Non-aqueous secondary battery

Abstract

To prevent reaction between deposited metals generated in a non-aqueous secondary battery and a non-aqueous electrolyte, thereby stabilizing battery characteristics.SOLUTION: An added carbon dioxide reacts with a deposited metal, preventing the non-aqueous solvent, additives, and electrolyte that make up the non-aqueous electrolyte from sacrificially reacting with the deposited metal, thereby stabilizing the battery characteristics over the long term.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, research and development into various secondary batteries has progressed, with many of them achieving improvements in various performance areas, such as lifespan, input / output performance, and energy density. The required performance levels vary depending on the application, but when considering applications such as electric vehicles (EVs), it is necessary to achieve both lifespan and input / output performance.

[0003] To improve the lifespan and input / output performance, it is conceivable to use high-performance additives and low-viscosity solvents in batteries. For example, Patent Document 1 discloses that the lifespan of secondary batteries is improved by formulating additives. Furthermore, Patent Document 2 discloses an additive that prevents the decomposition of acetonitrile. These electrolyte configurations enhance battery performance by controlling the properties of the solid electrolyte interface (SEI) formed on the surface of the negative electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-166553 [Patent Document 2] International Publication No. 2012 / 057311 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in actual use, secondary batteries not only repeat ideal charge-discharge reactions, but also, in most cases, experience some metal deposition. For example, in lithium-ion secondary batteries, metallic lithium is deposited, and the deposited metal undergoes a reduction reaction with the electrolyte, resulting in a decrease in battery capacity. In particular, nitrile compounds such as acetonitrile, which have both a high dielectric constant and low viscosity and are effective in improving battery performance, easily react with the electrodeposited metal, resulting in a rapid decrease in capacity. Thus, Patent Documents 1 and 2 do not address the issues and solutions arising from the electrodeposited metal. Even when attempts were made to improve performance by controlling the SEI characteristics and ionic conductivity using specific additives, solvents, and electrode configurations, they did not fundamentally prevent the unexpected reaction between the electrodeposited metal and the electrolyte.

[0006] An object of the present disclosure is to prevent or suppress reaction between deposited metal and a nonaqueous electrolyte in a nonaqueous secondary battery, thereby stabilizing the battery characteristics. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have found that the problems can be solved by the following technical means. That is, the present invention is as follows. (1) A nonaqueous secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution contains an electrolyte and a nonaqueous solvent, the electrolyte containing at least an imide salt, and the nonaqueous solvent containing at least a nitrile compound, the nonaqueous electrolyte solution having an ionic conductivity of more than 10 mS / cm, and the nonaqueous secondary battery containing carbon dioxide. (2) The nonaqueous secondary battery according to item 1, wherein the nonaqueous secondary battery contains a gas, the carbon dioxide is contained in the gas and / or outside the gas, and the content of the carbon dioxide relative to the volume of the gas is 10 to 90% by volume. (3) The nonaqueous secondary battery according to item 1 or 2, wherein the nonaqueous electrolyte solution contains acetonitrile as a nitrile compound, the content of the acetonitrile is 5 to 97% by volume relative to the volume of the nonaqueous solvent, and the ionic conductivity is 11 to 30 mS / cm. (4) The nonaqueous secondary battery according to any one of items 1 to 3, wherein the electrolyte contains at least lithium bis(fluorosulfonyl)imide, the negative electrode contains graphite, and the surface of the negative electrode contains lithium carbonate, and the abundance ratio of lithium element as lithium metal to lithium element in the lithium carbonate is 0.3 or less. (5) The volume of carbon dioxide contained per 1 Ah of battery capacity is 1 cm under room temperature and atmospheric pressure conditions. 3 5. The nonaqueous secondary battery according to any one of items 1 to 4, wherein: [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent or suppress the impairment of the functions of the additives and solvents in the nonaqueous electrolyte solution due to reaction with the electrodeposited metal, thereby stabilizing the battery characteristics. In turn, it is possible to provide a nonaqueous secondary battery with improved charge-discharge stability by using a nonaqueous electrolyte solution containing a nitrile compound, and it is also possible to maintain a low rate of maximum capacity deterioration of the battery. [Brief explanation of the drawings]

[0009] [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. [Figure 3] 1 shows TOF-SIMS spectra of the negative electrode surface according to the present embodiment and a reference example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. In this specification, a numerical range indicated using "to" includes the numerical values ​​before and after it.

[0011] <Non-aqueous secondary battery> The nonaqueous secondary battery according to this embodiment includes a positive electrode, a negative electrode, and a nonaqueous electrolyte solution containing an electrolyte salt and a nitrile compound. The ionic conductivity of the nonaqueous electrolyte solution is specified as described below, and the nonaqueous secondary battery contains carbon dioxide. Furthermore, according to the present invention, it has been found that when the solvent itself is highly reactive with the negative electrode, such as a nitrile compound, additives alone may be insufficient to stabilize battery performance. While not wishing to be bound by theory, this is thought to be due to the growth of a coating by the additive or the consumption of the additive, which reduces the effective volume of the solution and causes the solution to dry up, resulting in non-uniform reactions. Therefore, in this embodiment, it has been found that stabilizing battery performance using a nonaqueous electrolyte solution configuration in which the functionality of the additives and solvents is not impaired by sacrificial reactions with the electrodeposited metal is effective. A possible means of preventing or suppressing the reaction of the deposited metal with the electrolyte solution is to deactivate the reactivity of the deposited metal through reactions other than those involving the electrolyte solvent and electrolyte additive.

[0012] The nonaqueous secondary battery of this embodiment is a secondary battery including a positive electrode, a negative electrode, and the nonaqueous electrolyte solution. For example, it may be a lithium-ion battery. More specifically, it may be the lithium-ion battery shown in the schematic plan view of FIG. 1 and the schematic cross-sectional view of FIG. 2. The lithium-ion battery 100 shown in FIGS. 1 and 2 includes a separator 170, a positive electrode 150 and a negative electrode 160 sandwiching the separator 170 from both sides, 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) sandwiching a laminate of the separator 170, the positive electrode 150, and the negative electrode 160, and a battery exterior 110 that houses them. The laminate of the positive electrode 150, the separator 170, and the negative electrode 160 is impregnated with the nonaqueous electrolyte solution according to this embodiment.

[0013] <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 an alkali metal salt. The non-aqueous electrolyte according to 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, for example, lithium-ion batteries.

[0014] <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 alkali metal salts 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 alkali metal salts and additives other than the electrode protection additive. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; and aprotic solvents. 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.

[0015] The non-aqueous solvent according to this embodiment contains a nitrile compound as an aprotic solvent. The nitrile compound according to this embodiment is preferably a liquid having a high dielectric constant and low viscosity at room temperature, such as acetonitrile, propionitrile, isobutyronitrile, or butyronitrile. The non-aqueous solvent may contain at least one nitrile compound, or may contain multiple nitrile compounds, or may contain compounds other than the nitrile compounds described above. Among nitrile compounds, the non-aqueous solvent preferably contains a nitrile compound having 4 or less carbon atoms, and more preferably acetonitrile, from the viewpoints of being liquid at room temperature, having low viscosity, a high dielectric constant, and being easily available. The inclusion of acetonitrile in the non-aqueous solvent improves the ionic conductivity of the non-aqueous electrolyte solution, thereby enhancing the diffusibility of ions within the battery. Therefore, when the non-aqueous electrolyte solution contains acetonitrile, ions can be effectively diffused to the region near the current collector, which is difficult for ions to reach during high-load discharge, especially in a positive electrode having a thick positive electrode active material layer and a high loading of positive electrode active material. This makes it possible to obtain a sufficient capacity even during high load discharge, and a non-aqueous secondary battery with excellent load characteristics can be obtained.

[0016] Furthermore, the inclusion of the nitrile compound in the nonaqueous solvent can improve the rapid charging characteristics of nonaqueous secondary batteries. During constant current (CC)-constant voltage (CV) charging of a nonaqueous secondary battery, 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. Using the nitrile compound as the nonaqueous solvent in a nonaqueous electrolyte solution not only broadens the range of CC charging (lengthens the CC charging time) but also increases the charging current, significantly shortening the time from the start of charging to fully charging a nonaqueous secondary battery. Additionally, this property can promote ion diffusion within the negative electrode, thereby reducing metal precipitation and contributing to safety and stability. From this perspective, the ionic conductivity of the nonaqueous electrolyte solution in this embodiment is preferably greater than 10 mS / cm at room temperature, e.g., about 25°C, more preferably 11 mS / cm or higher, and even more preferably 12 mS / cm or higher. The upper limit of the ionic conductivity of the nonaqueous electrolyte solution is not limited, but may be, for example, 30 mS / cm or lower.

[0017] Nitrile compounds are susceptible to electrochemical reductive decomposition due to the properties of the nitrile group, and therefore, when using the nitrile compounds, it is preferable to use other solvents (e.g., aprotic solvents other than nitrile compounds) in combination as the non-aqueous solvent and / or to add an electrode protection additive for forming a protective film on the electrode.

[0018] The content of the nitrile compound in the non-aqueous solvent is preferably 5 to 97% by volume, based on the total amount of the non-aqueous solvent. From the viewpoint of ionic conductivity, the lower limit of the content of the nitrile compound is more preferably 10% by volume or more, even more preferably 20% by volume or more, and particularly preferably 30% by volume or more, based on the total amount of the non-aqueous solvent. From the viewpoint of electrical stability, the upper limit of the content of the nitrile compound is more preferably 85% by volume or less, even more preferably 60% by volume or less, and particularly preferably 50% by volume or less, based on the total amount of the non-aqueous solvent. Furthermore, acetonitrile is preferred as the nitrile compound, and the preferred content of acetonitrile is also the same as the above-mentioned range. When the content of the nitrile compound 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 tends to be increased, which tends to enable the non-aqueous secondary battery to exhibit high-power characteristics and further promote the dissolution of the salt. Furthermore, when the content of the nitrile compound in the non-aqueous solvent is within the above-mentioned 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 nitrile compound.

[0019] Examples of aprotic solvents other than nitrile compounds include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds having sulfur atoms, chain fluorinated carbonates, cyclic ethers, alkoxy group-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvents have been substituted with halogen atoms.

[0020] Acetonitrile, which is one component of non-aqueous solvents, is easily electrochemically reductively decomposed. Therefore, by adding vinylene carbonate to the non-aqueous solvent in addition to acetonitrile, the non-aqueous electrolyte solution according to this embodiment stabilizes the charge / discharge capacity of the battery when used in a non-aqueous secondary battery.

[0021] When the non-aqueous solvent according to this embodiment contains acetonitrile, vinylene carbonate (VC) as a cyclic carbonate, and ethylene sulfite as an organic compound having a sulfur atom, when the non-aqueous electrolyte solution is used in a non-aqueous secondary battery, the battery can be operated at a high current density.

[0022] Vinylene carbonate-derived anode protective coatings have high resistance, which tends to lead to performance degradation during rapid charging and at low temperatures. Ethylene sulfite has a lower lowest unoccupied molecular orbital (LUMO) level than other oxygen-sulfur compounds and can reductively decompose to form anode protective coatings at lower potentials than vinylene carbonate. This allows for the reduction of the amount of vinylene carbonate added to resolve the issues associated with vinylene carbonate-derived anode protective coatings. Furthermore, ethylene sulfite-derived anode protective coatings have low resistance over a wide temperature range and promote the formation of anode SEI that is highly resistant to acetonitrile and its decomposition products, thereby providing nonaqueous electrolytes and nonaqueous secondary batteries that can operate stably at high current densities.

[0023] 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.

[0024] 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;

[0025] 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;

[0026] Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0027] 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;

[0028] 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;

[0029] Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0030] Examples of mononitriles other than the above-mentioned nitrile compounds include valeronitrile, benzonitrile, and acrylonitrile;

[0031] Alkoxy-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

[0032] 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;

[0033] Cyclic nitriles include, for example, benzonitrile;

[0034] 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;

[0035] Chain ethers include, for example, dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0036] Examples of fluorinated ethers include Rf 20 -OR 21 (In the formula, Rf 20 represents an alkyl group containing a fluorine atom, and R 21 represents a monovalent organic group which may contain a fluorine atom;

[0037] Ketones, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0038] 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:

[0039] 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:

[0040] 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:

[0041] In the present embodiment, the aprotic solvent other than the nitrile compound may be used alone or in combination of two or more.

[0042] In the present embodiment, the non-aqueous solvent preferably contains one or more of a cyclic carbonate and a chain carbonate in combination with the nitrile compound, from the viewpoint of improving the stability of the non-aqueous electrolyte solution. From this viewpoint, the non-aqueous solvent preferably contains a cyclic carbonate in combination, and more preferably contains both a cyclic carbonate and a chain carbonate.

[0043] When a cyclic carbonate other than vinylene carbonate (VC) is used together with the nitrile compound, it is particularly preferred that such cyclic carbonate includes ethylene carbonate and / or fluoroethylene carbonate.

[0044] <Electrolyte salt> The nonaqueous electrolyte solution of this embodiment is for a nonaqueous secondary battery and may contain a salt as the electrolyte salt. The electrolyte salt is not particularly limited, but an imide salt is preferred from the viewpoint of solubility in nitrile compounds. The imide salt is an electrolyte salt containing an imide anion as the anion. For example, this embodiment, which relates to a lithium-ion secondary battery, may contain a lithium-containing imide salt as the salt. The nonaqueous electrolyte solution may contain, for example, LiPF6 as a salt other than the imide salt.

[0045] <Lithium salt> The imide salt containing lithium is LiN(SO2C m F 2m+1 )2 (wherein m is an integer of 0 to 8), and specifically, it is preferable to contain at least one of LiN(SO2F)2 and LiN(SO2CF3)2, and when the negative electrode contains graphite, LiN(SO2F)2, i.e., lithium bis(fluorosulfonyl)imide (hereinafter sometimes abbreviated as "LiFSI") is particularly preferable. In this embodiment, only one or both of these imide salts may be contained, or an imide salt other than these imide salts may be contained.

[0046] When a nitrile compound is contained in a non-aqueous solvent, the saturation concentration of the lithium-containing imide salt relative to the nitrile compound is higher than that of LiPF. Therefore, it is preferable to include the lithium-containing imide salt at a molar concentration such that LiPF is less than or equal to the lithium-containing imide salt, since this suppresses association and precipitation of the lithium salt and the nitrile compound at low temperatures. Furthermore, from the viewpoint of ion supply, it is preferable that the content of the lithium-containing imide salt is 0.5 mol to 3 mol per liter of non-aqueous solvent. A non-aqueous electrolyte containing a nitrile compound containing at least one of LiN(SO2F)2 and LiN(SO2CF3)2 can effectively suppress the decrease in ionic conductivity at low temperatures, such as −10°C or −30°C, thereby achieving excellent low-temperature characteristics. Thus, limiting the content can more effectively suppress the increase in resistance during high-temperature heating and is expected to prevent metal precipitation.

[0047] The lithium salt may further include fluorine-containing inorganic lithium salts other than LiPF, such as LiBF, LiAsF, LiSiF, LiSbF, and LiB. 12 F b H 12-b (wherein b is an integer of 0 to 3) may also be included. "Inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion and is soluble in acetonitrile. "Fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion but contains a fluorine atom in the anion and is soluble in acetonitrile. Fluorine-containing inorganic lithium salts are excellent in that they form a passivation 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 may be used alone or in combination of two or more. Compounds that are double salts of LiF and Lewis acids are desirable as fluorine-containing inorganic lithium salts. Among these, fluorine-containing inorganic lithium salts containing phosphorus atoms are more preferred because they facilitate 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 as the fluorine-containing inorganic lithium salt, it is preferable because it makes it easier to capture excess free acid components that may cause battery deterioration, and from this viewpoint, LiBF4 is particularly preferable.

[0048] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte solution of this embodiment is not particularly limited, but is preferably 0.01 mol or more, more preferably 0.02 mol or more, and even more preferably 0.03 mol or more per 1 L of non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of 0.01 mol or more, the ionic conductivity tends to increase and high-power characteristics tend to be exhibited. Furthermore, the content of the fluorine-containing inorganic lithium salt is preferably less than 1.5 mol, more preferably less than 0.5 mol, and even more preferably less than 0.1 mol per 1 L of non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of less than 1.5 mol, the ionic conductivity tends to increase and high-power characteristics can be exhibited, and the decrease in ionic conductivity due to an increase in viscosity at low temperatures tends to be suppressed. This tends to further improve the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery while maintaining the excellent performance of the non-aqueous electrolyte solution.

[0049] 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 soluble in acetonitrile.

[0050] 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).

[0051] In order to ensure the effects of its 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 solvent 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.

[0052] 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.

[0053] 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-nan 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 C may 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.

[0054] <Other electrode protection additives> The other electrode protection additives are not particularly limited as long as they do not impede the solution of the problems of the present invention, and may substantially overlap with the substance that serves as a solvent for dissolving lithium salts (i.e., the above-mentioned nonaqueous solvent). The electrode protection additive is preferably a substance that contributes to improving the performance of the nonaqueous electrolyte solution and nonaqueous secondary battery in this embodiment, but also includes substances that are not directly involved in the electrochemical reaction.

[0055] Specific examples of other electrode protection additives include 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, Fluoroethylene carbonates such as 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; unsaturated bond-containing cyclic carbonates such as 4,5-dimethylvinylene carbonate and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone. Examples of suitable anhydrides include lactones, cyclic ethers such as 1,4-dioxane, cyclic sulfur compounds such as 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, 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 formed by dehydration condensation of two different carboxylic acids, or a carboxylic acid and a sulfonic acid. These may be used alone or in combination of two or more.

[0056] The content of the electrode protection additive in the non-aqueous electrolyte solution in this embodiment is not particularly limited, but the content of the electrode protection additive relative to the total amount of the non-aqueous solvent is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, and even more preferably 0.5 to 4% by volume.

[0057] In this embodiment, the higher the content of the electrode protection additive, the more suppressed the deterioration of the nonaqueous electrolyte solution. However, the lower the content of the electrode protection additive, the more improved the high-power performance of the nonaqueous secondary battery in a low-temperature environment. Therefore, by adjusting the content of the electrode protection additive within the above-mentioned range, the excellent performance based on the high ionic conductivity of the nonaqueous electrolyte solution tends to be maximized without impairing the basic functions of the nonaqueous secondary battery. By preparing a nonaqueous electrolyte solution with such a composition, the cycle performance of the nonaqueous secondary battery, the high-power performance in a low-temperature environment, and all other battery characteristics tend to be further improved.

[0058] <Other optional additives> In this embodiment, for the purpose of improving the charge / discharge cycle characteristics, high-temperature storage properties, and safety (e.g., preventing overcharge) of the nonaqueous secondary battery, an optional additive selected from sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters [ethyl diethylphosphonoacetate (EDPA): (C2H5O)2(P=O)-CH2(C=O)OC2H5, tris(trifluoroethyl)phosphate (TFEP): (CF3CHO)3P=O, triphenylphosphate (TPP): (C6H5O)3P=O: (CH2=CHCHO)3P=O, triallyl phosphate, etc.], nitrogen-containing cyclic compounds with no steric hindrance around the unshared electron pair [pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.], and derivatives of these compounds may be appropriately added to the nonaqueous electrolyte solution. In particular, phosphate esters are effective in suppressing side reactions during storage.

[0059] The content of other optional additives in this embodiment is calculated as a mass percentage relative to the total mass of all components constituting the non-aqueous electrolyte solution. There are no particular restrictions on the content of other optional additives, but it is preferably in the range of 0.01 mass% to 10 mass% of the total amount of the non-aqueous electrolyte solution, more preferably 0.02 mass% to 5 mass% and even more preferably 0.05 mass% to 3 mass%. By adjusting the content of other optional additives within the above range, it tends to be possible to add even better battery characteristics without impairing the basic functions of a non-aqueous secondary battery.

[0060] <2. Positive electrode and positive electrode current collector> 1 and 2 is composed of a positive electrode active material layer made from 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. For example, the positive electrode in this embodiment of the lithium-ion secondary battery preferably contains a lithium-containing compound containing Fe, and more preferably also contains nickel (Ni) in a relatively high proportion.

[0061] 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.

[0062] 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.

[0063] 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.} A metal phosphate compound containing lithium and a transition metal element represented by the following formula, and / or the following general formula (2) containing at least one transition metal element selected from the group consisting of, for example, Ni, Mn, and Co: Li p Ni q Co r Mn s M t O u ·····(2) {In the formula, 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 and discharge state of the battery.} At least one Li-containing metal oxide selected from Li-containing metal oxides represented by the following formula is preferred.

[0064] 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, and lithium-containing composite metal oxides represented by Li z MO2 (where M 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).

[0065] 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 reduction of the amount of Co, which is a rare metal, and increase in the energy density are achieved. Examples of such a positive electrode active material include, 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 thereby can be mentioned.

[0066] On the other hand, the higher the Ni content ratio in the positive electrode active material layer, the more likely the deterioration progresses at a low voltage. In the positive electrode active material of the Li-containing metal oxide represented by the general formula (2), active points that oxidatively deteriorate the non-aqueous electrolyte essentially exist, 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 particularly affected. In particular, when acetonitrile is contained as the non-aqueous solvent, the addition effect of the acid anhydride is extremely large, so the consumption of the acid anhydride on the positive electrode side is a fatal problem.

[0067] Furthermore, the decomposition products of these additives that are incorporated into and deposited on the positive electrode side not only increase the internal resistance of non-aqueous secondary batteries but also accelerate the degradation of the lithium salt. Furthermore, the original purpose of protecting the negative electrode surface is insufficient. To deactivate the active sites that essentially cause oxidative degradation of non-aqueous electrolytes, it is important to control Jahn-Teller distortion or to include a component that acts as a neutralizer. Therefore, it is preferable that the positive electrode active material contain at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0068] 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.

[0069] 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 Irepresents 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:

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] <3. Negative electrode and negative electrode current collector> 1 and 2 is composed of a negative electrode active material layer made of 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.

[0080] 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.

[0081] 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.

[0082] The negative electrode active material layer in lithium-ion secondary batteries 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.

[0083] 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.

[0084] 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.

[0085] 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, if necessary, 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 (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.

[0086] 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.

[0087] <Negative electrode coating> The negative electrode of the nonaqueous secondary battery of this embodiment includes a coating, which contains a carbonate. The carbonate includes an alkali metal cation or an alkaline earth metal cation, such as lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, or calcium carbonate. For example, in the lithium-ion secondary battery of this embodiment, the possibility of lithium metal precipitation is high. However, due to the effect of deactivating the precipitated metal obtained by the configuration of this embodiment, at least lithium carbonate is included as the carbonate. From this perspective, for example, when the nonaqueous electrolyte contains LiFSI, it is preferable that lithium carbonate is included on the negative electrode surface, and the abundance ratio of lithium element as lithium metal to lithium element in lithium carbonate is more preferably 0.3 or less, and even more preferably close to 0. Furthermore, for example, in a calcium-ion secondary battery, at least calcium carbonate is included as the carbonate. Carbonate is formed by the association of carbon dioxide and metal, and by preventing metal precipitation, it prevents short circuits while suppressing consumption of the electrolyte solvent and additives. Here, the element ratios on the negative electrode surface may be calculated, for example, by performing XPS measurement, evaluating the abundance ratios (atom %) of elements contained in metals and carbonates from the signals obtained, and then calculating based on the ratios. For example, signals corresponding to the 1s of lithium metal and Li element in lithium carbonate can be observed at 52 to 53 eV and 53 to 54 eV in the XPS spectrum, so the abundance ratios of elements may be calculated based on the intensity ratios of these signals.

[0088] <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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] By using such a separator 170, it is possible to achieve the excellent input / output characteristics and low self-discharge characteristics required for secondary batteries for high-power applications, in particular.

[0093] 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.

[0094] 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 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%.

[0095] 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 3 150 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 ion migration rate is determined not by the separator structure but by the 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 12 mS / cm, and even more preferably 15 mS / cm.

[0096] 5. Carbon Dioxide The nonaqueous secondary battery according to this embodiment contains carbon dioxide. The carbon dioxide may be added as a component of the gas contained within the battery, or may exist within and / or outside the gas within the battery. Here, the term "gas" in this embodiment refers to compounds other than hydrogen that are always in a gaseous state in an environment under atmospheric pressure at a temperature range of 20 to 60°C, and does not include vapor generated from a liquid in the same environment. The term "outside the gas" refers to a portion of the battery interior that is different from the gas, such as the electrolyte. Carbon dioxide reacts with precipitated alkali metals and their alkali metal compounds to produce carbonates, thereby deactivating the reactivity of the alkali metals. For example, in a nonaqueous lithium-ion secondary battery containing lithium ions, carbon dioxide reacts with precipitated components to produce lithium carbonate.

[0097] Carbon dioxide may be enclosed in the battery using a highly airtight syringe or the like, or may be enclosed in the battery by adding an additive that undergoes a reaction to give carbon dioxide, or may be added by dissolving carbon dioxide in a non-aqueous electrolyte solution under high pressure and then enclosing the non-aqueous electrolyte solution in the battery and then reducing the pressure and heating the solution; however, the method is not limited to these, as any method of enclosing carbon dioxide within the battery is expected to cause a reaction with the alkali metal.

[0098] Furthermore, while a certain amount of carbon dioxide can be dissolved in a solvent at temperatures below room temperature or under high pressure conditions, the effect of adding carbon dioxide in this embodiment was observed even at high temperatures or under normal pressure, so it is presumed that the carbon dioxide functions sufficiently even in gaseous form, regardless of its dissolved state. On the other hand, when a secondary battery is initially charged or repeatedly charged and discharged, an oxidation-reduction reaction occurs on the exposed surfaces of the negative and positive electrodes, causing the decomposition of trace amounts of water, electrolyte solvents, additives, etc., resulting in the gradual introduction of various gaseous components such as hydrogen, hydrocarbons, and carbon monoxide into the battery, which may dilute the carbon dioxide and slow the reaction rate. Therefore, from the viewpoint of maintaining a high carbon dioxide reaction rate, the carbon dioxide content is preferably at a certain concentration or higher even after the initial charge, preferably 10% by volume or more, more preferably 15% by volume or more, and even more preferably 20% by volume or more, relative to the gas volume inside the battery. The upper limit is preferably 80% by volume or less, more preferably 85% by volume or less, even more preferably 90% by volume or less, and particularly preferably 95% by volume or less.

[0099] In this embodiment, the amount of carbon dioxide to be contained in the battery by any process, i.e., the volume, is not particularly limited, but it is preferable that the amount be equivalent to the metal to be electrodeposited. Furthermore, the amount of metal to be electrodeposited is proportional to the battery capacity. From this perspective, under conditions of room temperature, e.g., about 25°C, and atmospheric pressure, the volume of carbon dioxide contained is 0.001 to 2 cm per 1 Ah of battery capacity. 3 is preferred, 1cm 3 Less than 0.005 to 1 cm is preferable. 3 is more preferably 0.01 to 0.5 cm 3 When the volume of carbon dioxide content falls within the above range, the effect of adding carbon dioxide commensurate with the metal to be electrodeposited can be obtained, and at the same time, deformation due to the internal pressure of the gas tends to be prevented even in a battery exterior that is relatively prone to deformation, such as a laminate.

[0100] Since battery manufacturing processes are often carried out in dry air or an inert atmosphere, and there is a risk of other gases being mixed in when carbon dioxide gas is added, the concentration of carbon dioxide added by any process may be quantified by testing only a portion of the population. For example, the components that make up the gas may be quantified by any method such as gas chromatography, and the carbon dioxide volume and concentration may be calculated based on the equation of state, assuming that the gas is an ideal gas.

[0101] <6. Battery exterior> The configuration of the battery exterior 110 of the nonaqueous secondary battery 100 shown in FIGS. 1 and 2 is not particularly limited, and for example, either a battery can or a laminate film exterior can be used. In this embodiment, the amount of carbon dioxide added is preferably adjusted within a range that prevents deformation of both the battery can and the laminate film exterior. As the battery can, for example, a metal can made of steel, stainless steel, aluminum, clad material, or the like, such as a rectangular, rectangular tube, cylindrical, oval, flat, coin, or button-shaped can, can be used. As the laminate film exterior, for example, a laminate film having a three-layer structure of a heat-melt resin / metal film / resin can be used.

[0102] 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.

[0103] 7. How to make a battery 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] In this embodiment, a nonaqueous electrolyte solution containing a nitrile compound and having an ionic conductivity exceeding 10 mS / cm is used. When the ionic conductivity exceeds 10 mS / cm, the high ionic conductivity tends to improve input performance, output performance, and battery resistance. Due to this high ionic conductivity, ions released from the positive electrode during the initial charge of a nonaqueous secondary battery may 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 ions diffuse and are occluded in a portion of the negative electrode active material layer that does not face the positive electrode active material layer, these ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of these unreleased ions becomes the irreversible capacity. For these reasons, the initial charge / discharge efficiency of a nonaqueous secondary battery containing the nonaqueous electrolyte solution of this embodiment may be low.

[0109] 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 they are the same, current tends to concentrate at the edge portions of the negative electrode active material layer during charging, making it easier for metal deposition to occur.

[0110] 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 the nonaqueous electrolyte solution of this embodiment, 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.

[0111] Reducing the ratio of the total area of ​​the 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 number of ions released from the positive electrode during the initial charge that are occluded in the portion of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the number of 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 total area of ​​the 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 an electrolyte with an ionic conductivity of more than 10 mS / cm, while also improving the initial charge / discharge efficiency of the battery and suppressing dendrite formation.

[0112] 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 solution 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 electrolyte salt participates in the electrochemical reaction, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), suppressing an increase in internal resistance. Furthermore, the reaction product is not firmly fixed only to the negative electrode 160, but also has a favorable effect on components other than the negative electrode 160, such as the positive electrode 150 and separator 170, in any form. Therefore, it is highly effective to perform the initial charging while taking into account the electrochemical reaction of the electrolyte salt dissolved in the nonaqueous electrolyte solution.

[0113] 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.

[0114] 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]

[0115] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0116] (1) Preparation of non-aqueous electrolyte Various non-aqueous solvents and various additives were mixed in an inert atmosphere to obtain predetermined concentrations of non-aqueous electrolyte solutions. Furthermore, the ionic conductivity of these non-aqueous electrolyte solutions was measured at 25°C. The composition and ionic conductivity of the electrolyte solutions are shown in Table 1. The abbreviations in Table 1 are as follows: LiPF6: Lithium hexafluorophosphate LiFSI: Lithium bis(fluorosulfonyl)imide AcN: acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate ES: Ethylene sulfite VC: vinylene carbonate

[0117] (2) Fabrication of non-aqueous secondary batteries (2-1) Preparation of the positive electrode A slurry containing lithium iron phosphate as the positive electrode active material, polyvinylidene fluoride as the binder, and carbon black as the conductive additive in a ratio of 90:7:3 was applied to an aluminum current collector foil, dried, and pressed to obtain a positive electrode.

[0118] (2-2) Preparation of negative electrode Graphite was used as the negative electrode active material, and a slurry of 96:1.5:1.5:1 mixed with carbomethyl cellulose and styrene butadiene rubber as binders and carbon black as a conductive additive was applied to a copper current collector foil, which was then dried and pressed to obtain a negative electrode.

[0119] (2-3) Assembly of non-aqueous secondary batteries The positive and negative electrodes were cut to a predetermined size and alternately stacked with separators to obtain a laminate. This laminate was placed in a laminate film, and three sides were heat-sealed. A nonaqueous electrolyte solution and additives were then added to the dry cell using a syringe in an argon box, followed by immediate heat sealing to obtain a laminated nonaqueous secondary battery. Two or more nonaqueous secondary batteries with the same configuration were fabricated, and some were used to confirm the carbon dioxide concentration, while the remaining batteries were used for testing.

[0120] (2-4) Initial charging and aging The nonaqueous secondary batteries were charged to 3.6 V at a current of 0.1 C, and then discharged at 0.1 C with the discharge cut-off voltage set to 2.0 V. Here, 1 C represents the current value at which the battery can be fully charged in 1 hour, and therefore 0.1 C represents the current value at which the battery can be fully charged in 10 hours. Thereafter, each nonaqueous secondary battery was subjected to charging and discharging at a predetermined current value and number of times in a thermostatic chamber set at a predetermined temperature, thereby carrying out aging. The volume of each battery was measured by Archimedes' method, and for Examples 1 to 4 and Comparative Example 1, the total gas volume per capacity was found to be 1 cm. 3 In Comparative Example 2, no carbon dioxide was added, and only the gas in the argon box was added, and the total gas volume was 1 cm 3 The results were as follows: No obvious deformation due to gas was observed in any of the batteries. Furthermore, the internal gas was sampled from some of the nonaqueous secondary batteries obtained by the aging process using a syringe, and the concentration was quantified using the following procedure (note that the batteries used for the gas test were not subjected to the following procedures). (1) A syringe was inserted into the exterior of the battery, and 50 μL of gas was collected from each of the two syringes. (2) Using the first syringe, GC-TCD measurements were performed using a column (Molsieve 5A) to quantify hydrogen, argon, and methane. (3) Using the second syringe, GC-MS measurements were performed using a column (Carboxen 1010) to quantify argon, carbon monoxide, carbon dioxide, methane, ethane, and ethylene.

[0121] (2-5) Cycle test Some of the nonaqueous secondary batteries obtained by the aging were charged and discharged at a current of 1 C for 10 cycles in a thermostatic chamber at 25°C, followed by 200 cycles in a thermostatic chamber at 45°C. The discharge capacity retention rate was evaluated based on the discharge capacity at the first cycle. The maximum value of capacity deterioration observed per cycle was taken as the maximum capacity deterioration rate (%), and the capacity irreversibility rate (the ratio of the undischarged capacity to the charged capacity) was calculated. The ratio of the CV charge time to the charge time for 200 cycles was also calculated.

[0122] (2-6) Lithium electrodeposition inspection The laminated film on the exterior was cut in an argon box, the negative electrode was removed, and XPS measurement was performed to confirm the presence or absence of a metallic lithium signal at 52 to 53 eV in the spectrum. When the nonaqueous secondary battery of this embodiment contains lithium carbonate, the lithium carbonate signal was observed at 54 to 56 eV, close to the metallic lithium signal. The presence or absence of the metallic lithium signal was determined by whether a shoulder-shaped or asymmetric tail-shaped signal was observed at 52 to 53 eV.

[0123] [Table 1]

[0124] In Examples 1 to 4, metallic lithium was not detected, and the signal intensity of metallic lithium relative to that of lithium carbonate in the XPS spectra was less than 0.3. Furthermore, no sudden drop in capacity or significant extension of CV time was observed during the cycle life performance test. By adding atmospheric carbon dioxide at a concentration above a certain level, any precipitation was quickly deactivated, suppressing the impact of side reactions of the nitrile compound during repeated charge / discharge cycles. This is presumably why the charging capacity derived from the high ionic conductivity of the nitrile solvent was maintained. Furthermore, in Examples 1 to 4, the effect of carbon dioxide was presumably to reduce the amount of solvent and additives that sacrificially react with the electrodeposition site, maintaining uniformity of the reaction and thus maintaining a low maximum capacity degradation rate. In Comparative Example 1, metallic lithium was detected by XPS, and in addition to observing rapid capacity degradation, the CV time accounted for more than 10% of the total charge time, significantly affecting cycle performance and charge performance. In Comparative Example 1, the extended CV time despite high ionic conductivity is presumably due to side reactions of the nitrile compound caused by the precipitated metal.

[0125] The TOF-SIMS of the negative electrode surface of Example 5 was measured to obtain a mass spectrum (FIGS. 3(a) and (b)). Furthermore, when comparing this with the TOF-SIMS spectrum (FIGS. 3(c) and (d)) of the negative electrode surface of a reference example battery in which all of the acetonitrile in the electrolyte used in Example 5 was replaced with ethyl methyl carbonate, signals of equivalent components were obtained, as shown in FIGS. 3(a) to (d). This suggests that reductive decomposition of acetonitrile was prevented, and a good coating was formed and maintained in Example 5. [Industrial Applicability]

[0126] 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, etc., as well as an industrial storage battery for power tools, drones, electric motorcycles, etc., and even as a residential power storage system. [Explanation of symbols]

[0127] 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, wherein the non-aqueous electrolyte solution contains an electrolyte and a non-aqueous solvent, the electrolyte containing at least an imide salt, and the non-aqueous solvent containing at least a nitrile compound, the non-aqueous electrolyte solution having an ionic conductivity of more than 10 mS / cm, and the non-aqueous secondary battery containing carbon dioxide.

2. 2. The nonaqueous secondary battery according to claim 1, wherein the nonaqueous secondary battery contains a gas, the carbon dioxide is contained in the gas and / or outside the gas, and the content of the carbon dioxide relative to the volume of the gas is 10 to 90% by volume.

3. 3. The nonaqueous secondary battery according to claim 1, wherein the nonaqueous electrolyte solution contains acetonitrile as a nitrile compound, the content of the acetonitrile is 5 to 97% by volume relative to the volume of the nonaqueous solvent, and the ionic conductivity is 11 to 30 mS / cm.

4. 3. The nonaqueous secondary battery according to claim 1, wherein the electrolyte contains at least lithium bis(fluorosulfonyl)imide, the negative electrode contains graphite, and the negative electrode contains lithium carbonate on a surface thereof, and the abundance ratio of lithium element as lithium metal to lithium element in the lithium carbonate is 0.3 or less.

5. The volume of carbon dioxide contained per 1 Ah of battery capacity is 1 cm under the conditions of room temperature and atmospheric pressure. ３ 3. The nonaqueous secondary battery according to claim 1, wherein:

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