JP2002203597A - Non-aqueous electrolytic solution and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new electrolytic solution which has non-combustibility (self-fire-extinguishing nature), high conductivity and electrochemical stability, and excellent in safety as the optimal electrolytic solution for a lithium secondary battery. SOLUTION: The non-aqueous electrolytic solution and the lithium secondary battery containing this have a lithium salt for the lithium secondary battery, which has at least a positive electrode containing a compound that can storage/ discharge lithium; and a negative electrode containing a material chosen from charcoal genius substance or a compound, and lithium metal or a lithium alloy which can storage/discharge lithium; is dissolved in the non-water solvent containing (a) annular calboxylate and (b) phosphate ester, and further containing at least one sort expressed by formula (I)/formula (II) in this non- water solvent. In the formula, R1 and R2 express alkyl group having 1 to 4 carbon numbers, independently, and R3 to R8 express halogen atom or alkyl group of straight chain or branch with 1 to 4 carbon numbers/or alkyl group having 1 to 4 carbon numbers.

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 for a lithium secondary battery and a lithium secondary battery using the same. More specifically, a non-aqueous electrolyte solution in which a solute lithium salt is dissolved in a non-aqueous solvent containing a cyclic carboxylate and a specific phosphate, to which a cyclic carbonate compound having a specific structure is added, and a lithium secondary battery using the same. Next battery.

The non-aqueous electrolyte of the present invention has flame retardancy (self-extinguishing properties), has high electrical conductivity and electrochemical stability, and is excellent in a secondary battery using the electrolyte. It is possible to provide a highly safe secondary battery in which the decomposition rate (heat generation rate, pressure rise rate) during thermal decomposition of the battery is suppressed along with the battery charge / discharge characteristics.

[0003]

_2. Description of the Related Art A carbon material such as graphite is used as a negative electrode active material, and LiCoO ₂ , LiNiO ₂ , and LiMn ₂ are used as a positive electrode active material.
A rechargeable lithium battery using a lithium-transition metal composite oxide such as O ₄ is rapidly growing as a new compact secondary battery having a high voltage of 4 V and a high energy density.
The electrolyte of such a lithium secondary battery is generally prepared by mixing a high-dielectric solvent such as ethylene carbonate or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate or diethyl carbonate in an organic solvent. Is used.

[0004] In a lithium secondary battery using an organic non-aqueous electrolyte, if the electrolyte leaks due to damage to the battery or an increase in pressure inside the battery due to any cause, there is a risk that the electrolyte may catch fire.

[0005] Therefore, studies on blending a flame retardant with an organic non-aqueous electrolyte to impart flame retardancy are being vigorously pursued.
It is known to use phosphate esters as flame retardant electrolytes for lithium batteries. For example, JP-A-58-206
No. 078, JP-A-60-23973, JP-A-61-227377, JP-A-61-284070
JP-A No. 4-184870 and JP-A-4-184870 disclose O = P (O) such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tris (2-chloroethyl) phosphate.
R) It is disclosed that a type ₃ phosphate ester is used. Further, JP-A-8-88023 discloses a self-extinguishing electrolytic solution in which at least one of R is a halogen-substituted alkyl.

However, among the phosphate esters used in these, electrolytic solutions containing trimethyl phosphate exhibit excellent flame retardancy, but depending on the material of the negative electrode used in the battery, trimethyl phosphate is reduced. It is easy to decompose, it is necessary to increase the blending amount of trimethyl phosphate in the electrolyte, and when using natural graphite or artificial graphite as the negative electrode, the charge and discharge characteristics of the battery, such as charge and discharge efficiency and discharge capacity, have recently been It does not satisfy the required characteristics.

A phosphoric acid ester having a halogen atom such as chlorine or bromine in a molecule is inferior in oxidation-reduction resistance and has a sufficient charge when applied to a 4V class secondary battery or the like which generates a high voltage. A battery with discharge characteristics cannot be obtained. Furthermore,
A trace amount of free halogen ions present as impurities corrode aluminum used as a positive electrode current collector and cause deterioration of battery characteristics. Further, Japanese Patent Application Laid-Open No. 4-184870 cited above discloses that a cyclic phosphate is used as an electrolyte. Japanese Patent Application Laid-Open No. 11-67267 discloses an electrolyte for a lithium battery in which 20 to 55% by volume of the cyclic phosphate is used in combination with a cyclic carbonate. In the case of blending an ester, in order to make the electrolytic solution of this system flame-retardant while increasing the blending amount, 2
It is necessary to compound 0% by volume or more of the cyclic phosphate, and there is a disadvantage that the conductivity decreases as the amount of the compound increases.

[0008] JP-A-11-260401 and JP-A-2000-11080 disclose that a phosphoric acid ester is used in combination with a vinylene carbonate derivative or a specific cyclic carbonate to provide flame retardancy and improve charge / discharge characteristics. Is disclosed. However, when a lithium secondary battery is misused or abused, the battery may be placed in a high-temperature atmosphere, or the battery itself may reach a high temperature state due to an internal short circuit or external short circuit. It has been suggested to happen. When the battery is placed in a high temperature state of 100 ° C. or more, an extremely large heat is generated by an electrolyte containing a main solvent of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or the like as proposed so far. It is suggested that cracked gas may be generated. Therefore, from the viewpoint of improving the safety of the battery, a flame-retardant electrolytic solution having a suppressed battery thermal decomposition rate has been desired.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and provides an electrolyte with flame retardancy (self-extinguishing property), high conductivity, and high electrochemical performance. Electrolyte for a lithium secondary battery which is also stable, and a lithium battery using the same, which has excellent charge / discharge characteristics and has a reduced thermal decomposition rate during thermal decomposition of the battery, and has both safety and reliability. It is intended to provide a secondary battery.

[0010]

Means for Solving the Problems The inventors of the present invention have made intensive studies in view of such circumstances, and as a result, have dissolved a solute lithium salt in a non-aqueous solvent containing a cyclic carboxylate and a specific phosphate, and By adding a cyclic carbonate compound of a specific structure, it has flame retardancy (self-extinguishing),
In addition to obtaining an electrolytic solution having excellent electrical conductivity and electrochemical stability, in a secondary battery using the present electrolytic solution,
With the excellent battery charge / discharge characteristics, it has been found that a highly safe secondary battery in which the decomposition rate (heat generation rate, pressure rise rate) during the thermal decomposition of the battery is suppressed can be realized.
The present invention has been completed.

Therefore, the present invention provides a method for storing lithium.
A positive electrode containing a releasable compound; a negative electrode containing a carbonaceous material or compound capable of occluding and releasing lithium or a material selected from lithium metal or a lithium alloy; and a nonaqueous electrolytic solution comprising a lithium salt and a nonaqueous solvent. A non-aqueous electrolyte solution for a lithium secondary battery, wherein a lithium salt is dissolved in a non-aqueous solvent containing (a) a cyclic carboxylic acid ester and (b) a phosphoric acid ester; (C) General formula (I):

[0012]

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Wherein R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a branched alkyl group, and / or General formula (II):

[0014]

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(Wherein, R ^{3 to} R ⁸ each independently represent
A hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms), and a lithium secondary battery containing the same.

The amount of the nonaqueous solvent in the total amount of the components (a) and (b) is (a) 10 to 90% by volume of the cyclic carboxylic acid ester and (b) 10 to 90% by volume of the phosphoric acid ester.
It is a non-aqueous solvent containing% by volume.

The amount of at least one of the vinylene carbonate compound represented by the general formula (1) and / or the vinylethylene carbonate compound represented by the general formula (II) is determined by the amount of the nonaqueous electrolyte in which a lithium salt is dissolved in the nonaqueous solvent and the general formula (I) and / or
Or it is 0.01 to 15% by weight of the total amount of the compound of the general formula (II).

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. (Non-Aqueous Electrolyte) The non-aqueous electrolyte of the present invention comprises a lithium salt, a non-aqueous solvent containing (a) a cyclic carboxylate and (b) a phosphate, and (c) vinylene of the general formula (I). It contains at least one of a carbonate compound and / or a vinylethylene carbonate compound of the following general formula (II).

The cyclic carboxylic acid ester (a) of the present invention
Is, for example, γ-butyrolactone, γ-valerolactone,
γ-caprolactone, γ-octanolactone, β-butyrolactone, δ-valerolactone, ε-caprolactone, and the like, and γ-butyrolactone, γ-
Valerolactone, δ-valerolactone and ε-caprolactone are preferred. These can be used alone or in combination of two or more.

In the phosphate ester (b) of the present invention,
As the chain phosphate ester, a trialkyl phosphate having an alkyl group having 1 to 4 carbon atoms can be preferably mentioned, and particularly preferably, a formula (III):

[0021]

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(Wherein, R ^{9 to} R ¹¹ each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms and / or a fluorine-substituted alkyl group, and R ⁹ + R ¹⁰ + R ¹¹
Wherein the total number of carbon atoms is 3 to 7), and the cyclic phosphate is represented by the formula (IV):

[0023]

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(Wherein R ¹² represents a linear or branched alkyl group having 1 to 4 carbon atoms and / or a fluorine-substituted alkyl group, and R ¹³ represents an alkylene group having 2 to 8 carbon atoms. Represent)
Is a cyclic phosphate ester represented by

The alkyl group represented by R ^{9 to} R ^{11 in the} formula (III) includes a methyl group, an ethyl group, a propyl group and a butyl group. Examples of the fluorine-substituted alkyl group represented by R ^{9 to} R ¹¹ include a trifluoroethyl group, a pentafluoropropyl group, a hexafluoroisopropyl group, and a heptafluorobutyl group.

Specific examples of preferred fluorine-free chain phosphate esters include methyl ethyl propyl phosphate, methyl ethyl butyl phosphate, ethyl propyl butyl phosphate, methyl propyl butyl phosphate, methyl diethyl phosphate, Methyl dipropyl phosphate, methyl dibutyl phosphate, dimethyl ethyl phosphate, dimethyl propyl phosphate,
Dimethyl butyl phosphate, trimethyl phosphate, ethyl dipropyl phosphate, ethyl dibutyl phosphate, diethyl propyl phosphate, diethyl butyl phosphate, triethyl phosphate,
Propyldibutyl phosphate, dipropylbutyl phosphate, tripropyl phosphate and tributyl phosphate.

Particularly preferred chain phosphates containing no fluorine are the chain phosphates of formula (II), such as methyl ethyl propyl phosphate, methyl ethyl butyl phosphate, methyl diethyl phosphate, and phosphoric acid phosphate. Examples thereof include methyldipropyl, dimethylethyl phosphate, dimethylpropyl phosphate, dimethylbutyl phosphate, trimethyl phosphate, diethylpropyl phosphate, and triethyl phosphate. Trialkyl phosphates in which the total number of carbon atoms of R ⁹ , R ¹⁰ and R ^{11 in} the formula (II) is 3 to 5 are more particularly preferred. Specific examples thereof include trimethyl phosphate, dimethylethyl phosphate, It is methyl diethyl phosphate.

Specific examples of the fluorine-substituted phosphate ester include, for example, trifluoroethyl dimethyl phosphate, pentafluoropropyl dimethyl phosphate, heptafluorobutyl dimethyl phosphate, trifluoroethyl methyl ethyl phosphate, pentafluoropropyl phosphate Methyl ethyl, heptafluorobutyl methyl ethyl phosphate, trifluoroethyl methyl propyl phosphate, pentafluoropropyl methyl propyl phosphate, heptafluorobutyl methyl propyl phosphate, trifluoroethyl methyl butyl phosphate, pentafluoropropyl methyl butyl phosphate , Heptafluorobutyl methyl butyl phosphate, trifluoroethyl diethyl phosphate, pentafluoropropyl diethyl phosphate, heptafluorobutyl diethyl phosphate, trifluoroethyl phosphate Chirupuropiru, phosphoric acid pentafluoropropyl ethylpropyl, phosphoric acid heptafluorobutyl ethyl propyl, trifluoroethyl ethyl butyl phosphate, pentafluoropropyl ethyl butyl phosphate,
Heptafluorobutylethyl butyl phosphate, trifluoroethyldipropyl phosphate, pentafluoropropyldipropyl phosphate, heptafluorobutyldipropyl phosphate, trifluoroethylpropylbutyl phosphate, pentafluoropropylpropylbutyl phosphate, phosphoric acid Heptafluorobutylpropylbutyl, trifluoroethyldibutylphosphate, pentafluoropropyldibutylphosphate, heptafluorobutyldibutylphosphate and the like can be mentioned.

Specific examples of preferred fluorine-substituted phosphate esters include trifluoroethyldimethylphosphate, pentafluoropropyldimethylphosphate, trifluoroethylmethylethylphosphate, pentafluoropropylmethylethylphosphate, and trifluorophosphate. Examples thereof include ethylmethylpropyl and pentafluoropropylmethylpropyl phosphate, and trimethyl phosphate, dimethylethyl phosphate, dimethylpropyl phosphate, methyldiethyl phosphate, and trifluoroethyldimethylphosphate are particularly preferable.

R ^{12 in the} formula (IV) is a linear or branched alkyl group having 1 to 4 carbon atoms and / or a fluorine-substituted alkyl group, and specific examples thereof include a methyl group, an ethyl group,
Examples thereof include a propyl group, a butyl group, a trifluoroethyl group, a pentafluoropropyl group, a hexafluoroisopropyl group and a heptafluorobutyl group, and a methyl group and an ethyl group are preferred.

R ^{13 in the} formula (IV) is a linear or branched alkylene group having 2 to 8 carbon atoms, and specific examples thereof include an ethylene group, a propylene group, a trimethylene group, a butylene group and a tetramethylene group. Group, 1,1-dimethylethylene group, bentamethylene group, 1,1,2-trimethylethylene group, hexamethylene group, tetramethylethylene group, heptamethylene group, octamethylene group, and the like. preferable.

Specific examples of the cyclic phosphate of the formula (IV) include ethylene methyl phosphate, ethylene ethyl phosphate, ethylene-n-propyl phosphate, ethylene isopropyl phosphate, ethylene-n-butyl phosphate, phosphorus Ethylene-sec-butyl, ethylene-t-butyl phosphate, propylene methyl phosphate, propylene ethyl phosphate, propylene-n-propyl phosphate, propylene isopropyl phosphate, propylene-n-butyl phosphate, propylene phosphate- sec-butyl, propylene-t-butyl phosphate,
Trimethylene methyl phosphate, trimethylene ethyl phosphate, trimethylene-n-propyl phosphate, trimethylene isopropyl phosphate, trimethylene-n-butyl phosphate, trimethylene-sec-butyl, trimethylene-t-butyl phosphate, Butylene methyl phosphate, Butylene ethyl phosphate, Butylene-n-propyl, Butylene isopropyl phosphate, Butylene-n-butyl phosphate,
Butylene phosphate-sec-butyl, butylene phosphate-t-
Butyl, isobutylene methyl phosphate, isobutylene ethyl phosphate, isobutylene phosphate-n-butyl, isobutylene phosphate-sec-butyl, isobutylene phosphate-t-
Butyl, tetramethylenemethyl phosphate, tetramethyleneethyl phosphate, tetramethylene-n-propyl,
Tetramethylene isopropyl phosphate, tetramethylene-n-butyl phosphate, tetramethylene-sec-butyl phosphate, tetramethylene-t-butyl phosphate, pentamethylenemethyl phosphate, pentamethyleneethyl phosphate, pentamethylene-phosphate n-propyl, pentamethyleneisopropyl phosphate, pentamethylene-n-butyl phosphate, pentamethylene-sec-butyl phosphate, pentamethylene-t-butyl phosphate, trimethylethylenemethyl phosphate,
Trimethylethylene ethyl phosphate, trimethylethylene-n-propyl phosphate, trimethylethylene isopropyl phosphate, trimethylethylene-n-butyl phosphate, trimethylethylene-sec-butyl phosphate, trimethylethylene-t-butyl phosphate, phosphoric acid Hexamethylenemethyl, hexamethyleneethyl phosphate, hexamethylene-n-propyl, hexamethyleneisopropyl, hexamethylene-n-butyl, hexamethylene-sec-butyl, hexamethylene-t-
Butyl, tetramethylethylene methyl phosphate, tetramethylethylene ethyl phosphate, tetramethylethylene-n-propyl, phosphate tetramethylethyleneisopropyl, tetramethylethylene-n-butyl phosphate, tetramethylethylene phosphate-sec -Butyl, tetramethylethylene-t-butyl phosphate, heptamethylenemethyl phosphate, heptamethyleneethyl phosphate, heptamethylene-n-propyl phosphate, heptamethyleneisopropyl phosphate, heptamethylene-n-butyl phosphate, phosphorus Heptamethylene acid-sec-butyl, Heptamethylene phosphate-t
-Butyl, octamethylenemethyl phosphate, octamethyleneethyl phosphate, octamethylene-n-propyl, octamethyleneisopropyl, octamethylene-n-butyl, octamethylene-sec-sec-
Butyl, octamethylene-t-butyl phosphate and the like can be mentioned, and ethylene methyl phosphate and ethylene ethyl phosphate are preferable.

Specific examples of the fluorine-substituted cyclic phosphate of the formula (IV) include, for example, ethylene trifluoroethyl phosphate, ethylene pentafluoropropyl phosphate, ethylene hexafluoroisopropyl phosphate, ethylene heptafluorobutyl phosphate, phosphorus Propylene trifluoroethyl phosphate, propylene pentafluoropropyl phosphate,
Propylene hexafluoroisopropyl phosphate, propylene heptafluorobutyl phosphate, trimethylene trifluoroethyl phosphate, trimethylene pentafluoropropyl phosphate, trimethylene hexafluoroisopropyl phosphate, trimethylene heptafluorobutyl phosphate, butylene triphosphate Fluoroethyl, butylene pentafluoropropyl phosphate, butylene hexafluoroisopropyl phosphate, butylene heptafluorobutyl phosphate, tetramethylene trifluoroethyl phosphate, tetramethylene pentafluoropropyl phosphate, tetramethylene hexafluoroisopropyl phosphate, phosphoric acid Tetramethylene heptafluorobutyl, dimethylethylene trifluoroethyl phosphate, dimethylethylene pentafluoropropyl phosphate, phosphoric acid Methyl ethylene hexafluoroisopropyl, dimethyl ethylene heptafluorobutyl phosphate, pentamethylene trifluoroethyl phosphate, pentamethylene pentafluoropropyl phosphate, pentamethylene hexafluoroisopropyl phosphate, pentamethylene heptafluorobutyl phosphate, trimethyl ethylene phosphate Trifluoroethyl, trimethylethylene pentafluoropropyl phosphate, trimethylethylene hexafluoroisopropyl phosphate, trimethylethylene heptafluorobutyl phosphate, hexamethylene trifluoroethyl phosphate, hexamethylene pentafluoropropyl phosphate, hexamethylene hexafluorophosphate Isopropyl, hexamethylene heptafluorobutyl phosphate, tetramethylethylene trifluorophosphate Tetramethylethylene pentafluoropropyl phosphate, tetramethylethylene hexafluoroisopropyl phosphate, tetramethylethylene heptafluorobutyl phosphate, heptamethylene trifluoroethyl phosphate, heptamethylene pentafluoropropyl phosphate, heptamethylene hexaphosphate Fluoroisopropyl, heptamethylene heptafluorobutyl phosphate, octamethylene trifluoroethyl phosphate, octamethylene pentafluoropropyl phosphate, octamethylene hexafluoroisopropyl phosphate, octamethylene heptafluorobutyl phosphate, and the like. Ethylene trifluoroethyl acid is preferred.

The phosphate ester of the present invention may be used alone or
You may mix and use seeds.

The non-aqueous solvent of the present invention contains the components (a) and (b), and the ratio of the components (a) and (b) in the total amount is as follows: component (a): 40 to 90% by volume and ( Component b): 10 to 60% by volume, preferably component (a): 40 to 60%
85% by volume and component (b): 15 to 60% by volume, more preferably component (a): 45 to 85% by volume and component (b): 15 to 55% by volume.

In the above volume ratio, the value measured at 25 ° C. is used as the volume ratio of each component. In the case of a solid such as ethylene carbonate at room temperature, a value measured in a molten state by heating to a melting point is used.

The non-aqueous solvent of the present invention may contain, in addition to the above-mentioned components (a) and (b), other known electrolytes for lithium secondary batteries as long as the characteristics of the present invention are not impaired. May be used as a mixture.

The non-aqueous electrolytic solution of the present invention comprises:
General formula (I):

[0039]

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(Wherein R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms or a branched alkyl group); and / or The following general formula (II):

[0041]

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(Wherein, R ^{3 to} R ⁸ each independently represent
A hydrogen atom or an alkyl group having 1 to 4 carbon atoms or a branched alkyl group).

R ¹ and R ^{2 in} the formula (I) each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a branched alkyl group. Specific examples of the alkyl group represented by R ¹ and R ² include a methyl group, an ethyl group, an n-propyl group, a 1-propyl group, an n-butyl group, a sec-butyl group, and a tert-butyl group. A methyl group and an ethyl group are preferred.

Specific examples of the vinylene carbonate compound of the general formula (I) of the present invention include vinylene carbonate,
4-methylvinylene carbonate, 4-ethylvinylene carbonate, 4.5-dimethylvinylenecarbonate, 4,5-diethylvinylenecarbonate, 4-methyl-5-ethylvinylenecarbonate, and the like, and vinylene carbonate, 4-methyl Vinylene carbonate and 4-ethylvinylene carbonate are preferred, and vinylene carbonate is particularly preferred.

R ^{3 to} R ⁸ in the formula (II) each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a branched alkyl group. Specific examples of the alkyl group represented by R ^{3 to} R ⁸ include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a sec-butyl group, and a tert-butyl group. A methyl group and an ethyl group are preferred.

Specific examples of the vinylethylene carbonate compound of the general formula (II) of the present invention include 4-vinylethylene carbonate, 4-vinyl-4-methylethylene carbonate, 4-vinyl-4-ethylethylene carbonate, Vinyl-4-n-propyl ethylene carbonate, 4-vinyl-5-methyl ethylene carbonate,
-Vinyl-5-ethylethylene carbonate, 4-vinyl-5-n-propylethylene carbonate and the like, and 4-vinylethylene carbonate and 4-vinyl-4-methylethylene carbonate are preferred.
-Vinyl ethylene carbonate is particularly preferred.

In the present invention, the vinylene carbonate compound of the general formula (I) and the vinylethylene carbonate compound of the general formula (II) may be used alone or in combination of two or more.

The amount of at least one vinylene carbonate compound represented by the general formula (I) and / or the vinylethylene carbonate compound represented by the general formula (II) in the nonaqueous electrolytic solution of the present invention is determined by the above-mentioned nonaqueous solvent and the general formula 0.01 to 15% by weight of the total amount of the compound of the formula (I) and / or (II),
Preferably, it is 0.1 to 10% by weight, more preferably 0.1 to 10% by weight.
5 to 10% by weight.

The addition of such a vinylene carbonate compound and / or a vinylethylene carbonate compound to the non-aqueous solvent improves the charge-discharge characteristics (charge-discharge efficiency, charge-discharge capacity) of the battery generated when the non-aqueous solvent is used. Has the effect of doing

The lithium salt which is a solute of the non-aqueous electrolyte of the present invention may be a lithium salt of an inorganic acid or a compound represented by the general formula (V):

[0051]

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(Wherein m and n are each independently:
Which represents an integer of 1 to 4).

As the inorganic lithium salt of the present invention, LiP
F₆Or LiBF_FourCan be mentioned. General formula
As the lithium salt of an organic acid represented by (V), LiN
(SO_TwoCF_Three)_Two, LiN (SO_TwoC_TwoF_Five)_Two, LiN
(SO_TwoC_ThreeF₇)_Two, LiN (SO_TwoC_FourF₉)_Two, LiN
(SO_TwoCF_Three) ・ (SO_TwoC_TwoF_Five), LiN (SO_TwoCF
_Three) ・ (SO_TwoC_ThreeF₇), LiN (SO_TwoCF_Three) ・ (SO
_TwoC_FourF₉), LiN (SO_TwoC_TwoF _Five) ・ (SO_TwoC
_ThreeF₇), LiN (SO_TwoC_TwoF_Five) ・ (SO_TwoC_FourF₉), L
iN (SO_TwoC_ThreeF₇) ・ (SO_TwoC_FourF₉)
And LiN (S0_TwoCF_Three)_Two, LiN (SO_TwoC
_TwoF_Five)_Two, LiN (SO_TwoCF_Three) ・ (SO_TwoC_FourF₉) Is good
Good.

As a solute of the electrolytic solution of the present invention, LiPF ₆
Alternatively, a lithium salt of an inorganic acid of LiBF ₄ or a lithium salt of an organic acid represented by the above formula (V) is dissolved in the above nonaqueous solvent, and a compound of the general formula (I) and / or the general formula (II) is further added. As a result, a high conductivity and an electrochemically excellent electrolytic solution can be obtained, and a battery having excellent charge / discharge capacity and charge / discharge cycle characteristics can be obtained.

The lithium salt of the present invention has a solute concentration in the electrolytic solution of usually 0.5 to 2 mol / dm ³ , preferably 0.5 to 2 mol / dm ³ .
Used to be 1.5 mol / dm ³ . If it is less than 0.5 mol / dm ³ or more than 2 mol / dm ³ , the conductivity of the electrolytic solution is undesirably reduced.

(Lithium Secondary Battery) The lithium secondary battery of the present invention comprises the above-mentioned electrolytic solution, a negative electrode and a positive electrode.

As the negative electrode material constituting the battery, graphite capable of occluding and releasing lithium, non-graphitizable carbon and amorphous carbon, or lithium metal and lithium and aluminum, tin, zinc, silver, lead, etc. An alloy with a metal or the like can be used. These negative electrode materials may be used as a mixture of two or more. As the shape of the negative electrode, a sheet electrode which is mixed with a binder and a conductive agent as necessary and then applied to a current collector and a pellet electrode which has been subjected to press molding can be used.

As the material of the current collector for the negative electrode, metals such as copper, nickel, and stainless steel are used, and among these, copper foil is preferable in terms of easy processing into a thin film and cost. As the positive electrode material constituting the battery, lithium manganese oxide, lithium cobalt oxide, lithium transition metal composite oxide material such as lithium nickel oxide and the like material that can occlude and release lithium can be used, Lithium transition metal composite oxides are preferred.

The shape of the positive electrode is not particularly limited. For example, after mixing with a binder and a conductive agent as necessary, a sheet electrode applied to a current collector and a pellet electrode subjected to press molding may be used. Can be used. As the material of the positive electrode current collector, a metal such as aluminum, titanium, and tantalum or an alloy thereof is used. Among these, aluminum or its alloy is desirable in terms of energy density because it is lightweight.

Known shapes such as a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are laminated can be used. It is. As the separator constituting the battery, a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene can be used.

[0061]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist. In addition, the performance of the electrolyte solution and the battery performance were evaluated by the following methods.

1. Self-extinguishing property evaluation of electrolyte solution: width 15 mm,
A glass fiber filter in the form of a strip having a length of 300 mm and a thickness of 0.19 mm is immersed in a beaker containing an electrolyte for at least 10 minutes.
The electrolyte was sufficiently impregnated into the glass fiber filter paper. Next, after removing excess electrolyte adhering to the glass fiber filter paper at the edge of the beaker, one end of the glass fiber filter paper was hung vertically with a clip. Approximately 3 lighter gas flames from the lower end
After heating for 2 seconds, the presence or absence of self-extinguishing property with the fire source removed, and the time until the fire was extinguished were measured.

2. Measurement of conductivity of electrolyte: conductivity meter CM-30S and conductivity cell CG- manufactured by Toa Denpa Kogyo KK
The conductivity at 25 ° C. was measured using 511B.

3. Measurement of Battery Charge / Discharge Characteristics: <Preparation of Negative Electrode> A negative electrode was prepared as follows. A carbon material as a negative electrode active material was mixed with a fluororesin as a binder at a weight ratio of 90:10, and this was dispersed in a solvent (N-methylpyrrolidone) to form a slurry. A negative electrode sheet was obtained by coating both sides on a copper foil as a body and drying. The obtained negative electrode sheet is 20 mm in width and 1 in length.
The negative electrode was cut into 50 mm.

<Preparation of Positive Electrode> The positive electrode was prepared as follows. A weight ratio of acetylene black as a conductive agent and fluororesin as a binder was added to lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material at a weight ratio of 90:
The mixture was mixed at 5: 5, dispersed in N-methylpyrrolidone to form a slurry, applied to both surfaces of an aluminum foil as a positive electrode current collector, and dried to obtain a positive electrode sheet.
The obtained positive electrode sheet was cut into a width of 20 mm and a length of 150 mm to obtain a positive electrode.

<Preparation of Battery> Electrode terminals were attached to the negative electrode and the positive electrode obtained as described above,
It was wound through a porous polypropylene film separator having a length of 200 mm and a length of 200 mm to produce a device for evaluating battery charge / discharge characteristics. This element was housed in a closed cell with electrode terminals under a dry argon atmosphere, and the airtightness in the battery was maintained after the nonaqueous electrolyte was injected. Charging is 4.2V, 5
The charging was performed by a 0 mA constant current constant voltage charging method, and the process was terminated when 8 hours had elapsed. Discharging was performed at a constant current of 10 mA, and was terminated when the voltage reached 2.5 V. With this charge / discharge cycle, charge / discharge characteristics were measured. The battery discharge capacity of the device thus manufactured is about 50 mAh.

4. Measurement of thermal stability (thermal decomposition rate) of battery: <Preparation of rechargeable battery> The element for evaluating battery charge / discharge characteristics obtained as described above was housed in a closed cell with electrode terminals under a dry argon atmosphere. Then, after injecting the non-aqueous electrolyte, the airtightness in the battery was maintained. Charging is 4.2V, 5
The discharge was performed at a constant current of 10 mA, and the discharge was terminated when the voltage reached 2.5 V. After repeating this charge / discharge cycle twice, the charge / discharge was terminated at a final voltage of 4.2 V, and a charged battery element was produced. The charging capacity of the battery element thus manufactured is about 50 mAh.

<Measurement of Battery Thermal Stability> The battery thermal stability was measured by subjecting the thus obtained rechargeable battery element to a predetermined high-pressure sealed cell (withstand pressure of 105
X 105 Pa), and using a high-temperature and high-pressure calorimeter (Radex-solo manufactured by SYSTAG), the thermal decomposition of the battery when the temperature was raised from 25 ° C to 300 ° C at a rate of 1 ° C per minute. The heat generation rate and the pressure rise rate in the process were measured, and the thermal stability (thermal decomposition rate) of the battery was measured.

Examples 1 to 11 and Comparative Examples 1 to 3 The solutes and additives shown in Table 1 were dissolved in the non-aqueous mixed solvents shown in Table 1 to prepare an electrolyte having a solute concentration of 1 mol / dm ³ . . Next, the self-extinguishing property (flame retardancy) and the electrical conductivity of this electrolytic solution were measured. Furthermore, artificial graphite as a negative electrode active material,
A cylindrical battery element using LiCoO ₂ as the positive electrode active material was prepared, and the charge / discharge capacity and the thermal stability of the battery were measured using the electrolytic solutions shown in Table 1. The results are shown in Table 1. FIG. 1 shows the results of the initial charge / discharge curve of the cylindrical battery element manufactured using the electrolytic solution of Example 1, and FIGS. 2A and 2B show the results of the thermal stability (heat generation temperature and pressure change) of the charged battery element. As shown in FIG. 2b.

[0070]

[Table 1]

The meanings of the abbreviations in the table are shown below. GBL: γ-butyrolactone GVL: γ-valerolactone ECL: ε-cabrolactone TMP: trimethyl phosphate TEP: triethyl phosphate EDMP: dimethylethyl phosphate DAMP: diethylmethyl phosphate EC: ethylene carbonate DEC: diethyl carbonate VC: vinylene carbonate VEC: 4-vinylethylene carbonate LiBETI: LiN (SO ₂ C ₂ F ₅ ) ₂

[0072]

The electrolytic solution for a lithium secondary battery of the present invention comprises:
The present invention has excellent flame retardancy (self-extinguishing), good charge / discharge cycle characteristics, low thermal decomposition rate during thermal decomposition of batteries, high safety and high reliability, etc. Has the effect of

[0073]

[Brief description of the drawings]

FIG. 1 is a diagram showing an initial charge / discharge curve of a cylindrical battery element manufactured using the electrolytic solution prepared in Example 1.

FIG. 2a is a view showing the thermal stability (cell temperature change) of a cylindrical battery element manufactured using the electrolytic solution prepared in Example 1.

FIG. 2b is a view showing the thermal stability (pressure change) of a cylindrical battery element manufactured using the electrolytic solution prepared in Example 1.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenichi Ishigaki 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Prefecture Within Tsukuba Research Laboratory, Mitsubishi Chemical Corporation (72) Inventor Takashi Fujii 8-Chome, Ami-cho, Inashiki-gun, Ibaraki Prefecture No. 3-1 Mitsubishi Chemical Corporation Tsukuba Research Laboratory (72) Inventor Minoru Furuta 3-1, Chuo, Ami-cho, Inashiki-gun, Inashiki-gun, Ibaraki Prefecture F-term in Tsukuba Research Laboratory Mitsubishi Chemical Corporation 5H029 AJ12 AK03 AL07 AL12 AM03 AM04 AM05 AM06 AM07 HJ01 HJ02 HJ07

Claims (7)

[Claims] 1. A positive electrode containing a compound capable of occluding and releasing lithium; a negative electrode containing a carbonaceous substance or compound capable of occluding and releasing lithium, or a material selected from lithium metal or lithium alloy; and a lithium salt and a non-aqueous solvent A non-aqueous electrolyte solution for a lithium secondary battery comprising at least: a non-aqueous electrolyte solution comprising: (a) a cyclic carboxylate ester; and (b) a phosphate ester. And (c) a compound represented by the following general formula (I): (Wherein R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms or a branched alkyl group); and / or
Or the general formula (II): (Wherein, R ^{3 to} R ⁸ each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms)
A non-aqueous electrolyte solution characterized by adding at least one vinylethylene carbonate compound represented by the formula: 2. The amount of the nonaqueous solvent in the total amount of the component (a) and the component (b) is (a) 10 to 90% by volume of the cyclic carboxylic acid ester and (b) 10% by volume of the phosphoric acid ester.
The non-aqueous electrolyte according to claim 1, which is a non-aqueous solvent containing about 90% by volume. 3. The amount of at least one of the vinylene carbonate compound represented by the general formula (I) and / or the vinylethylene carbonate compound represented by the general formula (II) is such that the lithium salt is dissolved in the non-aqueous solvent. The nonaqueous electrolytic solution according to claim 1 or 2, which is 0.01 to 15% by weight of the total amount of the nonaqueous electrolytic solution and the compound represented by the general formula (I) and / or the general formula (II). 4. The cyclic carboxylate is γ-butyrolactone, γ-valerolactone, γ-caprolactone,
The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the non-aqueous electrolyte is at least one selected from the group consisting of γ-octanolactone, β-butyrolactone, δ-valerolactone, and ε-caprolactone. 5. The phosphoric ester of the general formula (III): (Wherein, R ^{9 to} R ¹¹ each independently represent a carbon number of 1 to
4 represents a linear or branched alkyl group and / or a fluorine-substituted alkyl group, wherein the total number of carbon atoms of R ⁹ + R ¹⁰ + R ¹¹ is 3 to 7);
Or the general formula (IV): (Wherein, R ¹² represents a linear or branched alkyl group having 1 to 4 carbon atoms and / or a fluorine-substituted alkyl group, and R ¹³ represents an alkylene group having 2 to 8 carbon atoms). The non-aqueous electrolyte according to any one of claims 1 to 4, which is a cyclic phosphate. 6. The lithium salt is LiPF ₆ , LiBF ₄ or the general formula (V): (Wherein m and n each independently represent an integer of from 1 to 4).
The non-aqueous electrolyte according to any one of claims 1 to 5. 7. A positive electrode comprising a compound capable of occluding and releasing lithium, comprising the non-aqueous electrolyte solution according to claim 1; a carbonaceous substance or compound capable of occluding and releasing lithium; or lithium metal. Or a non-aqueous electrolyte comprising a lithium salt and a non-aqueous solvent.