Non-aqueous electrolytes and non-aqueous secondary batteries

Abstract

To provide a non-aqueous electrolyte having excellent high-temperature durability using a cyclic anion-containing lithium salt containing sulfamic acid ions as an impurity.SOLUTION: A non-aqueous electrolyte containing a non-aqueous solvent, lithium salt, and an additive, the lithium salt contains a cyclic anion-containing lithium salt represented by the following formula (1), the non-aqueous electrolyte contains sulfamic acid ions, the additive contains a dinitrile compound represented by the following formula (2), the content of the sulfamic acid ion is 150 ppm or less based on the total amount of the non-aqueous electrolyte, and the content of the dinitrile compound is 5 or more in molar ratio to the content of the sulfamic acid ion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a non-aqueous electrolyte and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries, including lithium-ion batteries, are characterized by their light weight, high energy output, and long lifespan, and are widely used as power sources for various portable electronic devices. In recent years, non-aqueous electrolytes have also seen increased use in industrial applications such as power tools, as well as in vehicles like electric cars and electric bicycles. Furthermore, they are attracting attention in the field of power storage, such as residential energy storage systems.

[0003] Common examples of non-aqueous electrolytes for lithium-ion batteries include combinations of highly dielectric solvents such as cyclic carbonate esters and low-viscosity solvents such as chain carbonate esters. Furthermore, it is desirable to add electrode protective additives such as vinylene carbonate to form a Solid Electrolyte Interface (SEI) on the negative electrode surface, thereby suppressing the reductive decomposition of the non-aqueous solvent.

[0004] In recent years, lithium salts containing cyclic anions have attracted attention as materials for non-aqueous electrolytes.

[0005] For example, Patent Document 1 reports a non-aqueous electrolyte that maintains high ionic conductivity without electrode corrosion by using a lithium salt containing a cyclic anion.

[0006] Patent document 2 reports a method for producing disulfonyl fluoride compounds and lithium salts containing cyclic anions. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2010 / 110388 [Patent Document 2] International Publication No. 2006 / 106960 [Overview of the project] [Problems that the invention aims to solve]

[0008] In lithium salts containing cyclic anions manufactured by the route described in Patent Document 1 or 2, sulfamate ions were introduced as impurities due to a side reaction during the manufacturing process, and as a result, the desired high-temperature durability of non-aqueous secondary batteries using lithium salts containing cyclic anions could not be obtained.

[0009] This invention has been made in view of the above circumstances. The object of this invention is to provide a non-aqueous electrolyte with excellent high-temperature durability using a cyclic anion-containing lithium salt containing sulfamate ions as an impurity. [Means for solving the problem]

[0010] The inventors of the present invention conducted extensive research to solve the above-mentioned problems, and as a result, discovered that the above problems can be solved by using a non-aqueous electrolyte having the following configuration, thus completing the present invention. That is, the present invention is as follows: (1) A non-aqueous electrolyte containing a non-aqueous solvent, a lithium salt, and an additive, The lithium salt is given by the following formula (1): [ka] {where, R f Each of these independently represents a fluorine atom or a perfluoro group with 4 or fewer carbon atoms, and n is an integer from 1 to 5. It contains a lithium salt containing a cyclic anion represented by, The aforementioned non-aqueous electrolyte contains sulfamate ions, The aforementioned additive is given by the following formula (2): [ka] {In the formula, R represents a linear or branched divalent aliphatic alkyl group having 1 to 12 carbon atoms, which may contain an oxygen atom.} It contains a dinitrile compound represented by, The sulfamate ion content is 150 ppm by mass or less relative to the total amount of the non-aqueous electrolyte, and A non-aqueous electrolyte in which the content of the dinitrile compound is 5 or more in molar ratio to the content of the sulfamate ion. (2) The non-aqueous electrolyte according to item 1, wherein the content of the sulfamate ion is 5000 ppm by mass or less relative to the content of the cyclic anion lithium salt. (3) The non-aqueous electrolyte according to item 1 or 2, wherein the content of the sulfamate ion is 0.01 ppm by mass or more relative to the total amount of the non-aqueous electrolyte. (4) The non-aqueous electrolyte according to any one of items 1 to 3, wherein the content of the dinitrile compound is 0.1% by mass or more and 25% by mass or less based on the total amount of the non-aqueous electrolyte. (5) A non-aqueous electrolyte according to any one of items 1 to 4, containing acetonitrile in an amount of 3% to 97% by volume relative to the total amount of the non-aqueous solvent. (6) The lithium salt containing a cyclic anion represented by formula (1) is given by the following formula (1-2): [ka] A non-aqueous electrolyte described in any one of items 1 to 5, which is a lithium salt containing a cyclic anion represented by [formula]. (7) A non-aqueous secondary battery comprising a non-aqueous electrolyte as described in any one of items 1 to 6. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a non-aqueous electrolyte with excellent high-temperature durability. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic plan view showing an example of a non-aqueous secondary battery according to this embodiment. [Figure 2] Figure 1 is a cross-sectional view of a non-aqueous secondary battery along line AA. [Modes for carrying out the invention]

[0013] The following describes in detail embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment"). The present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit thereof. In this specification, numerical ranges indicated using "~" include the numerical values ​​indicated before and after them.

[0014] <1.Non-aqueous electrolyte> A non-aqueous electrolyte refers to an electrolyte in which water is 1% by mass or less relative to the total amount of the non-aqueous electrolyte. In this embodiment, it is preferable that the non-aqueous electrolyte contains as little water as possible, but it may contain a very small amount of water as long as it does not hinder the solving of the problem of the present invention. The amount of water is 300 ppm by mass or less, preferably 200 ppm by mass or less, per the total amount of the non-aqueous electrolyte. As long as the non-aqueous electrolyte has the configuration necessary to achieve the solving of the problem of the present invention, other components can be appropriately selected and applied from known non-aqueous electrolyte materials used in lithium-ion batteries.

[0015] The non-aqueous electrolyte of this embodiment can be manufactured by mixing a lithium salt and, optionally, various additives (sometimes simply referred to as "additives" in this specification) in a non-aqueous solvent by any means. The various additives refer collectively to electrode protection additives and other optional additives, and their content is as shown below.

[0016] Unless otherwise specified, the content of each compound in the non-aqueous solvent is defined as follows: for each component described in <2-1. Non-aqueous solvent> and the electrode protection additive described in <2-3. Electrode protection additive>, the mixing ratio is defined as a volume percentage relative to the total amount of each component constituting the non-aqueous solvent; for the lithium salt described in <2-2. Lithium salt>, the mixing ratio is defined as the number of moles per liter of non-aqueous solvent; and for <2-4. Other optional additives>, the mixing ratio is defined as parts by mass when the lithium salt and the entire non-aqueous solvent are considered to be 100 parts by mass.

[0017] Furthermore, in this embodiment, if the electrolyte contains compounds other than those specifically indicated in items <2-1> to <2-4> below, if the compound is a liquid at room temperature (25°C), it shall be treated in the same manner as a non-aqueous solvent, and the mixing ratio shall be expressed as a volume % relative to the total amount of each component (including the compound) constituting the non-aqueous solvent. On the other hand, if the compound is a solid at room temperature (25°C), the mixing ratio shall be expressed as parts by mass when the lithium salt and the entire non-aqueous solvent are considered to be 100 parts by mass.

[0018] <2-1. Non-aqueous solvents> In this embodiment, "non-aqueous solvent" refers to the elements of a non-aqueous electrolyte excluding lithium salts and various additives. If the non-aqueous electrolyte contains electrode protection additives, "non-aqueous solvent" refers to the elements of the non-aqueous electrolyte excluding lithium salts and additives other than electrode protection additives. 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 solvents other than aprotic solvents, as long as it does not hinder the resolution of the problem of the present invention.

[0019] The non-aqueous solvent in the non-aqueous electrolyte of this embodiment may contain acetonitrile as an aprotic solvent. The inclusion of acetonitrile in the non-aqueous solvent improves the ionic conductivity of the non-aqueous electrolyte, thereby increasing the diffusibility of lithium ions within the battery. Therefore, even in positive electrodes where the positive electrode active material layer is thickened and the amount of positive electrode active material is increased, lithium ions can diffuse well to areas near the current collector, which are difficult for lithium ions to reach during high-load discharge. Thus, it becomes possible to extract sufficient capacity even during high-load discharge, and a non-aqueous secondary battery with excellent load characteristics can be obtained.

[0020] Furthermore, the inclusion of acetonitrile in the non-aqueous solvent can improve the rapid charging characteristics of non-aqueous secondary batteries. In constant current (CC)-constant voltage (CV) charging of non-aqueous secondary batteries, the capacity per unit time during the CC charging period is greater than the capacity per unit time during the CV charging period. When acetonitrile is used as the non-aqueous solvent in the non-aqueous electrolyte, the area in which CC charging can be performed can be enlarged (the CC charging time can be extended), and the charging current can also be increased, thus significantly shortening the time it takes to bring a non-aqueous secondary battery from the start of charging to a fully charged state.

[0021] Furthermore, acetonitrile is readily reductively decomposed electrochemically. Therefore, when using acetonitrile, it is preferable to use another solvent (for example, 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.

[0022] The acetonitrile content is preferably 3% by volume or more and 97% by volume or less relative to the total amount of the non-aqueous solvent. More preferably, the acetonitrile content is 5% by volume or more, 10% by volume or more, or 20% by volume or more, and even more preferably 30% by volume or more, relative to the total amount of the non-aqueous solvent. This value is more preferably 85% by volume or less, more preferably 66% by volume or less, and even more preferably 50% by volume or less. When the acetonitrile content is 3% by volume or more relative to the total amount of the non-aqueous solvent, the ionic conductivity tends to increase, leading to the development of high-power characteristics, and furthermore, the dissolution of lithium salt can be promoted. Because the additives described later suppress the increase in the internal resistance of the battery, when the acetonitrile content in the non-aqueous solvent is within the above range, it tends to be possible to further improve high-temperature cycle characteristics and other battery characteristics while maintaining the excellent performance of acetonitrile.

[0023] Examples of aprotic solvents other than acetonitrile include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds having sulfur atoms, linear carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy-substituted nitriles, cyclic nitriles, short-chain fatty acid esters, linear ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms.

[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, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;

[0025] Examples of fluoroethylene carbonates 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, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one;

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

[0027] Examples of organic compounds containing a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propanesultone, 1,4-butanesultone, 1-propene-1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite;

[0028] Examples of linear carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate.

[0029] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0030] Other mononitriles besides acetonitrile include, for example, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0031] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile;

[0032] Examples of cyclic nitriles include benzonitrile;

[0033] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelicaate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelicaate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelicaate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate Propyl, isopropyl hydroangelicaate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelicaate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyrate, isobutyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelicaate, 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 hydroangelicaate, and tert-butyl caproate;

[0034] Examples of linear ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0035] Examples of fluorinated ethers include R f aa -ORbb {wherein, R f aa is an alkyl group containing a fluorine atom, and R bb is an organic group which may contain a fluorine atom};

[0036] Examples of the ketone include acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0037] Examples of the compound in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms include compounds in which the halogen atom is fluorine; can be mentioned.

[0038] Here, examples of the fluoride of the chain carbonate include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, methyl 2,2,3,3-tetrafluoropropyl carbonate, and the like. The above-mentioned fluorinated chain carbonate has the following general formula: R cc -O-C(O)O-R dd {wherein, R cc and R dd are at least one selected from the group consisting of CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2R f ee and R f ee is an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with at least one fluorine atom, and R cc and / or R dd contains at least one fluorine atom} can be represented by.

[0039] Furthermore, 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 ff -C(O)OR gg {where, R ff is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2R f hh CFHR f hh , and CH2R f ii At least one selected from the group consisting of R gg These include CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2R f ii At least one selected from the group consisting of R f hh R is a C1-C3 alkyl group in which at least one fluorine atom may substitute for a hydrogen atom, f ii is an alkyl group having 1 to 3 carbon atoms in which at least one fluorine atom replaces a hydrogen atom, and R ff and / or R gg It contains at least one fluorine atom, R ff If R is CF2H, gg It can be represented as {not CH3}.

[0040] In this embodiment, aprotic solvents other than acetonitrile may be used individually or in combination of two or more.

[0041] In this embodiment, the non-aqueous solvent preferably contains one or more cyclic carbonates and linear carbonates together with acetonitrile, from the viewpoint of improving the stability of the non-aqueous electrolyte. From this viewpoint, it is more preferable to use a cyclic carbonate together with acetonitrile in this embodiment, and even more preferable to use both cyclic carbonates and linear carbonates together with acetonitrile.

[0042] When a cyclic carbonate is used with acetonitrile, it is particularly preferable that such cyclic carbonate includes ethylene carbonate, vinylene carbonate, and / or fluoroethylene carbonate.

[0043] <2-2. Lithium Salts> (Lithium salt containing cyclic anions) The non-aqueous electrolyte according to this embodiment is The following general formula (1): [ka] {where, R f Each of these independently represents a fluorine atom or a perfluoro group with 4 or fewer carbon atoms, and n is an integer from 1 to 5. It contains a lithium salt containing a cyclic anion represented by [the specified formula].

[0044] The lithium salt containing a cyclic anion represented by formula (1) has low metal corrosiveness, and when used in a non-aqueous electrolyte, it can suppress the elution of Al ions from the positive electrode current collector and provide excellent high-temperature durability.

[0045] In particular, in non-aqueous electrolytes containing acetonitrile, the use of a lithium salt containing a cyclic anion represented by formula (1) improves high-temperature durability. The mechanism is presumed to be as follows.

[0046] The lithium salt containing a cyclic anion represented by formula (1) dissociates into lithium ions and a cyclic anion in a non-aqueous electrolyte containing acetonitrile. The cyclic anion electrically interacts with acetonitrile, weakening the metal-coordinating ability of the nitrile groups of acetonitrile. This suppresses metal elution that occurs at high temperatures when acetonitrile forms complexes with transition metals in the positive electrode active material, and inhibits the migration of the metal complex to the negative electrode. Consequently, degradation of the negative electrode SEI due to reduction deposition of the metal complex at the negative electrode is suppressed, improving high-temperature durability.

[0047] In addition, the decomposition products generated by the reductive decomposition of cyclic anions at the anode deposit on the anode and act as SEI, improving the anode SEI's resistance to the reductive deposition of metal complexes at the anode and suppressing the reductive decomposition of the solvent at the anode.

[0048] R in equation (1) f Regarding this, the perfluoro group having 4 or fewer carbon atoms may be, for example, a perfluoroalkyl group having 1 to 4 carbon atoms. In formula (1), one or more fluorine atoms (fluorine atoms of n difluoromethylene groups) may be substituted with a perfluoroalkyl group having 4 or fewer carbon atoms. When fluorine atoms are substituted with a perfluoroalkyl group, the number of fluorine atoms substituted with the perfluoroalkyl group is preferably 2 or less, and more preferably 1. The number of carbon atoms in the perfluoroalkyl group is preferably 2 or less, and a trifluoromethyl group is preferred as the perfluoroalkyl group. More preferably, the cyclic anion-containing lithium salt represented by formula (1) is a compound in which fluorine atoms are not substituted with a perfluoroalkyl group.

[0049] In equation (1), n ​​is an integer between 1 and 5. Specifically, lithium salts containing cyclic anions with n between 1 and 5 include the lithium salts represented by the following compounds (1-1) to (1-5). Among these, compound (1-2) with n = 2 is preferred from the viewpoint of easily obtaining an electrolyte with high ionic conductivity. [ka]

[0050] The content of the cyclic anion-containing lithium salt represented by formula (1) is preferably 0.1 moles or more, and more preferably 0.5 moles or more, per liter of non-aqueous solvent. When it is within the above range, the ionic conductivity tends to increase, and high power characteristics can be exhibited. Furthermore, the content of the cyclic anion-containing lithium salt represented by formula (1) is preferably less than 3 moles, more preferably 2.5 moles or less, and even more preferably 1.5 moles or less, per liter of non-aqueous solvent. When the content of the cyclic anion-containing lithium salt represented by formula (1) is within the above range, the ionic conductivity of the non-aqueous electrolyte increases, enabling the battery to exhibit high power characteristics, and also tends to suppress the decrease in ionic conductivity due to the increase in viscosity of the non-aqueous electrolyte at low temperatures. This tends to improve the high-temperature cycle characteristics and other characteristics of the battery while maintaining the excellent performance of the non-aqueous electrolyte.

[0051] Furthermore, in order to improve the volumetric energy density of non-aqueous secondary batteries, the basis weight of the positive electrode active material layer contained in the positive electrode is 24-200 mg / cm³. 2 When adjusted within the range, the content of the cyclic anion-containing lithium salt represented by formula (1) is preferably 1 mole or more, more preferably 1.2 moles or more, even more preferably 1.5 moles or more, and particularly preferably 2 moles or more. When the content of the cyclic anion-containing lithium salt represented by formula (1) is within the above range, rapid ion conduction becomes possible even in the deep part of the positive electrode away from the positive electrode-electrolyte interface, and there is a tendency to be able to improve the volumetric energy density while maintaining a balance with the output performance in non-aqueous secondary batteries.

[0052] Furthermore, as a method for measuring the content of cyclic anion-containing lithium salts from the electrolyte, for example, perfluorobenzene is used as an internal standard. 19 One possible method is to combine the measurement of cyclic anion content by F-NMR with the measurement of lithium ion content by ICP emission spectroscopy.

[0053] Furthermore, in non-aqueous electrolytes, excess LiPF6 can cause a decrease in battery performance at high temperatures, while cyclic anion-containing lithium salts suppress this decrease through mechanisms such as their contribution to the negative electrode SEI. Therefore, the molar ratio of cyclic anion-containing lithium salt to LiPF6 is preferably greater than 10, more preferably 15 or greater, even more preferably 20 or greater, and particularly preferably 25 or greater. When the molar ratio of cyclic anion-containing lithium salt to LiPF6 is within the above range, the decrease in battery performance at high temperatures, such as 50°C or higher, can be effectively suppressed, and excellent high-temperature durability can be obtained.

[0054] (Method for producing a lithium salt containing a cyclic anion (compound (1))) As a method for producing the cyclic anion-containing lithium salt represented by the above formula (1) (hereinafter also referred to as compound (1)), conventionally known methods, such as the method described in Patent Document 2, can be employed. That is, the following general formula (3): HO2C-(CR2) m -SO2F (3) This method involves starting with a fluorosulfonyl group-containing carboxylic acid compound represented by {wherein R may be the same or different, and is either a fluorine atom or a trifluoromethyl group, and m is either 1 or 2}, and proceeding through an electrolytic step, a cyclization step, and a cation exchange step to produce compound (1).

[0055] The reaction scheme for compound (1-2) is shown below, with R being a fluorine atom as an example. Starting from the fluorosulfonyl group-containing carboxylic acid compound represented by compound (3-1), compound (4) is obtained by an electrolytic step, then compound (5) is obtained by a cyclization step, and finally compound (1-2) is obtained by a cation exchange step. [ka]

[0056] When compound (1) is produced using a reaction scheme that includes an electrolytic step for compound (3), compound (1) may contain sulfamate ions as a by-reaction product. Sulfamate ions are NH2SO3 - Anion type or NH3 represented by + SO3 - The zwitterionic form or NH3 is represented by + It exists as a cationic type represented by SO3H. The countercation of the anionic sulfamate ion is not particularly limited, but for example, H + Li + kaNa + or K + Examples include: The counteranions of cationic sulfamate ions are not particularly limited, but for example, OH - Cl - F - NO3 - SO4 2- These are some examples.

[0057] In non-aqueous electrolytes containing compound (1), high-temperature durability decreases due to the presence of a large amount of sulfamate ions. In particular, high-temperature durability is significantly reduced in non-aqueous electrolytes containing acetonitrile.

[0058] In detail, it is believed that the sulfamate ion, due to its highly reactive sulfonamide group, promotes the corrosion reaction of the positive electrode Al current collector during charging and also coordinates with the transition metal of the positive electrode active material to promote metal dissolution. In particular, in a non-aqueous electrolyte containing acetonitrile, it is thought that the nitrile group of acetonitrile coordinates with the transition metal to further promote metal dissolution. These phenomena were newly discovered through the inventors' research and are not described in Patent Documents 1 or 2.

[0059] The sulfamate ion content in the non-aqueous electrolyte is 150 ppm by mass or less, preferably 110 ppm by mass or less, more preferably 50 ppm by mass or less, and even more preferably 25 ppm by mass or less, relative to the total amount of the non-aqueous electrolyte. By adjusting the sulfamate ion content within the above range, corrosion of the positive electrode Al current collector and a decrease in high-temperature durability due to metal elution in the positive electrode active material can be suppressed.

[0060] Furthermore, the sulfamate ion content in the non-aqueous electrolyte is preferably 0.01 ppm by mass or more, more preferably 0.1 ppm by mass or more, and even more preferably 1 ppm by mass or more, relative to the total amount of the non-aqueous electrolyte. By adjusting the sulfamate ion content within the above range, the decomposition products obtained by the reduction of sulfamate ions at the negative electrode act as negative electrode SEI, thereby improving the high-temperature durability of the battery.

[0061] Furthermore, the sulfamate ion content in the cyclic anion-containing lithium salt is preferably 5000 ppm by mass (0.5% by mass) or less relative to the content of the cyclic anion-containing lithium salt represented by formula (1). When the sulfamate ion content is within the above range, corrosion of the positive electrode Al current collector and a decrease in high-temperature durability due to metal elution in the positive electrode active material can be suppressed. From a similar viewpoint, the sulfamate ion content is more preferably 2000 ppm by mass or less, and most preferably 500 ppm by mass or less, relative to the content of the cyclic anion-containing lithium salt represented by formula (1). The lower limit of the sulfamate ion content is not particularly limited, but may be 0 ppm by mass or more, 0.01 ppm by mass or more, 1 ppm by mass or more, or 10 ppm by mass or more, relative to the content of the cyclic anion-containing lithium salt represented by formula (1).

[0062] The sulfamate ion content is measured by ion chromatography. More specifically, it is measured by the method described in the examples.

[0063] A fluorine-containing cyclic sulfonylimide salt having a desired sulfamate ion content can be obtained, for example, by distilling and purifying compound (4) obtained by the electrolytic step of compound (3), and then obtaining compound (1) through a cyclization reaction and cation exchange step, or by purifying compound (1) by recrystallization.

[0064] The lithium salt in this embodiment may further include, along with the cyclic anion-containing lithium salt, one or more selected from lithium-containing imide salts, fluorine-containing inorganic lithium salts, organolithium salts, and other lithium salts.

[0065] The method for measuring the lithium salt content in this embodiment is the same as the method for measuring cyclic anion-containing lithium salts described above.

[0066] (LiPF6) The non-aqueous electrolyte of this embodiment may further contain LiPF6 as a lithium salt. The LiPF6 content in the non-aqueous electrolyte of this embodiment is preferably less than 0.5 moles, more preferably less than 0.1 moles, and even more preferably less than 0.01 moles per liter of non-aqueous solvent. When the LiPF6 content is within the above range, the generation of acidic components due to the thermal decomposition reaction of LiPF6 can be suppressed, and the increase in resistance of the negative electrode due to the excessive deposition of inorganic components in the negative electrode SEI can be kept to a minimum.

[0067] (Lithium-containing imide salt) Specifically, the imide salt preferably contains at least one of LiN(SO2F)2 and LiN(SO2CF3)2.

[0068] When acetonitrile is included in the non-aqueous solvent, the saturation concentration of the lithium-containing imide salt relative to acetonitrile is higher than the saturation concentration of LiPF6. Therefore, it is preferable to include the imide salt at a molar concentration such that LiPF6 ≤ lithium-containing imide salt, as this suppresses the association and precipitation of the lithium salt and acetonitrile at low temperatures. Furthermore, it is preferable that the lithium-containing imide salt content be between 0.5 moles and 3.0 moles per liter of the non-aqueous solvent, from the viewpoint of ensuring sufficient ion supply to the non-aqueous electrolyte according to this embodiment.

[0069] A non-aqueous electrolyte containing acetonitrile and at least one of LiN(SO2F)2 and LiN(SO2CF3)2 can effectively suppress the reduction in ionic conductivity at low temperatures such as -10°C or -30°C, thereby obtaining excellent low-temperature characteristics. In this embodiment, by limiting the content of lithium-containing imide salt, it is also possible to more effectively suppress the increase in resistance during high-temperature heating.

[0070] (Fluorine-containing inorganic lithium salt) The lithium salt used in the non-aqueous electrolyte of this embodiment may include fluorine-containing inorganic lithium salts other than LiPF6, such as LiBF4, LiAsF6, Li2SiF6, LiSbF6, and Li2B 12 F b H 12-bThe formula may include fluorine-containing inorganic lithium salts such as [wherein b is an integer from 0 to 3]. Here, "inorganic lithium salt" refers to a lithium salt that does not contain carbon atoms as anions and is soluble in acetonitrile. Also, "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain carbon atoms as anions, contains fluorine atoms as anions, and is soluble in acetonitrile. Fluorine-containing inorganic lithium salts are excellent in that they form a passive film on the surface of the aluminum foil, which is the positive electrode current collector, and suppress corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts can be used individually or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is preferred, and among these, a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferred because it makes it easier to release free fluorine atoms. When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferred because it makes it easier to capture excess free acid components that may cause battery degradation, and from this viewpoint, LiBF4 is particularly preferred.

[0071] In the lithium salt used in the non-aqueous electrolyte of this embodiment, the content of fluorine-containing inorganic lithium salt is preferably 0.01 moles or more, more preferably 0.1 moles or more, and even more preferably 0.25 moles or more per liter of non-aqueous solvent. When the content of fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase, and high power characteristics can be exhibited. Furthermore, this content is preferably less than 2.8 moles, more preferably less than 1.5 moles, and even more preferably less than 1 mole per liter of non-aqueous solvent. When the content of fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity increases, high power characteristics can be exhibited, and the decrease in ionic conductivity due to viscosity increase at low temperatures tends to be suppressed. This tends to improve high-temperature cycle characteristics and other battery characteristics while maintaining the excellent performance of the non-aqueous electrolyte.

[0072] (Organolithium salts) The lithium salt in this embodiment may include organolithium salts. An "organolithium salt" refers to a lithium salt other than an imide salt that contains a carbon atom as an anion and is soluble in acetonitrile.

[0073] Examples of organolithium salts include organolithium salts having an oxalic acid group. Specific examples of organolithium salts having an oxalic acid group include, for example, organolithium salts represented as LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2, respectively. Among these, at least one lithium salt selected from the lithium salts represented as LiB(C2O4)2 and LiBF2(C2O4) is preferred. Furthermore, it is more preferable to use one or more of these together with a fluorine-containing inorganic lithium salt. These organolithium salts having an oxalic acid group may be added to a non-aqueous electrolyte or incorporated into the negative electrode (negative electrode active material layer).

[0074] In this embodiment, the amount of organolithium salt added to the non-aqueous electrolyte is preferably 0.005 moles or more, more preferably 0.01 moles or more, even more preferably 0.02 moles or more, and particularly preferably 0.05 moles or more, per liter of non-aqueous solvent, from the viewpoint of ensuring better effects from its use. However, if the amount of the organolithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, precipitation may occur. Therefore, the amount of organolithium salt having an oxalic acid group added to the non-aqueous electrolyte is preferably less than 1.0 mole, more preferably less than 0.5 moles, and even more preferably less than 0.2 moles, per liter of non-aqueous solvent.

[0075] Organolithium salts having an oxalic acid group are known to be poorly soluble in low-polarity organic solvents, particularly in linear carbonates. The content of the organolithium salt in the non-aqueous electrolyte according to this embodiment may be, for example, 0.01 moles or more and 0.5 moles or less per liter of non-aqueous solvent.

[0076] Furthermore, organolithium salts containing oxalic acid groups may contain trace amounts of lithium oxalate, and when mixed as a non-aqueous electrolyte, they may react with trace amounts of water contained in other raw materials, potentially generating a white precipitate of lithium oxalate. Therefore, it is preferable to limit the lithium oxalate content in the non-aqueous electrolyte according to this embodiment to a range of 500 ppm or less.

[0077] (Other lithium salts) The lithium salt in this embodiment may include other lithium salts in addition to those mentioned above.

[0078] Other specific examples of lithium salts include, for example, LiClO4, LiAlO4, LiAlCl4, LiB 10 Cl 10 , inorganic lithium salts that do not contain a fluorine atom as an anion, such as chloroborane Li; LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiCnF (2n+1) SO3 {wherein n≧2}, organolithium salts such as lower aliphatic carboxylic acid Li, tetraphenylborate Li, and LiB(C3O4H2)2; LiPF5 (CF3) and other LiPF n (C p F 2p+1 ) 6-n Organic lithium salts represented by the formula [wherein n is an integer from 1 to 5, and p is an integer from 1 to 8]; LiBF3 (CF3) and other LiBF q (C s F 2s+1 ) 4-q Organic lithium salts represented by the formula [wherein q is an integer from 1 to 3, and s is an integer from 1 to 8]; Lithium salts bound to polyvalent anions; The following formula (XXa): LiC(SO2R jj )(SO2R kk )(SO2R ll ) (XXa) {where, R jj , R kk , and Rll These may be identical or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (XXb): LiN(SO2OR mm )(SO2OR nn ) (XXb) {where, R mm , and R nn These may be identical or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, and The following formula (XXc): LiN(SO2R oo )(SO2OR pp ) (XXc) {where, R oo , and R pp These may be identical or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. Examples include organolithium salts represented by each of the above, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

[0079] The amount of other lithium salts added to the non-aqueous electrolyte may be appropriately set in the range of, for example, 0.01 moles or more and 0.5 moles or less per liter of non-aqueous solvent.

[0080] <2-3. Additives for electrode protection> The non-aqueous electrolyte according to this embodiment may contain an additive for protecting the electrodes (electrode protection additive). The electrode protection additive may substantially overlap with the substance that acts as a solvent for dissolving the lithium salt (i.e., the non-aqueous solvent mentioned above). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte and the non-aqueous secondary battery, but it also includes substances that do not directly participate in the electrochemical reaction.

[0081] Specific examples of electrode protection additives include, for example, 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, such as ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propanesultone, 1,4-butanesultone, 1-propene-1,3-sultone, and tetramethylene sulfoxide; These include, and they can be used individually or in combination of two or more types.

[0082] The content of the electrode protection additive in the non-aqueous electrolyte 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, based on the total amount of the non-aqueous solvent.

[0083] In this embodiment, the higher the content of the electrode protection additive, the more the degradation of the non-aqueous electrolyte is suppressed. However, the lower the content of the electrode protection additive, the better the high-power characteristics of the non-aqueous secondary battery in low-temperature environments. Therefore, by adjusting the content of the electrode protection additive within the above range, it is possible to achieve excellent performance based on the high ionic conductivity of the electrolyte without impairing the basic functions of the non-aqueous secondary battery. Furthermore, by preparing a non-aqueous electrolyte with such a composition, it is possible to further improve the cycle performance, high-power performance in low-temperature environments, and other battery characteristics of the non-aqueous secondary battery.

[0084] Acetonitrile is readily reductively decomposed electrochemically. Therefore, non-aqueous solvents containing acetonitrile preferably contain one or more cyclic aprotic polar solvents as electrode protective additives for forming a protective film on the negative electrode, and more preferably contain one or more unsaturated bond-containing cyclic carbonates.

[0085] As the unsaturated bond-containing cyclic carbonate, vinylene carbonate is preferred, and the vinylene carbonate content is preferably 0.1% to 10% by volume in the non-aqueous electrolyte, more preferably 0.2% to less than 7% by volume, and even more preferably 0.5% to less than 5% by volume. This makes it possible to more effectively improve low-temperature durability and provide a secondary battery with excellent low-temperature performance.

[0086] As an electrode protection additive, vinylene carbonate suppresses the reductive decomposition reaction of acetonitrile on the negative electrode surface, but 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, and cycle degradation at low temperatures can be suppressed.

[0087] (acid anhydride) In this embodiment, the non-aqueous secondary battery is stabilized by the decomposition of a portion of the non-aqueous electrolyte during the initial charge, which forms a SEI on the negative electrode surface. To more effectively strengthen this SEI, an acid anhydride can be added to the non-aqueous electrolyte, battery components, or non-aqueous secondary battery. When acetonitrile is included as the non-aqueous solvent, the strength of the SEI tends to decrease with increasing temperature, but the addition of an acid anhydride promotes the strengthening of the SEI. Therefore, by using such an acid anhydride, the increase in internal resistance over time due to thermal history can be effectively suppressed.

[0088] Specific examples of acid anhydrides include, for example, chain-like acid anhydrides such as acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic acid anhydrides such as malonic acid anhydride, succinic anhydride, glutaric acid anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic acid anhydride, 2,3-naphthalenedicarboxylic acid anhydride, or naphthalene-1,4,5,8-tetracarboxylic dianhydride; and mixed acid anhydrides with structures formed by the dehydration condensation of two different carboxylic acids, or different types of acids such as a carboxylic acid and a sulfonic acid. These can be used individually or in combination of two or more.

[0089] In this embodiment, since it is preferable to enhance the SEI before the reductive decomposition of the non-aqueous solvent, the non-aqueous secondary battery preferably contains at least one cyclic acid anhydride that acts early during the initial charge. These cyclic acid anhydrides may contain only one type or multiple types. Alternatively, other cyclic acid anhydrides may be included. Furthermore, it is preferable that the cyclic acid anhydride contains at least one of succinic anhydride, maleic anhydride, and phthalic anhydride.

[0090] A non-aqueous electrolyte containing at least one of succinic anhydride, maleic anhydride, and phthalic anhydride allows for the formation of a robust SEI on the negative electrode, more effectively suppressing the increase in resistance during high-temperature heating. The inclusion of succinic anhydride is particularly preferable. This allows for the more effective formation of a robust SEI on the negative electrode while suppressing side reactions.

[0091] If the non-aqueous electrolyte according to this embodiment contains an acid anhydride, the amount of acid anhydride is preferably in the range of 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the non-aqueous electrolyte, 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.

[0092] It is preferable that the non-aqueous electrolyte contains the acid anhydride. On the other hand, as long as the acid anhydride can act 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. As for how to incorporate the acid anhydride into the battery component, for example, it may be incorporated into the battery component during manufacturing, or it may be impregnated into the battery component by post-treatment such as coating, immersion, or spray drying.

[0093] (Dinitrile compounds) The non-aqueous electrolyte according to this embodiment is The following general formula (2): [ka] The present invention includes a dinitrile compound represented by {wherein R represents a linear or branched divalent aliphatic alkyl group having 1 to 12 carbon atoms, which may contain an oxygen atom}. The dinitrile compound can improve the high-temperature durability of non-aqueous electrolytes containing sulfamate ions. In particular, the dinitrile compound can significantly improve the high-temperature durability of non-aqueous electrolytes containing acetonitrile and sulfamate ions.

[0094] In detail, sulfamate ions are thought to undergo an imidation reaction with dinitrile compounds at high temperatures, inactivating the highly reactive sulfonamide group into a less reactive sulfonimide group. This suppresses the corrosion reaction of the positive electrode Al current collector by sulfamate ions and the elution of transition metals from the positive electrode active material. Furthermore, the decomposition products generated by the reductive decomposition of the sulfonimide compound at the negative electrode are thought to accumulate at the negative electrode and act as SEI, suppressing the reductive decomposition of the solvent. In particular, in non-aqueous electrolytes containing acetonitrile, the corrosion reaction of the positive electrode Al current collector and the elution of transition metals from the positive electrode active material are thought to be significantly suppressed, as is the reductive decomposition of acetonitrile.

[0095] In the above general formula (2), the number of carbon atoms in the linear or branched divalent aliphatic alkyl group R is preferably 1 to 12, more preferably 1 to 10, and particularly preferably 1 to 8.

[0096] Specific examples of linear dinitrile compounds include malononitrile, succinonitrile, glutalonitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane, 1,9-dicyanononane, 1,10-dicyanodecane, and 1,12-dicyanododecane.

[0097] Specific examples of branched dinitrile compounds include methyl succinonitrile, tetramethyl succinonitrile, 2-methyl glutalonitrile, 2,4-dimethyl glutalonitrile, 1,4-dicyanopentane, 1,4-dicyanoheptane, 1,5-dicyanoheptane, 2,6-dicyanoheptane, 1,7-dicyanooctane, 2,7-dicyanooctane, 1,8-dicyanononane, 2,8-dicyanononane, and 1,6-dicyanodecane.

[0098] Specific examples of dinitrile compounds containing oxygen atoms include ethylene glycol bis(propionitrile) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, and 1,5-bis(2-cyanoethoxy)pentane.

[0099] Among the specific examples of the above compounds, preferred are malononitrile, succinonitrile, glutaronitrile, adiponitrile, methyl succinonitrile, 2-methylglutaronitrile, and ethylene glycol bis(propionitrile) ether; more preferably succinonitrile, glutaronitrile, methyl succinonitrile, 2-methylglutaronitrile, and ethylene glycol bis(propionitrile) ether; and even more preferably succinonitrile, methyl succinonitrile, and ethylene glycol bis(propionitrile) ether. These can be used individually or in combination of two or more.

[0100] The content of dinitrile compounds in the non-aqueous electrolyte is preferably 25% by mass or less, more preferably 15% by mass or less, and even more preferably 5% by mass or less, based on the total amount of the non-aqueous electrolyte. Furthermore, the content of dinitrile compounds in the non-aqueous electrolyte is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and particularly preferably 3% by mass or more, based on the total amount of the non-aqueous electrolyte. By adjusting the content of dinitrile compounds within the above range, it is possible to suppress corrosion reactions of the positive electrode Al current collector and elution of transition metals from the positive electrode active material while maintaining properties such as high ionic conductivity and high power characteristics, thereby suppressing various degradation phenomena in high-temperature environments.

[0101] The content of dinitrile compounds in the non-aqueous electrolyte is preferably 5 or more, more preferably 100 or more, more preferably 300 or more, and even more preferably 500 or more, in molar ratio with respect to the sulfamate ion content. Furthermore, the content of dinitrile compounds in the non-aqueous electrolyte is preferably 200,000 or less, more preferably 10,000 or less, even more preferably 2,000 or less, and particularly preferably 1,000 or less, in molar ratio with respect to the sulfamate ion content. By adjusting the content of dinitrile compounds relative to the sulfamate ion content within the above range, it is possible to form an excellent negative electrode SEI while suppressing corrosion reactions of the positive electrode Al current collector and the elution of transition metals from the positive electrode active material, thereby suppressing various degradation phenomena in high-temperature environments.

[0102] <2-4. Other optional additives> In this embodiment, optional additives (additives other than acid anhydrides and electrode protection additives) may be appropriately included in the non-aqueous electrolyte for purposes such as improving the charge-discharge cycle characteristics of the non-aqueous secondary battery, improving high-temperature storage capabilities, and enhancing safety (e.g., preventing overcharging).

[0103] Optional additives include, for example, sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters [ethyldiethyl phosphonoacetate (EDPA); (C2H5O)2(P=O)-CH2(C=O)OC2H5, tris(trifluoroethyl) phosphate (TFEP); (CF3CH2O)3P=O, triphenyl phosphate (TPP); (C6H5O)3P=O, triallyl phosphate; (CH2=CHCH2O)3P=O, triamyl phosphate, trioctyl phosphate, tris(2-butoxyethyl) phosphate, tris(2-ethylhexyl) phosphate, etc.], nitrogen-containing cyclic compounds without steric hindrance around lone pairs of electrons [pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.]. In particular, phosphate esters are effective as optional additives because they suppress side reactions during storage and improve the impregnation of non-aqueous electrolytes into the separator.

[0104] If the non-aqueous electrolyte according to this embodiment contains other optional additives, the amount of such additives is preferably in the range of 0.01% to 10% by mass, more preferably 0.02% to 5% by mass, and even more preferably 0.05 to 3% by mass, based on the total amount of the non-aqueous electrolyte. By adjusting the amount of other optional additives within the above range, it is possible to add even better battery characteristics without impairing the basic functions of the non-aqueous secondary battery.

[0105] <3.Non-aqueous secondary battery> The non-aqueous electrolyte of this embodiment can be used in a non-aqueous secondary battery. The non-aqueous secondary battery according to this embodiment is configured such that a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are housed in a suitable battery casing, although this does not impose any particular limitations.

[0106] The non-aqueous secondary battery according to this embodiment may specifically be the non-aqueous secondary battery 100 shown in Figures 1 and 2. Here, Figure 1 is a schematic plan view of the non-aqueous secondary battery, and Figure 2 is a cross-sectional view taken along line AA of Figure 1.

[0107] The non-aqueous secondary battery 100 shown in Figures 1 and 2 is composed of pouch-type cells. The non-aqueous secondary battery 100 houses a laminated electrode body, which is constructed by stacking a positive electrode 150 and a negative electrode 160 with a separator 170 in between, and a non-aqueous electrolyte (not shown) within a space 120 of the battery casing 110. The battery casing 110 is made of, for example, aluminum laminate film, and is sealed by heat-sealing the upper and lower films at the outer periphery of the space formed by two aluminum laminate films. The laminate, in which the positive electrode 150, separator 170, and negative electrode 160 are stacked in order, is impregnated with the non-aqueous electrolyte. However, in Figure 2, in order to avoid complexity in the drawing, the individual layers constituting the battery casing 110, as well as the individual layers of the positive electrode 150 and negative electrode 160, are not shown separately.

[0108] The aluminum laminate film constituting the battery casing 110 is preferably made by coating both sides of an aluminum foil with a polyolefin-based resin.

[0109] The positive electrode 150 is connected to the positive electrode lead 130 within the non-aqueous secondary battery 100. Although not shown in the diagram, the negative electrode 160 is also connected to the negative electrode lead 140 within the non-aqueous secondary battery 100. The positive electrode lead 130 and the negative electrode lead 140 each have one end extended outside the battery casing 110 so that they can be connected to external devices, and their ionomer portions are heat-sealed to one side of the battery casing 110.

[0110] The non-aqueous secondary battery 100 shown in Figures 1 and 2 has one stacked electrode body each for the positive electrode 150 and the negative electrode 160, but the number of stacked positive electrodes 150 and negative electrodes 160 can be appropriately increased depending on the capacity design. In the case of a stacked electrode body having multiple positive electrodes 150 and negative electrodes 160, the tabs of the same electrode may be joined together by welding or the like and then joined to a single lead body by welding or the like and taken out of the battery. The tabs of the same electrode can be made from the exposed part of the current collector, or from a metal piece welded to the exposed part of the current collector, and so on.

[0111] The positive electrode 150 consists of a positive electrode current collector and a positive electrode active material layer. The negative electrode 160 consists of a negative electrode current collector and a negative electrode active material layer.

[0112] The positive electrode active material layer contains the positive electrode active material, and the negative electrode active material layer contains the negative electrode active material.

[0113] The positive electrode 150 and the negative electrode 160 are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via a separator 170. The following describes each element constituting the non-aqueous secondary battery according to this embodiment.

[0114] <4. Positive electrode> The positive electrode 150 consists of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode mixture contains a positive electrode active material and, if necessary, a conductive additive and a binder.

[0115] The positive electrode active material layer contains a material capable of intercalating and releasing lithium ions as the positive electrode active material. Such a material can achieve high voltage and high energy density.

[0116] Examples of positive electrode active materials include positive electrode active materials containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and the following general formula (a t ): Li p Ni q Co r Mns M t O u ·····(a t ) {Wherein, M is at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and 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 lithium (Li)-containing metal oxides represented by

[0117] Specific examples of the positive electrode active material include, for example, lithium cobalt oxide represented by LiCoO2; lithium manganese oxide represented by LiMnO2, LiMn2O4, and Li2Mn2O4; lithium nickel oxide 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 represents two or more metal elements selected from the group consisting of Ni, Mn, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2), such as lithium-containing composite metal oxides, etc.

[0118] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (a t ) is 0.5 < q < 1.2, it is preferable because both reduction of the usage amount of Co, which is a rare metal, and increase in the energy density can be achieved. Examples of such positive electrode active materials 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 Mn0.1 O2, LiLiLi 0.85 Co 0.075 Mn 0.075 O2, LiLiLi 0.8 Co 0.15 Al 0.05 O2, LiLiLi 0.81 Co 0.1 Al 0.09 O2, LiLiLi 0.85 Co 0.1 Al 0.05 Examples include lithium-containing composite metal oxides such as O2.

[0119] On the other hand, the higher the Ni content ratio of the Li-containing metal oxide, the more likely it is that degradation will progress at low voltages. General formula (a t Layered rock salt type cathode active materials, represented as ), inherently contain active sites that cause oxidative degradation of the electrolyte. These active sites can unintentionally consume electrode protection additives.

[0120] Furthermore, these additive decomposition products 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 lithium salts. In particular, when LiPF6 is included as the lithium salt, degradation can lead to the generation of HF, which is thought to promote the elution of transition metals. In non-aqueous electrolytes containing acetonitrile as the non-aqueous solvent, complexes are formed between metal cations and acetonitrile, accelerating battery degradation.

[0121] Furthermore, degradation of electrode protection additives or lithium salts can lead to insufficient protection of the negative electrode surface, which was the original purpose. In particular, in non-aqueous electrolytes containing acetonitrile as a non-aqueous solvent, insufficient protection of the negative electrode surface leads to reductive decomposition of acetonitrile, causing a rapid deterioration of battery performance, which is a critical problem.

[0122] To deactivate the active sites that essentially cause oxidative degradation of non-aqueous electrolytes, the presence of components that control Jahn-Teller strain or act as neutralizers is important. 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.

[0123] For similar reasons, 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 even 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, as this does not hinder the permeation of lithium ions.

[0124] In the non-aqueous secondary battery according to this embodiment, it is preferable to use a lithium phosphorus metal oxide having an olivine crystal structure containing iron (Fe) atoms, as shown in the following formula (Xba): Li w M II PO4(Xba) {In formula, M II This represents one or more transition metal elements, including at least one transition metal element containing Fe, and the value of w is determined by the charge / discharge state of the battery, representing a number between 0.05 and 1.10. It is more preferable to use a lithium phosphate metal oxide having an olivine structure. These lithium-containing metal oxides may be those in which some of the transition metal elements are substituted with Al, Mg, or other transition metal elements for purposes such as stabilizing the structure, those in which these metal elements are included in the grain boundaries, those in which some of the oxygen atoms are substituted with fluorine atoms, etc., or those in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material.

[0125] Examples of positive electrode active materials include metal phosphate oxides containing lithium and a transition metal element, and metal silicate oxides containing lithium and a transition metal element. From the viewpoint of obtaining a higher voltage, metal phosphate oxides 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 are particularly preferred as lithium-containing metal oxides, and metal phosphate oxides containing Li and Fe are more preferred from the viewpoint of lithium phosphate metal oxide represented by the above formula (Xba).

[0126] A lithium phosphate metal oxide different from the lithium phosphate metal oxide represented by the above formula (Xba) is given by the following formula (Xa): Li v M I D2(Xa) {In the formula, D represents the chalcogen element, M} I This represents one or more transition metal elements, including at least one transition metal element, and the value of v is determined by the charge / discharge state of the battery, representing a number between 0.05 and 1.10. Compounds represented by may also be used.

[0127] In this embodiment, only lithium-containing metal oxides as described above may be used as the positive electrode active material, or other positive electrode active materials may be used in combination with the lithium-containing metal oxide. Examples of other positive electrode active materials include metal oxides or metal chalcogenides having tunnel and layered structures; sulfur; conductive polymers, etc. Examples of metal oxides or metal chalcogenides having tunnel and layered structures include MnO2, FeO2, FeS2, V2O5, V6O 13 Examples of conductive polymers include oxides, sulfides, and selenides of metals other than lithium, such as TiO2, TiS2, MoS2, and NbSe2. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0128] The other positive electrode active materials mentioned above can be used individually or in combination of two or more. It is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co, as this enables reversible and stable intercalation and release of lithium ions and achieves a high energy density.

[0129] When lithium-containing metal oxide and other positive electrode active materials are used in combination as positive electrode active materials, the ratio of lithium-containing metal oxide to the total positive electrode active material is preferably 80% by mass or more, and more preferably 85% by mass or more.

[0130] The positive electrode active material layer is formed by dispersing a slurry containing a positive electrode mixture, which is a mixture of the positive electrode active material and, if necessary, a conductive additive and a binder, in a solvent, onto a positive electrode current collector, drying (solvent removal), and pressing as necessary. Known solvents can be used for this purpose. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0131] Examples of conductive additives include acetylene black, carbon black such as Ketjenblack, carbon fibers, and graphite. The content ratio 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 positive electrode active material.

[0132] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The binder content is preferably 6 parts by mass or less, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of positive electrode active material.

[0133] The positive electrode current collector is made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive electrode current collector may have a carbon coating on its surface or may be processed into a mesh shape. 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.

[0134] The basis weight per side of the positive electrode, excluding the positive electrode current collector, is set at 15 mg / cm³ from the viewpoint of improving the volumetric energy density in non-aqueous secondary batteries. 2 Preferably, the concentration is 17.5 mg / cm³. 2 It is more preferable that the concentration be 24 mg / cm³ or higher. 2 It is even more preferable that the above conditions are met. Furthermore, the basis weight per positive electrode side, excluding the positive electrode current collector, is 200 mg / cm². 2 Preferably, it is 100 mg / cm³ 2 More preferably, the following is 60 mg / cm³ 2 It is even more preferable that the following conditions are met: By limiting the basis weight per positive electrode side, excluding the positive electrode current collector, to the above range, it is possible to provide a non-aqueous secondary battery that achieves high output performance even when designing an electrode active material layer with a high volumetric energy density.

[0135] Here, the basis amount refers to the electrode area of ​​1 cm² when forming an electrode active material layer on one side of the current collector. 2 This indicates the mass of electrode active material contained per unit area. When electrode active material layers are formed on both sides of the current collector, the electrode area of ​​each side is 1 cm². 2 This indicates the mass of electrode active material contained in that area. When a large amount of electrode active material is applied to the electrode current collector, the amount of electrode active material per unit volume of the battery becomes relatively larger than other battery materials that are not related to the battery capacity, such as current collector foil and separators, resulting in a higher battery capacity. The basis weight when forming an electrode active material layer on one side of a current collector can be calculated using the following formula (12). Basis weight [mg / cm³] 2 ] = (electrode mass [mg] - electrode current collector mass [mg]) ÷ electrode area [cm 2] ·····(12)

[0136] <5. Negative electrode> The negative electrode 160 consists 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.

[0137] The negative electrode mixture contains a negative electrode active material and, if necessary, a conductive additive and a binder.

[0138] Examples of anode active materials that can be used include amorphous carbon (hard carbon), graphite (artificial graphite, natural graphite), pyrolysis carbon, coke, glassy carbon, calcined organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, carbon colloids, and carbon materials such as carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymer compounds. The anode active material can be used alone or in combination of two or more types.

[0139] In this embodiment, it is preferable to use graphite or a compound containing one or more elements selected from the group consisting of Ti, V, Sn, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, and B as the negative electrode active material.

[0140] From the perspective of increasing the battery voltage, lithium ions are used as the negative electrode active material in the negative electrode active material, resulting in a 0.4V vs. Li / Li + It is preferable to include a material that can absorb at a lower potential than the current.

[0141] The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of the negative electrode active material and, if necessary, a conductive additive and a binder, in a solvent, onto a negative electrode current collector, drying (solvent removal), and pressing as necessary. Known solvents can be used for this purpose, including, for example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0142] Examples of conductive additives include acetylene black, carbon black such as Ketjenblack, carbon fibers, and graphite. The content ratio 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.

[0143] Examples of binders include carboxymethylcellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Diene rubbers, such as styrene-butadiene rubber, are also acceptable. The binder content is preferably 10 parts by mass or less, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the negative electrode active material.

[0144] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, or stainless steel foil. The negative electrode current collector may also have a carbon coating on its surface or be processed into a mesh shape. 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.

[0145] <6. Separator> In this embodiment, the non-aqueous secondary battery 100 preferably includes a separator 170 between the positive electrode 150 and the negative electrode 160, from the viewpoint of providing safety such as preventing short circuits and shutting down the positive electrode 150 and the negative electrode 160. The separator 170 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 microporous membrane made of synthetic resin, and among these, a microporous membrane made of synthetic resin is preferred.

[0146] Suitable examples of synthetic resin microporous membranes include polyolefin-based microporous membranes, such as those containing polyethylene or polypropylene as the main component, or those containing both of these polyolefins. Examples of nonwoven fabrics include heat-resistant resin porous membranes made of glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, aramid, etc.

[0147] The separator 170 may have a configuration in which one type of microporous membrane is laminated in a single layer or multiple layers, or it may have two or more types of microporous membranes laminated together. The separator 170 may also have a configuration in which a mixed resin material obtained by melt-kneading two or more types of resin materials is laminated in a single layer or multiple layers.

[0148] For the purpose of imparting functionality, inorganic particles may be present on the surface or inside the separator, and other organic layers may be further coated or laminated. The separator may also include a cross-linked structure. These methods may be combined as needed to enhance the safety performance of non-aqueous secondary batteries.

[0149] By using such a separator 170, it is possible to achieve the good input / output characteristics and low self-discharge characteristics particularly required for lithium-ion batteries used in the high-power applications mentioned above. The thickness of the separator is preferably 1 μm or more from the viewpoint of separator strength, preferably 500 μm or less from the viewpoint of permeability, more preferably 5 μm to 30 μm, and even more preferably 10 μm to 25 μm. If short-circuit resistance is important, the thickness of the separator is even more preferably 15 μm to 20 μm, but if high energy density is important, it is even more preferably 10 μm to less than 15 μm. The porosity of the 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 at high power. Furthermore, when prioritizing improved output performance while ensuring safety, a ratio of 50% to 70% is particularly preferable, and when prioritizing a balance between short-circuit resistance and output performance, a ratio of 40% to less than 50% is particularly preferable. The air permeability of the separator should be 1 second / 100 cm, considering the balance with the separator's thickness and porosity. 3 More than 400 seconds / 100cm 3 The following is preferable: 100 seconds / 100 cm 3 More than 350 / 100cm 3 The following is preferable. Furthermore, if prioritizing both short-circuit resistance and output performance, the air permeability should be 150 seconds / 100cm. 3 More than 350 seconds / 100cm 3 The following is particularly preferable, and if prioritizing improved output performance while ensuring safety, 100 / 100cm 3 seconds or more 150 seconds / 100cm 3A value less than the specified value is particularly preferred. On the other hand, when a non-aqueous electrolyte with low ionic conductivity is combined with a separator within the above range, the rate of lithium ion migration is limited not by the separator's structure, but by the high ionic conductivity of the electrolyte, and the expected input / output characteristics tend not to be obtained. For this reason, the ionic conductivity of the non-aqueous electrolyte at 25°C is preferably 10 mS / cm or higher, more preferably 15 mS / cm or higher, and even more preferably 20 mS / cm or higher. However, the thickness, air permeability, and porosity of the separator, as well as the ionic conductivity of the non-aqueous electrolyte, are not limited to the above examples.

[0150] <7. Battery casing> In this embodiment, the battery casing 110 of the non-aqueous secondary battery 100 can be constructed using either a battery can (not shown) or a laminate film casing. As the battery can, for example, metal cans such as rectangular, rectangular tube, cylindrical, elliptical, flat, coin-shaped, or button-shaped cans made of steel, stainless steel (SUS), aluminum, or clad material can be used. As the laminate film casing, for example, a laminate film consisting of a three-layer structure of heat-melt resin / metal film / resin can be used.

[0151] The laminate film casing can be used by stacking two sheets with the heat-melt resin side facing inward, or by folding the film so that the heat-melt resin side faces inward, and sealing the ends with heat seal. When using the laminate film casing, the positive electrode lead body 130 (or positive electrode terminal and lead tab connected to the positive electrode terminal) may be connected to the positive electrode current collector, and the negative electrode lead body 140 (or negative electrode terminal and lead tab connected to the negative electrode terminal) may be connected to the negative electrode current collector. In this case, the laminate film casing may be sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or lead tabs connected to the positive electrode terminal and the negative electrode terminal, respectively) extended to the outside of the casing.

[0152] <8. Method for manufacturing a battery> The non-aqueous secondary battery 100 in this embodiment is manufactured by a known method using the above-mentioned non-aqueous electrolyte, a positive electrode 150 having a positive electrode active material layer on one or both sides of the current collector, a negative electrode 160 having a negative electrode active material layer on one or both sides of the current collector, a battery casing 110, and a separator 170 if necessary.

[0153] First, a laminate is formed consisting of a positive electrode 150, a negative electrode 160, and, if necessary, a separator 170. For example, a laminate with a wound structure can be formed by winding long positive electrodes 150 and negative electrodes 160 in a laminated state with the long separator interposed between them; a laminate with a laminated structure can be formed by cutting the positive electrode 150 and negative electrode 160 into multiple sheets having a certain area and shape, and alternately stacking the resulting positive electrode sheets and negative electrode sheets via a separator sheet; a laminate with a laminated structure can be formed by folding a long separator in a zigzag pattern and alternately inserting positive electrode sheets and negative electrode sheets between the zigzag-folded separators; and so on.

[0154] Next, the laminate described above is housed in the battery casing 110 (battery case), the electrolyte according to this embodiment is poured into the battery case, and the laminate is immersed in the electrolyte and sealed to produce the non-aqueous secondary battery according to this embodiment. Alternatively, a gel-like electrolyte membrane can be prepared in advance by impregnating a substrate made of polymer material with the electrolyte, and a laminated structure can be formed using a sheet-like positive electrode 150, a negative electrode 160, and an electrolyte membrane, and a separator 170 if necessary, and then housed in the battery casing 110 to produce the non-aqueous secondary battery 100.

[0155] Furthermore, if the electrode arrangement is designed such that there is an overlap between the outer edge of the negative electrode active material layer and the outer edge of the positive electrode active material layer, or if there is a section of the non-opposing part of the negative electrode active material layer that is too narrow, then misalignment of the electrodes may occur during battery assembly, potentially degrading the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the position of the electrodes in the electrode body used in the non-aqueous secondary battery in advance using tapes such as polyimide tape, polyphenylene sulfide tape, or polypropylene (PP) tape, or adhesives.

[0156] In non-aqueous electrolytes containing acetonitrile, due to acetonitrile's high ionic conductivity, lithium ions released from the positive electrode during the initial charge of a non-aqueous secondary battery may diffuse throughout the negative electrode. In non-aqueous secondary batteries, it is common to have a larger negative electrode active material layer than the positive electrode active material layer. However, if lithium ions diffuse and are intercalated in areas of the negative electrode active material layer that do not face the positive electrode active material layer, these lithium ions will remain in the negative electrode without being released during the initial discharge. As a result, the contribution of these unreleased lithium ions becomes irreversible capacity. For these reasons, non-aqueous secondary batteries using non-aqueous electrolytes containing acetonitrile may have low initial charge-discharge efficiency.

[0157] 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 areas are the same, current concentration is more likely to occur at the edges of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0158] There are no particular restrictions on 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. However, for the reasons mentioned above, it is preferable that the ratio be 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 non-aqueous secondary battery using a non-aqueous electrolyte containing acetonitrile, the initial charge-discharge efficiency can be improved by 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.

[0159] 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 proportion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to reduce as much as possible the amount of lithium ions absorbed into 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 first discharge and become irreversible capacity) from the lithium ions released from the positive electrode during the first charge. 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 acetonitrile, increase the initial charge-discharge efficiency of the battery, and further suppress the formation of lithium dendrites.

[0160] The non-aqueous secondary battery 100 in this embodiment can function as a battery after the initial charge, but it is stabilized by the decomposition of a portion of the electrolyte during the initial charge. There are no particular restrictions on the method of initial charging, but it is preferable to perform the initial charge at 0.001 to 0.3C, more preferably at 0.002 to 0.25C, and even more preferably at 0.003 to 0.2C. Performing the initial charge via constant voltage charging also yields favorable results. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, a stable and robust negative electrode SEI is formed on the electrode surface, suppressing an increase in internal resistance, and the reaction products are not firmly fixed only on the negative electrode 160, but also have a good effect on components other than the negative electrode 160, such as the positive electrode 150 and the separator 170. For this reason, performing the initial charge while considering the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte is very effective.

[0161] In this embodiment, the non-aqueous secondary battery 100 can also be used as a battery pack in which multiple non-aqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charge and discharge state of the battery pack, when a positive electrode active material represented by the above formula (Xba) is used in the positive electrode, the operating voltage range per battery is preferably 1.5 to 4.0V, and particularly preferably 2.0 to 3.8V.

[0162] Also, the general formula (a t When using a positive electrode active material represented by ), the operating voltage range per battery is preferably 2 to 5V, more preferably 2.5 to 5V, and particularly preferably 2.75V to 5V. [Examples]

[0163] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples.

[0164] (1) Preparation of non-aqueous electrolyte Non-aqueous electrolytes (S01) to (S03) were prepared by mixing various non-aqueous solvents to predetermined concentrations under an inert atmosphere, and then adding various lithium salts to predetermined concentrations. In addition, the additives shown in Table 1 were mixed into non-aqueous electrolyte (S01) at specific concentrations relative to the total volume of the non-aqueous electrolyte. The compositions of these non-aqueous electrolytes are shown in Table 1.

[0165] Compound (1-2) was synthesized by the method described below, with compound (1-2) from lot A used in electrolytes (S01) and (S02), and compound (1-2) from lot B used in electrolyte (S03).

[0166] The abbreviations for non-aqueous solvents and lithium salts in Table 1 have the following meanings, respectively. (Non-aqueous solvents) AN: Acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate ES: Ethylene sulfite VC: Vinylen carbonate (Lithium salt) (1-2): Compound represented by the above formula (1-2) LiFSI: Lithium bis(fluorosulfonyl)imide (LiN(SO2F)2) LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2) (Additives) SN: Sucinonitrile (others) Sul: Sulfamate ion DN: Dinitrile compound

[0167] • Preparation of compounds (1-2) <Analysis method> The analytical methods, raw materials, and reaction conditions used in the preparation of compound (1-2) were as follows.

[0168] (Nuclear magnetic resonance analysis (NMR): 1 H-NMR, and19 (Molecular structure analysis by F-NMR) Regarding the products obtained during the preparation of compounds (1-2), 1 H-NMR (400 MHz), and 19 Molecular structure analysis was performed using F-NMR (337 MHz) under the following measurement conditions. [Measurement conditions] Measurement device: JNM-ECZ400S type nuclear magnetic resonance spectrometer (manufactured by JEOL Ltd.) Observation nucleus: 1 H, 19 F Solvents: Deuterated chloroform, deuterated dimethyl sulfoxide Reference substance: Tetramethylsilane ( 1 H, 0.00 ppm), trichlorofluoromethane ( 19 F, 0.00 ppm) Reference substance concentration: 5% by mass Measured sample concentration: 20% by mass Pulse width: 6.5 μs Waiting time: 2 seconds Total number of times: 8 times ( 1 H), 1024 times ( 19 F)

[0169] <Content of compound (1-2)> 19 The content of compound (1-2) was determined from the integral value of representative peaks based on the F-NMR measurement results.

[0170] In this embodiment, the following structural formula: [ka] The content of the lithium salt (compound (1-2)) of the fluorine-containing cyclic sulfonimide represented by was calculated from the integral value of the -115.4 ppm (4F) peak.

[0171] (ICP emission spectroscopy) The molecular structure of the prepared compounds (1-2) was analyzed under the following measurement conditions. [Measurement conditions] Measuring device: SPS3520UV-DD (manufactured by Hitachi High-Tech Science Corporation) Measured atom: Li Sample preparation conditions: A temporarily diluted solution with a concentration of 1% by mass was obtained by mixing 0.1 g of the product with 9.9 g of ultrapure water. Subsequently, 1.5 g of the temporarily diluted solution was mixed with 28.5 g of a 1% by mass nitric acid aqueous solution to obtain a measurement sample. High-frequency power: 1.2 kW Plasma gas (argon) flow rate: 16 L / min Auxiliary gas (argon) flow rate: 0.5 L / min Carrier gas (argon) pressure: 0.24 MPa Carrier gas (argon) flow rate: 0.3 L / min Optical height: 12 mm Chamber gas (argon) flow rate: 0.6 L / min

[0172] (Ion chromatography method) For the prepared compound (1-2), the content of sulfamic acid ions was measured under the following measurement conditions. [Measurement conditions] Measuring device: Tosoh IC2010 (manufactured by Tosoh Corporation) Analysis mode: Suppress-anion Detector: Conductivity detector Column: Tosoh TSKgel guard column Super IC -AZ (4.6×150 mm) Column temperature: 40 °C Eluent composition: 7.5 mM sodium hydrogen carbonate + 1.1 mM sodium carbonate Flow rate: 0.8 mL / min Injection volume: 30 μL Collection time: 30 minutes Sample adjustment conditions: 0.1 g of the product was mixed with 99.9 g of ultrapure water to obtain a measurement sample. Quantification of sulfamic acid ions was performed by the absolute calibration curve method using a calibration curve obtained from the correlation between the area and concentration of the sulfamic acid ion peak in the ion chromatogram measured for an aqueous solution containing sulfamic acid ions at a predetermined concentration in advance.

[0173] <Raw materials used> The raw materials used in the preparation of compounds (1-2) are listed below. • 2,2-difluoro-2-(fluorosulfonyl)acetic acid (compound (3-1), manufactured by Fujifilm Wako Pure Chemical Corporation)

[0174] • Ammonia (manufactured by Sumitomo Seika Co., Ltd.)

[0175] • Lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0176] • Acetonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; moisture content was adjusted by adding dried molecular sieve 3A 1 / 16 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), dehydrating, and then removing the molecular sieve 3A 1 / 16). • Tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; moisture content adjusted by adding dried molecular sieve 3A 1 / 16 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), dehydrating, and then removing the molecular sieve 3A 1 / 16)).

[0177] • Activated carbon (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0178] <Reaction temperature> The reaction temperature is room temperature if no external heating or cooling device is used. If an external heating or cooling device such as a water bath or oil bath is used, the reaction temperature is the temperature of the medium used in the external heating or cooling device.

[0179] <Synthesis of Compounds (1-2) (Lot A)> (Electrolytic coupling reaction process) A Schlenk tube with an external diameter of 30 mm, a height of 170 mm, and a capacity of 50 mL was used. Under a nitrogen atmosphere, a stirring bar, acetonitrile (4.5 g), and water (22.6 g) were added, and the mixture was cooled to 0°C. Then, FO2SCF2CO2H (compound (3-1), 10.0 g, 56.1 mmol) was added. Platinum plate electrodes (13 mm × 50 mm) were placed 3 mm apart as the anode and cathode and immersed in the solution. While maintaining stirring under 0°C cooling, a current of 1.5 A (231 mA / cm²) was applied to the electrodes. 2 The current was applied for 3 hours. After the current was removed and stirring was stopped, the reaction solution separated into two phases. 5.2 g of liquid was obtained by separating the lower layer. The obtained liquid was dried using molecular sieves and then purified by distillation to obtain 5.0 g of liquid containing FO2SCF2CF2SO2F (compound (4-1)). FO2SCF2CF2SO2F (compound (4-1)) 19 F-NMR (deuterated chloroform): δ (ppm) 46.1 (2F), -108.7 (4F)

[0180] (Cyclization process) A 3 L autoclave was cooled to -78°C, and ammonia gas (240 g, 14.09 mol) and tetrahydrofuran (200 mL) were added. While maintaining the autoclave temperature below -55°C, a solution of FO2SCF2CF2SO2F (compound (4-1), 173 g, 0.59 mol) in tetrahydrofuran (200.0 mL) was added dropwise. After the addition was complete, the mixture was stirred overnight at room temperature. Then, while maintaining stirring, the internal pressure was returned to atmospheric pressure, and argon was blown into the autoclave at a rate of 0.5 L / min for 1.5 hours to remove ammonia. The reaction mixture was filtered to remove the white solid, and washed several times with tetrahydrofuran. The obtained filtrate was transferred to a 3 L flask, concentrated under reduced pressure, and then vacuum-dried at 40°C for 12 hours to obtain 150.5 g of solid. The obtained solid was sampled, 19 Analysis by F-NMR reveals the following structural formula: [ka] It was confirmed to be a fluorine-containing cyclic sulfonylimide ammonium salt (compound (1-N-2)) represented by [formula]. 19 F-NMR (deuterated dimethyl sulfoxide): δ (ppm) - 115.4 (4F)

[0181] (Cation exchange process) In a 1 L three-necked flask, under a nitrogen atmosphere, a stirring bar, tetrahydrofuran (564 mL), fluorine-containing cyclic sulfonylimide ammonium salt (compound (1-N-2), 242.0 g, 0.93 mol), and lithium hydroxide monohydrate (42.9 g, 1.02 mol) were added and the mixture was stirred at 75°C for 4 hours. The resulting reaction solution was concentrated under reduced pressure, then ion-exchanged water (628 mL) and activated carbon (82.7 g) were added and the mixture was stirred at 105°C for 3 hours. The resulting reaction solution was filtered under pressure to remove insoluble solids, and then concentrated under reduced pressure to obtain a solid (245 g). Tetrahydrofuran (1.27 L) was added to the obtained flesh-colored solid and the mixture was stirred at 50°C for 30 minutes. After removing the insoluble solids by pressure filtration, the mixture was concentrated under reduced pressure and then vacuum-dried at 70°C for 16 hours and 90°C for 6 hours to obtain 201 g of a white solid. The obtained solid was sampled and analyzed by ICP emission spectrometry, confirming that ammonium cations had been replaced with lithium cations. Furthermore, 19 Analysis by F-NMR reveals the following structural formula: [ka] It was confirmed to be a fluorine-containing cyclic sulfonimide lithium salt (compound (1-2)) represented by [formula]. The obtained crystals were sampled, 19 Analysis by F-NMR confirmed that the compound (1-2) was present at 99.3% by mass and sulfamate ions at 1658 ppm by mass. Compound (1-2) 19 F-NMR (deuterated dimethyl sulfoxide): δ (ppm) - 115.4 (4F)

[0182] <Synthesis of Compounds (1-2) (Lot B)> (Electrolytic coupling reaction process) The shape is a Schlenk tube with a diameter of 30 mm and a height of 170 mm and a capacity of 50 mL. Under a nitrogen atmosphere, a stir bar, acetonitrile (4.5 g), and water (22.6 g) were added, and then it was cooled to 0 °C. After that, FO2SCF2CO2H (Compound (3-1), 30.0 g, 168.2 mmol) was added. As the anode and cathode, platinum plate electrodes (13 mm × 50 mm) were installed at an interval of 3 mm and immersed in the solution. While maintaining stirring under cooling at 0 °C, a current of 1.5 A (231 mA / cm 2 ) was applied for 3 hours. After the electrolysis was completed and the stirring was stopped, the reaction solution separated into two phases. When the lower layer was separated, 17.2 g of a liquid was obtained. The obtained liquid was dried over molecular sieves and then purified by distillation to obtain 12.2 g of a liquid containing FO2SCF2CF2SO2F (Compound (4-1)). FO2SCF2CF2SO2F (Compound (4-1)) 19 F-NMR (deuterated chloroform): δ (ppm) 46.1 (2F), -108.7 (4F)

[0183] (Cyclization step) A 3 L autoclave was cooled to -78 °C, ammonia gas (240 g, 14.09 mmol), and tetrahydrofuran (200 mL) were added. Then, while maintaining the temperature inside the autoclave at -55 °C or lower, a solution of FO2SCF2CF2SO2F (Compound (4-1), 173 g, 0.59 mmol) in tetrahydrofuran (200.0 mL) was added dropwise. After the dropwise addition was completed, it was stirred overnight at room temperature. Then, while maintaining the stirring, the internal pressure was returned to normal pressure, and argon was blown into the autoclave at a rate of 0.5 L / min for 1.5 hours to discharge ammonia. The reaction solution was filtered to remove the white solid and washed several times with tetrahydrofuran. The obtained filtrate was transferred to a 3 L flask, concentrated under reduced pressure, and further dried in vacuo at 40 °C for 12 hours to obtain 160.2 g of a solid. The obtained solid was sampled and 19 analyzed by F-NMR to give the following structural formula:

Chemical formula

[0184] (Cation exchange process) In a 1 L three-necked flask, under a nitrogen atmosphere, a stirring bar, tetrahydrofuran (564 mL), fluorine-containing cyclic sulfonylimide ammonium salt (compound (1-N-2), 242.0 g, 0.93 mol), and lithium hydroxide monohydrate (42.9 g, 1.02 mol) were added and the mixture was stirred at 75°C for 4 hours. The resulting reaction solution was concentrated under reduced pressure, then ion-exchanged water (628 mL) and activated carbon (82.7 g) were added and the mixture was stirred at 105°C for 3 hours. The resulting reaction solution was filtered under pressure to remove insoluble solids, and then concentrated under reduced pressure to obtain a solid (245 g). Tetrahydrofuran (1.27 L) was added to the obtained flesh-colored solid and the mixture was stirred at 50°C for 30 minutes. After removing the insoluble solids by pressure filtration, the mixture was concentrated under reduced pressure and then vacuum-dried at 70°C for 16 hours and 90°C for 6 hours to obtain 212 g of a white solid. The obtained solid was sampled and analyzed by ICP emission spectrometry, confirming that ammonium cations had been replaced with lithium cations. Furthermore, 19 Analysis by F-NMR reveals the following structural formula: [ka] It was confirmed to be a fluorine-containing cyclic sulfonimide lithium salt (compound (1-2)) represented by [formula]. The obtained crystals were sampled, 19 Analysis by F-NMR confirmed that the compound (1-2) was present at 99.8% by mass and sulfamate ions at 322 ppm by mass. Compound (1-2) 19 F-NMR (deuterated dimethyl sulfoxide): δ (ppm) - 115.4 (4F)

[0185] [Table 1]

[0186] (2) Fabrication of a small non-aqueous secondary battery (2-1) Preparation of the positive electrode As the positive electrode active material, a composite oxide of lithium, nickel, manganese, and cobalt (LiNi 0.8 Mn 0.1 Co 0.1 A positive electrode mixture was obtained by mixing O2, carbon black powder as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 94:3:3.

[0187] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and mixed further to prepare a slurry containing the positive electrode mixture. This slurry containing the positive electrode mixture was applied to one side of a 20 μm thick aluminum foil, which would serve as the positive electrode current collector, at a basis weight of 8.4 mg / cm³. 2 The material was applied while adjusting the amount to achieve the desired consistency, and the solvent was dried and removed. Afterward, the density of the positive electrode active material layer was measured using a roll press to 2.72 g / cm³. 3 The material was rolled to obtain a positive electrode consisting of a positive electrode active material layer and a positive electrode current collector.

[0188] (2-2) Fabrication of the negative electrode (A) Graphite powder as the negative electrode active material, (B) carbon black powder as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a solid content mass ratio of 91:1:8 to obtain a negative electrode mixture.

[0189] Water was added as a solvent to the obtained negative electrode mixture and mixed further to prepare a negative electrode mixture-containing slurry. This slurry was then applied to one side of an 8 μm thick copper foil, which would serve as the negative electrode current collector, at a basis weight of 5.7 mg / cm³. 2 The material was applied while adjusting the amount to achieve the desired consistency, and the solvent was dried and removed. Afterwards, the density of the negative electrode active material layer was measured using a roll press to 1.60 g / cm³. 3 The material was rolled to obtain a negative electrode consisting of a negative electrode active material layer and a negative electrode current collector.

[0190] (2-3) Assembly of a small non-aqueous secondary battery The positive electrode obtained as described above was punched out into a disc shape with a diameter of 18 mm, and the negative electrode obtained as described above was punched out into a disc shape with a diameter of 18 mm. These two discs were then stacked on both sides of a separator-embedded insulating sleeve (EL-Cell Co., Ltd., ECC1-00-0210-W / X), 120 μL of non-aqueous electrolyte (S01~S03) was injected, and the positive electrode side was pressed down with an aluminum plunger and the negative electrode side with a SUS plunger to obtain a laminate. This laminate was then inserted into a battery case (EL-Cell Co., Ltd., PAT-Cell) and assembled. The battery case was then sealed and kept at 25°C for 12 hours to allow the non-aqueous electrolyte to fully permeate the laminate, thereby obtaining a small non-aqueous secondary battery.

[0191] (3) Evaluation of small non-aqueous secondary batteries First, the small non-aqueous secondary batteries obtained as described above underwent initial charge-discharge processing and initial charge-discharge capacity measurement according to the procedure in (3-1) below. Next, each small non-aqueous secondary battery was evaluated according to the procedure in (3-2) below. Charge and discharge were performed using the ACD-M01A charge-discharge device (product name) manufactured by Asuka Electronics Co., Ltd. and the IN804 programmable constant temperature bath (product name) manufactured by Yamato Scientific Co., Ltd. Here, 1C refers to the current value at which a fully charged battery is expected to complete discharge in one hour when discharged at a constant current. Specifically, in the evaluations (3-1) to (3-2) below, 1C refers to the current value at which a fully charged battery of 4.2V is expected to complete discharge in one hour when discharged at a constant current down to 3.0V.

[0192] The small non-aqueous secondary battery assembled according to the procedure in (2-3) above is a 3.7mAh class cell, with a fully charged battery voltage of 4.2V and a current value equivalent to 1C of 3.7mA. Hereafter, unless otherwise specified, the notation of current values ​​and voltages will be omitted for convenience.

[0193] (3-1) Initial charge / discharge process A small non-aqueous secondary battery was charged at an ambient temperature of 25°C with a constant current of 0.0925mA (equivalent to 0.025C) until it reached 3.1V. Then, charging continued at a constant voltage of 3.1V until the current decreased to 0.025mA. After a 3-hour rest period, the battery was charged again with a constant current of 0.185mA (equivalent to 0.05C) until it reached 4.2V. Then, charging continued at a constant voltage of 4.2V until the current decreased to 0.025C. The charging capacity at this point (the sum of the charging capacity up to 3.1V and the charging capacity up to 4.2V) was defined as the initial charging capacity (X). Subsequently, the battery was discharged to 3.0V with a constant current of 0.555mA (equivalent to 0.15C). The discharge capacity at this point was defined as the initial discharge capacity (Y). The initial efficiency was calculated based on the following formula. Initial efficiency = (Initial discharge capacity (Y) / Initial charge capacity (X)) × 100 [%] Next, charging was performed at a constant current of 0.74mA (equivalent to 0.2C) until the voltage reached 4.2V, and then at a constant voltage of 4.2V until the current decreased to 0.025C. After that, the battery was discharged to 3V at a current of 0.74mA (equivalent to 0.2C). Then, one cycle of charging and discharging was performed as described above.

[0194] (3-2) 50°C Cycle Test For the small non-aqueous secondary battery that underwent the initial charge-discharge treatment using the method described in (3-1) above, the ambient temperature was set to 50°C, and the battery was charged with a constant current of 1.85mA, equivalent to 0.5C, until it reached 4.2V. Then, charging was continued at a constant voltage of 4.2V until the current decreased to 0.025C. After that, the battery was discharged to a voltage of 3.0V with a constant current of 1.85mA, equivalent to 0.5C. This process, which involves one charge and one discharge, was defined as one cycle, and 95 charge-discharge cycles were performed. The discharge capacity at this time was defined as the discharge capacity at the 95th cycle (hereinafter sometimes denoted as (T)). The cycle capacity retention rate was calculated based on the following formula. 50°C cycle capacity retention rate = (Discharge capacity at the 95th cycle in the 50°C cycle test (T) / Initial discharge capacity in the initial charge / discharge treatment (Y)) × 100 [%]

[0195] Here, I will discuss the interpretation of each test.

[0196] The initial efficiency indicates the ratio of the initial discharge capacity to the initial charge capacity, and is generally lower than the charge / discharge efficiency of subsequent charges. This is because Li ions are utilized during the initial charge to form the negative electrode SEI, which reduces the amount of Li ions that can be discharged. Ideally, the initial charge / discharge efficiency should be 84% or higher, and 85% or higher is desirable.

[0197] The 50°C cycle capacity retention rate is an indicator of battery degradation due to repeated use. A higher value indicates less capacity loss due to repeated use, suggesting that the battery is suitable for long-term use. Therefore, it is desirable that the 50°C cycle capacity retention rate be 70% or higher.

[0198] The results of the initial charge / discharge treatment and the 50°C cycle test are shown in Table 2.

[0199] [Table 2]

[0200] As shown in Table 2, in Example 1, both the initial efficiency and the 50°C cycle capacity retention rate were within a favorable range. On the other hand, Comparative Examples 1 and 2 showed a 50°C cycle capacity retention rate of less than 70%.

[0201] Comparing Example 1 with Comparative Examples 1 and 2, it was found that using a lithium salt containing a cyclic anion as the lithium salt, and adjusting the content of the dinitrile compound and sulfamate ions to a preferred range, improved the 50°C cycle capacity retention rate. This is thought to be because the dinitrile compound suppressed the corrosion reaction of the positive electrode Al current collector by sulfamate ions and the elution of transition metals from the positive electrode active material, while forming an excellent negative electrode SEI. [Explanation of Symbols]

[0202] 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. An electrolyte for a non-aqueous secondary battery, comprising a non-aqueous solvent, a lithium salt, and an additive, The lithium salt is given by the following formula (1): 【Chemistry 1】 {In the formula, R ｆ Each of these independently represents a fluorine atom or a perfluoro group with four or fewer carbon atoms, and n is an integer from 1 to 5. It contains a lithium salt containing a cyclic anion represented by, The aforementioned non-aqueous electrolyte for secondary batteries contains sulfamate ions, The aforementioned additive is given by the following formula (2): 【Chemistry 2】 {In the formula, R represents a linear or branched divalent aliphatic alkyl group having 1 to 12 carbon atoms, which may contain an oxygen atom.} It contains a dinitrile compound represented by, The sulfamate ion content is 150 ppm by mass or less relative to the total amount of the electrolyte for the non-aqueous secondary battery, and An electrolyte for a non-aqueous secondary battery, wherein the content of the dinitrile compound is 5 or more in molar ratio to the content of the sulfamate ion.

2. The electrolyte for a non-aqueous secondary battery according to claim 1, wherein the content of the sulfamate ion is 5,000 ppm by mass or less relative to the content of the cyclic anion-containing lithium salt.

3. The non-aqueous secondary battery electrolyte according to claim 1 or 2, wherein the content of the sulfamate ions is 0.01 ppm by mass or more relative to the total amount of the non-aqueous secondary battery electrolyte.

4. The electrolyte for a non-aqueous secondary battery according to claim 1 or 2, wherein the content of the dinitrile compound is 0.1% by mass or more and 25% by mass or less with respect to the total amount of the electrolyte for the non-aqueous secondary battery.

5. The electrolyte for a non-aqueous secondary battery according to claim 1 or 2, comprising acetonitrile in an amount of 3% by volume or more and 97% by volume or less based on the total amount of the non-aqueous solvent.

6. The lithium salt containing a cyclic anion represented by formula (1) is given by the following formula (1-2): 【Transformation 3】 The electrolyte for a non-aqueous secondary battery according to claim 1 or 2, wherein the lithium salt containing a cyclic anion is represented by [formula].

7. A non-aqueous secondary battery comprising the electrolyte for a non-aqueous secondary battery according to claim 1 or 2.

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