JP7749143B2 - Electrolyte and battery using same - Google Patents

Description

The present invention relates to an electrolyte solution and a battery using the same. More specifically, it relates to an electrolyte solution constituting a battery such as a lithium-ion battery and a battery using the same.

In recent years, growing concern about environmental issues has led to a shift in energy resources away from fossil fuels such as oil and coal. This has led to an increase in the importance of batteries, and demand for them is expected to grow. Secondary batteries, which can be repeatedly charged and discharged, are increasingly being used in a variety of fields, including automobiles and aircraft, as well as in electronic devices such as mobile phones and laptops. Research and development is underway on various secondary batteries and the materials used in them. Lithium-ion batteries, which offer large capacity and are lightweight, are particularly anticipated as the type of secondary battery most likely to see increased use in the future, and are the subject of the most active research and development.

For example, with regard to electrodes, a technology has been disclosed that uses a positive electrode active material comprising particles containing a positive electrode material capable of absorbing and releasing an electrode reactant, and a coating of a specific metal salt formed on at least a portion of the particles, with the aim of improving battery capacity and charge/discharge cycle characteristics and suppressing gas generation (see Patent Document 1). Furthermore, with regard to electrolytes, a technology has been disclosed that improves battery cycle characteristics by using an electrolyte containing a sulfonylimide compound with a specific structure, such as lithium bisfluorosulfonylimide (LiFSI), and another fluorine-containing alkali metal salt (see Patent Document 2). Another technology has been disclosed that improves ionic conductivity in low-temperature environments by using an electrolyte containing an electrolyte and a sulfonylimide compound with a specific structure, such as lithium bisfluorosulfonylimide (LiFSI), in a specific ratio, in an electrolyte solution containing a carbonate-based solvent (see Patent Document 3). Furthermore, a nonaqueous electrolyte solution has been disclosed that contains an electrolyte and a compound containing a sulfonate anion with a specific structure, and various lithium salts have been disclosed as electrolytes (see Patent Document 4).

JP 2009-193780 A JP 2013-84591 A JP 2013-101900 A Japanese Patent Application Laid-Open No. 2022-159173

As mentioned above, technologies have been disclosed that use imide-based alkali metal salts with specific structures, such as LiFSI, to improve battery performance, but electrolytes containing LiFSI have the problem of high self-discharge when stored at high temperatures.

The present invention was made in consideration of the above-mentioned current situation, and aims to provide an electrolyte solution that contains a sulfonylimide compound such as LiFSI and that suppresses self-discharge at high temperatures.

The inventors investigated methods for suppressing self-discharge at high temperatures in electrolyte solutions containing sulfonylimide compounds such as LiFSI, and discovered that adding a sulfonic acid or sulfinic acid compound having a hydroxy group of a specific structure to an electrolyte solution containing a sulfonylimide compound can suppress self-discharge at high temperatures, leading to the present invention.

In other words, the present invention is as follows.

[1] The following formula (1):
MN(R ¹ SO ₂ )(R ² SO ₂ ) (1)
(in formula (1), M represents an alkali metal atom; ^{R 1} and R ² are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms), with a sulfonylimide compound represented by the following formula (2);

(in formula (2), ^R3 represents a hydrocarbon group which may have a substituent; M' represents a metal atom; a is an integer of 1 or more; b is a number of 1 or 2; c, d, e, and n are the same or different and each is an integer of 1 or more, and c×d=n×e).

[2] The electrolyte solution according to [1], wherein R ³ in the formula (2) is a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent.

[3] An electrolyte solution described in [1] or [2], characterized in that the compound represented by formula (2) is contained in an amount of 0.0005 to 1.5 mass% relative to 100 mass% of the electrolyte solution.

[4] An electrolyte solution described in any of [1] to [3], characterized in that it contains a sulfonylimide compound represented by formula (1) in a ratio of 0.01 to 5.0 mol/L.

[5] The electrolyte solution according to any one of [1] to [4], further comprising at least one of M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ , and M ¹ FSO ₃ (M ¹ represents an alkali metal atom).

[6] The following formula (1):
MN(R ¹ SO ₂ )(R ² SO ₂ ) (1)
(in formula (1), M represents an alkali metal atom; ^{R 1} and R ² are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms), with a sulfonylimide compound represented by the following formula (3);

(in formula (3), ^R4 represents a hydrocarbon group which may have a substituent, or a divalent group formed by linking multiple hydrocarbon groups which may have a substituent via an oxygen atom or a sulfur atom; ^R5 represents a hydrogen atom or a hydrocarbon group which may have a substituent; M″ ^m+ represents a metal cation or an onium cation, and represents an onium cation when ^R4 is a hydrocarbon group which may have a substituent; f is an integer of 1 or more, and g is a number of 1 or 2; h, i, j, and m are the same or different and each is an integer of 1 or more, and h×i=m×j).

[7] The electrolyte solution according to [6], wherein R ⁴ in the formula (3) is a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent.

[8] An electrolyte solution described in [6] or [7], characterized in that the compound represented by formula (3) is contained in an amount of 0.0005 to 1.5 mass% relative to 100 mass% of the electrolyte solution.

[9] An electrolyte solution described in any of [6] to [8], characterized in that it contains a sulfonylimide compound represented by formula (1) in a ratio of 0.01 to 5.0 mol/L.

[10] The electrolyte solution according to any one of [6] to [9], further comprising at least one of M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ , and M ¹ FSO ₃ (M ¹ represents an alkali metal atom).

[11] A battery characterized by being constructed using the electrolyte solution described in any one of [1] to [10].

[12] The battery comprises a lithium secondary battery represented by the following formula (5);
_{LiNixCoyMnzO2 ( 5 )}
(wherein x, y, and z are numbers satisfying x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ z ≦ 1.) The battery according to [11], characterized in that it is configured with a positive electrode containing a composite metal oxide represented by the formula (5) and/or LiFePO ₄ .

[13] A battery described in [11] or [12], characterized in that the battery is constructed with a negative electrode active material containing Si.

The electrolyte solution of the present invention contains a sulfonylimide compound such as LiFSI, yet has suppressed self-discharge at high temperatures, making it suitable for use as an electrolyte solution for batteries intended for use at high temperatures.

The present invention will be described in detail below.
It should be noted that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

1. Electrolyte The electrolyte of the present invention is characterized by containing a sulfonylimide compound represented by the above formula (1) and a compound represented by the above formula (2) or a compound represented by the above formula (3). By adding the compound represented by the above formula (2) or the above formula (3), decomposition of the sulfonylimide compound can be suppressed, thereby improving the stability of the electrolyte. This makes it possible to suppress self-discharge even when a battery using this electrolyte is stored at high temperatures. In addition, it is possible to suppress an increase in resistance during high-temperature cycling.
The electrolytic solution of the present invention may contain, in addition to the sulfonylimide compound represented by the formula (1), at least one of the compound represented by the formula (2) or the compound represented by the formula (3), but may also contain both the compound represented by the formula (2) and the compound represented by the formula (3).

The concentration of the sulfonylimide compound represented by formula (1) in the electrolytic solution of the present invention is preferably 0.01 to 5.0 mol/L. By including the sulfonylimide compound at such a concentration, the electrolytic solution has better ionic conductivity. The concentration of the sulfonylimide compound is more preferably 0.05 to 2.5 mol/L, and even more preferably 0.1 to 1.5 mol/L.
The concentration of the sulfonylimide compound represented by the formula (1) is preferably 0.01 to 5.0 mol/kg, more preferably 0.05 to 2.5 mol/kg, and even more preferably 0.1 to 1.5 mol/kg.

The content of the compound represented by formula (2) or the compound represented by formula (3) in the electrolyte solution of the present invention is preferably 0.0005 to 1.5% by mass relative to 100% by mass of the entire electrolyte solution. By including the compound represented by formula (2) or the compound represented by formula (3) in such a proportion, the ionic conductivity of the electrolyte solution can be improved while more sufficiently suppressing self-discharge of the electrolyte solution. The content of the compound represented by formula (2) or the compound represented by formula (3) is more preferably 0.001 to 1% by mass, even more preferably 0.01 to 0.5% by mass, and particularly preferably 0.05 to 0.3% by mass relative to 100% by mass of the entire electrolyte solution.
When the electrolytic solution of the present invention contains both the compound represented by the formula (2) and the compound represented by the formula (3), the total content ratio of these is preferably as described above.

The electrolyte solution of the present invention contains the above-mentioned sulfonylimide compound as an alkali metal salt, but may also contain an alkali metal salt other than the above-mentioned sulfonylimide compound.
The concentration of the alkali metal salt other than the sulfonylimide compound in the electrolytic solution of the present invention is not particularly limited, but is preferably 0 to 2.5 mol/L, more preferably 0 to 1.5 mol/L, and even more preferably 0.1 to 1.5 mol/L.
The concentration of the alkali metal salt other than the sulfonylimide compound is preferably 0 to 2.5 mol/kg, more preferably 0 to 1.5 mol/kg, and even more preferably 0.1 to 1.5 mol/kg.

When the electrolytic solution of the present invention contains an alkali metal salt other than the sulfonylimide compound represented by formula (1), the total concentration of the sulfonylimide compound represented by formula (1) and the alkali metal salt is preferably 0.5 to 5 mol/L, more preferably 0.8 to 2.5 mol/L, and even more preferably 1 to 1.5 mol/L.
When the electrolytic solution of the present invention contains an alkali metal salt other than the sulfonylimide compound represented by the above formula (1), the total concentration of the sulfonylimide compound represented by the above formula (1) and the alkali metal salt is preferably 0.5 to 5 mol/kg, more preferably 0.8 to 2.5 mol/kg, and even more preferably 1 to 1.5 mol/kg.

When the electrolytic solution of the present invention contains an alkali metal salt other than the sulfonylimide compound represented by formula (1) above, the proportion of the sulfonylimide compound represented by formula (1) above relative to 100 mol % of the electrolyte in the electrolytic solution (the total of the sulfonylimide compound and other alkali metal salts) is preferably 1 to 99 mol %. This allows the effects of the present invention, which are achieved by including the compound represented by formula (2) or the compound represented by formula (3) above, to be more fully exhibited. It is more preferably 5 to 90 mol %, even more preferably 10 to 85 mol %, and particularly preferably 10 to 70 mol %.

The proportion of solvent contained in the electrolytic solution of the present invention is preferably 50 to 1,500 parts by mass per 100 parts by mass of the electrolyte (the above-mentioned sulfonylimide compound and other alkali metal salts). It is more preferably 150 to 800 parts by mass, and even more preferably 300 to 700 parts by mass.

The electrolytic solution of the present invention may contain water at a rate of 1% by mass or less, but the water content is preferably 200 ppm by mass or less. This allows the effects of the present invention to be more fully exhibited. The water content is more preferably 100 ppm by mass or less, and even more preferably 50 ppm by mass or less. The electrolytic solution may not substantially contain water (it may be about 0 ppm by mass).
The water content can be measured using a Karl Fischer water content analyzer.

The electrolyte solution of the present invention may contain other components other than the sulfonylimide compound represented by the above formula (1), other alkali metal salts, the compound represented by the above formula (2), or the compound represented by the above formula (3), and the solvent.
The content of the other components is not particularly limited, but is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of the electrolyte solution.

The essential components and optional components contained in the electrolyte solution of the present invention will be further described below.
<Sulfonylimide Compound>
The electrolyte solution of the present invention is a compound represented by the following formula (1):
MN(R ¹ SO ₂ )(R ² SO ₂ ) (1)
(in formula (1), M represents an alkali metal atom; ^{R 1} and R ² are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms).

In the above formula (1), examples of alkali metals represented by M include lithium, sodium, potassium, rubidium, etc. Preferred are lithium, sodium, and potassium, and more preferred is lithium.

Examples of the alkyl group having 1 to 6 carbon atoms for R ¹ and R ² include straight-chain alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl (amyl), and n-hexyl; branched-chain alkyl groups such as i-propyl, sec-butyl, i-butyl, t-butyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, i-amyl, neopentyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, t-amyl, 1,3-dimethylbutyl, 3,3-dimethylbutyl, and 2-ethylbutyl; and cyclic alkyl groups such as cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclobutylmethyl, cyclopentyl, and cyclohexyl. Of these, straight-chain alkyl groups are preferred.

The alkyl groups in R ¹ and R ² preferably have 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 or 2 carbon atoms.

The fluoroalkyl group having 1 to 6 carbon atoms in R ¹ and R ² may be an alkyl group having 1 to 6 carbon atoms in which at least some of the hydrogen atoms bonded to the carbon atoms have been substituted with fluorine atoms. Specific examples of the alkyl group are as described above.
Examples of the fluoroalkyl group having 1 to 6 carbon atoms include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a pentafluoroethyl group, a fluoropropyl group, a fluoropentyl group, and a fluorohexyl group.

The fluoroalkyl groups in R ¹ and R ² preferably have 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 or 2 carbon atoms.

Examples of the sulfonylimide compound include lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide, potassium bis(fluorosulfonyl)imide, potassium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, and sodium (fluorosulfonyl)(trifluoromethylsulfonyl)imide.
Among these, lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, and lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide are preferred, and lithium bis(fluorosulfonyl)imide (LiFSI) is more preferred.

<Compound represented by the above formula (2)>
The following formula (2):

(in formula (2), ^R3 represents a hydrocarbon group which may have a substituent; M' represents a metal atom; a represents an integer of 1 or more; b represents a number of 1 or 2; c, d, e, and n are the same or different and each represents an integer of 1 or more, and c×d=n×e) is one embodiment of the electrolyte solution of the present invention.

In the formula (2), ^R3 represents a divalent hydrocarbon group which may have a substituent. The hydrocarbon group may have a linear or branched chain structure, a cyclic structure, or both a chain structure and a cyclic structure.
The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.
The number of carbon atoms in the hydrocarbon group is not particularly limited, but in the case of a chain structure, it is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 or 2.
When the hydrocarbon group has a cyclic structure or both a chain structure and a cyclic structure, the hydrocarbon group preferably has 3 to 12 carbon atoms, more preferably 3 to 10 carbon atoms, and even more preferably 5 to 8 carbon atoms.

The substituent that ^R3 in the above formula (2) may have is not particularly limited, and examples thereof include a carboxyl group, a sulfonic acid group, a phosphonic acid group, phosphoric acid, and esters and salts thereof; an amino group, a hydroxyl group, a ketone group, a sulfonic acid group, a thiol group, and a halogen group.

In the above formula (2), M' represents a metal atom, and M'n ⁺ represents a metal cation. The type of metal element for M' is not particularly limited, but is preferably either a Group 1 element of the periodic table, such as lithium, sodium, potassium, or rubidium; or a Group 2 element of the periodic table, such as beryllium, magnesium, calcium, or strontium. A Group 1 element of the periodic table is more preferred, and lithium is even more preferred.

In the above formula (2), a may be any integer of 1 or more, but is preferably an integer of 1 to 12. It is more preferably an integer of 1 to 6, and even more preferably an integer of 1 to 4.
In the above formula (2), c, d, e, and n are the same or different and each represents an integer of 1 or more, but c is preferably an integer of 1 to 4, and more preferably 1 or 2.
d is preferably an integer of 1 to 3, more preferably 1 or 2.

<Compound represented by the above formula (3)>
The following formula (3):

(In formula (3), ^R4 represents a hydrocarbon group which may have a substituent, or a divalent group formed by linking multiple hydrocarbon groups which may have a substituent via an oxygen atom or a sulfur atom. ^R5 represents a hydrogen atom or a hydrocarbon group which may have a substituent. M″ ^m+ represents a metal cation or an onium cation, and represents an onium cation when ^R4 is a hydrocarbon group which may have a substituent. f represents an integer of 1 or more, and g is a number of 1 or 2. h, i, j, and m are the same or different and each represents an integer of 1 or more, and h×i=m×j.) is one embodiment of the electrolyte solution of the present invention.

In the above formula (3), ^R4 represents a divalent hydrocarbon group which may have a substituent, or a divalent group formed by linking multiple hydrocarbon groups which may have a substituent via an oxygen atom or a sulfur atom. When ^R4 is a divalent hydrocarbon group which may have a substituent, examples of ^R4 include the same as those for ^R3 in the above formula (2).
When ^R4 is a divalent group formed by linking a plurality of hydrocarbon groups which may have a substituent with an oxygen atom or a sulfur atom, the divalent group is represented by the following formula (4):

(In formula (4), R ⁶ and R ⁷ are the same or different and represent a hydrocarbon group which may have a substituent; X is the same or different and represents an oxygen atom or a sulfur atom; and r is a number from 1 to 12.)
In the above formula (4), r may be a number from 1 to 12, but is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 2.
In the above formula (4), X may be either an oxygen atom or a sulfur atom, and when there are multiple Xs, they may contain both oxygen atoms and sulfur atoms.

In the above formula (4), the hydrocarbon group in R ⁶ and R ⁷ may have a linear or branched chain structure, a cyclic structure, or both a chain structure and a cyclic structure.
The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.
The number of carbon atoms in the hydrocarbon group is not particularly limited, but in the case of a chain structure, it is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 or 2.
When the hydrocarbon group has a cyclic structure or both a chain structure and a cyclic structure, the hydrocarbon group preferably has 3 to 12 carbon atoms, more preferably 3 to 10 carbon atoms, and even more preferably 5 to 8 carbon atoms.

^R5 in the above formula (3) represents a hydrogen atom or a hydrocarbon group which may have a substituent. The hydrocarbon group may have a linear or branched chain structure, a cyclic structure, or both a chain structure and a cyclic structure.
The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.
The number of carbon atoms in the hydrocarbon group is not particularly limited, but in the case of a chain structure, it is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 or 2.
When the hydrocarbon group has a cyclic structure or both a chain structure and a cyclic structure, the hydrocarbon group preferably has 3 to 12 carbon atoms, more preferably 3 to 10 carbon atoms, and even more preferably 5 to 8 carbon atoms.

In the above formulas (3) and (4), the substituents that the hydrocarbon groups in ^R5 , ^R6 , and ^R7 may have are not particularly limited, and examples thereof include the same substituents that the hydrocarbon group in ^R3 in the above formula (2) may have.

In the above formula (3), specific examples and preferred examples when M''m ⁺ is a metal cation are the same as those of M'n ⁺ in the above formula (2).
In the above formula (3), when M″ ^m+ is an onium cation, examples of the onium cation include ammonium cation, phosphonium cation, oxonium cation, sulfonium cation, fluoronium cation, and chloronium cation. Any of these may be used, but ammonium cation and phosphonium cation are preferred.

In the above formula (3), the preferred ranges of f, h, i, j, and m are the same as those of a, c, d, e, and n in the above formula (2).

The electrolytic solution of the present invention may contain other components as long as it contains the sulfonylimide compound represented by the above formula (1) and the compound represented by the above formula (2) or the compound represented by the above formula (3).
Examples of other components include electrolytes other than the sulfonylimide compound represented by the above formula (1), and additives other than the compound represented by the above formula (2) and the compound represented by the above formula (3).

<Other alkali metal salts>
When the electrolytic solution of the present invention contains an alkali metal salt other than the sulfonylimide compound represented by the above formula (1), the other alkali metal salt is not particularly limited as long as it is an alkali metal salt other than the above sulfonylimide compound, and examples thereof include alkali metal salts of fluorophosphates such as LiPF ₆ and LiPO ₂ F ₂ ; alkali metal salts of fluorosulfonic acids such as LiFSO ₃ ; alkali metal salts of trifluoromethanesulfonic acids such as LiCF ₃ SO ₃ ; imide-based alkali metal salts such as LiN(CF ₃ SO ₂ ) ₂ ; alkali metal salts of perfluoroalkanesulfonylmethides such as LiC(CF ₃ SO ₂ ) ₃ ; fluorophosphates such as LiPF _α (C _β F _{2 β + 1} ) _6-α (0≦α≦6, 1≦β≦2); alkali metal perchlorates such as LiClO ₄ ; and LiBF _γ (C _δ F _{2 δ + 1} ) _4-γ. Examples of suitable borates include fluoroborates (0≦γ≦4, 1≦δ≦2), alkali metal salts of oxalatoborates such as LiBOB, cyanoborates such as lithium tetracyanoborate, and alkali metal salts such as LiAsF ₆ , LiI, and LiSbF ₆ , and one or more of these can be used.

The other alkali metal salts are preferably M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ , and M ¹ FSO ₃ (M ¹ represents an alkali metal atom), and one preferred embodiment of the electrolyte solution of the present invention includes at least one of M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ , and M ¹ FSO ₃ (M ¹ represents an alkali metal atom).
Specific examples and preferred forms of the alkali metal atom of M ¹ in M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ and M ¹ FSO ₃ are the same as those of the alkali metal atom in the sulfonylimide compound.

<Solvent>
The solvent contained in the electrolytic solution of the present invention is non-aqueous and is not particularly limited as long as it can dissolve the electrolyte (sulfonylimide compound and other alkali metal salts), the compound represented by the formula (2), the compound represented by the formula (3), and other components described later. Examples of suitable solvents include: chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane; Examples of suitable non-aqueous solvents include ethers, lactones such as γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone, chain carboxylic acid esters such as ethyl acetate, methyl propionate, and methyl butyrate, fluorinated cyclic carbonates such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, tetrafluoroethylene carbonate, and 4-fluoro-5-methylethylene carbonate, fluorinated chain carbonates such as trifluorodimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethylmethyl carbonate, and chain nitriles such as acetonitrile, propionitrile, succinonitrile, and adiponitrile. These non-aqueous solvents may be used alone or in combination of two or more. Among these, preferred are chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and 4,5-difluoroethylene carbonate; and chain carboxylic acid esters such as ethyl acetate, methyl propionate, and methyl butyrate.

The content of the solvent is not particularly limited and may be any as long as it does not significantly impair the effects of the present invention, but when cyclic carbonates are used among the solvents, the content is preferably 5% by volume or more, more preferably 10% by volume or more, based on the total amount of non-aqueous solvents in the non-aqueous electrolyte solution. The content of the cyclic carbonates is preferably 50% by volume or less, more preferably 40% by volume or less, even more preferably 30% by volume or less, and particularly preferably 25% by volume or less, based on the total amount of non-aqueous solvents in the non-aqueous electrolyte solution.
The range of the content of the cyclic carbonates relative to the total amount of the nonaqueous solvent in the nonaqueous electrolyte solution is preferably 5 to 50% by volume, more preferably 5 to 40% by volume, even more preferably 10 to 30% by volume, and particularly preferably 10 to 25% by volume.

Furthermore, when chain carboxylic acid esters and chain carbonates are used among the above solvents, their contents are not particularly limited, but are preferably 50% by volume or more, more preferably 60% by volume or more, even more preferably 70% by volume or more, and particularly preferably 75% by volume or more, based on the total amount of nonaqueous solvents in the nonaqueous electrolyte solution. Furthermore, the contents of chain carboxylic acid esters and chain carbonates are preferably 95% by volume or less, more preferably 90% by volume or less, based on the total amount of nonaqueous solvents in the nonaqueous electrolyte solution.
The range of the content of the chain carboxylic acid esters and chain carbonates relative to the total amount of the nonaqueous solvent in the nonaqueous electrolyte solution is preferably 50 to 95% by volume, more preferably 60 to 95% by volume, even more preferably 70 to 90% by volume, and still more preferably 75 to 90% by volume.

Furthermore, when cyclic carbonates are used in combination with chain carboxylic acid esters and/or chain carbonates as a solvent, the volume ratio of the cyclic carbonates to the chain carboxylic acid esters and/or chain carbonates ((cyclic carbonates)/(chain carboxylic acid esters and/or chain carbonates)) is preferably 5/95 to 50/50. It is more preferably 5/95 to 40/60, even more preferably 10/90 to 30/70, and particularly preferably 10/90 to 25/75.

<Other ingredients>
In the electrolytic solution of the present invention, other components besides the sulfonylimide compound represented by the above formula (1), other alkali metal salts, the compound represented by the above formula (2), the compound represented by the above formula (3), and the solvent include, for example, carbonate compounds such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 2-vinyl ethylene carbonate, phenyl ethylene carbonate, and erythritol carbonate; sulfonates such as 1,3-propane sultone, 1,4-butane sultone, 1,5-pentane sultone, 1,4-hexane sultone, 4,6-heptane sultone, methyl methanesulfonate, methyl benzenesulfonate, and methyl trifluoromethanesulfonate; sulfonic acid esters; sulfone compounds such as sulfolane, 3-methylsulfolane, ethylmethylsulfone, diphenylsulfone, and bis(4-fluorophenyl)sulfone; carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, and phenylsuccinic anhydride; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; sulfamic acid (amidosulfuric acid, H _3NSO3 ); sulfamates (alkali metal salts such as lithium salts, sodium salts, and potassium salts; alkaline earth metal salts such as calcium salts, strontium salts, and barium salts; _other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts, and nickel salts; ammonium salts; guanidine salts, etc.); phosphates such as monofluorophosphates and difluorophosphates; fluorosulfonic acid compounds such as lithium fluorosulfonate ( _LiFSO3 ), sodium fluorosulfonate ( _NaFSO3 ), potassium fluorosulfonate ( _KFSO3 ), and magnesium fluorosulfonate (Mg( _FSO3 ) ₂ ); hydrocarbon compounds such as heptane, octane, cycloheptane, cyclohexylbenzene, and amylbenzene; and the like, and one or more of these can be used.

2. Battery The present invention also provides a battery comprising the electrolyte solution of the present invention.
The electrolyte solution of the present invention is an electrolyte solution that contains the sulfonylimide compound represented by the above formula (1) and that is effectively suppressed in self-discharge when stored at high temperatures, and a battery constructed containing this electrolyte solution is also a battery that is effectively suppressed in self-discharge when stored at high temperatures.

The shape of the battery of the present invention is not particularly limited, and any of the conventionally known battery shapes can be used, such as cylindrical, prismatic, laminated, coin, large, etc. Furthermore, when used as a high-voltage power source (several tens of volts to several hundreds of volts) for installation in electric vehicles, hybrid electric vehicles, etc., it can also be made into a battery module consisting of individual batteries connected in series.

The battery of the present invention is preferably an alkali metal battery, and more preferably a secondary battery, and in one preferred embodiment of the present invention, the battery is a lithium ion secondary battery.
The positive electrode, negative electrode, and separator that constitute the battery of the present invention will be described below.

The positive electrode constituting the above-mentioned battery is not particularly limited, but is typically a positive electrode active material composition containing a positive electrode active material, a conductive additive, a binder, a dispersion solvent, etc., supported on a positive electrode current collector and typically formed into a sheet.

Examples of methods for manufacturing positive electrodes include applying a positive electrode active material composition to a positive electrode current collector using a doctor blade method or immersing the positive electrode current collector in the positive electrode active material composition and then drying it; kneading and molding the positive electrode active material composition, drying the resulting sheet, and bonding it to a positive electrode current collector via a conductive adhesive, followed by pressing and drying; and applying or casting a positive electrode active material composition to which a liquid lubricant has been added onto a positive electrode current collector, forming it into the desired shape, removing the liquid lubricant, and then stretching it uniaxially or multiaxially.

The material for the positive electrode current collector is not particularly limited, and conductive metals such as aluminum, aluminum alloys, SUS (stainless steel), and titanium can be used. Among these, aluminum is preferred because it is easy to process into a thin film and is inexpensive.

The positive electrode active material may be any material capable of absorbing and releasing ions, and any known positive electrode active material may be used. Specifically, the materials include composite metal oxides such as ternary oxides represented by M ² CoO ₂ , M ² NiO ₂ , M ² MnO ₂ , M ² Ni _x Co _y Mn _z O ₂ and M ² Ni _x Co _y Al _z O ₂ (x, y, z are numbers that satisfy x + y + z = 1, 0≦x≦1, 0≦y≦1, 0≦z≦1), nickel manganese oxides represented by M ² _p Ni _q Mn _(2-q) O ₄ (0.9≦p≦1.1, 0<q<1), compounds with an olivine structure such as M ³ APO ₄ (A=Fe, Mn, Ni, Co), and solid solution materials incorporating multiple transition metals (electrochemically inactive layered M ² ₂ MnO ₃ and electrochemically active layered M Examples of the positive electrode active material include a solid solution of ^CoO with ^a transition metal such as Co ^or Ni ( ^M2 represents an alkali metal ion). These positive electrode active materials may be used alone or in combination.
Among these, the positive electrode active material is a compound represented by the following formula (5):
_{LiNixCoyMnzO2 ( 5 )}
(In formula (5), x, y, and z are numbers that satisfy x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1.) and/or _LiFePO4 are preferred. A battery configured with a positive electrode containing such a positive electrode active material is one of the preferred embodiments of the present invention.

Conductive additives include acetylene black, carbon black, graphite, metal powder materials, single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, etc., and one or more of these can be used.

Examples of binders include fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide-based resins such as polyamideimide; polyolefin-based resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; cellulose-based resins such as carboxymethyl cellulose; and the like. One or more of these can be used. These binders may be dissolved in a solvent or dispersed in a solvent when used.

The amount of conductive additive and binder can be adjusted appropriately taking into account the intended use of the battery (emphasis on output, emphasis on energy, etc.), ionic conductivity, etc.

When manufacturing a positive electrode, solvents used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, water, etc. These solvents may be used in combination. The amount of solvent used is not particularly limited and may be determined appropriately depending on the manufacturing method and materials used.

The negative electrode constituting the above-mentioned battery is not particularly limited, but is typically a negative electrode active material composition containing a negative electrode active material, a dispersion solvent, a binder, and optionally a conductive additive, etc., supported on a negative electrode current collector and typically formed into a sheet.

Conductive metals such as copper, iron, nickel, silver, and stainless steel (SUS) can be used as materials for the negative electrode current collector. Copper is preferred because it can be easily processed into a thin film.

The negative electrode active material may be any conventionally known negative electrode active material used in batteries, as long as it is capable of absorbing and releasing ions. Specifically, examples of the negative electrode active material include alkali metals, metal alloys such as alkali metal-aluminum alloys, graphite materials such as artificial graphite and natural graphite, mesophase sintered bodies made from coal and petroleum pitch, carbon materials such as non-graphitizable carbon, Si-based negative electrode materials such as Si, Si alloys, and SiO, and Sn-based negative electrode materials such as Sn alloys.
Among these, a Si-based negative electrode material containing Si is preferred as the negative electrode active material. A battery comprising a negative electrode containing such a negative electrode active material is one of the preferred embodiments of the present invention.

The negative electrode can be manufactured using the same method as the positive electrode. Furthermore, the conductive additives, binders, and solvents for dispersing materials used in manufacturing the negative electrode are the same as those used in manufacturing the positive electrode.

The separator is disposed to separate the positive electrode from the negative electrode.
The separator constituting the battery is not particularly limited, and any separator that is commonly used can be used.
Examples of the separator include a porous sheet made of a polymer capable of absorbing and retaining a non-aqueous electrolyte solution (e.g., a polyolefin-based microporous separator or a cellulose-based separator), a nonwoven fabric separator, a porous metal body, etc. Among these, a polyolefin-based microporous separator is preferred because it is chemically stable against organic solvents.

Examples of materials for the porous sheet include polyethylene, polypropylene, and laminates having a three-layer structure of polypropylene/polyethylene/polypropylene.

Examples of materials for the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., and the above-mentioned materials can be used alone or in combination depending on the mechanical strength required of the nonaqueous electrolyte layer.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "% by mass."

Synthesis Example 1: Synthesis of lithium 2-(2-hydroxyethoxy)ethanesulfonate 3.2 g of lithium sulfite n-hydrate, 10 mL of ion-exchanged water, and 3.3 g of ethylene glycol mono-2-chloroethyl ether were added to a 100 mL flask and heated under reflux for 22 hours. After volatile matter was distilled off under reduced pressure, 10 mL of ethanol was added, and the insoluble matter was removed by filtration. After the ethanol was distilled off from the filtrate under reduced pressure, the precipitated solid was washed with a large amount of acetone and dried to obtain 1.9 g of the target compound.

Synthesis Example 2: Synthesis of tetrabutylphosphonium hydroxyethanesulfonate 5.0 g of 40% tetrabutylphosphonium hydroxide was added dropwise to 1.3 g of a 70% aqueous solution of hydroxyethanesulfonic acid at 0° C., followed by stirring for 1 hour. Thereafter, water was distilled off using an evaporator, and the resulting mixture was dehydrated by vacuum drying at 70° C., yielding 2.78 g of the target product.

Synthesis Example 3: Synthesis of tetraethylphosphonium hydroxyethanesulfonate 10.8 g of 8% tetraethylphosphonium hydroxide was added dropwise to 0.88 g of a 70% aqueous solution of hydroxyethanesulfonic acid at 0° C., followed by stirring for 1 hour. Thereafter, water was distilled off using an evaporator, and the resulting mixture was dehydrated by vacuum drying at 70° C., yielding 1.28 g of the target product.

Synthesis Example 4: Synthesis of tetramethylammonium hydroxyethanesulfonate 3.7 g of 25% tetramethylammonium hydroxide was added dropwise to 1.8 g of a 70% aqueous solution of hydroxyethanesulfonic acid at 0° C., followed by stirring for 1 hour. Thereafter, water was distilled off using an evaporator, and the resulting mixture was dehydrated by vacuum drying at 60° C., yielding 1.98 g of the target product.

Synthesis Example 5: Synthesis of lithium 2-methoxyethanesulfonate

8.05 g (85.1 mmol) of 2-chloroethyl methyl ether, 11.82 g (75 mmol at 60%) of lithium sulfite n-hydrate, and 20 g of ion-exchanged water were added and heated under reflux for 20 hours, after which the water was distilled off under reduced pressure. After drying overnight under vacuum at 60°C, the mixture was dissolved in methanol, and the insoluble matter was removed by filtration. The methanol was removed under reduced pressure, and acetone was added to the resulting viscous substance. The acetone-soluble matter was extracted, and the acetone was evaporated to dryness to obtain the target compound.

Synthesis Example 6: Synthesis of sodium 2-methoxyethanesulfonate The synthesis of lithium 2-methoxyethanesulfonate was carried out in the same manner as in Synthesis Example 5, except that 10.02 g (79.5 mmol) of sodium sulfite was used instead of lithium sulfite n-hydrate.

Synthesis Example 7: Synthesis of tetrabutylphosphonium 2-methoxyethanesulfonate An aqueous solution of sodium 2-methoxyethanesulfonate (1.0 g) was mixed with 2 ml of hydrochloric acid and stirred for 2 hours. The mixture was diluted with isopropyl alcohol, and insoluble matter was filtered off. The filtrate was concentrated under reduced pressure to obtain 2-methoxyethanesulfonic acid. This 2-methoxyethanesulfonic acid was diluted with water, and a 40% aqueous solution of tetrabutylphosphonium hydroxide was added dropwise at 0°C until the pH reached 7, followed by stirring for 1 hour. Water was removed using an evaporator, and the mixture was dehydrated by vacuum drying at 60°C to obtain the target product.

Synthesis Example 8: Synthesis of tetramethylammonium 2-methoxyethanesulfonate The synthesis of tetrabutylphosphonium 2-methoxyethanesulfonate was carried out in the same manner as in Synthesis Example 7, except that 8% tetramethylammonium hydroxide was used instead of the 40% aqueous tetrabutylphosphonium hydroxide solution.

Examples 1-1 to 1-15, Comparative Example 1-1
An electrolyte solution was prepared by dissolving LiFSI (manufactured by Nippon Shokubai Co., Ltd.) in dimethyl carbonate (DMC) to a concentration of 2.9 mol/L (3.56 mol/Kg). 0.1 wt % of each of the compounds listed in Table 1 was added to the electrolyte solution.
The electrolyte solutions immediately after preparation (initial stage), after one month of storage at 40° C., and after three months of storage at 40° C. were analyzed by anion chromatography, and F ⁻ and SO ₄ ⁻ ions were calibrated. The results are shown in Table 1.

Examples 1-16 to 1-21
An electrolyte solution was prepared by dissolving LiFSI (manufactured by Nippon Shokubai Co., Ltd.) in dimethyl carbonate (DMC) to a concentration of 2.9 mol/L (3.56 mol/Kg). 0.5 wt % of each of the compounds listed in Table 1 was added to the electrolyte solution.
The electrolyte solutions immediately after preparation (initial stage), after one month of storage at 40° C., and after three months of storage at 40° C. were analyzed by anion chromatography, and F ⁻ and SO ₄ ⁻ ions were calibrated. The results are shown in Table 1.

Examples 2-1 to 2-15, Comparative Example 2-1
Commercially available _LiPF6 and LiFSI (manufactured by Nippon Shokubai Co., Ltd.) were dissolved in a commercially available mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC/EMC = 3/7 (vol/vol)) to a concentration of 0.6 mol/L (0.59 mol/Kg), and 0.1 wt % of each of the compounds listed in Table 2 was added to the resulting solution to prepare an electrolyte solution.
The electrolyte solutions immediately after preparation (initial stage), after one month of storage at 40° C., and after three months of storage at 40° C. were analyzed by anion chromatography, and F ⁻ and SO ₄ ⁻ ions were calibrated. The results are shown in Table 2.

Examples 2-16 to 2-21
Commercially available _LiPF6 and LiFSI (manufactured by Nippon Shokubai Co., Ltd.) were dissolved in a commercially available mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC/EMC = 3/7 (vol/vol)) to a concentration of 0.6 mol/L (0.59 mol/Kg), and 0.5 wt % of each of the compounds listed in Table 2 was added to the solution to prepare an electrolyte solution.
The electrolyte solutions immediately after preparation (initial stage), after one month of storage at 40° C., and after three months of storage at 40° C. were analyzed by anion chromatography, and F ⁻ and SO ₄ ⁻ ions were calibrated. The results are shown in Table 2.

Examples 3-1 to 3-50, Comparative Example 3-1
(1) Preparation of laminated battery A ternary positive electrode (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , manufactured by Umicore), acetylene black (Denka Black), graphite (SP270), and polyvinylidene fluoride (PVdF, #1120) were weighed in a mass ratio of 100:3:3:3 and dispersed in NMP to prepare a slurry. The prepared slurry was coated on one side of aluminum foil, dried, and roll-pressed to prepare a positive electrode.
An aqueous slurry having a composition (mass ratio) of graphite (SMG/SFG15=85/15):carbon fiber (VGCF):styrene butadiene rubber (SBR):carboxymethyl cellulose (CMC)=100:2:1.5:1.5 was prepared, and the slurry was coated on one side of a copper foil, dried, and roll-pressed to prepare a negative electrode.
The resulting positive and negative electrodes were cut, polarity leads were ultrasonically welded, and the electrodes were placed opposite each other with a 20 μm polyethylene (PE) separator, and the three sides were sealed with a laminate exterior.
700 μL of the electrolyte solution of the example or comparative example was added to one of the unsealed sides.
The electrolyte solution used was prepared by dissolving LiFSI and _LiPF6 in a mixed solvent of EC/EMC = 3/7 (vol/vol) so that each was 0.6 mol/L (0.59 mol/Kg), and adding the compounds shown in Tables 3 and 4 in the proportions shown in Tables 3 and 4.
After the electrolyte injection, the battery was precharged at 0.2 C (6 mA) for 2 hours in an unsealed state. It was then vacuum-sealed and left at room temperature for 3 days. After 3 days, it was charged at 0.5 C (15 mA) for 5 hours to 4.2 V, then charged and discharged at 0.2 C (6 mA) until it reached 2.75 V. One piece of the laminate was then opened and vacuum-sealed again to release the gas.
After degassing, the battery was charged and discharged under the following conditions as a cell conditioning step.
[Conditioning conditions]
1st cycle: Charge: 3mA, 4.2V, constant current/constant voltage charge, 0.3mA cutoff ⇒ Discharge: 6mA, discharge, 2.75V cutoff 2nd cycle: Charge: 6mA, 4.2V, constant current/constant voltage charge, 0.6mA cutoff ⇒ Discharge: 6mA, discharge, 2.75V cutoff 3rd cycle: Charge: 6mA, 4.2V, constant current/constant voltage charge, 0.6mA cutoff ⇒ Discharge: 30mA, discharge, 2.75V cutoff (2) Characteristic Evaluation Using the completed batteries obtained in (1) above, the DCR increase rate was calculated and the OCV after high-temperature storage was measured by the following method. The results are shown in Tables 3 and 4.
<DCR increase rate>
The completed battery was charged at a constant current of 30 mA, 4.2 V, and a 0.6 mA cutoff current until fully charged. The DCR was measured at 25°C from the fully charged state. For the DCR measurement, the battery was waited 30 minutes after full charge and then discharged at 6 mA (0.2 C) for 10 seconds. After another 30-minute wait, the battery was discharged at 30 mA (1 C) for 10 seconds. After another 30-minute wait, the battery was discharged at 90 mA (3 C) for 10 seconds. An IV line was created from the relationship between the difference in voltage immediately before and 10 seconds after discharge at each discharge current and the current, and the slope of the line was calculated as the DCR.
After the DCR measurement, the battery was subjected to a 45° C. cycle test for 700 cycles, and the DCR was measured at 25° C. in the same manner as in the initial state.
The cycle conditions were: charge: 4.2 V, 30 mA (1 C), 0.6 mA (0.05 C), termination, 10 minutes rest ⇒ discharge: 30 mA (1 C), 2.75 V, termination, 10 minutes rest.
The DCR increase rate was calculated as 100 x (DCR after the cycle test)/(DCR before the cycle test) (%).
<OCV after high temperature storage>
After conditioning, the cell was charged at room temperature at a constant current and constant voltage of 1 C (30 mA) with a termination of 0.02 C (0.6 mA) at 4.2 V to a fully charged state, and then stored at 65° C. for 31 days. The open circuit voltage (OCV) of the cell was measured before and after storage.

Examples 3-51 to 3-75
Finished batteries were fabricated in the same manner as in Examples 3-1 to 3-50, except that the compounds added were changed as shown in Table 5. The DCR increase rate was calculated and the OCV after high-temperature storage was measured in the same manner as in Examples 3-1 to 3-50. Furthermore, the low-temperature discharge retention rate was calculated by the following method. The calculation of the low-temperature discharge retention rate was also performed for Comparative Example 3-1. The results are shown in Table 5.
<Low temperature discharge maintenance rate>
The battery was charged at 25°C at a constant current of 6 mA and a constant voltage of 4.2 V with a termination of 0.6 mA. After storing the battery at -25°C for 2 hours, the discharge capacity was determined by discharging at a constant current of 30 mA (1C) at -25°C with a termination of 2.75 V.
Low-temperature discharge capacity retention rate = 100 × (1 C discharge capacity at -25°C) / (1 C discharge capacity at 25°C = discharge capacity at the third conditioning cycle)
was calculated.

Examples 4-1 to 4-25, Comparative Example 4-1
The DCR increase rate was calculated and the OCV after high-temperature storage was measured in the same manner as in Examples 3-1 to 3-50, except that the compounds to be added were changed as shown in Table 6. The results are shown in Table 6.

Examples 4-26 to 4-30
The calculation of the DCR increase rate, the OCV measurement after high-temperature storage, and the calculation of the low-temperature discharge capacity retention rate were performed in the same manner as in Examples 3-51 to 3-75, except that the compound to be added was changed as shown in Table 7. The calculation of the low-temperature discharge capacity retention rate was also performed for Comparative Example 4-1. The results are shown in Table 7.

Examples 5-1 to 5-36, Comparative Examples 5-1 to 5-7
The DCR increase rate was calculated and the OCV after high-temperature storage was measured in the same manner as in Examples 3-1 to 3-50, except that the concentrations of LiFSI and _LiPF6 were changed as shown in Tables 8 and 9 and the compounds to be added were changed as shown in Tables 8 and 9. The results are shown in Tables 8 and 9.

Examples 6-1 to 6-36, Comparative Examples 6-1 to 6-7
(1) Preparation of electrode (preparation of positive electrode)
A ternary positive electrode active material _{, LiNi0.8Co0.1Mn0.1O2} (manufactured by Beijing Dangsheng Co. _, Ltd.), acetylene black (AB, manufactured by Denka Co., Ltd., product name: Denka Black ₍ registered trademark)), graphite (manufactured by Nippon Graphite Industries Co., Ltd., product number: SP270), and polyvinylidene fluoride (PVdF, manufactured by Kureha Corporation, product number: KF1120) were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry (positive electrode active material: AB: graphite: PVdF = 93:3:3:3 (mass ratio of solids)). Next, the obtained positive electrode mixture slurry was applied to one side of an aluminum foil (positive electrode current collector, manufactured by Nippon Foil Co., Ltd., thickness 15 μm) using an applicator so that the coating weight after drying would be 19.4 mg/ ^cm² , and the resultant was dried on a hot plate at 110°C for 10 minutes. The resultant was further dried in a vacuum drying furnace at 110°C for 12 hours. Thereafter, the resultant was pressure-molded using a roll press to a density of 3.1 g/ ^cm³ , thereby obtaining a sheet-like positive electrode.
(Preparation of negative electrode)
A silicon oxide (SiO)/graphite composite material (manufactured by BTR, product number: BSO-600) as a negative electrode active material, a conductive additive (manufactured by Showa Denko K.K., product number: VGCF-H (registered trademark) and (manufactured by Imerys, product number: Super-P (registered trademark)), styrene-butadiene rubber (SBR, binder), and carboxymethyl cellulose (CMC, binder) were dispersed in ultrapure water to prepare a negative electrode mixture slurry (negative electrode active material: VGCF: Super-P: SBR: CMC = 90: 2: 3: 3: 2 (solid content mass ratio)). Subsequently, the obtained negative electrode mixture slurry was applied to a copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil & Powder Co., Ltd., thickness 15 μm) so that the coating weight after drying was 6.8 mg/cm The mixture was applied to one side using an applicator so that the density became ² , and then dried on a hot plate at 80° C. for 10 minutes. The mixture was further dried in a vacuum drying oven at 100° C. for 12 hours. Thereafter, the mixture was pressure-molded using a roll press until the density became 1.3 g/cm ³ , thereby obtaining a sheet-like negative electrode.
(2) Characteristic Evaluation LiFSI and _LiPF6 were dissolved in a mixed solvent of EC/fluoroethylene carbonate (FEC)/EMC = 2/1/7 (vol/vol) to the concentrations shown in Tables 10 and 11, and the compounds of formula (2) shown in Tables 10 and 11 were added in the amounts shown in Tables 10 and 11. Battery evaluation was performed under the same conditions as in Examples 3-1 to 3-50 using this electrolyte solution and the positive and negative electrodes prepared in (1) above. The results are shown in Tables 10 and 11.

Examples 7-1 to 7-24, Comparative Examples 7-1 to 7-7
(1) Fabrication of Laminated Battery The positive electrode active material was changed to commercially available LiFePO4, _and acetylene black (HS-100) and PVdF (Kureha #L7208) were weighed in a composition (mass) ratio of 100:9:6 and dispersed in NMP to prepare a slurry. The prepared slurry was coated on one side of aluminum foil (coating weight 20.20 mg/ ^cm2 ), dried, and roll-pressed to prepare a positive electrode.
An aqueous slurry with a composition of graphite (SMG/SFG15=85/15):VGCF:SBR:CMC=100:2:1.5:1.5 was prepared, and applied to a copper foil at a coating weight of 8.8 mg/ ^cm2. The coating was then dried and roll-pressed to prepare a negative electrode.
Using the prepared positive and negative electrodes, 25 mAh laminate batteries were produced using the same materials and methods as in Examples 3-1 to 3-50. The electrolyte solution used was prepared by dissolving LiFSI and _LiPF6 in a 3/7 (vol/vol) EC/EMC mixed solvent to give the ratios shown in Tables 12 and 13, and adding the compounds of formula (2) shown in Tables 12 and 13 in the amounts shown in Tables 12 and 13.
After the injection, the battery was charged at a constant current of 5 mA for 3 hours, and then one piece was opened and vacuum-sealed again to degas the cell. After degassing, the cell was stored at 25°C for 48 hours and then charged and discharged under the following conditioning conditions to complete a battery for evaluation.
[Conditioning conditions]
1st cycle: Charge: 2.5 mA, 3.6 V, constant current/constant voltage, charge, 0.25 mA cutoff, → Discharge: 5 mA, discharge, 2.0 V cutoff. 2nd cycle: Charge: 2.5 mA, 3.6 V, constant current/constant voltage, charge, 0.5 mA cutoff, → Discharge: 5 mA, discharge, 2.0 V cutoff. 3rd cycle: Charge: 2.5 mA, 3.6 V, constant current/constant voltage, charge, 0.5 mA cutoff, → Discharge: 25 mA, discharge, 2.0 V cutoff. (2) Characteristic Evaluation: Using the evaluation battery obtained in (1) above, the DCR increase rate was calculated and the self-discharge capacity rate after high-temperature storage was measured by the following method. The results are shown in Tables 12 and 13.
<DCR increase rate>
After conditioning, the cell was charged at a constant current of 25 mA, a constant voltage of 3.6 V, and a cutoff of 0.5 mA until it reached a fully charged state. The DCR was measured at 25° C. from the fully charged state. The DCR measurement was performed as follows.
After full charge, the battery was left to stand for 30 minutes, then discharged at 5 mA (0.2 C) for 10 seconds. After another 30-minute wait, the battery was discharged at 25 mA (1 C) for 10 seconds. After another 30-minute wait, the battery was discharged at 75 mA (3 C) for 10 seconds. An IV line was created from the relationship between the difference in voltage immediately before discharge began and 10 seconds after discharge at each discharge current, and the current, and the slope was calculated as the DCR.
Thereafter, a 45°C cycle test was carried out under the following cycle conditions: constant current constant voltage charge: 25 mA, 3.6 V, 0.5 mA termination ⇒ constant current discharge: 25 mA discharge, 2.0 V termination, for 700 cycles, and the DCR after the cycles was determined in the same manner as in the initial stage.
The DCR increase rate was calculated as 100 x (DCR after the cycle test)/(DCR before the cycle test) (%).
<Self-discharge capacity rate measurement after high-temperature storage>
The self-discharge amount was calculated as a self-discharge capacity rate after storage at 65° C. for 31 days using the following formula.
100 × {(discharge capacity before storage) − (discharge capacity after storage)} / (discharge capacity before storage)
The completed battery was charged and discharged under the following conditions (25° C.), and the discharge capacity before storage was confirmed.
Charge: 3.6V 25mA constant current constant voltage charge 0.5mA termination ⇒ Constant current discharge: 2.5mA 2.0V termination For storage at high temperatures, after checking the discharge capacity, the cells were charged at a constant current and constant voltage of 1C (25mA) at room temperature and 0.02C (0.5mA) termination at 3.6V, and then fully charged and stored at 65°C for 31 days.
The discharge capacity after storage was determined by discharging the battery after 31 days of storage at a constant current of 2.5 mA at 25° C. with a cut-off voltage of 2.0 V.

Examples 8-1 to 8-10, Comparative Example 8-1
The DCR increase rate was calculated and the OCV after high-temperature storage was measured in the same manner as in Examples 3-1 to 3-50, except that the ratio of EC and EMC in the mixed solvent in the electrolyte was changed as shown in Table 14 and the compounds to be added were changed as shown in Table 14. The results are shown in Table 14.

Claims (13)

The following formula (1):
MN(R ¹ SO ₂ )(R ² SO ₂ ) (1)
(in formula (1), M represents an alkali metal atom; ^{R 1} and R ² are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms), with a sulfonylimide compound represented by the following formula (2);
(in formula (2), ^R3 represents a hydrocarbon group which may have a substituent; M' represents a metal atom; a is an integer of 1 or more; b is a number of 1 or 2; c, d, e, and n are the same or different and each is an integer of 1 or more, and c×d=n×e). 2. The electrolyte solution according to claim 1, wherein ^R3 in the formula (2) is a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent. An electrolyte solution as described in claim 1, characterized in that the compound represented by formula (2) is contained in an amount of 0.0005 to 1.5 mass% relative to 100 mass% of the electrolyte solution. The electrolyte solution described in claim 1, characterized in that it contains the sulfonylimide compound represented by formula (1) at a ratio of 0.01 to 5.0 mol/L. 2. The electrolyte solution according to claim 1, further comprising at least one of M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ , and M ¹ FSO ₃ (M ¹ represents an alkali metal atom). The following formula (1):
MN(R ¹ SO ₂ )(R ² SO ₂ ) (1)
(in formula (1), M represents an alkali metal atom; ^{R 1} and R ² are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms), with a sulfonylimide compound represented by the following formula (3);
(in formula (3), ^R4 represents a hydrocarbon group which may have a substituent, or a divalent group formed by linking multiple hydrocarbon groups which may have a substituent via an oxygen atom or a sulfur atom; ^R5 represents a hydrogen atom or a hydrocarbon group which may have a substituent; M″ ^m+ represents a metal cation or an onium cation, and represents an onium cation when ^R4 is a hydrocarbon group which may have a substituent; f is an integer of 1 or more, and g is a number of 1 or 2; h, i, j, and m are the same or different and each is an integer of 1 or more, and h×i=m×j). 7. The electrolyte solution according to claim 6, wherein R ⁴ in the formula (3) is a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent. An electrolyte solution as described in claim 6, characterized in that it contains the compound represented by formula (3) in a proportion of 0.0005 to 1.5 mass% relative to 100 mass% of the electrolyte solution. The electrolyte solution described in claim 6, characterized in that it contains the sulfonylimide compound represented by formula (1) at a ratio of 0.01 to 5.0 mol/L. 7. The electrolyte solution according to claim 6, further comprising at least one of M ¹ PF ₆ , M ¹ BF ₄ , M ¹ PO ₂ F ₂ and M ¹ FSO ₃ (M ¹ represents an alkali metal atom). A battery characterized by comprising an electrolyte solution according to any one of claims 1 to 10. The battery has the following formula (5):
_{LiNixCoyMnzO2 ( 5 )}
(wherein x, y, and z are numbers satisfying x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ z ≦ 1), and/or a positive electrode containing _LiFePO4 . 13. The battery according to claim 12, wherein the battery is configured to include a negative electrode active material containing Si.