JP2002343426A - Nonaqueous electrolyte and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte which can realize a battery of superior safety, having a high flashing point and a superior service life property with little capacity lowering and deterioration in load characteristics, during high temperature storage as a decomposition reaction of a solvent is suppressed, and to provide a secondary battery containing this nonaqueous electrolyte. SOLUTION: The nonaqueous electrolyte contains the nonaqueous solvent including cyclic carboxylic acid ester, a sulfonic acid derivative, and a lithium salt. By using the electrolyte containing the cyclic carboxylic acid ester, the lithium salt such as LiPF6 , and sulfonic acid derivatives, the nonaqueous electrolyte secondary battery can be provided, in which the deterioration in the load characteristics or resistance at a service life test including a high temperature storage test, is significantly suppressed. In addition, the nonaqueous electrolyte enables providing the nonaqueous electrolyte secondary battery of superior safety, having the high flashing point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte and a secondary battery using the same. More specifically, the present invention relates to a non-aqueous electrolyte containing a non-aqueous solvent, an additive, and a lithium salt, which enables a battery having excellent safety and long life characteristics, and a secondary battery using the same.

[0002]

BACKGROUND OF THE INVENTION A battery using a non-aqueous electrolyte has a high voltage, a high energy density, and a high reliability such as storability, so that it is widely used as a power source for consumer electronic devices. Have been.

[0003] As such a battery, there is a non-aqueous electrolyte secondary battery, a typical example of which is a lithium battery. As an electrolytic solution used for this, LiBF is added to an aprotic organic solvent.
₄ , LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiCF
A solution in which a Li electrolyte such as ₃ SO ₃ and Li ₂ SiF ₆ is mixed is used (edited by Jean-Paul Gabano, “Lithium
Battery ", ACADEMIC PRESS (1983)).

[0004] As aprotic organic solvents, carbonates are known, and use of various carbonate compounds such as ethylene carbonate, propylene carbonate and dimethyl carbonate has been proposed (Japanese Patent Laid-Open No. 4-1 / 1991).
No. 84872, JP-A-10-27625).
As other aprotic solvents that can be used, sulfur solvents have been proposed. For example, cyclic sulfones (JP-A-57-187878 and JP-A-61-16478), chain-like sulfones (JP-A-3-152879, JP-A-8-241732), sulfoxides ( 57-141878, JP-A-61-16478),
Examples thereof include sultones (JP-A-63-102173) and sulfites (JP-A-61-64080). Further, esters (JP-A-4-14769)
And the use of aromatic compounds (JP-A-4-249870).

One of the mainstream lithium secondary batteries at present is a lithium ion secondary battery. This battery includes a negative electrode made of an active material capable of inserting and extracting lithium, a positive electrode made of a composite oxide of lithium and a transition metal, an electrolyte, and the like.

As a negative electrode active material of a lithium ion secondary battery, a carbon material capable of occluding and releasing lithium is often used. In particular, highly crystalline carbon such as graphite has a flat discharge potential and a true discharge potential. It has features such as high density and good filling properties, and has been adopted as most negative electrode active materials of currently marketed lithium ion secondary batteries.

[0007] In addition, a mixed solvent of a high dielectric constant carbonate solvent such as propylene carbonate and ethylene carbonate and a low viscosity carbonate solvent such as diethyl carbonate, methyl ethyl carbonate and dimethyl carbonate is used in the electrolyte solution, and LiBF ₄ , LiPF ₆ , LiN
(SO ₂ CF ₃ ) ₂ and LiN (SO ₂ CF ₂ CF ₃ ) ₂
For example, a solution in which a Li electrolyte is mixed is used.

When using highly crystalline carbon such as graphite for the negative electrode, it is important to suppress the reductive decomposition reaction of the electrolytic solution on the graphite negative electrode. For this reason, as a non-aqueous solvent having a high dielectric constant used in the electrolytic solution, ethylene carbonate or a mixed solvent of ethylene carbonate and propylene carbonate, which is solid at ordinary temperature but hardly undergoes reductive decomposition reaction continuously, is used. Thus, it has been proposed to suppress the reductive decomposition reaction of the non-aqueous solvent.

However, it is known that even when ethylene carbonate is used, a reductive decomposition reaction of a trace amount of the electrolytic solution continuously occurs on the surface of the negative electrode (J. Electrochem.
c., 147 (10), 3628-3632 (2000), J. Electrochem. Soc., 146
(11), 4014-4018 (1999), J. Power Sources No. 81-82, 8-
12 (1999)) For example, when the battery is repeatedly used for a long period of time, and the battery is stored at a high temperature, the capacity of the battery is considered to be reduced, which is not always sufficient.

From the viewpoint of safety, an electrolyte having a high flash point is desired. However, an electrolyte solution that completely satisfies the demands of excellent load characteristics and life characteristics and high safety has not yet been obtained, and development of such an electrolyte is required.

[0011]

SUMMARY OF THE INVENTION It is possible to provide a battery having a high flash point, excellent safety, a suppressed decomposition reaction of a solvent, and excellent life characteristics with little reduction in capacity and deterioration in load characteristics during high-temperature storage. It is an object of the present invention to provide an electrolyte solution. It is another object of the present invention to provide a secondary battery including the non-aqueous electrolyte.

[0012]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte containing a non-aqueous solvent containing a cyclic carboxylic acid ester, a sulfonic acid derivative and a lithium salt.

A non-aqueous electrolyte in which the sulfonic acid derivative is at least one compound selected from an alkanesulfonic acid derivative and an arylsulfonic acid derivative is a preferred embodiment of the present invention.

The above non-aqueous electrolyte in which the cyclic carboxylic acid ester is γ-butyrolactone is a preferred embodiment of the present invention.

The non-aqueous electrolytic solution according to the present invention, wherein the non-aqueous solvent is a non-aqueous solvent containing at least one other non-aqueous solvent having a cyclic structure selected from cyclic carbonate and cyclic sulfone in addition to γ-butyrolactone. This is a preferred embodiment.

The above non-aqueous electrolyte in which the lithium salt is a lithium salt containing LiPF ₆ is a preferred embodiment of the present invention.

The lithium salt is LiPF₆Plus L
iBF₄, LiClO₄, LiAsF₆, LiN (SO
₂C_kF_{(2k + 1)})₂(K = 1 to 8), Li
PF _n(C_kF_{(2k + 1)})_(6-n)(N = 1 ~
5, k = 1 to 8).
The above-mentioned non-aqueous electrolyte containing a lithium salt is preferably used in the present invention.
This is a preferable mode.

In a preferred embodiment of the present invention, the non-aqueous electrolyte further contains a vinylene carbonate derivative represented by the general formula (1).

Embedded image (R ¹ and R ² are hydrogen, a methyl group, an ethyl group, or a propyl group.)

The present invention relates to a negative electrode active material comprising metallic lithium, a lithium-containing alloy, a metal or alloy capable of being alloyed with lithium, an oxide capable of doping and undoping lithium ions, and a doping and undoping lithium ions. Negative electrode containing transition metal nitride, carbon material capable of doping / dedoping lithium ion, or a mixture thereof, and transition metal oxide, composite oxide of lithium and transition metal as positive electrode active material Or a lithium secondary battery including the positive electrode containing any of these, or a mixture thereof, and the above nonaqueous electrolyte.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte according to the present invention and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte will be specifically described. In the present invention, the non-aqueous electrolyte is
A non-aqueous electrolytic solution containing a cyclic carboxylic acid ester, a sulfonic acid derivative and an electrolyte,
The present invention provides a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte.

Non-aqueous solvent The non-aqueous solvent constituting the electrolytic solution of the present invention contains at least a cyclic carboxylic acid ester. The cyclic carboxylate has a low vapor pressure, a low viscosity, and a high dielectric constant. For this reason, the viscosity of the electrolyte can be reduced without lowering the flash point of the electrolyte and the degree of dissociation of the electrolyte, so that the electrolyte is an index related to the load characteristics of the battery without increasing the flammability of the electrolyte. Conductivity can be increased.

Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone, γ-valerolactone and δ-valerolactone.
Lactones such as valerolactone, and methyl γ-butyrolactone, ethyl γ-valerolactone, ethyl δ-
Examples thereof include alkyl-substituted lactones such as valerolactone. Among them, γ-butyrolactone is particularly preferably used.

As the non-aqueous solvent of the present invention, a cyclic carboxylic acid ester may be used alone, but may be used together with another non-aqueous solvent.

As the other non-aqueous solvent that can be used together with the cyclic carboxylate in the electrolytic solution of the present invention, any non-aqueous solvent commonly used for non-aqueous batteries can be used. Preferred examples thereof include cyclic carbonates such as ethylene carbonate, cyclic sulfones such as sulfolane, cyclic carbamates such as N-methyloxazolidinone, cyclic ethers such as dioxolan, chain carbonates such as dimethyl carbonate, and methyl propionate. Chain carboxylate, chain ether such as dimethoxyethane, chain sulfone such as diethyl sulfone, chain carbamate such as methyl-N, N-dimethyl carbamate, chain phosphoric acid such as trimethyl phosphate Esters can be mentioned.

Of these, from the viewpoint of electrochemical stability,
Cyclic carbonate, chain carbonate, cyclic sulfone,
Linear sulfones are preferred.

Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate,
Examples thereof include 1,2-pentylene carbonate and 2,3-pentylene carbonate. In particular, ethylene carbonate and propylene carbonate having a high dielectric constant are preferably used.

Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl Carbonate, ethylpentyl carbonate, dipentyl carbonate, methyl heptyl carbonate, ethyl heptyl carbonate, diheptyl carbonate, methyl hexyl carbonate, ethyl hexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate,
Dioctyl carbonate, methyl trifluoroethyl carbonate and the like can be mentioned.

Specific examples of the sulfones include sulfolane,
2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, dipropylsulfone,
Methyl ethyl sulfone, methyl propyl sulfone and the like can be mentioned.

In the case of a battery using graphite as the negative electrode active material, it is particularly desirable to contain ethylene carbonate.

Specific examples of the combination of the non-aqueous solvent include γ-butyrolactone and ethylene carbonate, γ-butyrolactone.
Butyrolactone and ethylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and propylene carbonate and dimethyl carbonate, γ-butyrolactone and Propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and propylene carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate Methyl ethyl mosquito Boneto, .gamma.-butyrolactone, ethylene carbonate, propylene carbonate and diethyl carbonate, .gamma.-butyrolactone, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, .gamma.-butyrolactone, ethylene carbonate, dimethyl carbonate and diethyl carbonate,
γ-butyrolactone, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ- Butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate Ne DOO, .gamma.-butyrolactone and sulfolane, .gamma.-butyrolactone, ethylene carbonate and sulfolane, .gamma.-butyrolactone, propylene carbonate and sulfolane, .gamma.-butyrolactone, ethylene carbonate, propylene carbonate and sulfolane, gamma
-Butyrolactone, sulfolane, dimethyl carbonate and the like.

The mixing ratio of the cyclic carboxylic acid ester in the non-aqueous solvent is from 100 to 10%, more preferably from 90 to 20%, particularly preferably from 80 to 30%, by weight. With such a ratio, the conductivity of the electrolytic solution relating to the charge / discharge characteristics of the battery can be increased.

In order to improve the flash point of the solvent in order to improve the safety of the battery, it is preferable to use a non-aqueous solvent having a cyclic structure (hereinafter referred to as a cyclic non-aqueous solvent) as the non-aqueous solvent. The cyclic non-aqueous solvent may be used alone or as a mixture of two or more. When the flash point of the solvent is to be improved, a mixture of a cyclic non-aqueous solvent and a non-aqueous solvent having a chain structure may be used. In this case, it is desirable to use the chain structure so that the weight ratio is less than 20% with respect to the whole non-aqueous solvent. The cyclic nonaqueous solvent and the nonaqueous solvent having a chain structure may be used alone or in combination.

In this case, examples of desirable combinations of the cyclic non-aqueous solvents include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate, γ-butyrolactone and ethylene carbonate and sulfolane. Can be exemplified.

Examples of preferred non-aqueous solvents having a chain structure to be mixed with a cyclic non-aqueous solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diheptyl carbonate, and the like.
Examples thereof include methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, methyl heptyl carbonate, ethyl butyl carbonate, ethyl heptyl carbonate, dimethyl sulfone, diethyl sulfone, dipropyl sulfone, and dibutyl sulfone.

The non-aqueous electrolyte of the present invention may contain other general non-aqueous solvents other than those described above as long as the object of the present invention is not impaired. Specific examples thereof include amides such as dimethylformamide and the like. Examples include cyclic amides such as N-methylpyrrolidone, cyclic ureas such as N, N-dimethylimidazolidinone, and polyethylene glycol derivatives and oligoethylene glycol derivatives.

Sulfonic Acid Derivative The electrolytic solution of the present invention contains a sulfonic acid derivative as an additive in addition to the non-aqueous solvent. As sulfonic acid derivatives,
Examples thereof include esters and salts of sulfonic acids. Specific examples of the sulfonic acid derivative include alkanesulfonic acid derivatives such as alkanesulfonic acid esters and salts such as methanesulfonic acid methyl ester, and arylsulfonic acid esters such as benzenesulfonic acid methyl ester and lithium benzenesulfonic acid salt. And aryl sulfonic acid derivatives such as salts.

Preferred examples of these sulfonic acid derivatives include aryl sulfonic acid derivatives, more preferably benzene sulfonic acid derivatives. A specific example of the benzenesulfonic acid derivative is a compound having a structure represented by the following general formula (2).

Embedded image (R ³ is an alkyl group or a metal. R ^{4 to} R ⁸ may be the same or different from each other, may combine with each other to form a ring, and include hydrogen, halogen, a sulfonate group, a metal sulfonate, Groups, carboxylic acid ester groups, carboxylic acid metal groups, and organic groups having 1 to 10 carbon atoms.)

Examples of the metal include an alkali metal and an alkaline earth metal, and an alkali metal is particularly desirable.
Specific examples of the alkali metal include lithium, sodium, and potassium, with lithium being most desirable. Examples of the organic group having 1 to 10 carbon atoms include a hydrocarbon group, a halogenated hydrocarbon group, a hydrocarbon group containing a hetero atom, and a halogenated hydrocarbon group containing a hetero atom. Heteroatoms include oxygen, nitrogen, sulfur, phosphorus,
Boron and the like. Examples of the halogen include fluorine and chlorine.

Specific examples of the organic group having 1 to 10 carbon atoms include a trifluoromethyl group, a trifluoromethoxy group,
Trifluoroethyl group, trifluoroethoxy group, pentafluoroethyl group, pentafluoroethoxy group, methyl group, methoxy group, ethyl group, ethoxy group, vinyl group,
Vinyloxy, ethynyl, propyl, propyloxy, isopropyl, 1-propenyl, 2-propenyl, 1-propynyl, 2-propynyl, allyloxy,
Propargyloxy group, butyl group, butoxy group, sec-butyl group, t-butyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 2-methyl-2-propenyl group, 1-methylenepropyl group, 1 -Methyl-2-propenyl group, 1,2-dimethylvinyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, butenyloxy group, butynyloxy group, pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2-methylpropyl group, 2,2-dimethylpropyl group,
Phenyl group, phenoxy group, methylphenyl group, ethylphenyl group, vinylphenyl group, ethynylphenyl group,
Fluorovinylphenyl group, fluoroethynylphenyl group, fluorophenyl group, difluorophenyl group, trifluoromethylphenyl group, chlorophenyl group, fluoromethoxyphenyl group, difluoromethoxyphenyl group, methoxycarbonyl group, ethoxycarbonyl group, trifluoroethoxycarbonyl group And a trifluoromethylcarbonyl group. R ^{4 to} R exemplified above
Of the ^eight substituents, the number of carbon atoms of the substituent is desirably three or less from the viewpoint of solubility of phenylsulfonic acid or metal phenylsulfonic acid in the electrolytic solution.

In the present invention, it is particularly desirable that at least one of R ^{4 to} R ⁸ is either a sulfonic acid ester group or a metal sulfonic acid group.

Specific examples of the benzenesulfonic acid derivatives described above include the following compounds. In the following, esters are methyl esters,
Ethyl ester, propyl ester, butyl ester,
Indicates that it is any of phenyl ester, trifluoromethyl ester and pentafluoropropyl ester.

Naphthalene sulfonic acid ester, benzene sulfonic acid ester, benzene di (sulfonic acid ester), benzene tri (sulfonic acid ester), sulfobenzoic acid diester, toluene sulfonic acid ester, toluene di (sulfonic acid ester), toluent (sulfonic acid) Ester), trifluoromethylbenzene (sulfonate), trifluoromethylbenzenedi (sulfonate), trifluoromethylbenzenetri (sulfonate), lithium naphthalenesulfonate, lithium benzenesulfonate, trifluoromethyl Lithium benzenesulfonate, dilithium benzenedisulfonate, dilithium trifluoromethylbenzenedisulfonate, trilithium benzenetrisulfonate, sulfobenzo Dilithium salt, lithium methoxycarbonylbenzenesulfonate, lithium ethoxycarbonylsulfonate, lithium vinyloxycarbonylsulfonate, lithium allyloxycarbonylsulfonate, lithium ethynyloxycarbonylsulfonate, lithium propargyloxycarbonylbenzenesulfonate , Lithium trifluoroethyloxycarbonylbenzenesulfonate, lithium toluenesulfonate, dilithium toluenedisulfonate,

Of the benzene-sulfonic acid derivatives exemplified above, benzenedi (sulfonic acid ester) and dilithium benzenedisulfonic acid are particularly desirable.
Further, meta-benzenedi (sulfonic acid ester) and dilithium ortho-benzenedisulfonic acid are preferred. More specifically, meta-benzenedisulfonic acid dimethyl ester, meta-benzenedisulfonic acid diethyl ester, meta-benzenedisulfonic acid dipropyl ester,
Dilithium ortho-benzenedisulfonate is most desirable.

By using a sulfonic acid derivative in an electrolyte containing a cyclic carboxylic acid ester such as γ-butyrolactone, the effect of suppressing the reductive decomposition reaction of the electrolyte on the negative electrode is high, and it can be used during high-temperature storage or cycle use. The battery capacity at the time is suppressed.

Further, the sulfonic acid derivative suppresses an increase in the impedance of the positive electrode during a high-temperature storage test or a cycle test, thereby suppressing deterioration in load characteristics. This effect is particularly noticeable when LiPF ₆ is used as a lithium salt for the electrolyte. The sulfonic acid derivative described above may be added alone to the electrolytic solution, or a mixture of a plurality of sulfonic acid derivatives may be added.

When the amount of the sulfonic acid derivative added to the electrolytic solution is small, the effect is hardly exhibited, and when too large, the interface impedance of the negative electrode may increase.
For this reason, the amount added to the electrolyte is 0.00
01 wt% to 30 wt% is preferred, and 0.001 wt%
10 to 10% by weight is more preferable, and 0.1 to 7% by weight.
Is more preferable, and 0.2 to 5% by weight is most preferable.

Other Additives In the present invention, in addition to the sulfonic acid derivative of the present invention,
By including other additives together, it is possible to impart more excellent characteristics to the electrolyte solution. As other additives that may be added in the present invention, if they alone have an action of suppressing electrolysis on the negative electrode, the electrolysis on the negative electrode is further suppressed, and the self-discharge of the battery is further reduced. Can be suppressed. As a result, there is obtained an effect that the load characteristics, high-temperature storage characteristics, and cycle characteristics of the battery are improved.

It is desirable that the compound contained simultaneously with the sulfonic acid derivative alone has the function of suppressing electrolysis on the negative electrode. With this configuration, electrolysis on the negative electrode is further suppressed, and the self-discharge of the battery can be further reduced. As a result, the load characteristics, high-temperature storage characteristics, and cycle characteristics of the battery are improved.

Other additives having the function of suppressing electrolysis on the negative electrode include vinylene carbonate derivatives represented by the following general formula (1); cyclic carbonates having a vinyl group such as vinyl ethylene carbonate and divinyl ethylene carbonate; Carboxylic anhydrides such as maleic acid, norbornene dicarboxylic anhydride, diglycolic acid, vinyl phthalic anhydride; compounds having a carbon-carbon triple bond such as methylpropargyl carbonate, dipropargyl carbonate, ethynyl phthalic anhydride; vinyl methyl sulfone And vinylsulfones such as divinylsulfone and vinylphenylsulfone.

[0050]

Embedded image (R ¹ and R ² are hydrogen, a methyl group, an ethyl group, or a propyl group.)

Of these compounds, vinylene carbonate derivatives represented by the general formula (1) are preferred. Specific examples of the vinylene carbonate derivative represented by the general formula (1) include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl ethylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, and dipropyl vinylene carbonate. Among these, vinylene carbonate can be mentioned as a more preferable one.

When the sulfonic acid derivative and the compound having the effect of suppressing electrolysis on the negative electrode are simultaneously added to the electrolytic solution of the present invention, the addition ratio is 1: 100 to 100 by weight. : 1, preferably 1:20 to
20: 1, more preferably 1:10 to 20: 1. In particular, when the compound having the effect of suppressing electrolysis on the negative electrode is vinylene carbonate, the ratio of the sulfonic acid derivative to vinylene carbonate is 1: 5 to 20: 1.
Is desirable. When the sulfonic acid derivative and the compound having the effect of suppressing electrolysis on the negative electrode described above are simultaneously added to the electrolytic solution, the total amount added is 40
It is desirable that the content be not more than% by weight.

Lithium Salt The electrolyte of the present invention is preferably a lithium salt. Lichi
As a specific example of the um salt, LiPF₆, LiBF₄, L
iCLO₄, LiAsF₆, Li₂SiF₆, LiOS
O₂C_kF_{(2k + 1)} (K = 1 to 8), Li
PF_n(C_kF _{(2k + 1)})_(6-n) (N = 1 ~
5, k = 1 to 8) and the like.
You. In addition, a lithium salt represented by the following general formula is also used.
be able to. LiC (SO₂R⁹) (SO₂R¹⁰)
(SO₂R¹¹), LiN (SO₂OR¹²) (SO₂
OR¹³), LiN (SO₂R¹⁴) (SO₂O
R^Fifteen) (Where R⁹~ R^FifteenAre identical to each other
May be different from each other, and have 1 to 8 carbon atoms.
Alkyl group). These lithium salts are used alone
Or a mixture of two or more.
Also, (C₂H₅)₄NPF ₆, (C₂H₅)₄NBF
₄, (C₂H₅)₄NCLO₄, (C₂H₅)₄NAs
F₆, (C₂H₅)₄N₂SiF₆, (C₂H₅)₄N
OSO₂C_kF_{(2k +1)}(K is an integer from 1 to 8),
(C₂H₅)₄NPF_n(C_kF_{(2k + 1)})
_(6-n)(N = 1-5, k = 1-8)
May contain traalkyl ammonium salt, etc.
No.

As the lithium salt of the present invention, LiPF ₆
It is desirable to contain Since LiPF ₆ has a high degree of dissociation, it can increase the conductivity of the electrolytic solution, and has an effect of suppressing the reductive decomposition reaction of the electrolytic solution on the negative electrode.

In the electrolytic solution of the present invention, it is recommended to use LiPF ₆ alone or use LiPF ₆ and another lithium salt. As the electrolyte used other than LiPF ₆ , any electrolyte which is usually used as a non-aqueous electrolyte electrolyte can be used. Specifically, among the specific examples of the lithium salt described above, lithium salts other than LiPF ₆ can be exemplified.

Specific examples of the combination of LiPF ₆ and another lithium salt include LiPF ₆ , LiBF ₄ and LiP
F ₆ and LiN (SO ₂ C _k F _{(2k + 1)} ) ₂ (k =
1-8), LiPF ₆ , LiBF ₄ and LiN (S
O ₂ C _k F _{(2k + 1)} ) ₂ (k = 1 to 8).

The ratio of LiPF _{6 in} the lithium salt is desirably 100 to 1% by weight, preferably 100 to 10% by weight, and more preferably 100 to 50% by weight.

The amount of the lithium salt mixed with the electrolyte is 0.1 to 3 mol / l, preferably 0.5 to 2 mol / l, based on the nonaqueous electrolyte. Is desirable.

Nonaqueous Electrolyte The nonaqueous electrolyte of the present invention contains a cyclic carboxylic acid ester, a sulfonic acid derivative and a lithium salt.

Suitable non-aqueous electrolytic solution in the [0060] present invention contains a cyclic carboxylic acid ester and a sulfonic acid derivative and LiPF _6, may be added other additives as necessary. Examples of the additives include hydrogen fluoride, water, oxygen, nitrogen, and the like, in addition to the compounds described above.

When hydrogen fluoride is used as an additive, a method for adding hydrogen fluoride to the electrolyte is to directly blow a predetermined amount of hydrogen fluoride gas into the electrolyte. When the lithium salt used in the present invention is a lithium salt containing fluorine such as LiPF ₆ or LiBF ₄ , the water is converted into an electrolyte by utilizing a reaction between water and an electrolyte shown in the following (formula 1). Added to
It may be generated in an electrolytic solution. _{LiMF n + H 2 O → LiPF} (n-2) O + 2HF ( Equation 1) (where, M = P, B, etc., when M is P, n = 6, M
When B is n = 4)

As a method of adding water to the electrolyte, water may be directly added to the electrolyte or water may be previously contained in the battery electrode, and after the electrolyte is injected into the battery, Water may be supplied from inside to the electrolyte.

When water is added to the electrolyte and HF is generated indirectly in the electrolyte, two molecules of HF are generated almost quantitatively from one molecule of water. Calculate and add according to the concentration. Specifically, the desired H
Water of 0.45 times (weight ratio) the amount of F is added.

As the compound that generates HF by utilizing the reaction between the electrolyte and water, a protic compound having a strong acidity other than water can be used. As such a compound, specifically, methanol, ethanol, ethylene glycol, propylene glycol, acetic acid, acrylic acid, maleic acid,
1,4-dicarboxy-2-butene and the like can be raised. The addition amount of hydrogen fluoride is preferably 0.0001 to 0.7% by weight based on the whole electrolytic solution, and 0.001 to 0.7% by weight.
-0.3 wt% is more preferable, 0.001-0.2 wt% is more preferable, and 0.001-0.1 wt% is particularly preferable.

The non-aqueous electrolyte according to the present invention as described above
Not only suitable as a non-aqueous electrolyte for lithium secondary batteries, but also as a non-aqueous electrolyte for primary batteries, a non-aqueous electrolyte for electrochemical capacitors, an electric double layer capacitor, an electrolyte for aluminum electrolytic capacitors Can also be used.

Secondary Battery The non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode, a positive electrode,
The non-aqueous electrolyte is basically configured to include,
Usually, a separator is provided between the negative electrode and the positive electrode.

The negative electrode active material constituting the negative electrode includes metallic lithium, a lithium-containing alloy, a metal or alloy capable of being alloyed with lithium, an oxide capable of doping / dedoping lithium ions, and a lithium ion doping / doping. Either a transition metal nitride which can be de-doped, a carbon material which can be doped or de-doped with lithium ions, or a mixture thereof can be used.

Examples of metals or alloys that can be alloyed with lithium include silicon, silicon alloys, tin, and tin alloys. Examples of oxides that can be doped and undoped with lithium ions include tin oxide and silicon oxide, and transition metal oxides that can be doped and undoped with lithium ions.

Among these, lithium ions are
Carbon materials that can be de-dove are preferred. Such a carbon material may be carbon black, activated carbon, artificial graphite, natural graphite or amorphous carbon, and may be in any form of fibrous, spherical, potato, or flake. .

Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or lower, mesophase pitch carbon fiber (MCF), and the like. There are natural graphite and artificial graphite, and as the artificial graphite, graphitized MCMB, MCF and the like are used. Further, as the graphite material, a material containing boron can be used, and a material coated with a metal such as gold, platinum, silver, copper, or Sn, coated with amorphous carbon, A mixture of graphite and graphite can also be used. These carbon materials may be used alone or in combination of two or more.

As the carbon material, the spacing d _{(002 ) of} the (002) plane measured by X-ray analysis is 0.340 nm.
The following carbon materials are preferable, and the true density is 1.70 g / cm
Graphite of ³ or more or a highly crystalline carbon material having properties close thereto is preferred. When such a carbon material is used, the energy density of the battery can be increased.

As the positive electrode active material constituting the positive electrode, Fe
S₂, MoS₂, TiS₂, MnO ₂, V₂O₅Such as
Transition metal oxide or transition metal sulfide, LiCoO₂,
LiMnO₂, LiMn₂O₄, LiNiO₂, LiN
i_xCo_(1-x)O₂, LiNi_xCo_yMn
_(1-xy)O₂Such as lithium and transition metal
Composite oxide, polyaniline, polythiophene,
Roll, polyacetylene, polyacene, dimercaptochi
Conductive polymers such as azizole / polyaniline composite
Materials, carbon materials such as fluorinated carbon, activated carbon, etc.
It is.

Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. One type of the positive electrode active material may be used, or two or more types may be used in combination. Since the positive electrode active material generally has insufficient conductivity, the positive electrode is used together with a conductive auxiliary to constitute a positive electrode. Examples of the conductive assistant include carbon materials such as carbon black, amorphous whiskers, and graphite.

The separator is a film that electrically insulates the positive electrode and the negative electrode and allows lithium ions to pass therethrough, and examples thereof include a porous film and a polymer electrolyte. As the porous film, a microporous polymer film is suitably used, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like. In particular, a porous polyolefin film is preferable, and specific examples thereof include a porous polyethylene film, a porous polypropylene film, and a multilayer film of a porous polyethylene film and polypropylene. Other resins having excellent thermal stability may be coated on the porous polyolefin film.

Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved and a polymer which is swollen with an electrolyte. The electrolyte of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer.

Such a non-aqueous electrolyte secondary battery can be formed in a cylindrical shape, a coin shape, a square shape, a film shape or any other shape. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose. Next, the structures of the cylindrical and coin type batteries will be described. The negative electrode active material, the positive electrode active material, and the separator constituting each battery are commonly used.

For example, in the case of a cylindrical non-aqueous electrolyte secondary battery, a negative electrode obtained by applying a negative electrode active material to a negative electrode current collector such as a copper foil and a positive electrode current collector such as an Al foil A positive electrode coated with a substance is wound around a separator into which a non-aqueous electrolyte is injected, and is housed in a battery can with an insulating plate placed above and below the wound body.

The non-aqueous electrolyte secondary battery according to the present invention can be applied to a coin-type non-aqueous electrolyte secondary battery. In a coin-type battery, a disc-shaped negative electrode, a separator filled with a non-aqueous electrolyte, a disc-shaped positive electrode, and, if necessary, a spacer plate of stainless steel or aluminum are stacked in this order on a coin-type battery can. It is stored.

[0079]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

[0080] (Examples 1 to 3, and Reference Example 1) 1. Preparation of Battery < Preparation of Nonaqueous Electrolyte> Ethylene carbonate (EC), γ-butyrolactone (γ-BL) and dibutyl carbonate (DBC) were used as nonaqueous solvents, and EC: γ-BL: DB
C was mixed at a ratio of 30: 65: 5 (weight ratio), and then a non-aqueous electrolyte was prepared using LiPF ₆ as an electrolyte so that the electrolyte concentration was 1 mol / liter. Next, based on this non-aqueous solvent, the additives were respectively 1% by weight of dimethyl meta-benzenesulfonate (Example 1), 2% by weight of dimethyl ester of meta-benzenesulfonic acid (Example 2), and A non-aqueous electrolyte of the present invention was obtained by adding a mixture of 2% by weight of acid dimethyl ester and 2% by weight of vinylene carbonate (Example 3). The case where the addition of the additive was omitted was referred to as Reference Example 1 (blank 1).

<Preparation of Negative Electrode> Natural graphite (LF made of Chuetsu graphite)
-18A) 87 parts by weight and 13 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed and dispersed in N-methylpyrrolidinone as a solvent to prepare a natural graphite mixture slurry. Next, this negative electrode mixture slurry was applied to a 18-μm-thick strip-shaped copper foil-made negative electrode current collector and dried. For a coin-type battery, it was compression-molded and punched out into a 14 mm disc shape to obtain a coin-shaped natural graphite electrode. The thickness of the natural graphite electrode mixture was 110 μm, and the weight was 20 mg per area of a circle having a diameter of 14 mm.

<Preparation of LiCoO ₂ electrode> LiCoO ₂
(HLC-2 manufactured by Honjo FMC Energy Systems Co., Ltd.)
1) 90 parts by weight, 6 parts by weight of graphite as a conductive agent, 1 part by weight of acetylene black, and polyvinylidene fluoride 3 as a binder
Parts by weight were mixed and dispersed in N-methylpyrrolidone as a solvent to prepare a LiCoO ₂ mixture slurry. This LiC
The oO ₂ Go slurry was applied and dried on an aluminum foil having a thickness of 20 microns. For a coin-type battery, this is compression-molded and punched into a 13.5 mm disc to form a coin-shaped Li.
A CoO ₂ electrode was obtained. The thickness of this LiCoO ₂ mixture is 9
0 microns, weight was 40 mg per area of a 13.5 mm diameter circle.

<Preparation of Coin-Type Battery> A separator made of a natural graphite electrode having a diameter of 14 mm, a LiCoO ₂ electrode having a diameter of 13.5 mm, and a microporous polypropylene film having a thickness of 25 μm and a diameter of 16 mm was made of stainless steel 203.
Natural graphite electrode, separator,
LiCoO ₂ electrodes were stacked in this order. Thereafter, 0.03 ml of the non-aqueous electrolyte was poured into the separator, and an aluminum plate (thickness: 1.2 mm, diameter: 16 mm, and a spring was housed. Finally, a battery can lid was inserted via a polypropylene gasket. By caulking, a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was produced while maintaining the airtightness in the battery.

2. Evaluation of battery characteristics < Evaluation of high-temperature storage characteristics by coin-type battery> Using a coin-type battery prepared as described above,
A constant current, 4.2V constant voltage condition, charge until the current value at the time of 4.2V constant voltage becomes 0.05mA, after that,
The battery was discharged under the conditions of a constant current of 1 mA and a constant voltage of 3.0 V until the current value at a constant voltage of 3.0 V became 0.05 mA. Next, the battery was charged under the conditions of a constant current of 1 mA and a constant voltage of 3.85 V until the current value at a constant voltage of 3.85 V became 0.05 mA. Thereafter, the battery was stored (“aging”) in a thermostat at 45 ° C. for 7 days. After aging, under the conditions of a constant current and a constant voltage of 1 mA, the termination condition is a current value of 0.05 mA at the time of a constant voltage, and 4.2 V to 3.0 V.
Was performed once and the discharge capacity was measured ("low load discharge capacity"). At this time, the “resistance” of the battery was determined from the change in the battery voltage two minutes after the start of discharging. Next, the battery was charged to 4.2 V under the same conditions, and then discharged at a constant current of 5 mA, and discharged when the battery voltage reached 3.0 V, and the discharge was terminated. Discharge capacity ").
Then, the ratio of the high load discharge capacity to the low load discharge capacity at this time was determined, and this was defined as a “load characteristic index”. After the battery was once discharged to 3.0 V and then charged again to 4.2 V ("charging capacity"), the battery was charged at 60 ° C.
For 4 days ("high temperature storage"). The capacity ("remaining capacity") when the battery was discharged to 3.0 V after high-temperature storage was measured. Further, the load characteristic index after the high-temperature storage test was measured in the same manner as in the aging.

The results of the above examples were analyzed based on the following indices. The difference between the charge capacity before high-temperature storage and the remaining capacity after high-temperature storage is determined as an index indicating the self-discharge property of the battery, that is, the electrolysis property of the electrolyte. The ratio of the difference between the liquids was defined as “self-discharge ratio”. Self-discharge ratio = {(charge capacity of electrolyte solution containing additive-remaining capacity of electrolyte solution containing additive) / (charge capacity of blank-remaining capacity of blank)} x 100 (%) "Load characteristics after aging" The ratio of the “load characteristic index after high-temperature storage” to the “index” was defined as “load characteristic change rate”. Load characteristic change rate = (“Load characteristic index after high temperature storage” /
"Load characteristic index after aging") x 100 (%) "resistance after high temperature storage" against "resistance after aging"
Is defined as the “resistance change rate”. Resistance change rate = (“resistance after high-temperature storage” / “resistance before high-temperature storage (after aging)”) × 100 (%)

<Measurement Results> Evaluation Results of High-Temperature Storage Test on Coin-Type Batteries Table 1 shows the measurement results of the battery characteristics of the evaluated electrolytes.

[0087]

[Table 1]

(Example 4 and Reference Example 2) In <Preparation of Nonaqueous Electrolyte> in Example 2, LiPF ₆ and LiBF ₄ were mixed as electrolytes in a nonaqueous solvent to obtain 0.5 mol / L and 0 mol / L, respectively. A coin-type battery was prepared in the same manner except that the non-aqueous electrolyte was prepared so as to have a concentration of 0.5 mol / liter, and the high-temperature storage characteristics were evaluated. The case where the addition of the additive was omitted was referred to as Reference Example 2 (blank 2). Table 2 shows the measurement results of the battery characteristics of the evaluated electrolytes.

[0089]

[Table 2]

As shown in Reference Examples 1 and 2, the electrolyte containing no additive showed a significant increase in resistance after a high-temperature storage test.
In the first embodiment, the load characteristics were significantly reduced.
The electrolytes to which the sulfonic acid derivative of the present invention shown in 2, 4 were added exhibited an excellent effect particularly on load characteristics and suppression of deterioration of resistance. Further, as shown in Example 3, the electrolytic solution further containing vinylene carbonate exhibited excellent effects on load characteristics, suppression of deterioration of resistance and improvement of self-discharge.

[0091]

The present invention contains a cyclic carboxylic acid ester, and uses a lithium salt, preferably LiPF ₆ as an electrolyte,
In addition, by using an electrolyte containing a sulfonic acid derivative, a non-aqueous electrolyte secondary battery excellent in life characteristics in which load characteristics at the time of high-temperature storage and resistance deterioration are largely suppressed can be obtained. Further, by using the non-aqueous electrolyte of the present invention, a non-aqueous electrolyte secondary battery having a high flash point and excellent safety can be obtained.

Continued on the front page (72) Inventor Tatsuri Ishida 580-32 Nagaura, Sodegaura-shi, Chiba F-term in Mitsui Chemicals, Inc. 5H029 AJ04 AJ05 AJ07 AJ12 AK02 AK03 AK05 AK06 AK08 AK16 AK18 AL01 AL02 AL06 AL07 AL08 AL12 AL18 AM02 AM03 AM04 AM05 AM07 AM16 CJ08 DJ08 DJ09 EJ07 EJ11 HJ01 HJ02

Claims (16)

[Claims] 1. A non-aqueous electrolyte containing a non-aqueous solvent containing a cyclic carboxylic acid ester, a sulfonic acid derivative and a lithium salt. 2. The non-aqueous electrolyte according to claim 1, wherein the sulfonic acid derivative is at least one compound selected from an alkanesulfonic acid derivative and an arylsulfonic acid derivative. 3. The non-aqueous electrolyte according to claim 1, wherein the sulfonic acid derivative is a benzenesulfonic acid derivative. 4. The non-aqueous electrolyte according to claim 1, wherein the sulfonic acid derivative is benzenedisulfonic acid diester or benzenedisulfonic acid dilithium salt. 5. The method according to claim 1, wherein the amount of the sulfonic acid derivative is 0.01% by weight to 10% by weight.
The non-aqueous electrolyte according to any one of the above. 6. The non-aqueous electrolyte according to claim 1, wherein the cyclic carboxylate is γ-butyrolactone. 7. A non-aqueous solvent is added to γ-butyrolactone,
A non-aqueous solvent having at least one other cyclic structure selected from a cyclic carbonate and a cyclic sulfone, and the proportion of the cyclic compound contained in the non-aqueous solvent is 80% by weight or more. 7. The non-aqueous electrolyte according to any one of 1 to 6. 8. The non-aqueous electrolyte according to claim 7, wherein the other non-aqueous solvent having a cyclic structure is at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, sulfolane, and methyl sulfolane. . 9. The non-aqueous electrolyte solution according to claim 1, wherein the lithium salt contains LiPF _6. Wherein said lithium salt is added to the _{LiPF 6, LiBF 4, LiClO 4} , LiAsF 6, LiN
_{(SO 2 C k F (2k} + 1)) 2 (k = 1~8 _{integer), LiPF n (C k F} (2k + 1))
_{(6-n) wherein} at least one kind of lithium salt selected from (n = 1 to 5, k = 1 to 8) is contained. Water electrolyte. 11. The non-aqueous electrolyte according to claim 9, wherein the content of LiPF _{6 in} the lithium salt is 100 to 50% by weight. 12. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous electrolyte further contains a vinylene carbonate derivative represented by the general formula (1). Embedded image (R ¹ and R ² are hydrogen, a methyl group, an ethyl group, or a propyl group.) 13. The weight ratio of the sulfonic acid derivative to the vinylene carbonate derivative represented by the general formula (1) is 1:
13. The ratio is 100 to 100: 1.
The non-aqueous electrolyte according to the above. 14. As the negative electrode active material, metallic lithium, a lithium-containing alloy, a metal or alloy capable of being alloyed with lithium, an oxide capable of doping / dedoping lithium ions, and capable of doping / dedoping lithium ions Negative transition metal nitride, a carbon material capable of lithium ion doping / de-doping, or a mixture thereof, and a transition metal oxide as a positive electrode active material, a composite oxide of lithium and a transition metal, or A lithium secondary battery comprising: a positive electrode containing any of these mixtures; and the non-aqueous electrolyte according to claim 1. 15. The lithium secondary battery according to claim 14, wherein the negative electrode active material is a carbon material capable of doping / dedoping lithium ions. 16. The lithium secondary battery according to claim 14, wherein the positive electrode active material is a composite oxide of lithium and a transition metal.