JP2000090968A - Non-aqueous electrolyte and non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having excellent safety and battery characteristics by forming the non-aqueous electrolyte of a non-aqueous solvent including a specified fluorine contained carbonate compound and the electrolyte. SOLUTION: A fluorine contained carbonate compound expressed by formula I or formula II is used (In formulas I, II, R is a hydrocarbon group having 1-20 carbons, X and Y can be the same or different with/from each other and show a fluorine atom substituent hydrocarbon group having 1-10 carbons, and A is an alkylene group having 2-4 carbons. (m), (n) are each an integer 1-30). Desirably, in this non-aqueous electrolyte, the non-aqueous solvent contains cyclic carbonate and/or chain carbonate, and the cyclic carbonate is a cyclic carbonate compound containing an alkylene group having 2-5 carbons, and the chain carbonate is a chain carbonate compound containing a hydrocarbon radical having 1-5 carbons. As a negative electrode active material, carbon material such as graphite can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte containing a fluorine-containing carbonate compound, and more particularly, to a non-aqueous electrolyte secondary battery having excellent safety and excellent charge / discharge characteristics. It relates to a water electrolyte.

[0002] The present invention also relates to a non-aqueous electrolyte secondary battery containing such a non-aqueous electrolyte.

[0003]

BACKGROUND OF THE INVENTION In recent years, secondary batteries utilizing oxidation / reduction reactions of alkali metals have been actively studied. In particular, a battery using a carbon material capable of doping / dedoping lithium ions for a negative electrode and using a composite oxide of lithium and a metal for a positive electrode is called a lithium ion battery, and is small, lightweight, and Due to the high energy density, the field of application is rapidly expanding. By the way, the camera integrated V
With the emergence of new portable electronic devices such as TRs, mobile phones, and laptop computers one after another, in order to further improve the functions of such portable electronic devices, lithium-ion batteries have been required to increase the energy density or reduce the discharge current. It is desired to improve the performance such as increasing the size.

In such a lithium ion battery,
A non-aqueous electrolyte is used to exchange lithium ions between a positive electrode and a negative electrode. Lithium ion batteries that use water as a solvent are hydrolyzed because the potential of the electrodes is high. Therefore, a lithium ion battery in which an alkali metal salt is dissolved in a nonaqueous solvent is usually used.

As the non-aqueous solvent, a polar aprotic organic solvent which easily dissolves an alkali metal salt and is hardly electrolyzed is used. Representative examples thereof include ethylene carbonate, propylene carbonate, dimethyl carbonate, and dimethyl carbonate. Methyl ethyl carbonate, carbonates such as diethyl carbonate, γ-butyrolactone,
Esters such as methyl formate, methyl acetate, and methyl propionate; and ethers such as dimethoxyethane, tetrahydrofuran, and dioxolan. The dissolved alkali metal salts include LiPF ₆ and LiB.
F ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiClO ₄ , LiCF ₃ SO ₃
And the like.

It is desired that such a non-aqueous electrolyte has high conductivity and low viscosity in order to improve the discharge performance of the battery used. Further, it is desired that the positive electrode and the negative electrode be chemically and electrochemically stable so that the performance of the battery is not deteriorated by repeating charge and discharge.

Further, since many of such non-aqueous electrolytes are flammable, when the non-aqueous electrolyte leaks from the battery,
It is expected that the battery may explode or burn, and it is desired to improve the safety of the nonaqueous electrolyte.

For this reason, for example, a nonaqueous electrolytic solution to which a flame-retardant phosphate ester is added (see Japanese Patent Application Laid-Open No. 8-22839), and a non-aqueous electrolytic solution using a halogen compound (see Japanese Patent Application Laid-Open No.
48072) and the like. Among halogen compounds, fluorine compounds in particular have properties such as high electrochemical stability and high flash point.

In addition, when an accident occurs in the battery and the battery is short-circuited, the electrolytic solution is electrolyzed by overcharging, or exposed to high temperature from the outside, the energy stored in the battery is reduced. Is released as heat, and so-called thermal runaway may occur. For this reason, commercially available batteries have taken sufficient measures to prevent overcharge, prevent overcurrent, and shut down the separator when the internal temperature rises.However, the safety of nonaqueous electrolytes should be further improved. Is desired.

In a process in which a battery undergoes thermal runaway, for some reason, the temperature rises to a temperature at which a chemical reaction between the electrode and the electrolyte starts, and the heat generation rate of the chemical reaction increases when the heat radiation rate of the battery increases. , The temperature rise due to heat generation stops,
It is known to lead to thermal runaway. To prevent such thermal runaway from occurring, it is effective to reduce the heat generation rate between the electrolyte and the electrode.

In view of the above circumstances, the present inventors have:
In order to achieve the above object, the present inventors conducted intensive studies and found that by using a non-aqueous solvent containing a specific fluorine-containing carbonate compound, the reaction rate between the positive electrode and the electrolytic solution, which was one of the causes of increasing the heat generation rate, was reduced. The inventors have found that a small electrolytic solution can be obtained, and have completed the present invention.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems associated with the prior art as described above, and to provide a non-aqueous electrolyte having excellent safety and excellent battery characteristics. It is intended to provide a non-aqueous electrolyte secondary battery containing the same.

[0013]

The non-aqueous electrolyte according to the present invention comprises a non-aqueous solvent containing a fluorine-containing carbonate compound represented by the following general formula [1] or [2], and an electrolyte.

R—OCOO— (AO) _n —CH ₂ —X [1] X—CH ₂ O— (AO) _n —COO— (AO) _m —CH ₂ —Y [2]

(In the formulas [1] and [2], R represents 1 to 2 carbon atoms.
0 hydrocarbon group, X and Y may be the same or different from each other, each represents a fluorine atom-substituted hydrocarbon group having 1 to 10 carbon atoms, and A represents an alkylene group having 2 to 4 carbon atoms. Show. M and n are integers of 1 to 30. In addition, the non-aqueous solvent preferably contains a cyclic carbonate and / or a chain carbonate. The cyclic carbonate is a cyclic carbonate compound containing an alkylene group having 2 to 5 carbon atoms, The chain carbonate is preferably a chain carbonate compound containing a hydrocarbon group having 1 to 5 carbon atoms.

The electrolytes are LiPF ₆ , LiBF ₄ , Li
OSO ₂ R ₁ ,

[0017]

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(In the formula, R ^{1 to} R ⁸ may be the same or different from each other, and are preferably at least one member selected from a perfluoroalkyl group having 1 to 6 carbon atoms.) .

The non-aqueous electrolyte secondary battery according to the present invention is characterized in that the non-aqueous electrolyte, a lithium-containing alloy, a carbon material capable of doping / dedoping lithium ions and a lithium ion A negative electrode containing any of tin oxide that can be doped and undoped, silicon that can be doped and undoped with lithium ions, and titanium oxide that can be doped and undoped with lithium ions, and lithium as a positive electrode active material And a positive electrode containing a composite oxide with a metal.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The non-aqueous electrolyte and the non-aqueous electrolyte secondary battery according to the present invention will be specifically described below.

[Non-Aqueous Electrolyte] The non-aqueous electrolyte according to the present invention comprises a non-aqueous solvent containing a fluorine-containing carbonate compound as an essential component, and an electrolyte.

First, each component constituting the non-aqueous electrolyte will be described. [Fluorine-containing carbonate compound] In the present invention, as the fluorine-containing carbonate compound, a compound represented by the following general formula [1] or [2] is preferably used. _{R-OCOO- (AO) n -CH} 2 -X [1] X-CH 2 O- (AO) n -COO- (AO) m -CH 2 -Y [2] ( Formula [1], [2] Wherein R is a hydrocarbon group having 1 to 20 carbon atoms, X and Y may be the same or different from each other, and each represents a fluorine-substituted hydrocarbon group having 1 to 10 carbon atoms, Represents an alkylene group of the formulas 2 to 4. m and n are integers of 1 to 30.)

Examples of the hydrocarbon group having 1 to 20 carbon atoms represented by R in the above formulas [1] and [2] include an alkyl group having 1 to 20 carbon atoms and an aryl group having 6 to 20 carbon atoms. Specifically, a methyl group (—CH ₃ ) and an ethyl group (—C
H ₂ CH ₃ ), n-propyl group (—CH ₂ CH ₂ CH ₃ ),
Isopropyl group (—CH (CH ₃ ) ₂ ), butyl group (—C
₄ H _9), a phenyl group, p-t-butylphenyl group, p-
Examples thereof include an octylphenyl group and a p-nonylphenyl group. Among them, a methyl group (—CH ₃ ) and an ethyl group (—
CH ₂ CH ₃ ), n-propyl group (—CH ₂ CH ₂ C)
H ₃ ), an isopropyl group (—CH (CH ₃ ) ₂ ), a p-octylphenyl group, and a p-nonylphenyl group are preferred.

The C 1-10 fluorine-substituted hydrocarbon group represented by X or Y is a group wherein at least one hydrogen atom of the C 1-10 hydrocarbon group is substituted by a fluorine atom. Specifically, a monofluoromethyl group (—C
H ₂ F), difluoromethyl group (—CHF ₂ ) trifluoromethyl group (—CF ₃ ), 2-fluoroethyl group (—C
H ₂ CH ₂ F), 2,2-difluoroethyl group (—CH ₂
CHF ₂ ), 2,2,2-trifluoroethyl group (—C
H ₂ CF ₃ ), 1,1,1,2,2-pentafluoroethyl group (—CF ₂ CF ₃ ), 3-fluoropropyl group (—
CH ₂ CH ₂ CH ₂ F), 3,3-difluoropropyl group (—CH ₂ CH ₂ CHF ₂ ), 3,3,3-trifluoropropyl group (—CH ₂ CH ₂ CF ₃ ), 2,2,2 3,3
3-pentafluoropropyl group (—CH ₂ CF ₂ C
F ₃ ), — (CF ₂ ) ₂ —CF ₃ , —CH ₂ (CF ₂ ) ₃ —C
F ₃ , —CH ₂ (CF ₂ ) ₅ CF ₃ , — (CH ₂ ) ₅ CF ₂ C
F ₃ , — (CH ₂ ) ₂ (CF ₂ ) ₅ CF ₃ , —CH ₂ (CF ₂ )
₇ CF _{3 and the} like. Among them, a monofluoromethyl group (—CH ₂ F) and a difluoromethyl group (—CH
F ₂ ) trifluoromethyl group (-CF ₃ ), 2-fluoroethyl group (-CH ₂ CH ₂ F), 1,1,1,2,2,-
A pentafluoroethyl group (—CF ₂ CF ₃ ) is preferred.

Specific examples of the alkylene group represented by A include —CH ₂ CH ₂ —, —CH ₂ CH (CH ₃ ) —,
CH ₂ CH (CH ₂ CH ₃ ) —, —CH ₂ CH ₂ CH ₂ —, —
CH ₂ CH ₂ CH ₂ CH ₂ —, —CH ₂ CH (CH ₂ OC
H ₃ ), preferably -CH ₂ CH _2- ,
—CH ₂ CH (CH ₃ ) —. Where m and n
Is an integer of 1 to 30, preferably 1 to 10,
More preferably, it is an integer of 1 to 3.

[0026] Formula [1], the fluorine-containing carbonate compound represented by _{[2], CH 3 -OCOO-} CH 2 CH 2 -O-CH 2 CH 2 F CH 3 CH 2 -OCOO-CH 2 CH _{2 -O-CH 2 CH 2 F} C 9 H 19 -C 6 H 4 -OCOO-CH 2 CH 2 -O-CH 2 C
_{H 2 F CH 3 -OCOO-CH} 2 CH 2 -O-CH 2 CF 3 CH 3 CH 2 -OCOO-CH 2 CH 2 -O-CH 2 CF 3 C 9 H 19 -C 6 H 4 -OCOO-CH ₂ CH ₂ O-CH ₂ CF
₃ (where -C ₆ H _4- represents a 1,4-phenylene group) CH ₃ -OCOO-CH ₂ CH (CH ₃ ) -O-CH ₂ CH
_{2 F CH 3 CH 2 -OCOO-} CH 2 CH (CH 3) -O-CH
_{2 CH 2 F C 9 H 19} -C 6 H 4 -OCOO-CH 2 CH (CH 3) -O
-CH ₂ CH ₂ F (where -C ₆ H ₄ - represents a 1,4-phenylene _{group) CH 3 -OCOO-CH 2 CH} (CH 3) -O-CH 2 CF
_{3 CH 3 CH 2 -OCOO-CH} 2 CH (CH 3) -O-CH
_{2 CF 3 C 9 H 19 -C} 6 H 4 -OCOO-CH 2 CH (CH 3) -O
-CH ₂ CF ₃ (proviso -C ₆ H ₄ - represents a 1,4-phenylene _{group) CH 3 -OCOO- (CH 2 CH} 2 O) 2 -CH 2 CH 2 F CH 3 CH 2 -OCOO- ( _{CH 2 CH 2 O) 2 -CH} 2 CH
_{2 F C 9 H 19 -C 6} H 4 -OCOO- (CH 2 CH 2 O) 2 -CH
_{2 CH 2 F CH 3 -OCOO- (} CH 2 CH 2 O) 2 -CH 2 CF 3 CH 3 CH 2 -OCOO- (CH 2 CH 2 O) 2 -CH2C
_{F 3 C 9 H 19 -C 6} H 4 -OCOO- (CH 2 CH 2 O) 2 -CH
₂ CF ₃ (-C ₆ H _4- represents a 1,4-phenylene group) CF ₃ CH ₂ O-CH ₂ CH ₂ -OCOO-CH ₂ CH ₂ O-
_{CH 2 CH 2 F CF 3 CH} 2 O- (CH 2 CH 2 O) 2 COO-CH 2 CH 2
_{O-CH 2 CH 2 F [} FCH 2 CH 2 -O-CH 2 CH 2 -O] 2 CO [CF 3 CH 2 -O-CH 2 CH 2 -O] 2 CO [FCH 2 CH 2 -O-CH _{2 CH (CH 3) -O]} 2 CO [CF 3 CH 2 -O-CH 2 CH (CH 3) -O] 2 CO [FCH 2 CH 2 -O- (CH 2 CH 2 O) 2] 2 CO _{[CF 3 CH 2 -O- (CH} 2 CH 2 O) 2] 2 CO [FCH 2 CH 2 -O- (CH 2 CH (CH 3) O)] 2 C
_{O [CF 3 CH 2 -O- (} CH 2 CH (CH 3) O)] , such as ₂ CO and the like. Among these, a particularly preferred fluorine-containing carbonate compound is CH ₃ —OCOO—CH ₂ CH ₂ —O—CH ₂ CH ₂ F CH ₃ —OCOO—CH ₂ CH ₂ —O—CH ₂ CF ₃ CH ₃ —OCOO—CH _{2 CH (CH 3) -O-} CH 2 CH
_{2 F CH 3 -OCOO-CH 2} CH (CH 3) -O-CH 2 CF
₃ CH ₃ CH ₂ —OCOO—CH ₂ CH ₂ —O—CH ₂ CH ₂ F CH ₃ CH ₂ —OCOO—CH ₂ CH ₂ —O—CH ₂ CF ₃ [FCH ₂ CH ₂ —O—CH ₂ CH ₂ —O] ₂ CO [CF ₃ CH ₂ —O—CH ₂ CH ₂ —O] ₂ CO.

The number of fluorine atoms in the fluorine-containing carbonate compound used in the present invention may be at least one, but is preferably from 1 to 10, particularly preferably from 1 to 6.
It is. When the number of fluorine atoms is in the range of 1 to 10, a fluorine-containing carbonate compound and a cyclic carbonate described below,
There is an advantage that compatibility with a non-aqueous solvent such as a chain carbonate is improved.

Such a fluorine-containing carbonate compound is physically safe, hardly thermally decomposed, flame-retardant, and hardly subjected to electrochemical oxidation and reduction. [Non-Aqueous Solvent] The above-mentioned fluorine-containing carbonate compound alone can be used as a non-aqueous solvent for a non-aqueous electrolyte, but can also be used as a mixed solvent with another non-aqueous solvent such as a carbonate ester. . In this case, in order to improve the safety of the battery, the fluorine-containing carbonate compound is
It is desirably contained in the nonaqueous solvent in an amount of 0.1 to 100% by weight, preferably 1 to 90% by weight, more preferably 20 to 70% by weight. In the non-aqueous electrolyte according to the present invention, it is preferable to use a mixed solvent containing the above-mentioned fluorine-containing carbonate compound and cyclic carbonate and / or chain carbonate especially from the viewpoint of improving ion conductivity.

[Cyclic Carbonate] Examples of the cyclic carbonate used in the present invention include carbonates represented by the following general formula [3].

[0030]

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Here, R ⁹ and R ¹⁰ may be the same or different from each other, and represent a hydrogen atom, a linear, branched, or cyclic alkyl group, or a part of hydrogen of these alkyl groups. Or a halogen-substituted alkyl group in which all are substituted with at least one of chlorine and bromine. As the linear alkyl group, a linear alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group is preferable. Examples of the branched alkyl group include an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.
Is preferred. . As the cyclic alkyl group, a cyclic alkyl group having 5 to 10 carbon atoms such as a cyclopentyl group, a cyclohexyl group, and a 1-methyl-cyclohexyl group is preferable.

The cyclic carbonate may be not only a 5-membered ring compound represented by the above formula [3] but also a 6-membered ring compound. Specific examples of the cyclic carbonate represented by the above formula [3] include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,3-propylene carbonate, 1 , 3-butylene carbonate, 2,4-pentylene carbonate, 1,3-pentylene carbonate, vinylene carbonate and the like.

Further, a halogen-substituted cyclic carbonate in which a methyl group such as the above-mentioned propylene carbonate has part or all of hydrogen substituted with at least one of fluorine, chlorine and bromine can be used.

In the present invention, as the cyclic carbonate, those containing an alkylene group having 2 to 5 carbon atoms are preferable, and ethylene carbonate and propylene carbonate are particularly preferable.

These cyclic carbonates can be used as a mixture of two or more kinds. [Chain Carbonate] Examples of the chain carbonate include carbonates represented by the following general formula [4].

[0036]

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In the formula, R ¹¹ and R ¹² may be the same or different from each other, and represent a linear, branched, or cyclic alkyl group;
Or a halogen-substituted alkyl group in which part or all of the hydrogen of these alkyl groups has been substituted with at least one of fluorine, chlorine and bromine. As the linear alkyl group, a linear alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group is preferable. As the branched alkyl group, a branched alkyl group having 3 to 10 carbon atoms such as an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group is preferable. . As the cyclic alkyl group, a cyclic alkyl group having 5 to 10 carbon atoms such as a cyclopentyl group, a cyclohexyl group, and a 1-methyl-cyclohexyl group is preferable.

Specific examples of such a chain carbonate include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, dibutyl carbonate, diisopropyl carbonate, methyl ethyl carbonate and the like.

Among such chain carbonates, in the present invention, chain carbonates containing a hydrocarbon group having 1 to 5 carbon atoms are preferable, and dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate are particularly preferable. [Solvent composition]

When a fluorine-containing carbonate compound or a mixed solvent of the fluorine-containing carbonate compound and the cyclic carbonate and / or the chain carbonate is used as the non-aqueous solvent, the fluorine-containing carbonate compound is 0.1 to 100% by weight in the non-aqueous solution. %, Preferably 1 to 90% by weight, particularly preferably 20 to 70% by weight, and said cyclic carbonate and / or chain carbonate is contained in a non-aqueous solvent at 0 to 99% by weight. It is desirable that it be contained in an amount of 9.9% by weight, preferably 10 to 99% by weight, particularly preferably 30 to 80% by weight.

A non-aqueous electrolyte using a non-aqueous solvent having the above composition has low reactivity between the positive electrode and the electrolyte, and can improve the safety of the battery. That is, the non-aqueous electrolyte containing the non-aqueous solvent having the solvent composition as described above has a maximum heat generation rate when mixed with the positive electrode in a charged state, as compared with a non-aqueous electrolyte containing no fluorine-containing carbonate compound. , About 1 /
It falls to 10 or less.

The maximum heat generation rate represents the maximum heat generation rate in the exothermic reaction (in the present invention, the reaction between the positive electrode and the nonaqueous electrolyte). When the maximum heat generation rate is measured under the same conditions,
If the maximum heat generation rate is small, the temperature rise is slow and safe. On the other hand, those having a large maximum heat generation rate have a sharp rise in temperature. For example, if sufficient cooling equipment is not provided, the heat generation rate exceeds the heat absorption rate, and there is a danger that the reactants may run out of heat. I have.

Such a maximum heat generation rate is measured using an accelerating calorimeter (hereinafter referred to as an ARC). ARC is one of the methods to evaluate the danger of reactive chemical substances (Thermochimica Acta, 3
7 (1980), 1-30). The ARC gradually raises the temperature of the reactive substance, and when detecting the reaction heat generated from the reactive substance, raises the surrounding temperature in accordance with the temperature rise of the reactive substance,
The reactive substance is placed in a pseudo-adiabatic state, whereby the exothermic decomposition of the reactive substance is faithfully reproduced. Further, in the present invention, when a fluorine-containing carbonate compound or a mixed solvent of the fluorine-containing carbonate compound and the cyclic carbonate and / or the chain carbonate is used as the non-aqueous solvent, the amount of the cyclic carbonate and the chain carbonate is used. The ratio is 0: 100 to 100: 0, preferably 20:80 to 80:20 (all by weight).

[Other Solvents] The non-aqueous electrolyte according to the present invention may contain other solvents other than the above as non-aqueous solvents as long as the characteristics of the electrolyte of the present invention are not impaired. As the solvent, cyclic esters such as γ-butyrolactone, γ-valerolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propyl acetate, propionic acid Chain esters such as methyl, methyl butyrate and methyl valerate, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3
Cyclic ethers such as -dioxolan, 2-methyl-1,3-dioxolan, chain ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether;
Examples thereof include sulfur-containing compounds such as sulfolane and dimethyl sulfate, and phosphorus-containing compounds such as trimethylphosphoric acid and triethylphosphoric acid. These solvents can be used alone or in combination of two or more.

[Electrolyte] The electrolyte used in the present invention is not particularly limited as long as it is usually used as an electrolyte for a non-aqueous electrolyte. Specifically, LiPF ₆ , LiBF ₄ , LiCl
O ₄ , LiAsF ₆ , LiAlCl ₆ , Li ₂ SiF ₆ , LiOSO
₂ R ₁ ,

[0046]

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Wherein R ^{1 to} R ⁸ may be the same or different and are each a perfluoroalkyl group having 1 to 6 carbon atoms, and the like. Examples thereof include an alkali metal salt substituted with a metal. These can be used alone or in combination of two or more.

Among these, in particular, LiPF ₆ , LiB
F ₄ , LiOSO ₂ R ₁ ,

[0049]

Embedded image Is preferred.

Such electrolytes are usually 0.1 to 3.0.
It is desirable that it is contained in the non-aqueous electrolyte at a concentration of 0.5 mol / l, preferably 0.5 to 2.0 mol / l.

[Non-Aqueous Electrolyte Secondary Battery] The non-aqueous electrolyte secondary battery according to the present invention comprises the above-mentioned non-aqueous electrolyte, lithium as a negative electrode active material, a lithium-containing alloy, and doping / de-doping of lithium ions. A negative electrode containing any of a carbon material capable of doping, tin oxide capable of doping and undoping lithium ions, silicon capable of doping and undoping lithium ions, and titanium oxide capable of doping and undoping lithium ions. And a positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material.

Such a non-aqueous electrolyte secondary battery can be applied to, for example, a cylindrical non-aqueous electrolyte secondary battery. As shown in FIG. 1, a cylindrical nonaqueous electrolyte secondary battery has a negative electrode 1 formed by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector 10. 2 is wound through a separator 3 into which a non-aqueous electrolyte is injected, and is housed in a battery can 5 with an insulating plate 4 placed above and below the wound body. A battery lid 7 is attached to the battery can 5 by caulking via a sealing gasket 6, and is electrically connected to the negative electrode 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. It is configured to function as a positive electrode. The separator is a porous film.

In this battery, the positive electrode lead 12 may be electrically connected to the battery lid 7 via the current interrupting thin plate 8. In such a battery, when the pressure inside the battery rises, the current interrupting thin plate 8 is pushed up and deformed, and the positive electrode lead 12 is cut off leaving the portion welded to the thin plate 8 to cut off the current.

As the negative electrode active material constituting the negative electrode 1, any of lithium metal, a lithium alloy, and a carbon material capable of doping / dedoping lithium ions can be used. Among these, it is preferable to use a carbon material capable of doping and undoping lithium ions. Such a carbon material may be graphite or amorphous carbon, and any carbon material such as activated carbon, carbon fiber, carbon black, and mesocarbon microbeads can be used.

The positive electrode active materials constituting the positive electrode 2 include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ ,
A composite oxide composed of lithium and a transition metal, such as LiNixCo (1-x) O ₂ , V ₂ O _5, or the like can be used.

The non-aqueous electrolyte secondary battery according to the present invention comprises:
The electrolyte contains the non-aqueous electrolyte described above, and the shape and form of the battery are not limited to those in FIG.
It may be a coin type or a square type.

[0057]

The non-aqueous electrolyte according to the present invention contains a fluorine-containing carbonate compound and uses a non-aqueous solvent having a specific solvent composition. Is excellent. Such a non-aqueous electrolyte has a practical level of ionic conductivity and does not separate the electrolyte.

Such a non-aqueous electrolyte can be suitably used as an electrolyte for a lithium ion secondary battery.

[0059]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

[0060]

Example 1 Preparation of Non-Aqueous Electrolyte Solution Propylene carbonate (PC) and dimethyl carbonate (D
MC) and a fluorine-containing carbonate compound represented by the following general formula, propylene carbonate: dimethyl carbonate: fluorine-containing carbonate compound (weight ratio) = 1
In a non-aqueous solvent mixed at a ratio of 5:15:70, Li was added.
A non-aqueous electrolyte was prepared by dissolving PF ₆ at 1 mol / l.

CH ₃ —OCOO—CH ₂ CH ₂ —O—CH ₂ CH ₂ F

Preparation of positive electrode for maximum heat generation rate measurement LiCoO ₂ and PVDF (poly (vinylidene fluoride))
And graphite were mixed in a weight ratio of 91: 3: 6, slurried with NMP, applied to an aluminum foil, dried, and pressed to produce a positive electrode. A non-aqueous electrolyte for charging (propylene) prepared by dissolving LiPF ₆ at a molar ratio of 1: 1 in a solvent in which the thus obtained positive electrode, Li negative electrode, propylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 1. LiPF ₆ was dissolved in a solvent in which carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1 so as to be 1 mol / liter), and the battery was charged at a constant voltage of 4.4 V. Two hours after charging, the potential was 4.38 V. This electrode was sufficiently washed and dried with dimethyl carbonate to remove dimethyl carbonate. This electrode was cut into about 2 mm square to produce a positive electrode for measuring the maximum heat generation rate.

Measurement of Maximum Heating Rate Under an argon atmosphere, 0.3 ml of the nonaqueous electrolyte prepared above was used.
And 1.00 g of the positive electrode for maximum heat generation rate measurement were mixed to prepare a measurement sample.

The measurement was performed using ARCT of COLUMBIA SCIENTIFIC.
The measurement was performed by an ordinary method using M (Accelerating Rate Calorimeter). The measurement temperature range was 40 to 350 ° C. Note that the heat generation rate represents the amount of self-temperature rise of the sample per unit time, and the maximum heat generation rate is the maximum value of the heat generation rate during the measurement period.

Table 1 shows the results.

[0066]

Examples 2 to 9 The procedure of Example 1 was repeated except that the fluorine-containing carbonate compound used was as shown in Table 1.
A non-aqueous electrolyte was prepared in the same manner as in Example 1, and the maximum heat generation rate was measured.

Table 1 shows the results.

[0068]

Comparative Example 1 A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the solvent composition used was changed to that shown in Table 1, and the maximum heat generation rate was measured.

Table 1 shows the results.

[0070]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 4 ... Insulating plate 5 ... Battery can 6 ... Sealing gasket 7 ... Battery cover 8 ...・ Current cutting thin plate 9 ・ ・ ・ ・ Negative electrode current collector 10 ・ ・ ・ ・ Positive electrode current collector 11 ・ ・ ・ ・ Negative electrode lead 12 ・ ・ ・ ・ Positive electrode lead

Claims (5)

[Claims] 1. A non-aqueous electrolyte comprising a non-aqueous solvent containing a fluorine-containing carbonate compound represented by the following general formula [1] or [2] and an electrolyte. _{R-OCOO- (AO) n -CH} 2 -X [1] X-CH 2 O- (AO) n -COO- (AO) m -CH 2 -Y [2] ( Formula [1], [2] Wherein R is a hydrocarbon group having 1 to 20 carbon atoms, X and Y may be the same or different from each other, and each represents a fluorine-substituted hydrocarbon group having 1 to 10 carbon atoms, Represents an alkylene group of the formulas 2 to 4. m and n are integers of 1 to 30.) 2. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent contains a cyclic carbonate and / or a chain carbonate. 3. The cyclic carbonate is a cyclic carbonate compound containing an alkylene group having 2 to 5 carbon atoms, and the chain carbonate is a chain carbonate containing a hydrocarbon group having 1 to 5 carbon atoms. The non-aqueous electrolyte according to claim 2, which is a compound. 4. The electrolyte according to claim 1, wherein the electrolyte is LiPF ₆ , LiBF ₄ , or LiOS.
O ₂ R ₁ , (Wherein, R ^{1 to} R ⁸ may be the same or different from each other and are perfluoroalkyl groups having 1 to 6 carbon atoms). Item 4. The non-aqueous electrolyte according to any one of Items 1 to 3. 5. A non-aqueous electrolyte according to claim 1, wherein the negative electrode active material is metallic lithium, a lithium-containing alloy, a carbon material capable of doping / dedoping lithium ions, and a lithium ion doping. A negative electrode containing any of undoped tin oxide, lithium ion-doped / undoped silicon, and lithium-ion doped / undoped titanium oxide; and lithium and transition metal as the positive electrode active material And a positive electrode containing a composite oxide.