from reductively decomposing at the anode have also been explored.

[0003] Patent Document 1 reports that battery swelling during high-temperature cycle tests can be improved by adding an additive such as an ester compound to a non-aqueous electrolyte solution. Patent Document 2 reports that by using acetonitrile as the electrolyte solvent and adding an inorganic lithium salt and a cyclic acid anhydride such as succinic anhydride, the negative electrode protective coating is strengthened, thereby delaying gas generation during use at high temperatures, and as a result, good battery characteristics are obtained. Patent Document 3 reports that by controlling the compounding ratio of the lithium salt, the generation of HF gas can be suppressed, thereby improving the long-term cycle performance at high temperatures. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-195201 [Patent Document 2] International Publication No. 2018 / 169028 [Patent Document 3] International Publication No. 2020 / 262670 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not specifically consider at the example level a battery using acetonitrile as an electrolyte solvent.

[0006] Here, in order to effectively use a highly polar and less reducing solvent such as acetonitrile from the viewpoint of suppressing gas generation in a high-temperature environment, it is important that the protective coating formed on the negative electrode does not dissolve in the highly polar solvent, i.e., that the protective coating remains stable.

[0007] Vinylene carbonate, a typical additive for forming a negative electrode coating, is generally effective in preventing the decomposition of acetonitrile on the negative electrode. However, because vinylene carbonate is easily soluble in acetonitrile under high temperature conditions, vinylene carbonate is continuously consumed to compensate for the coating that dissolves in the highly polar solvent, resulting in an increase in the amount of gas.

[0008] Such problems are not observed when using an electrolyte solution whose main component is carbonate, which is relatively less affected by reductive decomposition at the negative electrode, but are thought to occur only when using an electrolyte solution whose main component is a highly polar and easily reduced solvent. On the other hand, when assuming the use of a highly polar and easily reductively decomposed solvent as the electrolyte, there is room for improvement in the prior art including Patent Documents 1 to 3 above, from the viewpoint of providing a non-nonaqueous secondary battery that can be stably operated in a high-temperature environment.

[0009] An object of the present invention is to provide a non-aqueous secondary battery that can be stably operated in a high-temperature environment even when a solvent that is highly polar and easily reductively decomposed is used as the electrolyte. [Means for solving the problem]

[0010] One aspect of the present invention is as follows. [1] A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, the positive electrode has a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector, the non-aqueous electrolyte solution includes a lithium salt and a non-aqueous solvent, The lithium salt contains an inorganic lithium salt, The inorganic lithium salt contains 0.3 mol or more of lithium hexafluorophosphate per 1 L of the nonaqueous electrolyte solution, the non-aqueous solvent contains a nitrile compound represented by R-CN (wherein R is a hydrocarbon group having 1 to 4 carbon atoms or a halogenated hydrocarbon group having 1 to 4 carbon atoms) in a proportion of 5 to 90% by volume relative to the total amount of the non-aqueous solvent, the compound composed of an inorganic component is contained in an amount of 10.0 to 50.0 mass% on the surface of the negative electrode active material relative to the compound composed of an organic component excluding lithium carbonate; Non-aqueous secondary battery. [2] 2. The nonaqueous secondary battery according to item 1, wherein the compound composed of an inorganic component is at least one selected from the group consisting of lithium fluoride, lithium sulfite, and lithium sulfate. [3] 3. The nonaqueous secondary battery according to item 1 or 2, wherein the nitrile compound includes acetonitrile. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a nonaqueous secondary battery that can be stably operated in a high-temperature environment, even when a solvent that is highly polar and easily reductively decomposed is used as the electrolyte. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a plan view schematically illustrating an example of a nonaqueous secondary battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, in which: FIG. 1 is a block diagram showing a configuration of a semiconductor device according to an embodiment of the present invention; FIG. 2 is a block diagram showing a configuration of a semiconductor device according to an embodiment of the present invention;

[0014] In the present specification, when a plurality of structures represented by the same symbol exist in the same formula, the structures may be independently selected and may be the same or different from each other, unless otherwise specified. When a plurality of structures represented by the same symbol exist in different formulas, the structures may be independently selected and may be the same or different from each other, unless otherwise specified. In the present specification, various measurements are carried out based on the methods described in the Examples unless otherwise specified. In the present specification, the upper or lower limit of a numerical range described in a stepwise manner may be replaced by the upper or lower limit of a corresponding numerical range described in another stepwise manner, and may further be replaced by the corresponding value described in the Examples.

[0015] In this specification, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps, as long as the function of the step is achieved. In the contents shown in the drawings, the scale, shape, and length may be exaggerated for clarity.

[0016] <Non-aqueous secondary battery> The nonaqueous secondary battery of this embodiment is The battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. In such a nonaqueous secondary battery, the positive electrode has a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector, The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector.

[0017] the non-aqueous electrolyte solution includes a lithium salt and a non-aqueous solvent, The lithium salt contains an inorganic lithium salt, The inorganic lithium salt contains 0.3 mol or more of lithium hexafluorophosphate per 1 L of the nonaqueous electrolyte solution, The non-aqueous solvent contains a nitrile compound represented by R-CN (wherein R is a hydrocarbon group having 1 to 4 carbon atoms or a halogenated hydrocarbon group having 1 to 4 carbon atoms) in a proportion of 5 to 90% by volume relative to the total amount of the non-aqueous solvent. Here, the compound made of inorganic components is contained in the surface of the negative electrode active material in an amount of 10.0 to 50.0 mass % relative to the compound made of organic components excluding lithium carbonate.

[0018] The nonaqueous secondary battery of this embodiment may be, for example, a lithium ion battery, more specifically, a lithium ion battery whose plan view is schematically shown in FIG. 1 and whose cross-sectional view is schematically shown in FIG. 2. 1 and 2 includes a laminate including a separator 170, a positive electrode 150, and a negative electrode 160 that sandwich the separator 170. The lithium ion battery 100 further includes a positive electrode lead body 130 (connected to the positive electrode 150) and a negative electrode lead body 140 (connected to the negative electrode 160) that sandwich the laminate, and a battery exterior 110 that houses them. In this embodiment, the laminate obtained by stacking the positive electrode 150, the separator 170, and the negative electrode 160 is impregnated with a nonaqueous electrolyte solution.

[0019] <1.Non-aqueous electrolyte> In this embodiment, the term "non-aqueous electrolyte" refers to a non-aqueous electrolyte containing 1% by mass or less of water relative to the total amount of the non-aqueous electrolyte, and containing a non-aqueous solvent and a lithium salt. The non-aqueous electrolyte of this embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not impede the solution of the problems of the present invention. The water content is 300 ppm by mass or less, preferably 200 ppm by mass or less, relative to the total amount of the non-aqueous electrolyte. As long as the non-aqueous electrolyte has a configuration that achieves the problems of the present invention, the other components can be appropriately selected and applied from the constituent materials of known non-aqueous electrolytes used in lithium-ion batteries.

[0020] <1-1. Non-aqueous solvents> In this embodiment, the term "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte solution excluding the lithium salt and various additives. When the non-aqueous electrolyte solution contains an electrode protection additive, the term "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte solution excluding the lithium salt and additives other than the electrode protection additive. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; aprotic solvents; and the like. Among these, aprotic solvents are preferred as non-aqueous solvents. The non-aqueous solvent may contain a solvent other than an aprotic solvent, as long as it does not impede the solution of the problems of the present invention.

[0021] In the non-aqueous electrolyte, the non-aqueous solvent contains a non-aqueous solvent that is highly polar and easily reductively decomposed. The non-aqueous solvent contains 5 to 90% by volume of a nitrile compound represented by R-CN (wherein R is a hydrocarbon group having 1 to 4 carbon atoms or a halogenated hydrocarbon group having 1 to 4 carbon atoms), relative to the total volume of the non-aqueous solvent. R may be an alkylene group. Specific examples of such nitrile compounds include: CH3-CN, CF3-CN, CF2H-CN, CFH2-CN C2H5-CN, C2F5-CN, C2F4H-CN, C2F3H2-CN, C2F2H3-CN, C2FH4-CN, C3H7-CN, C3F7-CN, C3F6H-CN, C3F5H2-CN, C3F4H3-CN, C3F3H4-CN, C3F2H5-CN, C3FH6-CN, C4H9-CN, C4F9-CN, C4F8H-CN, C4F7H2-CN, C4F6H3-CN, C4F5H4-CN, C4F4H5-CN, C4F3H6-CN, C4F2H7-CN, C4FH8-CN, Among these, an embodiment in which R is a hydrocarbon group having one carbon atom (that is, an embodiment in which R-CN is acetonitrile) is preferred from the viewpoint of ionic conductivity.

[0022] By including the above-mentioned solvent as an aprotic solvent in the nonaqueous solvent, the ionic conductivity of the nonaqueous electrolyte solution is improved, thereby enhancing the diffusibility of lithium ions within the battery. In this case, even in a positive electrode having a thicker positive electrode active material layer and a higher loading of positive electrode active material, lithium ions can be diffused well to the region near the current collector, which is difficult for lithium ions to reach during high-load discharge. This makes it possible to extract sufficient capacity even during high-load discharge, resulting in a nonaqueous secondary battery with excellent load characteristics.

[0023] Furthermore, the inclusion of acetonitrile in the nonaqueous solvent can improve the rapid charging characteristics of nonaqueous secondary batteries. In constant current (CC)-constant voltage (CV) charging of nonaqueous secondary batteries, the charge capacity per unit time during the CC charging period is greater than the charge capacity per unit time during the CV charging period. When acetonitrile is used as the nonaqueous solvent in a nonaqueous electrolyte, the range in which CC charging is possible can be expanded (CC charging time can be extended), and the charging current can also be increased, significantly shortening the time from the start of charging to fully charging a nonaqueous secondary battery.

[0024] Acetonitrile, which is one embodiment of the solvent represented by "R-CN," is particularly susceptible to electrochemical reductive decomposition. Therefore, when using acetonitrile, it is preferable to use another solvent (e.g., an aprotic solvent other than acetonitrile) in combination with acetonitrile as a non-aqueous solvent, and / or to add an electrode protection additive for forming a protective film on the electrode.

[0025] The content of the solvent represented by "R-CN" in the non-aqueous solvent is 5 to 90% by volume, based on the total amount of the non-aqueous solvent. This content is preferably 10% by volume or more, based on the total amount of the non-aqueous solvent. Furthermore, this content is preferably 85% by volume or less, and more preferably 70% by volume or less, based on the total amount of the non-aqueous solvent. When the content of the solvent represented by "R-CN" is 5% by volume or more, based on the total amount of the non-aqueous solvent, the ionic conductivity of the non-aqueous electrolyte solution increases, which tends to enable the non-aqueous secondary battery to exhibit high-power characteristics and also promote the dissolution of the lithium salt. Furthermore, when the content of the solvent represented by "R-CN" is within the above range, the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery tend to be further improved while maintaining the excellent performance of the solvent represented by "R-CN."

[0026] Examples of aprotic solvents other than the above-mentioned solvents represented by "R-CN" include cyclic carbonates; fluoroethylene carbonate; lactones; organic compounds having a sulfur atom; chain fluorinated carbonates; cyclic ethers; mononitriles other than acetonitrile; alkoxy group-substituted nitriles; dinitriles; cyclic nitriles; short-chain fatty acid esters; chain ethers; fluorinated ethers; ketones; compounds in which some or all of the H atoms of the above-mentioned aprotic solvents have been substituted with halogen atoms; and the like.

[0027] Acetonitrile, which is one component of non-aqueous solvents, is easily electrochemically reductively decomposed. Therefore, when acetonitrile is selected as the solvent represented by "R-CN," adding vinylene carbonate to the non-aqueous solvent in addition to acetonitrile makes it easier to stabilize the charge / discharge capacity of the battery when used in a non-aqueous secondary battery.

[0028] When the nonaqueous solvent of the present embodiment contains the solvent represented by "R-CN" (in one embodiment, acetonitrile), vinylene carbonate (VC) as the cyclic carbonate, and ethylene sulfite as the organic compound having a sulfur atom, when the nonaqueous electrolyte solution is used in a nonaqueous secondary battery, the battery is likely to operate at a high current density.

[0029] Vinylene carbonate-derived anode protective coatings have high resistance, which can lead to performance degradation during rapid charging and in low-temperature environments, as well as battery swelling due to gas generation during decomposition. Ethylene sulfite has a lower lowest unoccupied molecular orbital (LUMO) level than other oxygen- and sulfur-containing compounds, and therefore can be reductively decomposed at a lower potential than vinylene carbonate to form anode protective coatings. Therefore, it is possible to solve the problems associated with vinylene carbonate-derived anode protective coatings by reducing the amount of vinylene carbonate added. Furthermore, the ethylene sulfite-derived anode protective coating has low resistance over a wide temperature range and promotes the formation of a negative electrode SEI (Solid Electrolyte Interface) that is highly resistant to acetonitrile and its decomposition products, making it easy to provide a nonaqueous electrolyte solution and a nonaqueous secondary battery that can operate stably at high current density.

[0030] In this embodiment, the total content of vinylene carbonate and ethylene sulfite in the nonaqueous electrolyte solution is preferably 0.1% by volume or more and less than 15% by volume with respect to the total amount of the nonaqueous solvent, from the viewpoint of suppressing an increase in internal resistance.

[0031] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate (VC), 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;

[0032] Fluoroethylene carbonates include, for example, 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one;

[0033] Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0034] Examples of organic compounds having a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite;

[0035] Examples of chain carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and diisobutyl carbonate;

[0036] Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0037] Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0038] Alkoxy-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

[0039] Dinitriles include, for example, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoctane, 2,7-dicyanoctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0040] Cyclic nitriles include, for example, benzonitrile;

[0041] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, and iso pivalate. propyl, isopropyl hydroangelate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate;

[0042] Chain ethers include, for example, dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0043] Examples of fluorinated ethers include Rf 20 -OR 21 (In the formula, Rf 20 represents an alkyl group containing a fluorine atom, and R 7 represents a monovalent organic group which may contain a fluorine atom;

[0044] Ketones, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0045] Examples of the compound in which some or all of the H atoms of the aprotic solvent have been substituted with halogen atoms include compounds in which the halogen atoms are fluorine; Examples include:

[0046] Examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The fluorinated chain carbonates are represented by the following general formula: R 1 -OC(O)OR 2 {where, R 1 and R 2 are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf 3 and Rf 3 is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R 1 , and / or R 2 contains at least one fluorine atom. It can be expressed as:

[0047] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R 10 -C(O)OR 11 {where, R 10is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2Rf 12 , CFHRf 12 , and CH2Rf 13 and R is at least one selected from the group consisting of 11 are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf 13 and Rf 12 is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with at least one fluorine atom, and Rf 13 is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R 10 , and / or R 11 contains at least one fluorine atom, and R 10 If is CF2H, R 11 is not CH3. It can be expressed as:

[0048] In this embodiment, the solvent represented by "R-CN" may be used alone or in combination of two or more.

[0049] In the present embodiment, the nonaqueous solvent preferably contains one or more of a cyclic carbonate and a chain carbonate in combination with the solvent represented by "R-CN" from the viewpoint of improving the stability of the nonaqueous electrolyte solution. From this viewpoint, the nonaqueous solvent preferably contains acetonitrile in combination with a cyclic carbonate, and more preferably contains acetonitrile in combination with both a cyclic carbonate and a chain carbonate.

[0050] When a cyclic carbonate other than vinylene carbonate (VC) is used together with acetonitrile, it is particularly preferred that such cyclic carbonate includes ethylene carbonate and / or fluoroethylene carbonate.

[0051] <1-2. Electrolyte salts> The nonaqueous electrolyte solution of this embodiment is suitable for use in lithium ion secondary batteries, which are one type of nonaqueous secondary battery. The nonaqueous electrolyte solution of this embodiment contains lithium hexafluorophosphate (LiPF) as an electrolyte salt, specifically, as an inorganic lithium salt (fluorine-containing inorganic lithium salt).

[0052] The content of lithium hexafluorophosphate is 0.3 mol or more, preferably 0.4 mol or more, and more preferably 0.5 mol or more per 1 L of nonaqueous electrolyte solution. When the content of lithium hexafluorophosphate is 0.3 mol or more per 1 L of nonaqueous electrolyte solution, the proportion of the coating derived from inorganic components increases, which tends to prevent dissolution of the coating in a high-temperature environment.

[0053] Regarding other electrolyte salts, in this embodiment, a lithium-containing imide salt may be included as a lithium salt. The lithium-containing imide salt is LiN(SO2C m F 2m+1 )2 (wherein m is an integer of 0 to 8), and specifically, it preferably contains at least one of LiN(SO2F)2 and LiN(SO2CF3)2. It may contain only one or both of these imide salts, or it may contain an imide salt other than these imide salts.

[0054] Other lithium salts include, for example, LiBF4, LiAsF6, Li2SiF6, LiSbF6, and Li2B 12 F b H 12-b (wherein b is an integer of 0 to 3). The term "inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion and is represented by "R-CN" and is soluble in the above-mentioned solvent. The term "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion, contains a fluorine atom in the anion, and is soluble in the above-mentioned solvent, represented by "R-CN".

[0055] Fluorine-containing inorganic lithium salts are excellent in that they form a passive film on the surface of the metal foil serving as the positive electrode current collector, thereby inhibiting corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts can be used alone or in combination of two or more. A compound that is a double salt of LiF and a Lewis acid is desirable as the fluorine-containing inorganic lithium salt. In this embodiment, a fluorine-containing inorganic lithium salt having a phosphorus atom is used, thereby realizing an embodiment that facilitates the release of free fluorine atoms. A typical fluorine-containing inorganic lithium salt is LiPF6, which dissolves and releases PF6 anions. When a fluorine-containing inorganic lithium salt having a boron atom is used in combination as the fluorine-containing inorganic lithium salt, it facilitates the capture of excess free acid components that may cause battery degradation. From this perspective, when a fluorine-containing inorganic lithium salt having a boron atom is used in combination with LiPF6, LiBF4 is particularly preferred as the "fluorine-containing inorganic lithium salt having a boron atom."

[0056] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte solution is preferably 0.3 mol or more per 1 L of the non-aqueous electrolyte solution. When the content of the fluorine-containing inorganic lithium salt is 0.3 mol or more per 1 L of the non-aqueous electrolyte solution, the ionic conductivity increases, which tends to result in high-power characteristics. Furthermore, the content of the fluorine-containing inorganic lithium salt is preferably less than 3.0 mol, more preferably less than 2.0 mol, and even more preferably less than 1.5 mol per 1 L of the non-aqueous electrolyte solution. When the content of the fluorine-containing inorganic lithium salt is less than 3.0 mol per 1 L of the non-aqueous electrolyte solution, the ionic conductivity increases, which tends to result in high-power characteristics and to suppress a decrease in ionic conductivity due to an increase in viscosity at low temperatures. In this case, the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery tend to be further improved while maintaining the excellent performance of the non-aqueous electrolyte solution.

[0057] The nonaqueous electrolyte solution of this embodiment may further contain an organic lithium salt. The "organic lithium salt" refers to a lithium salt that contains a carbon atom in the anion and is represented by "R-CN" and is soluble in the above-mentioned solvent.

[0058] Examples of organic lithium salts include organic lithium salts having an oxalic acid group. Specific examples of organic lithium salts having an oxalic acid group include organic lithium salts represented by LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2. Among these, at least one lithium salt selected from the group consisting of LiB(C2O4)2 and LiBF2(C2O4) is preferred. It is more preferred to use one or more of these together with a fluorine-containing inorganic lithium salt. This organic lithium salt having an oxalic acid group may be added to a nonaqueous electrolyte solution or incorporated into the negative electrode (negative electrode active material layer).

[0059] In order to ensure the desired effect of the use, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte solution is preferably 0.005 mol or more, more preferably 0.02 mol or more, and even more preferably 0.05 mol or more per 1 L of the non-aqueous electrolyte solution. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte solution is too large, precipitation may occur. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte solution is preferably less than 1.0 mol, more preferably less than 0.5 mol, and even more preferably less than 0.2 mol per 1 L of the non-aqueous solvent of the non-aqueous electrolyte solution.

[0060] It is known that organic lithium salts having an oxalic acid group are poorly soluble in low-polarity organic solvents, particularly chain carbonates. Organic lithium salts having an oxalic acid group may contain a trace amount of lithium oxalate. Furthermore, when mixed to form a non-aqueous electrolyte solution, they may react with trace amounts of water contained in other raw materials to generate new white precipitates of lithium oxalate. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of this embodiment is not particularly limited, but is preferably 0 to 500 ppm.

[0061] In addition to the lithium salts listed above, lithium salts generally used for non-aqueous secondary batteries may be added supplementarily as the lithium salt in this embodiment. Specific examples of other lithium salts include LiClO4, LiAlO4, LiAlCl4, and LiB 10 Cl 10 Inorganic lithium salts that do not contain fluorine atoms in the anion, such as chloroborane Li; LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiC n F (2n+1) SO3 {wherein n≧2}, organic lithium salts such as lower aliphatic carboxylic acids, Li tetraphenylborate, and LiB(C3O4H2)2; LiPF such as LiPF5(CF3) n (C p F 2p+1 ) 6-n an organic lithium salt represented by the formula (wherein n is an integer of 1 to 5 and p is an integer of 1 to 8); LiBF such as LiBF(CF); q (C s F 2s+1 ) 4-q an organic lithium salt represented by the formula (wherein q is an integer of 1 to 3, and s is an integer of 1 to 8); a lithium salt bound to a polyvalent anion; The following formula (a): LiC(SO2R A )(SO2R B )(SO2R C ) (a) {where, R A , R B , and R Cmay be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (b): LiN(SO2OR D )(SO2OR E ) (b) {where, R D , and R E may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, and The following formula (c) LiN(SO2R F )(SO2OR G ) (c) {where, R F , and R G may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.} One or more of these can be used together with the fluorine-containing inorganic lithium salt.

[0062] <1-3. Additives> The non-aqueous electrolyte solution of this embodiment may contain an additive for protecting the electrodes (electrode protection additive). The electrode protection additive may substantially overlap with the substance that serves as a solvent for dissolving the lithium salt (i.e., the above-mentioned non-aqueous solvent). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte solution and the non-aqueous secondary battery, but also includes substances that are not directly involved in the electrochemical reaction.

[0063] Specific examples of the electrode protection additive include: fluoroethylene carbonates represented by 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; unsaturated bond-containing cyclic carbonates, such as vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate; Lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone; cyclic ethers, such as 1,4-dioxane; cyclic sulfur compounds represented by ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, and tetramethylene sulfoxide; These may be used alone or in combination of two or more. Ad The content of the electrode protection additive in the non-aqueous electrolyte solution is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, even more preferably 0.4 to 8% by volume, and particularly preferably 0.5 to 4% by volume, relative to the total amount of the non-aqueous solvent.

[0064] In this embodiment, the higher the content of the electrode protection additive, the more the deterioration of the nonaqueous electrolyte solution is suppressed. However, the lower the content of the electrode protection additive, the more the high-power performance of the nonaqueous secondary battery in a low-temperature environment is improved. Therefore, by adjusting the content of the electrode protection additive within the above range, it is possible to exhibit excellent performance based on the high ionic conductivity of the electrolyte solution without impairing the basic functions of the nonaqueous secondary battery. Furthermore, by preparing a nonaqueous electrolyte solution with such a composition, it is possible to further improve the cycle performance of the nonaqueous secondary battery, the high-power performance in a low-temperature environment, and other battery characteristics.

[0065] The solvents represented by "R-CN," particularly acetonitrile, are susceptible to electrochemical reductive decomposition. Therefore, the nonaqueous solvent containing the solvent represented by "R-CN" preferably contains one or more cyclic aprotic polar solvents, more preferably one or more unsaturated bond-containing cyclic carbonates, as an electrode protection additive for forming a protective coating on the negative electrode.

[0066] The unsaturated bond-containing cyclic carbonate is preferably vinylene carbonate, and the content of vinylene carbonate in the nonaqueous electrolyte is preferably 0.1% by volume or more and 10% by volume or less, more preferably 0.2% by volume or more and less than 8% by volume, and even more preferably 0.5% by volume or more and less than 7% by volume. This can more effectively improve low-temperature durability, making it easier to provide a secondary battery with excellent low-temperature performance.

[0067] Vinylene carbonate, an additive for electrode protection, suppresses the reductive decomposition reaction of acetonitrile on the negative electrode surface. On the other hand, excessive film formation leads to a decrease in low-temperature performance. Therefore, by adjusting the amount of vinylene carbonate added within the above range, the interfacial (film) resistance can be kept low, which makes it easier to suppress cycle deterioration at low temperatures.

[0068] <Acid anhydride> The nonaqueous secondary battery of this embodiment is stabilized by the formation of an SEI on the negative electrode surface due to partial decomposition of the nonaqueous electrolyte during initial charging. To more effectively strengthen this SEI, an acid anhydride can be added. When acetonitrile is included as the nonaqueous solvent, the strength of the SEI tends to decrease with increasing temperature, but the addition of an acid anhydride promotes strengthening of the SEI. Therefore, the use of such an acid anhydride can effectively suppress the increase in internal resistance over time due to thermal history.

[0069] Specific examples of acid anhydrides include chain acid anhydrides such as acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic acid anhydrides such as malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, and naphthalene-1,4,5,8-tetracarboxylic dianhydride; and mixed acid anhydrides having a structure formed by dehydration condensation of different types of acids, such as two different types of carboxylic acids or a carboxylic acid and a sulfonic acid. These may be used alone or in combination of two or more types.

[0070] Since the nonaqueous secondary battery of this embodiment preferably strengthens the SEI before the reductive decomposition of the nonaqueous solvent, it is preferable that the acid anhydride contains at least one cyclic acid anhydride that acts early during the first charge. These cyclic acid anhydrides may be contained alone or in combination. Alternatively, a cyclic acid anhydride other than these cyclic acid anhydrides may be contained. Furthermore, the cyclic acid anhydride preferably contains at least one of succinic anhydride, maleic anhydride, and phthalic anhydride.

[0071] A nonaqueous electrolyte solution containing at least one of succinic anhydride, maleic anhydride, and phthalic anhydride can form a strong SEI on the negative electrode and more effectively suppress an increase in resistance during high-temperature heating. In particular, it is preferable to contain succinic anhydride. This makes it easier to more effectively form a strong SEI on the negative electrode while suppressing side reactions.

[0072] When the non-aqueous electrolytic solution of the present embodiment contains an acid anhydride, the content thereof is preferably in the range of 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 1 part by mass or less, and even more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, per 100 parts by mass of the non-aqueous electrolytic solution.

[0073] The acid anhydride is preferably contained in the non-aqueous electrolyte solution. On the other hand, as long as the acid anhydride can function in a non-aqueous secondary battery, at least one battery component selected from the group consisting of a positive electrode, a negative electrode, and a separator may contain the acid anhydride. The acid anhydride may be contained in the battery component during production of the battery component, or may be impregnated into the battery component by post-treatment such as coating, immersion, or spray drying.

[0074] Optional Additives In this embodiment, for the purpose of improving the charge / discharge cycle characteristics, high-temperature storage properties, and safety (e.g., prevention of overcharging) of the nonaqueous secondary battery, optional additives may be appropriately contained in the nonaqueous electrolyte solution.

[0075] Examples of optional additives include sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters (ethyl diethylphosphonoacetate (EDPA); (CHO)(P=O)-CH(C=O)OCH, tris(trifluoroethyl)phosphate (TFEP); (CFCHO)P=O, triphenylphosphate (TPP); (CHO)P=O, triallylphosphate; (CH=CHCHO)P=O, etc.), and nitrogen-containing cyclic compounds with no steric hindrance around the unshared electron pair (pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.). Phosphate esters are particularly effective as optional additives because they suppress side reactions during storage.

[0076] When the nonaqueous electrolyte solution of this embodiment contains other optional additives, the content thereof is preferably in the range of 0.01% by mass to 10% by mass, more preferably 0.02% by mass to 5% by mass, and even more preferably 0.05 to 3% by mass, relative to the total amount of the nonaqueous electrolyte solution. By adjusting the content of the other optional additives within the above ranges, it tends to be possible to impart even better battery characteristics without impairing the basic functions of a nonaqueous secondary battery.

[0077] <2. Positive electrode and positive electrode current collector> 1 and 2 is composed of a positive electrode active material layer made of a positive electrode mixture and a positive electrode current collector. The positive electrode 150 is not particularly limited as long as it functions as a positive electrode for a nonaqueous secondary battery, and may be a known positive electrode. The positive electrode in this embodiment preferably contains a lithium-containing compound containing Fe.

[0078] The positive electrode active material layer is disposed on one or both sides of the positive electrode current collector, and preferably contains a positive electrode active material and, if necessary, further contains a conductive additive and a binder.

[0079] The positive electrode active material layer preferably contains a material capable of absorbing and releasing lithium ions as the positive electrode active material, since use of such a material tends to enable a high voltage and a high energy density to be obtained.

[0080] The positive electrode active material contained in the positive electrode active material layer is a compound represented by the following general formula (1): Li w MPO4 (1) {In the formula, M represents one or more transition metal elements, and the value of w is determined depending on the charge / discharge state of the battery and represents a number from 0 to 1.2, preferably a number from 0.05 to 1.10.} and / or a metal phosphate compound containing lithium and a transition metal element, represented by the following general formula (2): Lip Ni q Co r Mn s M t O u ·····(2) {Wherein, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, 0 ≦ s < 0.5, 0 ≦ t < 0.3, 0.7 ≦ q + r + s + t ≦ 1.2, 1.8 < u < 2.2, and p is a value determined by the charge-discharge state of the battery.} At least one Li-containing metal oxide selected from lithium (Li)-containing metal oxides represented by the following is preferable.

[0081] Specific examples of the positive electrode active material include, for example, Li w Li compounds such as FePO4, or lithium cobalt oxides represented by LiCoO2; lithium manganese oxides represented by LiMnO2, LiMn2O4, and Li2Mn2O4; lithium nickel oxides represented by LiNiO2; LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.2 O2, Li z MO2 (wherein, M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2), and lithium-containing composite metal oxides represented thereby, etc. are exemplified.

[0082] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (2) is 0.5 < q < 1.2, it is preferable because both the reduction of the amount of rare metal Co used and the increase in the high energy density can be achieved. Such a positive electrode active material includes, for example, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.75 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.075 Mn 0.075 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.81 Co 0.1 Al 0.09 O2, LiNi 0.85 Co 0.1 Al 0.05 O2, etc., and lithium-containing composite metal oxides represented by the above are exemplified.

[0083] On the other hand, as the Ni content ratio increases in the positive electrode active material layer, the deterioration tends to progress at a low voltage. There are essentially active points in the positive electrode active material of the Li-containing metal oxide represented by the general formula (2) that oxidatively deteriorate the non-aqueous electrolyte, and these active points may accidentally consume the compound added to protect the negative electrode on the positive electrode side. Among them, acid anhydrides tend to be easily affected.

[0084] In addition, these additive decomposition products incorporated and deposited on the positive electrode side not only become factors for increasing the internal resistance of the non-aqueous secondary battery but also accelerate the deterioration of the lithium salt. Furthermore, the protection of the negative electrode surface, which was the original purpose, also becomes insufficient. To deactivate the active points that essentially oxidatively deteriorate the non-aqueous electrolyte, it is important to control the Jahn-Teller distortion or coexist with components that play a role as a neutralizing agent. Therefore, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0085] For the same reason, it is preferable that the surface of the positive electrode active material is coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. It is also more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, it is particularly preferable that the surface of the positive electrode active material is coated with at least one oxide selected from the group consisting of ZrO2, TiO2, Al2O3, NbO3, and LiNbO2, because this does not inhibit the permeation of lithium ions.

[0086] The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxides represented by formulas (1) and (2), and is not particularly limited as long as it contains lithium. Examples of such lithium-containing compounds include composite oxides containing lithium and a transition metal element, metal chalcogenides containing lithium, and metal silicate compounds containing lithium and a transition metal element. From the viewpoint of obtaining a higher voltage, the lithium-containing compound is preferably a metal phosphate compound containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti. More specifically, the lithium-containing compound is represented by the following formula (Xa): Li v M I D2 (Xa) {wherein D represents a chalcogen element, and M I represents one or more transition metal elements, and the value of v is determined depending on the charge / discharge state of the battery and represents a number between 0.05 and 1.10.}, and The following formula (Xb): Li t M II u SiO4 (Xb) {In formula, M II represents one or more transition metal elements, the value of t is determined depending on the charge / discharge state of the battery and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.} Examples of compounds include compounds represented by the following formulae:

[0087] The lithium-containing compound represented by the formula (Xa) has a layered structure, and the compounds represented by the formula (1) and the formula (Xb) have an olivine structure. These lithium-containing compounds may be, for the purpose of stabilizing the structure, a part of the transition metal element is substituted with Al, Mg, or another transition metal element, these metal elements are contained in the crystal grain boundaries, some of the oxygen atoms are substituted with fluorine atoms, or at least a part of the surface of the positive electrode active material may be coated with another positive electrode active material.

[0088] As the positive electrode active material in this embodiment, the lithium-containing compound as described above may be used alone, or the lithium-containing compound may be used in combination with other positive electrode active materials.

[0089] Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layer structure, sulfur, conductive polymers, etc. Examples of metal oxides or metal chalcogenides having a tunnel structure and a layer structure include MnO2, FeO2, FeS2, VO5, and VO. 13 Examples of the conductive polymer include oxides, sulfides, and selenides of metals other than lithium, such as TiO2, TiS2, MoS2, and NbSe2. Examples of the conductive polymer include conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0090] The other positive electrode active materials described above may be used singly or in combination of two or more, and are not particularly limited. However, it is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co, because it is possible to reversibly and stably store and release lithium ions and achieve a high energy density.

[0091] When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of the lithium-containing compound to the total positive electrode active material is preferably 80 mass% or more, and more preferably 85 mass% or more.

[0092] Examples of the conductive additive include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive additive is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the positive electrode active material.

[0093] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 8 parts by mass, per 100 parts by mass of the positive electrode active material.

[0094] The positive electrode active material layer is formed by dispersing a positive electrode mixture, which is a mixture of a positive electrode active material and, if necessary, a conductive additive and a binder, in a solvent to form a positive electrode mixture-containing slurry, which is then applied to a positive electrode current collector, dried (solvent removal), and, if necessary, pressed. The solvent is not particularly limited, and any conventionally known solvent can be used. Examples of such a solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0095] The positive electrode current collector is made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The surface of the positive electrode current collector may be coated with carbon or may be processed into a mesh. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

[0096] <3. Negative electrode and negative electrode current collector> 1 and 2 is composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode 160 can function as the negative electrode of a non-aqueous secondary battery.

[0097] The negative electrode active material layer is disposed on one or both sides of the negative electrode current collector, and preferably contains a negative electrode active material and, if necessary, a conductive additive and a binder.

[0098] Examples of negative electrode active materials include amorphous carbon (hard carbon), graphite (e.g., artificial graphite, natural graphite, etc.), pyrolytic carbon, coke, glassy carbon, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fiber, activated carbon, carbon colloid, and carbon black, as well as metal lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymer compounds. The negative electrode active materials may be used alone or in combination of two or more. From the viewpoint of the application of the nonaqueous electrolyte according to this embodiment, graphite is preferred as the negative electrode active material.

[0099] The negative electrode active material layer uses lithium ions as the negative electrode active material to increase the battery voltage. + It is preferable that the material contains a material capable of occluding at a potential lower than the potential of the metal.

[0100] Examples of the conductive additive include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive additive is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the negative electrode active material.

[0101] Examples of binders include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Also included are diene rubbers such as styrene-butadiene rubber. The binder content is preferably 10 parts by mass or less, more preferably 0.5 to 8 parts by mass, per 100 parts by mass of the negative electrode active material.

[0102] The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of a negative electrode active material and, optionally, a conductive additive and a binder, in a solvent to form a negative electrode mixture-containing slurry, which is then applied to a negative electrode current collector, dried (to remove the solvent), and, if necessary, pressed. The solvent is not particularly limited, and any conventionally known solvent can be used. Examples of such a solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0103] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, or stainless steel foil. The surface of the negative electrode current collector may be coated with carbon or may be processed into a mesh. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

[0104] In this embodiment, the surface of the negative electrode active material contains 10.0 to 50.0 mass % of compounds composed of inorganic components relative to the compounds composed of organic components excluding lithium carbonate. The "surface of the negative electrode active material" referred to here is the portion corresponding to the protective coating formed on the surface of the negative electrode, and the method for analyzing the components of such a negative electrode protective coating is as described in the Examples. The organic component includes lithium carbonate (for example, alkyl lithium), and the inorganic component includes at least one selected from the group consisting of lithium fluoride, lithium sulfate, and lithium sulfite. Thus, the ratio of the inorganic component coating amount {inorganic component coating amount (mg / g) / coating amount (mg / g)} is 10.0 to 50.0 mass %. By including at least a certain proportion of a dense inorganic coating that is poorly soluble in highly polar solvents on the negative electrode surface, it is possible to provide a nonaqueous secondary battery that can be stably operated in a high-temperature environment, even when a highly polar solvent that is easily reductively decomposed is used as the electrolyte.

[0105] <4. Separator> 2, the nonaqueous secondary battery 100 of this embodiment preferably includes a separator 170 between the positive electrode 150 and the negative electrode 160 from the viewpoint of preventing short circuits between the positive electrode 150 and the negative electrode 160 and providing safety such as shutdown. The separator 170 is not limited, but may be the same as those included in known nonaqueous secondary batteries, and is preferably an insulating thin film with high ion permeability and excellent mechanical strength. Examples of the separator 170 include woven fabric, nonwoven fabric, and synthetic resin microporous membrane, and among these, synthetic resin microporous membrane is preferred.

[0106] Suitable synthetic resin microporous films include, for example, microporous films containing polyethylene or polypropylene as a main component, or polyolefin-based microporous films containing both of these polyolefins. Suitable nonwoven fabrics include, for example, porous films made of heat-resistant resins such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

[0107] Separator 170 may be configured as a single layer or multiple layers of one type of microporous film, or may be configured as a layer of two or more types of microporous films. Separator 170 may be configured as a single layer or multiple layers of a mixed resin material obtained by melting and kneading two or more types of resin materials.

[0108] To provide functionality, inorganic particles may be present on the surface or inside of the separator, or other organic layers may be coated or laminated thereon. Furthermore, a crosslinked structure may be included. These methods may be combined as needed to enhance the safety performance of nonaqueous secondary batteries.

[0109] By using such a separator 170, it is possible to achieve the good input / output characteristics and low self-discharge characteristics required for the lithium ion battery for high-power applications described above.

[0110] The thickness of the microporous membrane usable as a separator is not particularly limited, but is preferably 1 μm or more from the viewpoint of membrane strength, and preferably 500 μm or less from the viewpoint of permeability. From the viewpoint of use in high-power applications requiring a relatively high heat output and better self-discharge characteristics than conventional ones, such as safety tests, and from the viewpoint of winding ease in large battery winding machines, the thickness of the microporous membrane is preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm. When prioritizing both short-circuit resistance and power performance, the thickness of the microporous membrane is more preferably 15 μm to 25 μm, but more preferably 10 μm to less than 15 μm when prioritizing both high energy density and power performance.

[0111] The porosity of a microporous membrane usable as a separator is preferably 30% to 90%, more preferably 35% to 80%, and even more preferably 40% to 70%, from the viewpoint of following the rapid movement of lithium ions during high power output. If priority is given to improving power performance while ensuring safety, the porosity of the microporous membrane is particularly preferably 50% to 70%, and if emphasis is placed on achieving both short-circuit resistance and power performance, the porosity is particularly preferably 40% to less than 50%.

[0112] The air permeability of a microporous membrane that can be used as a separator should be 1 second / 100 cm from the viewpoint of the balance between the membrane thickness and porosity. 3 More than 400 seconds / 100cm 3 Less than 100 seconds / 100cm is preferable.3 More than 350 / 100cm 3 When emphasis is placed on achieving both short circuit resistance and output performance, the air permeability of the microporous membrane is preferably 150 sec / 100 cm. 3 More than 350 seconds / 100cm 3 The following is particularly preferable. If you prioritize improving output performance while ensuring safety, 100 / 100cm 3 seconds or more 150 seconds / 100cm 3 It is particularly preferable that the ionic conductivity is less than 10 mS / cm. On the other hand, when a nonaqueous electrolyte solution with low ionic conductivity is combined with a separator within the above range, the lithium ion migration rate is determined not by the separator structure but by the high ionic conductivity of the nonaqueous electrolyte solution, and the expected input / output characteristics tend not to be obtained. Therefore, the ionic conductivity of the nonaqueous electrolyte solution is preferably 10 mS / cm or more, more preferably 15 mS / cm, and even more preferably 20 mS / cm. However, the membrane thickness, air permeability, and porosity of the separator, and the ionic conductivity of the nonaqueous electrolyte solution are not limited to the above examples.

[0113] <5. Battery exterior> The configuration of the battery exterior 110 of the nonaqueous secondary battery 100 shown in Figures 1 and 2 is not particularly limited, and for example, either a battery can or a laminate film exterior can be used. As the battery can, for example, a metal can made of steel, stainless steel, aluminum, clad material, or the like, which may be prismatic, rectangular, cylindrical, cylindrical, oval, flat, coin-shaped, or button-shaped, can be used. As the laminate film exterior, for example, a laminate film having a three-layer structure of heat-melt resin / metal film / resin can be used.

[0114] The laminate film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by folding the laminate film exterior so that the heat-melt resin side faces inward and sealing the ends with heat sealing. When using a laminate film exterior, the positive electrode lead body 130 (or a lead tab connected to a positive electrode terminal and a positive electrode terminal) may be connected to the positive electrode current collector, and the negative electrode lead body 140 (or a lead tab connected to a negative electrode terminal and a negative electrode terminal) may be connected to the negative electrode current collector. In this case, the laminate film exterior may be sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal, respectively) extended to the outside of the exterior.

[0115] 6. Battery manufacturing method The nonaqueous secondary battery 100 in this embodiment is produced by a known method using the above-mentioned nonaqueous electrolyte solution, a positive electrode 150 having a positive electrode active material layer on one or both sides of a current collector, a negative electrode 160 having a negative electrode active material layer on one or both sides of a current collector, a battery casing 110, and, if necessary, a separator 170.

[0116] First, a laminate consisting of a positive electrode 150, a negative electrode 160, and optionally a separator 170 is formed. For example: An embodiment in which a long positive electrode 150 and a long negative electrode 160 are wound in a stacked state with the long separator interposed between the positive electrode 150 and the negative electrode 160 to form a wound laminate; A mode in which the positive electrode 150 and the negative electrode 160 are cut into a plurality of sheets each having a certain area and shape, and the resulting positive electrode sheets and negative electrode sheets are alternately stacked with separator sheets interposed therebetween to form a laminate having a laminated structure; A mode in which a long separator is folded zigzag and positive electrode sheets and negative electrode sheets are alternately inserted between the zigzag-folded separators to form a laminated body; etc. are possible.

[0117] Next, the above-mentioned laminate is housed in a battery exterior 110 (battery case), the nonaqueous electrolyte solution according to this embodiment is poured into the battery case, and the laminate is immersed in the nonaqueous electrolyte solution and sealed, thereby producing the nonaqueous secondary battery according to this embodiment.

[0118] Alternatively, a gel-state electrolyte membrane may be prepared in advance by impregnating a substrate made of a polymer material with a nonaqueous electrolyte solution, and a laminated structure may be formed using sheet-like positive electrode 150, negative electrode 160, and electrolyte membrane, as well as separator 170 as needed, and then housed in battery exterior 110 to prepare nonaqueous secondary battery 100.

[0119] If the electrodes are arranged so that there is a portion where the outer peripheral edge of the negative electrode active material layer overlaps with that of the positive electrode active material layer, or there is a portion where the width is too small in the non-facing portion of the negative electrode active material layer, misalignment of the electrodes may occur during battery assembly, which may result in a deterioration in the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the positions of the electrodes of the electrode body used in the non-aqueous secondary battery in advance using tapes such as polyimide tape, polyphenylene sulfide tape, and polypropylene (PP) tape, adhesives, etc.

[0120] In this embodiment, when a nonaqueous electrolyte containing acetonitrile is used, its high ionic conductivity may cause lithium ions released from the positive electrode during the initial charge of the nonaqueous secondary battery to diffuse throughout the negative electrode. In nonaqueous secondary batteries, the area of ​​the negative electrode active material layer is generally larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are absorbed in a portion of the negative electrode active material layer that does not face the positive electrode active material layer, these lithium ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of these unreleased lithium ions will be the irreversible capacity. For these reasons, nonaqueous secondary batteries using a nonaqueous electrolyte containing acetonitrile may have low initial charge / discharge efficiency.

[0121] On the other hand, if the area of ​​the positive electrode active material layer is larger than that of the negative electrode active material layer or if the two are the same, current tends to concentrate at the edge portions of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0122] For the reasons described above, the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other is not particularly limited, but is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, even more preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In a nonaqueous secondary battery using a nonaqueous electrolyte solution containing acetonitrile, the initial charge-discharge efficiency can be improved by reducing the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other.

[0123] Reducing the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other means limiting the area of ​​the portion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to minimize the amount of lithium ions released from the positive electrode during the initial charge that are absorbed in the portion of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the amount of lithium ions that are not released from the negative electrode during the initial discharge and result in irreversible capacity). Therefore, by designing the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, it is possible to improve the load characteristics of the battery by using acetonitrile, increase the initial charge / discharge efficiency of the battery, and further suppress the formation of lithium dendrites.

[0124] The nonaqueous secondary battery 100 of this embodiment can function as a battery after initial charging, but is stabilized by partial decomposition of the nonaqueous electrolyte during initial charging. While there are no particular limitations on the initial charging method, the initial charging is preferably performed at 0.001 to 0.3 C, more preferably 0.002 to 0.25 C, and even more preferably 0.003 to 0.2 C. It is also preferable that the initial charging be performed via a constant voltage charge. By extending the voltage range in which the lithium salt participates in the electrochemical reaction, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), which has the effect of suppressing an increase in internal resistance. Furthermore, the reaction product is not firmly fixed only to the negative electrode 160, but also has some beneficial effect on components other than the negative electrode 160, such as the positive electrode 150 and separator 170. Therefore, it is highly effective to perform the initial charging while taking into account the electrochemical reaction of the lithium salt dissolved in the nonaqueous electrolyte.

[0125] The nonaqueous secondary battery 100 of this embodiment can also be used as a battery pack in which a plurality of nonaqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charge / discharge state of the battery pack, the operating voltage range per battery is preferably 2 to 5 V.

[0126] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present invention. [Example]

[0127] The present embodiment will be described in more detail below with reference to examples and comparative examples. The present embodiment is not limited to the following examples. Various parameters related to the present embodiment are measured based on the measurement methods in the examples section unless otherwise specified.

[0128] (1) Preparation of non-aqueous electrolyte In an inert atmosphere, various non-aqueous solvents and various additives were mixed to a predetermined concentration, and various lithium salts were added to the mixture to a predetermined concentration to prepare non-aqueous electrolyte solutions (S01) to (S05). The abbreviations for non-aqueous solvents, lithium salts, and additives in the table below have the following meanings. In Table 1, the values ​​in the "Lithium salt (mol / L)" column indicate the number of moles per 1 L of nonaqueous electrolyte solution, and the values ​​in the "Composition of nonaqueous solvent (volume %)" column indicate the volume relative to the total amount of nonaqueous solvent.

[0129] [Table 1]

[0130] (lithium salts) LiPF6: Lithium hexafluorophosphate LiFSI: Lithium bis(fluorosulfonyl)imide

[0131] (non-aqueous solvent) AcN: acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate VC: vinylene carbonate ES: Ethylene sulfite

[0132] (2) Fabrication of non-aqueous secondary batteries (2-1) Preparation of the positive electrode (A) LiFePO4 as a positive electrode active material, (B) carbon black powder as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 94:3:3 to obtain a positive electrode mixture.

[0133] The obtained positive electrode mixture was further mixed with N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one or both sides of a 15 μm-thick aluminum foil that forms a positive electrode current collector in an amount of 20 mg / cm.2 The slurry was applied while adjusting the density so that the positive electrode active material layer had a density of 2.3 g / cm 3 , and the solvent was then dried and removed in a hot air drying oven. 3 The cathodes (C1, C2, C3) were obtained by rolling the cathode active material layer and the cathode current collector. A lead was welded to C3. The cathodes were then vacuum dried at 120°C for 12 hours or more, thereby obtaining cathodes.

[0134] (2-2) Preparation of negative electrode (a) Graphite as a negative electrode active material, (b) carboxymethyl cellulose, and (c) styrene-butadiene rubber were mixed in a mass ratio of 97:1:2 to obtain a negative electrode mixture.

[0135] Water was added as a solvent to the obtained negative electrode mixture and further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one or both sides of a copper foil having a thickness of 10 μm to form a negative electrode current collector in an amount of 9 mg / cm. 2 The slurry was applied while adjusting the density so that the slurry would be 1.6 g / cm 3 , and the solvent was then dried and removed in a hot air drying oven. 3 The negative electrodes (A1, A2, A3) were obtained by rolling the negative electrode active material layer and the negative electrode current collector. A lead was welded to A3. The negative electrodes were then vacuum dried at 80°C for 12 hours or more.

[0136] (2-3) Assembly of non-aqueous secondary battery (laminate type) In a dry room with a dew point temperature of -80°C to -20°C, the cut positive electrode with lead (C3) and the cut negative electrode with lead (A3) were stacked together with a polyethylene microporous membrane separator (thickness 20 μm) in between to obtain a laminated electrode body. This laminated electrode body was then housed in an aluminum laminate film exterior. Next, a nonaqueous electrolyte solution was injected into the exterior body, and the exterior body was sealed to produce a laminated nonaqueous secondary battery having the appearance shown in Fig. 1 and the cross-sectional structure shown in Fig. 2. The battery was kept at 25°C for 48 hours, allowing the nonaqueous electrolyte solution to fully penetrate the laminated electrode body, thereby obtaining a laminated sheet-type nonaqueous secondary battery (hereinafter also simply referred to as a "laminated battery").

[0137] (3) Evaluation of non-aqueous secondary batteries The laminated battery obtained as described above was first subjected to an initial charge-discharge treatment and a final charge-discharge treatment according to the procedures (3-1) to (3-2) below. Next, the laminated battery was evaluated according to the procedure (3-3). The laminated battery was charged and discharged using TOSCAT-300 (trade name) manufactured by Toyo Systems Co., Ltd., and LU-123 (trade name) or BTS-408C (trade name) manufactured by ESPEC.

[0138] Here, 1C means the current value at which a fully charged battery is expected to be discharged completely in one hour when discharged at a constant current.

[0139] (3-1) Initial charge / discharge treatment of non-aqueous secondary batteries The ambient temperature of the fabricated nonaqueous secondary battery was set to 25°C, and it was charged at a constant current of 0.025C until the charge capacity reached 90% of the design capacity. After charging, the ambient temperature was set to 45°C, and aging was performed for 48 hours. Thereafter, the ambient temperature was set to 25°C, and it was discharged to 2.0V at a constant current of 0.1C.

[0140] (3-2) Final charge / discharge process After the treatment in (3-1), the ambient temperature of the nonaqueous secondary battery was set to 25°C, and the battery was charged to 3.6 V at a constant current of 0.2 C. Thereafter, the battery was continuously charged at a constant voltage for 2 hours while the current was decaying while maintaining the voltage at 3.6 V, or until the current value decayed to 0.05 C. The battery was then discharged to 2.0 V at a constant current of 0.2 C. (3-3) 50℃ cycle test The nonaqueous secondary batteries, which had been initially charged and discharged using the methods described in (3-1) and (3-2) above, were set to an ambient temperature of 50°C and allowed to reach 3.6 V at a constant current equivalent to 1 C. They were then charged at a constant voltage of 3.6 V until the current decayed to 0.05 C. They were then discharged to 2 V at a current equivalent to 1 C. One charge and one discharge constituted one cycle, and 300 charge and discharge cycles were performed. The amount of gas (cc / g) generated during this test (50°C cycle test) was calculated from the difference between the volume of the laminated battery after the 50°C cycle test and the volume before the 50°C cycle test. The amount of gas was calculated per gram of negative electrode active material.

[0141] (3-4) Analysis of the components of the negative electrode coating The nonaqueous secondary battery, which had been subjected to the initial charge-discharge treatment described in (3-1) and (3-2) above, was disassembled under an argon atmosphere, and the negative electrode was removed. The negative electrode protective coating was then extracted using heavy water. The components of the negative electrode protective coating were analyzed using NMR measurement for compounds composed of organic components such as alkyllithium, and IC measurement for compounds composed of inorganic components such as lithium fluoride, lithium sulfate, and lithium sulfite. The coating amount was calculated per gram of negative electrode active material.

[0142] (3-4-1) Extraction of electrode coating Under an argon atmosphere, 130 mg of the negative electrode (including the current collector) was placed in a glass screw tube, and 1 mL of heavy water was injected into each tube using a syringe. The tube was then sealed with a lid. After leaving the tube to stand for 72 hours, the electrode coating was extracted, and the extract was filtered through a cotton plug using a Pasteur pipette packed with glass wool.

[0143] (3-4-2) NMR measurement The obtained extract was placed in a 3 mm diameter NMR tube and sealed. Separately, tetrafluorobenzene (Tokyo Chemical Industry Co., Ltd.) was dissolved as a standard substance in deuterated chloroform (Sigma-Aldrich Co.) containing tetramethylsilane as a chemical shift standard, and the solution was placed in a 5 mm diameter NMR tube. The above 3 mm NMR tube was inserted into this NMR tube, and the NMR was measured by the double tube method. 1 H NMR measurement was performed. In addition, a heavy water solution of dimethyl sulfoxide (concentration 0.398 mg / mL) was prepared as a quantitative standard substance, and 1 H NMR measurements were carried out. The measurement equipment used was a JNM-ECS-400 FT NMR instrument manufactured by JEOL RESONANCE, Inc. Deuterated chloroform was used as the lock solvent, the number of integrations was 256, and tetramethylsilane (0 ppm) was used as the chemical shift standard. Quantitative calculations were performed by setting the integral value of the peak attributed to the protons of tetrafluorobenzene at 2000 and determining the integral value corresponding to one proton per unit concentration from the integral value of the signal of the standard substance, dimethyl sulfoxide, and using this value to calculate the integral values ​​of each peak.

[0144] (3-4-3) IC measurement The extract was diluted with distilled water, and IC measurements were performed under the following conditions (anion measurements: 1000-fold diluted solution measurement, carbonate ion measurements: 100-fold diluted solution measurement). IC conditions (anion measurement) Equipment:Tosoh,IC-2010 Column: Tosoh, TSKgel-Super IC-AZ (4.6 mm x 150 mm) Eluent: 6.3mM NaHCO3+1.7mM Na2CO3 Flow rate: 0.8mL / min Detection: Electrical conductivity Column temperature: 40℃ Injection volume: 30μL IC conditions (carbonate ion measurement) Equipment:Tosoh,IC-2001 Column: Tosoh, TSKgel-SCX (4.6 mm x 150 mm) Eluent: 0.1mM phosphoric acid Flow rate: 0.6mL / min Detection: Electrical conductivity Column temperature: 40℃ Injection volume: 30μL

[0145] [Examples 1 to 4 and Comparative Example 1] Using the positive and negative electrodes prepared above and the nonaqueous electrolyte solutions shown in Table 1, laminated batteries were prepared according to the method described in (2) above. Next, each nonaqueous secondary battery was evaluated according to the procedures described in (3-1) to (3-3) above. The evaluation results are shown in the table below. In Table 3, in the "A2 / A1 (%)" section, "A1" indicates the value of "coating amount (mg / g)" and "A2" indicates the value of "coating amount of inorganic component (mg / g)".

[0146] [Table 2]

[0147] [Table 3]

[0148] As shown in the table above, in Examples 1 to 4, the gas amount after the 50°C cycle test was 1.10 cc / g or less, and the ratio of the inorganic component coating amount {inorganic component coating amount (mg / g) / coating amount (mg / g)} was 10.0 mass% or more. On the other hand, in Comparative Example 1, the gas amount was 1.45 cc / g or more, and the ratio of the inorganic component coating amount was less than 9.5 mass%. This demonstrates that by controlling the inorganic component ratio in the anode protective coating so that it falls within the range of this embodiment, the gas amount in a high-temperature environment can be reduced. As such, the examples provided nonaqueous secondary batteries that could be stably operated in a high-temperature environment, even when a highly polar and easily reductively decomposed solvent was used in the electrolyte. [Industrial Applicability]

[0149] The nonaqueous secondary battery of the present invention is expected to be used as an automotive storage battery for hybrid vehicles, plug-in hybrid vehicles, electric vehicles, and the like, as well as an industrial storage battery for power tools, drones, electric motorcycles, and the like, and further as a residential power storage system. [Explanation of symbols]

[0150] 100 Nonaqueous secondary battery 110 Battery casing 120 Battery enclosure space 130 Positive electrode lead body 140 Negative electrode lead body 150 positive electrode 160 negative electrode 170 Separator

Claims

1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, the positive electrode has a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector, the non-aqueous electrolyte solution includes a lithium salt and a non-aqueous solvent, The lithium salt contains an inorganic lithium salt, The inorganic lithium salt contains 0.3 mol or more of lithium hexafluorophosphate per 1 L of the nonaqueous electrolyte solution, the non-aqueous solvent contains a nitrile compound represented by R—CN (wherein R is a hydrocarbon group having 1 to 4 carbon atoms or a halogenated hydrocarbon group having 1 to 4 carbon atoms) in a proportion of 5 to 90% by volume relative to the total amount of the non-aqueous solvent; the compound composed of an inorganic component is contained in an amount of 10.0 to 50.0 mass % on the surface of the negative electrode active material relative to the compound composed of an organic component excluding lithium carbonate; Non-aqueous secondary battery.

2. 2. The non-aqueous secondary battery according to claim 1, wherein the compound composed of the inorganic component is at least one selected from the group consisting of lithium fluoride, lithium sulfite, and lithium sulfate.

3. The nonaqueous secondary battery according to claim 1 , wherein the nitrile compound includes acetonitrile.

Images