WO2015159824A1

WO2015159824A1 - Nonaqueous electrolyte solution for secondary battery, and lithium-ion secondary battery

Info

Publication number: WO2015159824A1
Application number: PCT/JP2015/061262
Authority: WO
Inventors: 祐小野崎; 室谷　英介; 豊和遠田
Original assignee: 旭硝子株式会社
Priority date: 2014-04-18
Filing date: 2015-04-10
Publication date: 2015-10-22
Also published as: JP2017107639A

Abstract

　Provided are a nonaqueous electrolyte solution for secondary batteries, which can be used to obtain a lithium-ion secondary battery having excellent battery characteristics (cycle characteristics, rate characteristics, and initial charge and discharge efficiency), and a lithium-ion secondary battery using the nonaqueous electrolyte solution for secondary batteries.　The nonaqueous electrolyte solution for secondary batteries contains: a lithium salt including a compound represented by formula (1) (wherein M is B or P, R¹ is a C_1-10 alkylene group, X is a halogen atom, n is 0-4, m is 0 or 1, and p is 1 or 2); a specific fluorine-containing solvent (A); a cyclic carboxylic acid ester compound (B); and a saturated cyclic carbonate compound (C) that does not have any fluorine atoms. The ratio of the mass of the saturated cyclic carbonate compound (C) that does not have any fluorine atoms relative to the total mass of the nonaqueous electrolyte solution is 0.01-20mass%.

Description

Nonaqueous electrolyte for secondary battery and lithium ion secondary battery

The present invention relates to a non-aqueous electrolyte for a secondary battery and a lithium ion secondary battery.

The following are proposed as non-aqueous electrolytes capable of obtaining a lithium ion secondary battery with good battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency).
A lithium salt and a liquid composition, wherein the liquid composition is at least one fluorine-containing solvent selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound, and a fluorine-containing chain carbonate compound; A nonaqueous electrolytic solution containing a cyclic carboxylic acid ester compound and an unsaturated cyclic carbonate and / or a fluorinated cyclic carbonate (Patent Document 1).

However, even with the non-aqueous electrolyte, depending on the battery and charge / discharge conditions, the battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency) of the lithium ion secondary battery are still insufficient. A non-aqueous electrolyte that can further improve the battery characteristics is desired.

International Publication No. 2013/146359

An object of the present invention is to provide a non-aqueous electrolyte for a secondary battery capable of obtaining a lithium ion secondary battery excellent in battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency), and battery characteristics (cycle characteristics, rate characteristics). It is to provide a lithium ion secondary battery having excellent initial charge / discharge efficiency.

The present invention has the following configuration.
[1] A nonaqueous electrolytic solution containing an electrolyte and a liquid composition, wherein at least one of the electrolytes is a lithium salt, and the lithium salt is at least one compound represented by the following formula (1): A fluorine-containing solvent (A) containing a seed, wherein the liquid composition comprises at least one selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound; The carboxylic acid ester compound (B) and the saturated cyclic carbonate compound (C) having no fluorine atom, and having a mass of the saturated cyclic carbonate compound (C) having no fluorine atom with respect to the total mass of the nonaqueous electrolytic solution. A non-aqueous electrolyte for a secondary battery having a ratio of 0.01 to 20% by mass.

M is a boron atom or phosphorus atom, R ¹ is an optionally substituted alkylene group having 1 to 10 carbon atoms, X is a halogen atom, and n is 0 to It is an integer of 4, m is 0 or 1, and p is 1 or 2.
[2] The nonaqueous electrolytic solution for secondary battery according to [1], wherein the saturated cyclic carbonate compound (C) having no fluorine atom is at least one compound represented by the following formula (7).

However, R ¹⁴ to R ¹⁷ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.
[3] The non-aqueous electrolyte for secondary batteries according to [1] or [2], wherein the ratio of the mass of the fluorinated solvent (A) to the total mass of the non-aqueous electrolyte is 30 to 80% by mass.
[4] The lithium salt is a compound represented by the following formula (1-1), a compound represented by the following formula (1-2), a compound represented by the following formula (1-3), 1-4) and a non-secondary battery for a secondary battery according to any one of [1] to [3], comprising at least one selected from the group consisting of a compound represented by 1-4) and a compound represented by the following formula (1-5): Water electrolyte.

[5] The ratio of the mass of the compound represented by the formula (1) to the total mass of the nonaqueous electrolytic solution is 0.01 to 10% by mass, and any one of [1] to [4] Nonaqueous electrolyte for secondary batteries.
[6] The fluorine-containing ether compound is at least one selected from the group consisting of a compound represented by the following formula (2) and a compound represented by the following formula (3): [1] to [5] A non-aqueous electrolyte for a secondary battery.

R ² and R ³ are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, or a fluorinated group having 3 to 10 carbon atoms. A cycloalkyl group, an alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom, or a fluorinated alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom, and one or both of R ² and R ³ Is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a fluorinated alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom, and Y is a carbon number An alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkylene group having 2 to 5 carbon atoms having an etheric oxygen atom, or 2 carbon atoms having an etheric oxygen atom -5 fluorinated alkylene groups.
[7] The nonaqueous electrolytic solution for a secondary battery according to any one of [1] to [6], wherein the cyclic carboxylic acid ester compound (B) is at least one compound represented by the following formula (6): .

R ⁸ to R ¹³ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or an etheric oxygen atom having 2 carbon atoms. And q is an integer of 0 to 3.
[8] The fluorine-containing ether compound is CF ₃ CH ₂ OCF ₂ CHF ₂ , CF ₃ CH ₂ OCF ₂ CHFCF ₃ , CHF ₂ CF ₂ CH ₂ OCF ₂ CHF ₂ , CH ₃ CH ₂ CH ₂ OCF ₂ CHF ₂ , it is at least one selected from the group consisting of CH ₃ CH _{_₂} OCF ₂ CHF ₂ and _{_{_{_{CHF 2 CF 2 CH 2 OCF 2}}}} CHFCF 3, [1] ~ any of the non-aqueous electrolyte solution for a secondary battery [7] .
[9] The nonaqueous electrolytic solution for a secondary battery according to any one of [1] to [8], wherein the fluorine-containing solvent (A) is the fluorine-containing ether compound.
[10] The two of any one of [1] to [9], wherein the cyclic carboxylic acid ester compound (B) is at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and ε-caprolactone. Nonaqueous electrolyte for secondary batteries.
[11] The non-aqueous electrolyte for a secondary battery according to any one of [1] to [10], wherein the lithium salt contains LiPF ₆ .
[12] The non-aqueous electrolyte for secondary batteries according to any one of [1] to [11], wherein the ratio of the mass of the lithium salt to the total mass of the non-aqueous electrolyte is 5 to 25% by mass.
[13] For the secondary battery according to any one of [1] to [12], wherein the ratio of the mass of the cyclic carboxylic acid ester compound (B) to the total mass of the non-aqueous electrolyte is 4 to 60% by mass. Non-aqueous electrolyte.
[14] A negative electrode using as an active material at least one selected from the group consisting of a positive electrode having a material capable of inserting and extracting lithium ions as an active material, and a lithium metal, a lithium alloy, and a carbon material capable of inserting and extracting lithium ions. And a non-aqueous electrolyte for secondary batteries according to any one of [1] to [13].

According to the nonaqueous electrolytic solution for a secondary battery of the present invention, a lithium ion secondary battery excellent in battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency) can be obtained.
The lithium ion secondary battery of the present invention is excellent in battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency).

In the present specification, a compound represented by the formula (1) is referred to as a compound (1). The same applies to compounds represented by other formulas.
The following definitions of terms apply throughout this specification and the claims.
The “non-aqueous electrolyte” is an electrolyte that does not substantially contain water, and even if water is included, the water content of the secondary battery using the non-aqueous electrolyte does not deteriorate in performance. It means an electrolyte solution in a range of amounts. The amount of water that can be contained in the non-aqueous electrolyte is preferably 500 ppm by mass or less, more preferably 100 ppm by mass or less, and particularly preferably 50 ppm by mass or less with respect to the total mass of the non-aqueous electrolyte. The lower limit of the moisture content is 0 mass ppm.
The “liquid composition” includes a fluorine-containing solvent (A), a cyclic carboxylic acid ester compound (B), and a saturated cyclic carbonate compound (C) having no fluorine atom.
Other compounds (other solvents, additives, etc.) other than the electrolyte, the fluorine-containing solvent (A), the cyclic carboxylic acid ester compound (B), and the saturated cyclic carbonate compound (C) not having a fluorine atom are other components. Is distinguished from electrolytes and liquid compositions.
That is, the nonaqueous electrolytic solution in the present invention contains an electrolyte, a fluorine-containing solvent (A), a cyclic carboxylic acid ester compound (B), and a saturated cyclic carbonate compound (C) having no fluorine atom as essential components.
The “fluorinated ether compound” means a chain or cyclic compound having an ether bond and having a fluorine atom.
The “fluorinated chain carboxylic acid ester compound” means a chain compound having an ester bond in a chain structure and not having a ring structure having an ester bond and having a fluorine atom.
“Fluorine-containing chain carbonate compound” is a chain structure having a carbonate bond represented by —O—C (═O) —O—, having no ring structure having a carbonate bond, and having a fluorine atom Means a chain-like compound having
The “fluorinated alkane compound” means a compound in which one or more hydrogen atoms of an alkane are substituted with fluorine atoms, and hydrogen atoms remain.
The “cyclic carboxylic acid ester compound” means a cyclic compound having an ester bond as a part of the ring skeleton.
“Saturated cyclic carbonate compound having no fluorine atom” means that a ring skeleton is composed of a carbon atom and an oxygen atom, and a carbonate bond represented by —O—C (═O) —O— is formed as a part of the ring skeleton. A cyclic compound having a carbon-carbon unsaturated bond and a fluorine atom in the molecule.
“Fluorinated” and “fluorinated” mean that some or all of the hydrogen atoms bonded to the carbon atom are replaced with fluorine atoms.
The “fluorinated alkyl group” means a group in which part or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms. Among the partially fluorinated groups are hydrogen atoms and fluorine atoms.
The “perfluoroalkyl group” means a group in which all hydrogen atoms of an alkyl group are substituted with fluorine atoms.
“Carbon-carbon unsaturated bond” means a carbon-carbon double bond or a carbon-carbon triple bond.

<Non-aqueous electrolyte for secondary battery>
The non-aqueous electrolyte for secondary batteries of the present invention (hereinafter also simply referred to as non-aqueous electrolyte) includes an electrolyte and a liquid composition, and includes other components as necessary.
The lower limit of the ionic conductivity at 25 ° C. of the nonaqueous electrolytic solution is preferably 0.30 S / m. If the ionic conductivity at 25 ° C. of the non-aqueous electrolyte is 0.30 S / m or more, the battery characteristics of the secondary battery are further improved.

[Electrolytes]
At least one of the electrolytes is a lithium salt.
The electrolyte may be a lithium salt alone or a combination of a lithium salt and an electrolyte other than the lithium salt. Examples of the electrolyte other than the lithium salt include sodium salt or potassium salt of monofluorophosphoric acid or difluorophosphoric acid, NaPF _{6 and the} like.

(Lithium salt)
The lithium salt dissociates in the non-aqueous electrolyte and supplies lithium ions.
The nonaqueous electrolytic solution contains the following compound (1) as an essential component as a lithium salt.

M is a boron atom or phosphorus atom, R ¹ is an optionally substituted alkylene group having 1 to 10 carbon atoms, X is a halogen atom, and n is 0 to It is an integer of 4, m is 0 or 1, and p is 1 or 2.

When M is a boron atom and p is 1, n is 2.
When M is a boron atom and p is 2, n is 0.
When M is a phosphorus atom and p is 1, n is 4.
When M is a phosphorus atom and p is 2, n is 2.
When p is 2, both m may be 0, both may be 1, one may be 0 and the other may be 1.
When p is 2 and two m's are both 1, the two R ¹ groups may be different from each other or the same group.

Examples of the substituent for R ¹ include a halogen atom, a chain or cyclic alkyl group, an aryl group, a sulfonyl group, a cyano group, a hydroxyl group, and an alkoxy group.
X is preferably a fluorine atom or a chlorine atom, particularly preferably a fluorine atom.
As the compound (1), one type may be used alone, or two or more types may be used in combination.

When the non-aqueous electrolyte contains the compound (1) as a lithium salt, the non-aqueous electrolyte is excellent in battery characteristics such as cycle characteristics and rate characteristics. This is considered as follows.
It is considered that the compound (1) decomposes on the negative electrode during charging of the secondary battery, and forms a lithium ion conductive film (SEI) having a small interface resistance on the negative electrode surface. Conventionally, vinylene carbonate etc. are known as a film formation agent which forms such SEI. Since the compound (1) can form a favorable SEI having a lower interface resistance than conventional film forming agents such as vinylene carbonate, it becomes a non-aqueous electrolyte excellent in battery characteristics such as cycle characteristics and rate characteristics. Conceivable.

The lithium salt is at least one selected from the group consisting of the following compounds (1-1) to (1-5) from the viewpoint of easily obtaining a non-aqueous electrolyte excellent in battery characteristics such as cycle characteristics and rate characteristics. It is preferable to contain.

The lithium salt may contain other lithium salts other than the compound (1). Other lithium salts include LiPF ₆ , Li ₂ PO ₃ F, LiPO ₂ F ₂ , the following compound (11) (where k is an integer of 1 to 5), FSO ₂ N (Li) SO ₂ F _{_{_{_{, CF 3 SO 2 N (Li}}}} ) SO 2 CF 3, CF 3 CF 2 SO 2 N (Li) SO 2 CF 2 CF 3, CF 3 CFHSO 2 N (Li) SO 2 CFHCF 3, LiClO 4, LiBF 4 , etc. Is mentioned.

As another lithium salt, LiPF ₆ is preferably contained. That is, as the lithium salt, a combination of the compound (1) and LiPF ₆ is particularly preferable. When LiPF ₆ is included as the lithium salt, the ionic conductivity is good and the battery characteristics are excellent.
Another lithium salt may be used individually by 1 type, and may be used in combination of 2 or more type.

[Liquid composition]
The liquid composition contains a fluorinated solvent (A), a cyclic carboxylic acid ester compound (B), and a saturated cyclic carbonate compound (C) having no fluorine atom.

(Fluorine-containing solvent (A))
The fluorine-containing solvent (A) is a fluorine-containing solvent containing at least one selected from the group consisting of fluorine-containing ether compounds, fluorine-containing chain carboxylic acid ester compounds and fluorine-containing chain carbonate compounds. The fluorine-containing solvent (A) is a solvent having a fluorine atom in the molecule and is excellent in flame retardancy. A fluorine-containing solvent (A) may be used individually by 1 type, and may be used in combination of 2 or more type. When the number of fluorine-containing solvents (A) is two or more, the ratio can be arbitrarily determined.

Fluorine-containing ether compound:
The fluorine-containing solvent (A) preferably contains a fluorine-containing ether compound from the viewpoint of the solubility of the lithium salt, the flame retardancy, and the ionic conductivity of the non-aqueous electrolyte. The fluorine-containing ether compound is at least one selected from the group consisting of the following compound (2) and the following compound (3) from the viewpoints of lithium salt solubility, flame retardancy, and ionic conductivity of the non-aqueous electrolyte. Species are preferred.
A fluorine-containing ether compound may be used individually by 1 type, and may be used in combination of 2 or more type. When the number of fluorine-containing ether compounds is two or more, the ratio can be arbitrarily determined.

However, in the formula (2), R ² and R ³ are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, carbon A fluorinated cycloalkyl group having 3 to 10 carbon atoms, an alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom, or a fluorinated alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom. Further, either one or both of R ² and R ³ is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a carbon number having 2 to 10 carbon atoms having an etheric oxygen atom. Of the fluorinated alkyl group.
In Formula (3), Y represents an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkylene group having 2 to 5 carbon atoms having an etheric oxygen atom, or etheric oxygen A fluorinated alkylene group having 2 to 5 carbon atoms and having an atom.

Examples of the alkyl group and the alkyl group having an etheric oxygen atom in the compound (2) include a linear structure, a branched structure, or a group having a cyclic structure (cycloalkylalkyl group and the like).
One or both of R ² and R ³ in the compound (2) is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a carbon number having an etheric oxygen atom. 2 to 10 fluorinated alkyl groups. When either one or both of R ² and R ³ are these groups, the solubility of the lithium salt in the non-aqueous electrolyte and the flame retardancy of the non-aqueous electrolyte are excellent. R ² and R ³ in the compound (2) may be the same or different.

As the compound (2), R ² and R ³ are all fluorinated alkyl groups having 1 to 10 carbon atoms from the viewpoint of lithium salt solubility, flame retardancy, and ionic conductivity of the non-aqueous electrolyte. Compound (2-A): Compound (2-A) wherein R ² is a fluorinated alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom, and R ³ is a fluorinated alkyl group having 1 to 10 carbon atoms B); or a compound (2-C) in which R ² is a fluorinated alkyl group having 1 to 10 carbon atoms and R ³ is an alkyl group having 1 to 10 carbon atoms. Compound (2-A) or compound (2-C) is more preferable, and compound (2-A) is particularly preferable.

The total number of carbon atoms in the compound (2) is preferably 4 to 10 and more preferably 4 to 8 from the viewpoint that the boiling point is too low when the amount is too small and the viscosity increases when the amount is too large.
The molecular weight of the compound (2) is preferably 150 to 800, more preferably 150 to 500, and particularly preferably 200 to 500 from the viewpoint that if the molecular weight is too small, the boiling point is too low, and if it is too large, the viscosity becomes high.
The number of etheric oxygen atoms in the compound (2) is preferably 1 to 4, more preferably 1 or 2, and even more preferably 1. The number of etheric oxygen atoms in the compound (2) affects flammability.
40 mass% or more is preferable, as for the fluorine content in a compound (2), 50 mass% or more is more preferable, and 60 mass% or more is further more preferable. When the fluorine content in the compound (2) is high, the flame retardancy is excellent. If the fluorine content in the compound (2) is too large, the affinity of the lithium salt is lowered and phase separation is likely to occur, so 80 mass% or less is preferable, 75 mass% or less is more preferable, and 70 mass% or less is even more. preferable. The fluorine content is the ratio of the total mass of fluorine atoms to the molecular weight.

As the compound (2), from the viewpoint of excellent solubility in the liquid composition of the lithium salt, both of R ² and R ^3, the compound partially fluorinated alkyl group of which a hydrogen atom is preferred, R ² and A compound in which either one or both of the terminals of R ³ is CHF ₂ is more preferable.

Specific examples of the compound (2-A) and the compound (2-B), and specific examples of the fluorinated ether compound other than the compound (2-A) and the compound (2-B) include International Publication No. 2009/133899. And the like.

As compound (2), CF ₃ CH ₂ OCF ₂ CHF ₂ (produced by Asahi Glass Co., Ltd., Asahi Clin AE-) has excellent lithium salt solubility, flame retardancy, low viscosity, and low boiling point. _{_{_{_{3000), CF 3 CH 2 OCF}}}} 2 CHFCF 3, CHF 2 CF 2 CH 2 OCF 2 CHF 2, CH 3 CH 2 CH 2 OCF 2 CHF 2, CH 3 CH 2 OCF 2 CHF 2 and _CHF 2 _CF 2 _CH 2 OCF Preferably, at least one selected from the group consisting of ₂ CHFCF ₃ is selected from the group consisting of CF ₃ CH ₂ OCF ₂ CHF ₂ , CHF ₂ CF ₂ CH ₂ OCF ₂ CHF ₂ and CHF ₂ CF ₂ CH ₂ OCF ₂ CHFCF ₃ At least one selected from the above is particularly preferred.

Y in the compound (3) may have a linear structure or a branched structure. Y is preferably an alkylene group having 1 to 5 carbon atoms, more preferably an alkylene group having 2 to 4 carbon atoms. The alkylene group preferably has a linear structure or a branched structure. When the alkylene group in Y has a branched structure, the side chain is preferably an alkyl group having 1 to 3 carbon atoms or an alkyl group having 1 to 3 carbon atoms having an etheric oxygen atom.

The compound (3) is selected from the group consisting of —CH ₂ —, —CH ₂ CH ₂ —, —CH (CH ₃ ) CH ₂ — and —CH ₂ CH ₂ CH ₂ — in the formula (3). And one or both of the compound in which Y is —CH ₂ CH ₂ — and the compound in which Y is —CH (CH ₃ ) CH ₂ — is more preferable, and Y is —CH _2. CH ₂ -, compound and Y is -CH _(CH 3) CH ₂ - is still more preferably one of a compound.
Specific examples of the compound (3) include a compound represented by the following formula.

As the fluorinated ether compound, compound (2) alone, compound (3) alone, or a mixture of compound (2) and compound (3) is preferred, and compound (2) alone is more preferred. A compound (2) may be used individually by 1 type, and may be used in combination of 2 or more type. A compound (3) may be used individually by 1 type, and may be used in combination of 2 or more type.

Fluorine-containing chain carboxylic acid ester compound:
The fluorine-containing chain carboxylic acid ester compound preferably contains the following compound (4), more preferably only the compound (4), from the viewpoints of viscosity, boiling point and the like. A fluorine-containing chain carboxylic acid ester compound may be used individually by 1 type, and may be used in combination of 2 or more type. When the number of fluorine-containing chain carboxylic acid ester compounds is two or more, the ratio can be arbitrarily determined. When the compound (4) is included, the compound (4) may be used alone or in combination of two or more.

Provided that R ⁴ and R ⁵ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms, and one or both of R ⁴ and R ⁵ are 1 to 3 fluorinated alkyl groups.

Examples of the alkyl group and the fluorinated alkyl group in the compound (4) include a linear structure and a branched structure, respectively.
One or both of R ⁴ and R ⁵ are preferably a fluorinated alkyl group having 1 to 3 carbon atoms. By making one or both of R ⁴ and R ⁵ into a fluorinated alkyl group having 1 to 3 carbon atoms, the compound (4) is excellent in oxidation resistance and flame retardancy. R ⁴ and R ⁵ in the compound (4) may be the same or different.

R ⁴ is preferably a methyl group, an ethyl group, a difluoromethyl group, a trifluoromethyl group, a tetrafluoroethyl group, or a pentafluoroethyl group from the viewpoint of viscosity, boiling point, or availability of the compound, and a difluoromethyl group, Or a trifluoromethyl group is more preferable.
R ⁵ is a methyl group, an ethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a 2,2-difluoroethyl group, or 2,2,2-in terms of viscosity, boiling point, or availability of the compound. A trifluoroethyl group is preferred, a methyl group, an ethyl group, or a 2,2,2-trifluoroethyl group is more preferred, and a methyl group or an ethyl group is more preferred.

The total number of carbon atoms in the compound (4) is preferably from 3 to 8, more preferably from 3 to 6, and even more preferably from 3 to 5 from the viewpoint that if the amount is too small, the boiling point is too low and if the amount is too large, the viscosity increases.
The molecular weight of the compound (4) is preferably from 100 to 300, more preferably from 100 to 250, and particularly preferably from 100 to 200 from the viewpoint that if the molecular weight is too small, the boiling point is too low, and if it is too large, the viscosity increases.
The fluorine content in the compound (4) is preferably 25% by mass or more and more preferably 30% by mass or more from the viewpoint of excellent flame retardancy. Moreover, since the affinity of lithium salt will fall and phase separation will become easy when there is too much, 55 mass% or less is preferable and 50 mass% or less is more preferable.

Specific examples of the compound (4) include acetic acid (2,2,2-trifluoroethyl), methyl difluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate and the like. From the viewpoint of availability and battery performance such as cycle characteristics, methyl difluoroacetate and ethyl trifluoroacetate are preferable.

Fluorine-containing chain carbonate compound:
The fluorine-containing chain carbonate compound preferably contains the following compound (5), more preferably only the compound (5), from the viewpoints of viscosity and boiling point. A fluorine-containing chain carbonate compound may be used individually by 1 type, and may be used in combination of 2 or more type. When the number of fluorine-containing chain carbonate compounds is two or more, the ratio can be arbitrarily determined. When the compound (5) is contained, the compound (5) may be used alone or in combination of two or more.

Provided that R ⁶ and R ⁷ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms, and one or both of R ⁶ and R ⁷ are 1 to 3 fluorinated alkyl groups.

Examples of the alkyl group and the fluorinated alkyl group in the compound (5) include a linear structure and a branched structure, respectively.
One or both of R ⁶ and R ⁷ is a fluorinated alkyl group having 1 to 3 carbon atoms. By making one or both of R ⁶ and R ⁷ a fluorinated alkyl group having 1 to 3 carbon atoms, the solubility of the lithium salt in the non-aqueous electrolyte and the flame retardancy are excellent. R ⁶ and R ⁷ in the compound (5) may be the same or different.

The compound (5) is preferably a compound in which both R ⁶ and R ⁷ are fluorinated alkyl groups having 1 to 3 carbon atoms from the viewpoint of viscosity, boiling point, or availability of the compound. R ⁶ and R ⁷ are preferably CF ₃ CH ₂ — or CHF ₂ CF ₂ CH ₂ —.

The total number of carbon atoms in the compound (5) is preferably 4 to 10 and more preferably 4 to 7 from the viewpoint that if the amount is too small, the boiling point is too low and if the amount is too large, the viscosity becomes high.
The molecular weight of the compound (5) is preferably from 180 to 400, more preferably from 200 to 350, particularly preferably from 210 to 300 from the viewpoint that if the molecular weight is too small, the boiling point is too low, and if it is too large, the viscosity increases.
From the point which is excellent in a flame retardance, 25 mass% or more is preferable and, as for the fluorine content in a compound (5), 30 mass% or more is more preferable. Moreover, since the affinity of lithium salt will fall and phase separation will become easy when there is too much, 60 mass% or less is preferable and 50 mass% or less is more preferable.

Specific examples of the compound (5) include bis (2,2,2-trifluoroethyl) carbonate and bis (2,2,3,3-tetrafluoropropyl) carbonate. Bis (2,2,2-trifluoroethyl) carbonate is preferred from the viewpoint of battery performance such as viscosity, availability, and output characteristics.

Other fluorine-containing solvents:
The fluorine-containing solvent (A) may contain a fluorine-containing alkane compound as a fluorine-containing solvent other than the fluorine-containing ether compound, the fluorine-containing chain carboxylic acid ester compound, and the fluorine-containing chain carbonate compound. When the fluorine-containing alkane compound is contained, the vapor pressure of the non-aqueous electrolyte is suppressed and the flame retardancy is further improved.

The fluorine-containing alkane compound is preferably a fluorine-containing alkane compound having 4 to 12 carbon atoms. If the fluorine-containing alkane compound has 4 or more carbon atoms, the vapor pressure of the non-aqueous electrolyte is lowered. If the fluorine-containing alkane compound has 12 or less carbon atoms, the solubility of the lithium salt is good.

The fluorine content in the fluorine-containing alkane compound is preferably 50 to 80% by mass. If the fluorine content in the fluorine-containing alkane compound is 50% by mass or more, the flame retardancy is excellent. If the fluorine content in the fluorine-containing alkane compound is 80% by mass or less, the solubility of the lithium salt is easily maintained.

As the fluorinated alkane compound, a compound having a linear structure is preferable, and nC ₄ F ₉ CH ₂ CH ₃ , nC ₆ F ₁₃ CH ₂ CH ₃ , nC ₆ F ₁₃ H, nC ₈ F ₁₇ H, and the like. A fluorine-containing alkane compound may be used individually by 1 type, and may be used in combination of 2 or more type.

(Cyclic carboxylic acid ester compound (B))
When the liquid composition contains the cyclic carboxylic acid ester compound, the lithium salt is uniformly dissolved in the fluorine-containing solvent (A). In addition, the inclusion of the cyclic carboxylic acid ester compound (B) makes it difficult for the non-aqueous electrolyte and the electrode to react, and thermal runaway in the secondary battery is less likely to occur. A cyclic carboxylic acid ester compound (B) may be used individually by 1 type, and may be used in combination of 2 or more type.

As the cyclic carboxylic acid ester compound (B), a saturated cyclic carboxylic acid ester compound having no carbon-carbon unsaturated bond in the molecule is preferable from the viewpoint of stability to redox reaction.
The ring structure in the cyclic carboxylic acid ester compound (B) is preferably a 4- to 10-membered ring, more preferably a 4- to 7-membered ring, further preferably a 5- to 6-membered ring from the viewpoint of easy availability, and particularly a 5-membered ring. preferable.

The ring structure of the cyclic carboxylic acid ester compound (B) is preferably a ring structure having one ester bond from the viewpoint of viscosity and stability to redox reaction.
The cyclic carboxylic acid ester compound (B) may be a compound in which one or more hydrogen atoms of the alkylene group are substituted with a substituent. Examples of the substituent include a fluorine atom, a chlorine atom, an alkyl group, and a fluorinated alkyl group. The alkyl group preferably has 1 to 2 carbon atoms, and the fluorinated alkyl group preferably has 1 to 2 carbon atoms.

The cyclic carboxylic acid ester compound (B) preferably contains the following compound (6) from the viewpoints of stability to redox reaction, structural stability, and viscosity, and more preferably comprises only the compound (6). preferable. A compound (6) may be used individually by 1 type, and may be used in combination of 2 or more type.

R ⁸ to R ¹³ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or a carbon number having an etheric oxygen atom. 2 to 3 alkyl groups, and q is an integer of 0 to 3.

R ⁸ to R ¹³ may be the same or different.
R ⁸ to R ¹³ are preferably a hydrogen atom, a methyl group, or a fluorine atom, more preferably a hydrogen atom or a methyl group, from the viewpoints of stability to redox reaction, viscosity, and availability of the compound.
q is preferably 1 to 2 and more preferably 1 from the viewpoint of viscosity and availability of the compound.

Compound (6) includes cyclic ester compounds such as γ-butyrolactone, γ-valerolactone, γ-hexanolactone, δ-valerolactone, and ε-caprolactone, and carbon atoms forming the ring of the cyclic ester compound. Or an alkyl group having 2 to 3 carbon atoms in which at least one hydrogen atom has a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or an etheric oxygen atom The compound substituted by is mentioned. At least one selected from the group consisting of γ-butyrolactone, γ-valerolactone and ε-caprolactone is preferable, and γ-butyrolactone is particularly preferable because it is easily available and has a high effect of suppressing thermal runaway.

(Saturated cyclic carbonate compound having no fluorine atom (C))
By including the compound (1) as the lithium salt and the saturated cyclic carbonate compound (C) having no fluorine atom as the liquid composition, the non-aqueous electrolyte contains battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge) It becomes a non-aqueous electrolyte excellent in efficiency. The saturated cyclic carbonate compound (C) having no fluorine atom may be used alone or in combination of two or more.

The saturated cyclic carbonate compound (C) having no fluorine atom preferably contains the following compound (7) from the viewpoint of battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency), and consists only of the compound (7). It is more preferable. A compound (7) may be used individually by 1 type, and may be used in combination of 2 or more type.

However, R ¹⁴ to R ¹⁷ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.
Examples of the alkyl group in the compound (7) include a linear structure and a branched structure.
R ¹⁴ to R ¹⁷ may be the same or different.
R ¹⁴ to R ¹⁷ are preferably a hydrogen atom, a methyl group, or an ethyl group, and more preferably a hydrogen atom or a methyl group, from the viewpoint of battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency).

Specific examples of the compound (7) include ethylene carbonate, propylene carbonate, butylene carbonate and the like. From the viewpoint of battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency), ethylene carbonate is preferred.

[Other ingredients]
The nonaqueous electrolytic solution is a lithium salt, a fluorine-containing solvent (A), a cyclic carboxylic acid ester compound (B), and a saturated cyclic carbonate compound having no fluorine atom (as required) within a range not impairing the effects of the present invention. Other compounds (other solvents, additives, etc.) other than C) may be included.

(Other solvents)
The nonaqueous electrolytic solution may contain a solvent other than the fluorine-containing solvent (A), the cyclic carboxylic acid ester compound (B), and the saturated cyclic carbonate compound (C) having no fluorine atom.
Examples of other solvents include fluorine-containing saturated cyclic carbonate compounds, saturated chain carbonate compounds having no fluorine atom, and saturated cyclic sulfone compounds.

Examples of the fluorine-containing saturated cyclic carbonate compound include 4-fluoro-1,3-dioxolane-2-one, 4-trifluoromethyl-1,3-dioxolane-2-one, and 4,5-difluoro-1,3-dioxolane. -2-one and the like.

Examples of the saturated chain carbonate compound having no fluorine atom include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and the like.
Examples of the saturated cyclic sulfone compound include sulfolane and 3-methylsulfolane.

(Additive)
In order to improve the function of the non-aqueous electrolyte, the non-aqueous electrolyte may contain conventionally known additives as necessary. Examples of the additive include an overcharge inhibitor, a dehydrating agent, a deoxidizing agent, a property improving aid, and a surfactant.

Overcharge prevention agent:
As overcharge inhibitors, aromatic compounds (biphenyl, alkylbiphenyl, terphenyl, terphenyl partially hydrogenated, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, etc.), aromatic compounds Partially fluorinated products (2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, etc.), fluorine-containing anisole compounds (2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroaniol, etc.) ). An overcharge inhibitor may be used individually by 1 type, and may use 2 or more types together.

Dehydrating agent:
Examples of the dehydrating agent include molecular sieves, mirabilite, magnesium sulfate, calcium hydride, sodium hydride, potassium hydride, lithium aluminum hydride and the like. As the liquid composition or other solvent used for the non-aqueous electrolyte, those obtained by rectification after dehydration with a dehydrating agent are preferable. Moreover, what performed only the dehydration by the said dehydrating agent without performing rectification may be used.

Property improvement aids:
The characteristic improving aid is for improving capacity maintenance characteristics and cycle characteristics after high temperature storage. Examples of the property improving aid include unsaturated cyclic carbonate compounds (dimethyl vinylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 4-acetylin-1,3-dioxolan-2-one, 3-methyl-4-vinylethylene carbonate, 4,5-divinylethylene carbonate, 4,5-bis (2-methylvinyl) ethylene carbonate, etc.), sulfur-containing compounds (ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, Busulfan, sulfolene, dimethylsulfone, dibutyldisulfide, dicyclohexyldisulfide, tetramethylthiuram monosulfide, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide, etc.), hydrocarbon compounds Heptane, octane, cycloheptane and the like). A characteristic improvement adjuvant may be used individually by 1 type, and may use 2 or more types together.

Surfactant:
The surfactant assists the impregnation of the non-aqueous electrolyte into the electrode mixture or separator. As the surfactant, any of cationic surfactants, anionic surfactants, nonionic surfactants and amphoteric surfactants may be used. Anionic surfactants are easily available and have a high surfactant effect. Agents are preferred. As the surfactant, a fluorine-containing surfactant is preferable from the viewpoint of high oxidation resistance and good cycle characteristics and rate characteristics. Surfactant may be used individually by 1 type and may use 2 or more types together.

[Ratio of each component]
(Ratio of lithium salt)
5 mass% is preferable, as for the lower limit of the ratio of the mass of lithium salt with respect to the total mass of nonaqueous electrolyte solution, 7 mass% is more preferable, and 8 mass% is further more preferable. The upper limit of the ratio of the mass of the lithium salt to the total mass of the non-aqueous electrolyte is preferably 25% by mass, more preferably 20% by mass, and even more preferably 17% by mass.
If the ratio of lithium salt is more than the said lower limit, the ionic conductivity of a non-aqueous electrolyte will become high. If the proportion of the lithium salt is not more than the above upper limit value, the lithium salt is easily dissolved uniformly in the liquid composition, and the lithium salt does not precipitate even under low temperature conditions.

The lower limit of the ratio of the number of moles of the compound (1) to the total number of moles of the lithium salt is preferably 0.05 mol%, more preferably 0.1 mol%, still more preferably 0.5 mol%, and particularly preferably 1 mol%. The upper limit of the ratio of the number of moles of the compound (1) to the total number of moles of the lithium salt is preferably 95 mol%, more preferably 80 mol%, further preferably 60 mol%, and particularly preferably 40 mol%.
When the ratio of the compound (1) is equal to or higher than the lower limit, it is easy to obtain a nonaqueous electrolytic solution excellent in battery characteristics such as cycle characteristics and rate characteristics. If the proportion of the compound (1) is less than or equal to the upper limit value, by increasing the content of relatively LiPF _6, higher non-aqueous electrolyte solution of high practical in ion conductivity is easily obtained.

When LiPF ₆ is contained in the non-aqueous electrolyte, the lower limit value of the ratio of the number of moles of LiPF ₆ to the total number of moles of lithium salt is preferably 5 mol%, more preferably 20 mol%, further preferably 40 mol%, and more preferably 60 mol%. Is particularly preferred. The upper limit of the ratio of the number of moles of LiPF ₆ to the total number of moles of lithium salt is preferably 99.95 mol%, more preferably 99.9 mol%, further preferably 99.5 mol%, and particularly preferably 99 mol%.
When the proportion of LiPF ₆ is more than the lower limit, easily obtained high superior practicality in ionic conductivity non-aqueous electrolyte. If the ratio of LiPF ₆ is less than or equal to the above upper limit value, a nonaqueous electrolytic solution excellent in battery characteristics such as cycle characteristics and rate characteristics can be easily obtained by relatively increasing the content of the compound (1).

When LiPF ₆ is contained in the nonaqueous electrolytic solution, the lower limit value of the ratio of the total number of moles of the compound (1) and LiPF _{6 to} the total number of moles of the lithium salt is preferably 50 mol%, and more preferably 80 mol%. The upper limit of the ratio of the total number of moles of the compound (1) and LiPF ₆ with respect to the total number of moles of the lithium salt is 100 mol%.

The lower limit of the ratio of the mass of the compound (1) to the total mass of the nonaqueous electrolytic solution is preferably 0.01% by mass, more preferably 0.02% by mass, further preferably 0.1% by mass, Mass% is particularly preferred. 10 mass% is preferable, as for the upper limit of the ratio of the mass of the compound (1) with respect to the total mass of nonaqueous electrolyte solution, 8 mass% is more preferable, and 5 mass% is further more preferable.
If the ratio of compound (1) is more than the said lower limit, it will become easy to obtain the nonaqueous electrolyte solution excellent in battery characteristics, such as a cycle characteristic and a rate characteristic. If the ratio of the compound (1) is not less than the above upper limit value, the lithium salt is easily dissolved uniformly in the liquid composition, and the lithium salt does not precipitate even at low temperature conditions.

(Ratio of fluorine-containing solvent (A))
The lower limit of the ratio of the mass of the fluorinated solvent (A) to the total mass of the nonaqueous electrolytic solution is preferably 30% by mass, more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass. The upper limit of the ratio of the mass of the fluorinated solvent (A) to the total mass of the nonaqueous electrolytic solution is preferably 80% by mass, more preferably 75% by mass, further preferably 73% by mass, and particularly preferably 70% by mass.
If the proportion of the fluorinated solvent (A) is not less than the lower limit, the non-aqueous electrolyte is excellent in flame retardancy, has low positive electrode reactivity and negative electrode reactivity, hardly causes thermal runaway, and has high high voltage resistance. Have If the ratio of the fluorine-containing solvent (A) is not more than the upper limit value, the lithium salt is easily dissolved uniformly, and the lithium salt does not easily precipitate at a low temperature, so that the ionic conductivity is hardly lowered.

The lower limit of the ratio of the mass of the fluorinated solvent (A) to the total mass of the liquid composition is preferably 45 mass%, more preferably 50 mass%, further preferably 55 mass%, particularly preferably 60 mass%. The upper limit of the ratio of the mass of the fluorinated solvent (A) to the total mass of the liquid composition is preferably 90% by mass, more preferably 85% by mass, further preferably 80% by mass, and particularly preferably 75% by mass.
If the proportion of the fluorinated solvent (A) is not less than the lower limit, the non-aqueous electrolyte is excellent in flame retardancy, has low positive electrode reactivity and negative electrode reactivity, hardly causes thermal runaway, and has high high voltage resistance. Have If the ratio of the fluorine-containing solvent (A) is not more than the upper limit value, the lithium salt is easily dissolved uniformly, and the lithium salt does not easily precipitate at a low temperature, so that the ionic conductivity is hardly lowered.

When the fluorinated solvent (A) contains a fluorinated ether compound, the lower limit of the ratio of the mass of the fluorinated ether compound to the total mass of the fluorinated solvent (A) is preferably 25 mass%, more preferably 30 mass%. , 50% by mass is more preferable, 60% by mass is further preferable, and 70% by mass is particularly preferable. The upper limit of the ratio of the mass of the fluorinated ether compound to the total mass of the fluorinated solvent (A) is 100% by mass.
The fluorine-containing solvent (A) is particularly preferably composed only of a fluorine-containing ether compound from the viewpoints of the solubility of the lithium salt, the flame retardance of the non-aqueous electrolyte, and the ionic conductivity.

When the fluorine-containing solvent (A) of the non-aqueous electrolyte contains a fluorine-containing ether compound, the lower limit of the ratio of the mass of the fluorine-containing ether compound to the total mass of the non-aqueous electrolyte is preferably 10% by mass, and 20% by mass. Is more preferable, 30% by mass is further preferable, 45% by mass is further preferable, and 50% by mass is particularly preferable. The upper limit of the ratio of the mass of the fluorine-containing ether compound to the total mass of the nonaqueous electrolytic solution is preferably 80% by mass, more preferably 75% by mass, further preferably 73% by mass, and particularly preferably 70% by mass.

When the fluorinated solvent (A) contains a fluorinated chain carboxylic acid ester compound, the lower limit of the ratio of the mass of the fluorinated chain carboxylic acid ester compound to the total mass of the fluorinated solvent (A) is 0.01 mass. % Is preferred. The upper limit of the ratio of the mass of the fluorinated chain carboxylic acid ester compound to the total mass of the fluorinated solvent (A) is preferably 50 mass%, more preferably 40 mass%, further preferably 30 mass%, more preferably 20 mass%. Is particularly preferred.

When the fluorine-containing solvent (A) contains a fluorine-containing chain carbonate compound, the lower limit of the ratio of the mass of the fluorine-containing chain carbonate compound to the total mass of the fluorine-containing solvent (A) is preferably 0.01% by mass. The upper limit of the ratio of the mass of the fluorinated chain carbonate compound to the total mass of the fluorinated solvent (A) is preferably 50 mass%, more preferably 40 mass%, further preferably 30 mass%, particularly preferably 20 mass%. preferable.

When the fluorinated solvent (A) contains a fluorinated alkane compound, the ratio of the mass of the fluorinated alkane compound to the total mass of the nonaqueous electrolytic solution is preferably from 0.01 to 5 mass%. When the ratio of the fluorine-containing alkane compound is 0.01% by mass or more, the vapor pressure is low and the flame retardancy is excellent. When the proportion of the fluorine-containing alkane compound is 5% by mass or less, the solubility of the lithium salt is easily maintained.

When the fluorine-containing solvent (A) is used in combination with a fluorine-containing ether compound and at least one selected from a fluorine-containing chain carboxylic acid ester compound, a fluorine-containing chain carbonate compound and a fluorine-containing alkane compound, the ratio thereof is as follows: It can be decided arbitrarily.

(Ratio of cyclic carboxylic acid ester compound (B))
The lower limit of the ratio of the mass of the cyclic carboxylic acid ester compound (B) to the total mass of the non-aqueous electrolyte is preferably 4% by mass, more preferably 7% by mass, still more preferably 10% by mass, and particularly preferably 15% by mass. preferable. The upper limit of the ratio of the mass of the cyclic carboxylic acid ester compound (B) to the total mass of the nonaqueous electrolytic solution is preferably 60% by mass, more preferably 45% by mass, still more preferably 40% by mass, and particularly preferably 35% by mass. preferable.
If the ratio of the cyclic carboxylic acid ester compound (B) is equal to or higher than the lower limit, the non-aqueous electrolyte uniformly dissolves the lithium salt, the reactivity between the non-aqueous electrolyte and the electrode is small, and thermal runaway occurs. Hateful. If the ratio of the cyclic carboxylic acid ester compound (B) is not more than the upper limit value, the non-aqueous electrolyte is excellent in flame retardancy.

The lower limit of the ratio N _B / N _Li of the total number of moles N _B of the cyclic carboxylic acid ester compound (B) to the total number of moles N _Li of lithium atoms derived from the lithium salt contained in the non-aqueous electrolyte is 1. 5 is preferable, 2 is more preferable, 2.5 is more preferable, and 3 is particularly preferable. The upper limit value of N _B / N _Li is preferably 5.5, more preferably 5, more preferably 4.5, and particularly preferably 4.2.
When N _B / N _Li is equal to or greater than the lower limit, the non-aqueous electrolyte uniformly dissolves the lithium salt, the reactivity between the non-aqueous electrolyte and the electrode is small, and thermal runaway hardly occurs. When N _B / N _Li is not more than the above upper limit value, the non-aqueous electrolyte is excellent in flame retardancy.

(Proportion of saturated cyclic carbonate compound (C) having no fluorine atom)
The ratio of the mass of the saturated cyclic carbonate compound (C) having no fluorine atom to the total mass of the nonaqueous electrolytic solution is 0.01 to 20% by mass. The lower limit of the mass of the saturated cyclic carbonate compound (C) having no fluorine atom relative to the total mass of the nonaqueous electrolytic solution is preferably 0.05% by mass, more preferably 0.1% by mass, and 0.5% by mass. Particularly preferred. The upper limit of the ratio of the mass of the saturated cyclic carbonate compound (C) having no fluorine atom to the total mass of the nonaqueous electrolytic solution is preferably 15% by mass, more preferably 13% by mass, and particularly preferably 10% by mass.
If the ratio of the saturated cyclic carbonate compound (C) having no fluorine atom is not less than the lower limit value, a nonaqueous electrolytic solution excellent in battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency) is easily obtained. If the ratio of the saturated cyclic carbonate compound (C) having no fluorine atom is not more than the above upper limit value, the viscosity of the electrolytic solution does not become too high, and the electrolytic solution is excellent in rate characteristics.

(Ratio of other ingredients)
When the non-aqueous electrolyte contains another solvent, the upper limit of the ratio of the mass of the other solvent to the total mass of the non-aqueous electrolyte is preferably 30% by mass, more preferably 20% by mass, and further 15% by mass 10% by mass is preferable. The lower limit of the ratio of the mass of the other solvent to the total mass of the non-aqueous electrolyte is 0% by mass.
If the ratio of the other solvent is not more than the upper limit value, it is easy to suppress the reaction between the other solvent and the electrode, and a non-aqueous electrolyte solution having excellent stability can be obtained. Moreover, since it is easy to increase content of a fluorine-containing solvent (A), the nonaqueous electrolyte solution excellent in the flame retardance is easy to be obtained.

When the non-aqueous electrolyte contains a fluorine-containing saturated cyclic carbonate compound, the ratio of the mass of the fluorine-containing saturated cyclic carbonate compound to the total mass of the non-aqueous electrolyte is preferably 0.01 to 20% by mass, and 0.01 to 15 % By mass is more preferable, 0.01 to 10% by mass is further preferable, 0.01 to 5% by mass is further preferable, and 0.01 to 3% by mass is particularly preferable.
If the ratio of a fluorine-containing saturated cyclic carbonate compound is below an upper limit, a fluorine-containing saturated cyclic carbonate compound and an electrode will be hard to react, and nonaqueous electrolyte solution is excellent in stability and flame retardance.

When the non-aqueous electrolyte includes a saturated chain carbonate compound having no fluorine atom, the ratio of the mass of the saturated chain carbonate compound having no fluorine atom to the total mass of the non-aqueous electrolyte is 0.01 to 30% by mass. Is preferable, and 0.01 to 20% by mass is more preferable.
If the ratio of the saturated chain carbonate compound having no fluorine atom is not more than the upper limit value, the saturated chain carbonate compound having no fluorine atom and the electrode are unlikely to react, and the non-aqueous electrolyte is stable and flame retardant. Excellent.

When the liquid composition contains a saturated cyclic sulfone compound, the ratio of the mass of the saturated cyclic sulfone compound to the total mass of the nonaqueous electrolytic solution is preferably 0.01 to 20% by mass, more preferably 0.01 to 15% by mass. 0.01 to 10% by mass is more preferable, and 0.01 to 5% by mass is particularly preferable.
If the ratio of the saturated cyclic sulfone compound is not more than the above upper limit value, the saturated cyclic sulfone compound and the electrode are unlikely to react with each other, and the non-aqueous electrolyte is excellent in stability and flame retardancy.

When the non-aqueous electrolyte contains an overcharge inhibitor, the ratio of the mass of the overcharge inhibitor to the total mass of the non-aqueous electrolyte is preferably 0.01 to 5% by mass.
If the ratio of the non-aqueous electrolyte is equal to or higher than the lower limit, it becomes easier to suppress the secondary battery from bursting and firing due to overcharging, and the secondary battery can be used more stably.

When the non-aqueous electrolyte contains a characteristic improving aid, the ratio of the mass of the characteristic improving auxiliary to the total mass of the non-aqueous electrolytic solution is preferably 0.01 to 5% by mass.

When the non-aqueous electrolyte contains a surfactant, the upper limit of the ratio of the mass of the surfactant to the total mass of the non-aqueous electrolyte is preferably 5% by mass, more preferably 3% by mass, and further 2% by mass preferable. The lower limit of the ratio of the mass of the surfactant to the total mass of the non-aqueous electrolyte is preferably 0.05% by mass.

[Mechanism of action]
In the nonaqueous electrolytic solution of the present invention described above, the lithium salt contains the compound (1), and the liquid composition contains the saturated cyclic carbonate compound (C) having no fluorine atom, so that the surface of the electrode active material Therefore, it is estimated that a lithium ion secondary battery excellent in battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency) can be obtained.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, and the non-aqueous electrolyte of the present invention.

[Positive electrode]
Examples of the positive electrode include an electrode in which a positive electrode layer containing a positive electrode active material, a conductivity-imparting agent, and a binder is formed on a current collector.

(Positive electrode active material)
The positive electrode active material may be any material that can occlude and release lithium ions. As the positive electrode active material, known positive electrode active materials for lithium ion secondary batteries can be employed. Examples of positive electrode active materials include lithium-containing transition metal oxides, lithium-containing transition metal composite oxides using two or more transition metals, transition metal oxides, transition metal sulfides, metal oxides, olivine-type metal lithium salts, etc. Is mentioned. A positive electrode active material may be used individually by 1 type, and may use 2 or more types together.

Examples of the lithium-containing transition metal oxide include lithium cobalt oxide (LiCoO _{2 and the} like), lithium nickel oxide (LiNiO _{2 and the} like), lithium manganese oxide (LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _{3 and the} like). Can be mentioned.

As the metal contained in the lithium-containing transition metal composite oxide, Al, V, Ti, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Yb and the like are preferable. Examples of the lithium-containing transition metal composite oxide include lithium ternary composite oxides (Li (Ni _a Co _b Mn _c ) O ₂ (where a, b, c> 0, a + b + c = 1), etc.), and the like. Some of the transition metal atoms that are the main components of these lithium transition metal composite oxides are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, and Yb. And the like substituted with other metals.
The following are mentioned as a lithium containing transition metal complex oxide.
LiMn _0.5 Ni _0.5 O ₂ , LiMn _1.8 Al _0.2 O ₄ ,
LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiMn _1.5 Ni _0.5 O ₄ ,
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn _1.8 Al _0.2 O ₄ etc.

Examples of the transition metal oxide include TiO ₂ , MnO ₂ , MoO ₃ , V ₂ O ₅ , V ₆ O _{13 and the} like. Examples of the transition metal sulfide include TiS ₂ , FeS, and MoS ₂ . Examples of the metal oxide include SnO ₂ and SiO ₂ .

Olivine type metal lithium _{^{_{^{_{salt, Li L M 3 x M 4}}}}} y O z F g ( however, ^{M 3} is, Fe (II), Co ( II), Mn (II), Ni (II), V (II) Or Cu (II), M ⁴ is P or Si, and 0 ≦ L ≦ 3, 1 ≦ x ≦ 2, 1 ≦ y ≦ 3, 4 ≦ z ≦ 12, 0 ≦ g ≦ 1. ) Or a complex thereof.
Examples of the olivine type metal lithium salt include the following.
LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ) ₃ , LiFeP ₂ O ₇ ,
LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₂ FePO ₄ F,
Li ₂ MnPO ₄ F, Li ₂ NiPO ₄ F, Li ₂ CoPO ₄ F,
Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ NiSiO ₄ ,
Li ₂ CoSiO ₄ etc.

A material in which a substance having a composition different from that of the main constituent of the positive electrode active material is attached to the surface of the positive electrode active material can also be used. Surface adhering substances include oxides (aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, etc.), sulfates (lithium sulfate, sodium sulfate, potassium sulfate, Magnesium sulfate, calcium sulfate, aluminum sulfate, etc.), carbonates (lithium carbonate, calcium carbonate, magnesium carbonate, etc.) and the like.
The lower limit of the amount of the surface adhering substance relative to the positive electrode active material is preferably 0.1 mass ppm, more preferably 1 mass ppm, and particularly preferably 10 mass ppm. 20 mass% is preferable, the upper limit of the quantity of the surface adhesion substance with respect to a positive electrode active material is more preferable, 10 mass% is more preferable, and 5 mass% is especially preferable. The surface adhering substance can suppress the oxidation reaction of the nonaqueous electrolytic solution on the surface of the positive electrode active material, and can improve the battery life.

As the positive electrode active material, lithium-containing transition metal oxides (LiCoO ₂ , LiNiO ₂ , LiMnO _2, etc.) based on α-NaCrO ₂ structure, spinel from the viewpoint of high discharge voltage and high electrochemical stability. A lithium-containing transition metal oxide (LiMn ₂ O ₄ or the like) having a mold structure as a base is preferable.

(Conductivity imparting agent)
Examples of the conductivity-imparting agent include carbon materials, metal substances (such as Al), and conductive oxide powders.

(Binder)
Examples of the binder include resin binders (such as polyvinylidene fluoride) and rubber binders (hydrocarbon rubber, fluororubber, etc.).

(Current collector)
Examples of the current collector include a metal thin film mainly composed of Al or the like.

[Negative electrode]
Examples of the negative electrode include an electrode in which a negative electrode layer containing a powdered negative electrode active material, a conductivity-imparting agent, and a binder is formed on a current collector. In addition, when a negative electrode active material can maintain a shape by itself (for example, when it is a lithium metal thin film), a negative electrode can be formed only with a negative electrode active material.

(Negative electrode active material)
Examples of the negative electrode active material include at least one selected from the group consisting of a lithium metal, a lithium alloy, and a carbon material capable of inserting and extracting lithium ions.
Examples of the lithium alloy include a Li—Si alloy, a Li—Al alloy, a Li—Pb alloy, and a Li—Sn alloy.
Examples of the carbon material include graphite, coke, and hard carbon.

(Conductivity imparting agent, binder)
As the binder and the conductivity-imparting agent for the negative electrode, those equivalent to the positive electrode can be used.

(Current collector)
Examples of the current collector include a metal thin film mainly composed of Cu or the like.

[Separator]
A separator is interposed between the positive electrode and the negative electrode to prevent a short circuit. Examples of the separator include a porous film. A non-aqueous electrolyte is used by impregnating the porous membrane. Moreover, you may use as a gel electrolyte what impregnated the porous film with the nonaqueous electrolyte solution, and was made to gelatinize.

As the porous film, one that is stable with respect to the non-aqueous electrolyte and excellent in liquid retention can be used. As a porous film, a porous sheet or a nonwoven fabric is preferable. You may use what laminated | stacked the porous film and was made into 2 layers or 3 layers.
Examples of the material for the porous film include fluororesins (polyvinylidene fluoride, polytetrafluoroethylene, copolymers of ethylene and tetrafluoroethylene, etc.), polyimides, polyolefins (polyethylene, polypropylene, etc.), oxidation resistance, air permeability, Polyolefin is preferable from the viewpoint of availability.

In order to improve heat resistance and shape retention characteristics, an inorganic fine particle layer may be provided on the surface of either or both of the separator and the electrode. Examples of the inorganic fine particles include silica, alumina, titania, magnesia and the like.

[Battery exterior]
Examples of the material for the battery outer package include nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, and a film material.

[shape]
The shape of the lithium ion secondary battery may be selected according to the application, and may be any shape such as a coin shape, a cylindrical shape, a square shape, and a laminate shape. Moreover, the shape of a positive electrode and a negative electrode can be suitably selected according to the shape of a secondary battery.

[Charging voltage]
The charging voltage of the lithium ion secondary battery of the present invention is preferably 4.25 V or more, more preferably 4.30 V or more, further preferably 4.35 V or more, and particularly preferably 4.40 V or more in terms of the potential with respect to lithium.

[Mechanism of action]
The lithium ion secondary battery of the present invention described above is excellent in battery characteristics (cycle characteristics, rate characteristics, initial charge / discharge efficiency) because the non-aqueous electrolyte of the present invention is used.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Examples 1 to 9 are examples, and examples 10 to 14 are comparative examples.

[Production of evaluation cell]
(Negative electrode)
Artificial graphite (9.1 g) was stirred for 1 minute at a rotational speed of 2000 rpm using a rotation and revolution type stirrer (Shinky Corp., Awatori Nertaro AR-E310). 2 mass% carboxymethylcellulose aqueous solution (9.0g) was added, and the process stirred for 1 minute at the rotation speed 2000rpm using the said stirrer was performed twice. Distilled water (4.7 g) was added, and the step of stirring for 1 minute at a rotational speed of 2000 rpm was performed twice using the stirrer. A tetrafluoroethylene-propylene rubber aqueous dispersion latex binder (0.26 g) adjusted to a solid content concentration of 34% by mass was added and stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer to form a slurry for electrode coating. Obtained.
The slurry is coated on a copper foil having a thickness of 20 μm to a thickness of 210 μm, dried and then pressed with a roll press to a porosity of 15 to 25%, and then punched into a circle with a diameter of 16 mm for evaluation. Electrode (negative electrode).

(Positive electrode)
LiCoO ₂ (manufactured by AGC Seimi Chemical Co., Ltd., 32.0 g) and carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., 0.8 g) are mixed, and a revolving revolving stirrer (manufactured by Shinky Co., Ltd., Awatori Netaro AR-E310) The step of stirring for 30 seconds at 2000 rpm was performed three times. The step of adding N-methyl-2-pyrrolidone (6.0 g) and stirring with the stirrer at a rotation speed of 2000 rpm for 5 minutes was performed 4 times. The step of adding N-methyl-2-pyrrolidone (0.8 g) and stirring for 3 minutes at 2000 rpm using the stirrer was performed three times. A solution of polyvinylidene fluoride in N-methyl-2-pyrrolidone (11% by mass, 7.45 g) was added and stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer to obtain a slurry.
The slurry is applied to a thickness of 180 μm on an aluminum foil having a thickness of 20 μm, dried, pressed with a roll press machine so that the porosity is 35 to 40%, and then punched into a circle with a diameter of 15 mm. An evaluation electrode (positive electrode) was obtained.

(cell)
A cell comprising a LiCoO ₂ electrode-graphite electrode, with a positive electrode and a negative electrode facing each other, a polyolefin microporous membrane as an electrode separator for evaluation existing between each electrode, a non-aqueous electrolyte (0.02 mL) added thereto Was made.

[Charge / discharge test]
The cell is charged to 3.4 V with a constant current corresponding to 0.05 C at 25 ° C., further charged to 4.35 V with a current corresponding to 0.2 C, and the current value is 0.02 C at the charging lower limit voltage. The battery was charged until the current corresponding to Then, it discharged to 3.0V with the electric current corresponding to 0.2C. The initial charge / discharge efficiency was calculated from the following equation.
Initial charge / discharge efficiency = {(initial discharge capacity) / (initial charge capacity) × 100}

From the 2nd cycle to the 4th cycle, the battery was charged to 4.35V with a current corresponding to 0.2C, and further charged until the current value reached a current corresponding to 0.02C at the charge lower limit voltage. Then, it discharged to 3.0V with the electric current corresponding to 0.2C. In 5 cycles, the battery was charged to 4.35 V with a current corresponding to 0.5 C, and further charged until the current value reached a current corresponding to 0.02 C at the charge lower limit voltage. Thereafter, the battery was discharged to 3.0 V with a current corresponding to 1.0 C.

The rate test was conducted for 6 to 11 cycles. Charging was performed until a current corresponding to 0.02C was reached at a charging lower limit voltage after charging to 4.35V with a current corresponding to 0.5C. The discharge was performed at 0.1 C for 6 cycles, 0.2 C for 7 cycles, 0.5 C for 8 cycles, 1.0 C for 9 cycles, and 3.0 V at a current corresponding to 2.0 C for 10 cycles. As an evaluation of the rate characteristics, the discharge capacity maintenance rate at 1.0 C discharge relative to the discharge capacity at 0.1 C discharge was measured.

From 12 cycles to 100 cycles, the battery was charged to 4.35 V at a current corresponding to 0.5 C, and further charged until the current value reached a current corresponding to 0.02 C at the charge lower limit voltage. Then, it discharged to 3.0V with the electric current corresponding to 0.5C. The cycle characteristics were evaluated based on the discharge capacity retention rate of 50 cycles and 100 cycles with respect to the discharge capacity of the 12th cycle.

The compounds and abbreviations used in the examples are as follows.
(Lithium salt)
LPF: LiPF ₆ , LiFOB: Compound (1-1).

(Fluorine-containing solvent (A))
AE3000: CF ₃ CH ₂ OCF ₂ CHF ₂ (Asahi Glass Co., Ltd., AE-3000).

(Cyclic carboxylic acid ester compound (B))
GBL: γ-butyrolactone.

(Saturated cyclic carbonate compound having no fluorine atom (C))
EC: ethylene carbonate.

(Other ingredients)
DMC: dimethyl carbonate, EMC: ethyl methyl carbonate, VC: vinylene carbonate, FEC: 4-fluoro-1,3-dioxolan-2-one.

[Example 1]
After diffusing LPF (0.15 g) and LiFOB (0.03 g) which are lithium salts into AE3000 (0.71 g) which is a fluorine-containing ether solvent (A), the cyclic carboxylic acid ester compound (B) is obtained. GBL (0.34 g), EC (0.03 g) which is a saturated cyclic carbonate compound (C) having no fluorine atom, and DMC (0.22 g) which is another solvent were mixed to obtain a non-aqueous electrolyte solution 1. .
A cell was prepared using Nonaqueous Electrolytic Solution 1 (20 μL), and a charge / discharge test was performed. The results are shown in Table 1.

[Examples 2 to 14]
Nonaqueous electrolytes 2 to 14 were obtained in the same manner as in Example 1 except that the composition of each compound such as lithium salt was changed as shown in Tables 1 and 2. In Tables 1 and 2, the content (mass%) of each component is shown as a percentage of the content of each component with respect to the total content (mass) of each component contained in the non-aqueous electrolyte.
Moreover, except having changed these non-aqueous electrolyte solutions, the cell was produced like Example 1 and the charge / discharge test was done. The results are shown in Tables 1 and 2.

As shown in Tables 1 and 2, Examples 1 to 9 in which LiFOB as the compound (1) and EC as the saturated cyclic carbonate compound (C) having no fluorine atom are used in a specific amount do not have a fluorine atom. Examples 13 and 12 containing no saturated cyclic carbonate compound (C), 14 containing no compound (1), 11 containing no compound (1) and no saturated cyclic carbonate compound (C) having no fluorine atom In comparison, the initial charge / discharge efficiency, cycle characteristics, and rate characteristics were all improved.

The nonaqueous electrolytic solution of the present invention is useful as a nonaqueous electrolytic solution for a lithium ion secondary battery.
The lithium ion secondary battery of the present invention includes a mobile phone, a portable game machine, a digital camera, a digital video camera, an electric tool, a notebook computer, a portable information terminal, a portable music player, an electric vehicle, a hybrid vehicle, a train, an aircraft, an artificial It can be applied to various uses such as satellites, submarines, ships, uninterruptible power supplies, robots, and power storage systems. The lithium ion secondary battery of the present invention is particularly effective as a large secondary battery for electric vehicles, hybrid vehicles, trains, airplanes, artificial satellites, submarines, ships, uninterruptible power supplies, robots, power storage systems, and the like. is there.
It should be noted that the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2014-086255 filed on April 18, 2014 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims

A non-aqueous electrolyte containing an electrolyte and a liquid composition,
At least one of the electrolytes is a lithium salt;
The lithium salt includes at least one compound represented by the following formula (1):
A fluorinated solvent (A) in which the liquid composition comprises at least one selected from the group consisting of a fluorinated ether compound, a fluorinated chain carboxylic acid ester compound and a fluorinated chain carbonate compound; and a cyclic carboxylic acid ester compound (B) and the saturated cyclic carbonate compound (C) having no fluorine atom, and the ratio of the mass of the saturated cyclic carbonate compound (C) having no fluorine atom to the total mass of the non-aqueous electrolyte is 0.00. A nonaqueous electrolytic solution for a secondary battery, which is from 01 to 20% by mass.

However,
M is a boron atom or a phosphorus atom,
R 1 is an optionally substituted alkylene group having 1 to 10 carbon atoms,
X is a halogen atom,
n is an integer from 0 to 4,
m is 0 or 1,
p is 1 or 2.
The non-aqueous electrolyte for secondary batteries according to claim 1, wherein the saturated cyclic carbonate compound (C) having no fluorine atom is at least one compound represented by the following formula (7).

However, R 14 to R 17 are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.
The nonaqueous electrolysis for a secondary battery according to any one of claims 1 and 2, wherein the ratio of the mass of the fluorinated solvent (A) to the total mass of the nonaqueous electrolytic solution is 30 to 80 mass%. liquid.
The lithium salt is a compound represented by the following formula (1-1), a compound represented by the following formula (1-2), a compound represented by the following formula (1-3), a formula (1-4) The non-aqueous battery for a secondary battery according to any one of claims 1 to 3, comprising at least one selected from the group consisting of a compound represented by formula (1) and a compound represented by the following formula (1-5): Electrolytic solution.
The secondary according to any one of claims 1 to 4, wherein the ratio of the mass of the compound represented by the formula (1) to the total mass of the nonaqueous electrolytic solution is 0.01 to 10 mass%. Non-aqueous electrolyte for batteries.
The fluorine-containing ether compound is at least one selected from the group consisting of a compound represented by the following formula (2) and a compound represented by the following formula (3): A non-aqueous electrolyte for a secondary battery as described in 1.

However,
R 2 and R 3 each independently represents an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, or a fluorinated cycloalkyl having 3 to 10 carbon atoms. A group, an alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom, or a fluorinated alkyl group having 2 to 10 carbon atoms having an etheric oxygen atom,
One or both of R 2 and R 3 are a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a fluorine atom having 2 to 10 carbon atoms having an etheric oxygen atom. Alkyl group,
Y represents an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkylene group having 2 to 5 carbon atoms having an etheric oxygen atom, or 2 to 5 carbon atoms having an etheric oxygen atom. A fluorinated alkylene group;
The nonaqueous electrolytic solution for a secondary battery according to any one of claims 1 to 6, wherein the cyclic carboxylic acid ester compound (B) is at least one compound represented by the following formula (6).

However,
R 8 to R 13 each independently represents a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or an etheric oxygen atom having 2 to 3 carbon atoms. An alkyl group of
q is an integer of 0 to 3.
The fluorine-containing ether compound is CF 3 CH 2 OCF 2 CHF 2 , CF 3 CH 2 OCF 2 CHFCF 3 , CHF 2 CF 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 is OCF 2 CHF 2 and CHF 2 CF 2 CH 2, at least one selected from the group consisting of OCF 2 CHFCF 3, the non-aqueous electrolyte solution for a secondary battery according to any one of claims 1 to 7.
The nonaqueous electrolytic solution for secondary battery according to any one of claims 1 to 8, wherein the fluorine-containing solvent (A) is the fluorine-containing ether compound.
The secondary according to any one of claims 1 to 9, wherein the cyclic carboxylic acid ester compound (B) is at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and ε-caprolactone. Non-aqueous electrolyte for batteries.
The non-aqueous electrolyte for a secondary battery according to any one of claims 1 to 10, wherein the lithium salt contains LiPF 6 .
The nonaqueous electrolytic solution for a secondary battery according to any one of claims 1 to 11, wherein a ratio of a mass of the lithium salt to a total mass of the nonaqueous electrolytic solution is 5 to 25 mass%.
The non-chargeable secondary battery according to any one of claims 1 to 12, wherein a ratio of a mass of the cyclic carboxylic acid ester compound (B) to a total mass of the nonaqueous electrolytic solution is 4 to 60 mass%. Water electrolyte.
A positive electrode having a material capable of inserting and extracting lithium ions as an active material, a negative electrode having at least one selected from the group consisting of lithium metal, a lithium alloy, and a carbon material capable of inserting and extracting lithium ions as an active material; 14. A lithium ion secondary battery comprising the non-aqueous electrolyte for secondary battery according to any one of items 1 to 13.