JP2002280061A - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte and a lithium secondary battery having flame retardancy (self-extinguishing) and excellent charge / discharge characteristics. SOLUTION: This is a non-aqueous electrolyte for a lithium secondary battery in which a lithium salt is dissolved in a non-aqueous solvent, wherein the non-aqueous solvent is a phosphate ester, a bisphosphonate and / or
Or a non-aqueous electrolyte containing a host acid ester, and a positive electrode containing a compound capable of inserting and extracting lithium,
In a lithium secondary battery including a carbonaceous material capable of occluding and releasing lithium, a negative electrode including at least one selected from lithium metal or a lithium alloy, and a nonaqueous electrolyte in which a lithium salt is dissolved in a nonaqueous solvent. And a lithium secondary battery in which the non-aqueous solvent contains a phosphoric acid ester and a bisphosphonic acid ester and / or a host acid ester.

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 and a lithium secondary battery using the same. The non-aqueous electrolyte of the present invention has flame retardancy (self-extinguishing), and a secondary battery using the non-aqueous electrolyte exhibits excellent charge / discharge characteristics.

[0002]

2. Description of the Related Art A carbon material such as graphite is used as a negative electrode active material.
LiCoO ₂ , LiNiO ₂ , L
A lithium secondary battery using a lithium transition metal composite oxide such as iMn ₂ O ₄ is rapidly growing as a new small secondary battery having a high voltage of 4 V and a high energy density. Such lithium secondary batteries generally use a lithium salt in a non-aqueous solvent obtained by mixing a low-viscosity solvent such as dimethyl carbonate or diethyl carbonate with a high dielectric constant solvent such as ethylene carbonate or propylene carbonate as an electrolytic solution. The dissolved one is used.

[0003] In these lithium secondary batteries using an organic non-aqueous electrolyte, when the electrolyte leaks due to damage to the battery or an increase in pressure inside the battery due to some cause,
There is a risk of flammable combustion. Therefore, studies on adding a flame retardant to an organic non-aqueous electrolyte to impart flame retardancy have been energetically advanced. It is known to use phosphate esters as flame-retardant electrolytes for lithium batteries. For example, JP-A-58-206078 and JP-A-60-2
3973, JP-A-61-227377, JP-A-61-284070 and JP-A-4-1848.
No. 70 discloses use of an O = P (OR) ₃ type phosphate such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tris (2-chloroethyl) phosphate. Further, JP-A-8-8802
No. 3 discloses a self-extinguishing electrolytic solution in which at least one of the above R is a halogen-substituted alkyl.

However, among the phosphoric esters used in these, electrolytic solutions containing trimethyl phosphate exhibit excellent flame retardancy, but have the disadvantage that they are liable to reductive decomposition depending on the material of the negative electrode. . Therefore, in order to enhance the manifestation of the flame retardant effect, it is necessary to increase the blending amount in the electrolyte solution.However, when natural graphite or artificial graphite is used as the negative electrode, the charge / discharge characteristics of the battery, for example, the charge / discharge efficiency and discharge The capacity cannot satisfy the characteristics generally required recently.

A phosphate ester having a halogen atom such as chlorine or bromine in a molecule is inferior in oxidation-reduction resistance, and is insufficient when applied to a 4V class secondary battery which generates a high voltage. A battery having charge / discharge characteristics cannot be obtained. Furthermore, a trace amount of free halogen ions present as an impurity in these phosphate esters corrode aluminum used as a positive electrode current collector and cause deterioration of battery characteristics.

Japanese Patent Application Laid-Open No. 4-184870 discloses that a cyclic phosphate ester is used as an electrolytic solution. Further, Japanese Patent Application Laid-Open No. 11-67267 discloses that cyclic phosphate esters 20 to 55 are used. Disclosed is an electrolyte for a lithium battery in which a volume% is used in combination with a cyclic carbonate. However, in order to make this type of electrolyte sufficiently flame-retardant, it is necessary to incorporate 20% by volume or more of a cyclic phosphate ester. There is a disadvantage that it decreases.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to solve such problems, and is provided with flame retardancy (self-extinguishing properties), excellent charge / discharge characteristics, and safety. An object of the present invention is to provide a lithium secondary battery having both reliability and reliability.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, obtained by dissolving a lithium salt in a nonaqueous solvent containing a specific component. The present inventors have found that a secondary battery in which the above-mentioned problems have been solved can be realized by using a liquid, and the present invention has been completed.

That is, the gist of the present invention is a non-aqueous electrolyte solution for a lithium secondary battery in which a lithium salt is dissolved in a non-aqueous solvent, wherein the non-aqueous solvent is a phosphate ester, a bisphosphonate ester and / or a host acid. A non-aqueous electrolyte solution containing an ester. Another gist of the present invention is that a positive electrode containing a compound capable of occluding and releasing lithium, a carbonaceous material capable of occluding and releasing lithium, a negative electrode including at least one selected from lithium metal or a lithium alloy, and a lithium salt are provided. A lithium secondary battery comprising a non-aqueous electrolyte dissolved in a non-aqueous solvent, wherein the non-aqueous solvent contains a phosphoric acid ester and a bisphosphonate and / or a host acid ester. Battery.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. (Non-Aqueous Electrolyte) The phosphate ester used in the non-aqueous electrolyte of the present invention is not particularly limited, but may be a compound represented by the following general formula (III) or a compound represented by the following general formula (IV). Preferably it is.

[0011]

Embedded image

(Wherein, R ₁₃ , R ₁₄ and R ₁₅ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom, provided that R ₁₃ , R ₁₄ and R _{15 each have} a carbon number Is 3 to 12)

[0013]

Embedded image

Wherein R ₁₆ represents an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom, and R ₁₇ represents an alkylene group having 2 to 8 carbon atoms. , R ₁₃ , R ₁₄ and R ₁₅ each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms or an alkyl group substituted with a fluorine atom. However, the total number of carbon atoms of R ₁₃ , R ₁₄ and R ₁₅ is 3
-12, preferably 3-7. And R ₁₃ , R ₁₄
And when R ₁₅ is an alkyl group, specific examples thereof include a methyl group, an ethyl group, a propyl group and a butyl group.

When R ₁₃ , R ₁₄ and R ₁₅ are a fluorine-substituted alkyl group, specific examples include trifluoroethyl, pentafluoropropyl, hexafluoroisopropyl and heptafluorobutyl. Can be mentioned. Specific examples of the phosphoric ester of the general formula (III) include, for example, trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, dimethylpropyl phosphate, dimethylbutyl phosphate, diethylmethyl phosphate, and dipropyl phosphate. Methyl, dibutyl methyl phosphate, methyl ethyl propyl phosphate, methyl ethyl butyl phosphate, methyl propyl butyl phosphate and the like.

Specific examples of the fluorine-substituted phosphate ester include, for example, trifluoroethyldimethyl phosphate,
Pentafluoropropyldimethyl phosphate, heptafluorobutyldimethyl phosphate, trifluoroethylmethylethyl phosphate, pentafluoropropylmethylethyl phosphate, heptafluorobutylmethylethyl phosphate, trifluoroethylmethylpropyl phosphate, pentafluorophosphate Propylmethylpropyl, heptafluorobutylmethylpropyl phosphate, trifluoroethylmethylbutyl phosphate, pentafluoropropylmethylbutyl phosphate,
Heptafluorobutyl methyl butyl phosphate, trifluoroethyl diethyl phosphate, pentafluoropropyl diethyl phosphate, heptafluorobutyl diethyl phosphate, trifluoroethyl ethyl propyl phosphate, pentafluoropropyl ethyl propyl phosphate, heptafluorobutyl phosphate Ethylpropyl, trifluoroethylethylbutyl phosphate, pentafluoropropylethylbutyl phosphate, heptafluorobutylethylbutyl phosphate, trifluoroethyldipropyl phosphate, pentafluoropropyldipropyl phosphate, heptafluorobutyldipropyl phosphate , Trifluoroethyl propyl butyl phosphate, pentafluoropropyl propyl butyl phosphate, heptafluorobutyl propyl butyl phosphate, trifluoroethyl dibutyl phosphate Pentafluoropropyl dibutyl phosphate, heptafluorobutyl dibutyl, and the like.

Among these, trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, dimethylpropyl phosphate, methyl diethyl phosphate, trifluoroethyl dimethyl phosphate, pentafluoropropyl dimethyl phosphate, trifluoroethyl methyl ethyl phosphate , Pentafluoropropylmethylethyl phosphate, trifluoroethylmethylpropyl phosphate, pentafluoropropylmethylpropyl phosphate is preferred, especially trimethyl phosphate,
Dimethylethyl phosphate, dimethylpropyl phosphate, methyldiethyl phosphate, and trifluoroethyldimethylphosphate are preferred.

These may be used alone or in combination of two or more. In the general formula (IV), R ₁₆ represents a linear or branched, preferably linear, alkyl group or fluorine-substituted alkyl group having 1 to 4 carbon atoms, preferably 1 to 2 carbon atoms, preferably an alkyl group. Represent. Specific examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a trifluoroethyl group, a pentafluoropropyl group, a hexafluoroisopropyl group, and a heptafluorobutyl group. Of these, a methyl group and an ethyl group are preferred.

R ₁₇ has 2 to 8 carbon atoms, preferably 2 carbon atoms.
Represents a straight-chain or branched, more preferably a straight-chain alkylene group having 2 carbon atoms. Specific examples thereof include an ethylene group, a propylene group, a trimethylene group, a butylene group, a tetramethylene group, a 1,1-dimethylethylene group, a pentamethylene group, a 1,1,2-trimethylethylene group, a hexamethylene group, and a tetramethylene group. Examples include a methylethylene group, a heptamethylene group, and an octamethylene group. Of these, an ethylene group is preferred.

In the compound of the general formula (IV), R ₁₇
Is an ethylene group, and R ₁₆ is preferably a group selected from a methyl group, an ethyl group and a trifluoroethyl group. Specific examples of the cyclic phosphate of the general formula (IV) in which R ₁₆ is an alkyl group include ethylene methyl phosphate, ethylene ethyl phosphate, ethylene-n-propyl phosphate,
Ethylene isopropyl phosphate, ethylene-n-butyl phosphate, ethylene-sec-butyl phosphate, ethylene-t-butyl phosphate, propylene methyl phosphate, propylene ethyl phosphate, propylene-n-propyl phosphate, propylene phosphate Isopropyl, propylene-n-butyl phosphate, propylene-sec-butyl phosphate, propylene-t-butyl phosphate, trimethylenemethyl phosphate, trimethyleneethyl phosphate, trimethylene-n-propyl phosphate, trimethylene phosphate Isopropyl, trimethylene-n-butyl phosphate, trimethylene-sec-butyl phosphate, trimethylene-t-butyl phosphate, butylene methyl phosphate, butylene ethyl phosphate, butylene-n phosphate
-Propyl, butylene isopropyl phosphate, butylene-n-butyl phosphate, butylene-sec-butyl phosphate,
Butyl phosphate-t-butyl, isobutylene methyl phosphate, isobutylene ethyl phosphate, isobutylene phosphate-
n-butyl, isobutylene phosphate-sec-butyl, isobutylene-t-butyl phosphate, tetramethylene methyl phosphate, tetramethylene ethyl phosphate, tetramethylene-n-propyl phosphate, tetramethylene isopropyl phosphate, tetraphosphate Methylene-n-butyl, tetramethylene phosphate-sec-butyl, tetramethylene phosphate
t-butyl, pentamethylenemethyl phosphate, pentamethyleneethyl phosphate, pentamethylene-n-propyl, pentamethyleneisopropyl, pentamethylene-n-butyl, pentamethylene-sec
-Butyl, pentamethylene-t-butyl phosphate, trimethylethylenemethyl phosphate, trimethylethyleneethyl phosphate, trimethylethylene-n-propyl phosphate, trimethylethyleneisopropyl phosphate, trimethylethylene-n-butyl phosphate, phosphoric acid Trimethylethylene-
sec-butyl, trimethylethylene-t-butyl phosphate, hexamethylenemethyl phosphate, hexamethyleneethyl phosphate, hexamethylene-n-propyl, hexamethyleneisopropyl phosphate, hexamethylene-n-butyl, phosphorus Hexamethylene-sec-butyl, hexamethylene-t-butyl phosphate, tetramethylethylenemethyl phosphate, tetramethylethyleneethyl phosphate, tetramethylethylene-n-propyl phosphate, tetramethylethyleneisopropyl phosphate, phosphoric acid Tetramethylethylene-n-butyl, tetramethylethylene phosphate-sec-butyl, tetramethylethylene phosphate-
t-butyl, heptamethylene methyl phosphate, heptamethylene ethyl phosphate, heptamethylene-n-propyl phosphate, heptamethylene isopropyl phosphate, heptamethylene-n-butyl phosphate, heptamethylene-sec
-Butyl, heptamethylene-t-butyl phosphate, octamethylenemethyl phosphate, octamethyleneethyl phosphate,
Octamethylene phosphate n-propyl, octamethylene isopropyl phosphate, octamethylene n-butyl phosphate, octamethylene sec-butyl phosphate, octamethylene tert-butyl phosphate and the like can be mentioned. Among them, ethylene methyl phosphate and ethylene ethyl phosphate are preferable.

Specific examples of the fluorine-substituted cyclic phosphate of the general formula (IV) wherein R ₁₆ is a fluorine-substituted alkyl group include ethylene trifluoroethyl phosphate,
Ethylene pentafluoropropyl phosphate, ethylene hexafluoroisopropyl phosphate, ethylene heptafluorobutyl phosphate, propylene trifluoroethyl phosphate, propylene pentafluoropropyl phosphate, propylene hexafluoroisopropyl phosphate, propylene heptafluorobutyl phosphate, phosphorus Trimethylene trifluoroethyl phosphate, trimethylene pentafluoropropyl phosphate, trimethylene hexafluoroisopropyl phosphate, trimethylene heptafluorobutyl phosphate, butylene trifluoroethyl phosphate, butylene pentafluoropropyl phosphate, butylene hexafluorophosphate Isopropyl, butylene heptafluorobutyl phosphate, tetramethylene trifluoroethyl phosphate, tetramethylene pentafluorophosphate Pills, phosphate tetramethylene hexafluoroisopropyl, tetramethylene heptafluorobutyl phosphate, dimethyl ethylene trifluoroethyl phosphate, dimethyl ethylene pentafluoropropyl, phosphate dimethylethylene hexafluoroisopropyl, dimethylethylene heptafluorobutyl phosphoric acid,
Pentamethylene trifluoroethyl phosphate, pentamethylene pentafluoropropyl phosphate, pentamethylene hexafluoroisopropyl phosphate, pentamethylene heptafluorobutyl phosphate, trimethylethylene trifluoroethyl phosphate, trimethylethylene pentafluoropropyl phosphate, phosphoric acid Trimethylethylene hexafluoroisopropyl, trimethylethylene heptafluorobutyl phosphate, hexamethylene trifluoroethyl phosphate, hexamethylene pentafluoropropyl phosphate, hexamethylene hexafluoroisopropyl phosphate, hexamethylene heptafluorobutyl phosphate, tetramethyl phosphate Ethylene trifluoroethyl, tetramethylethylene pentafluoropropyl phosphate, tetramethylethylene hexaphosphate Fluoroisopropyl, tetramethylethylene heptafluorobutyl phosphate, heptamethylene trifluoroethyl phosphate, heptamethylene pentafluoropropyl phosphate, heptamethylene hexafluoroisopropyl phosphate, heptamethylene heptafluorobutyl phosphate, octamethylene triphosphate Fluoroethyl,
Octamethylenepentafluoropropyl phosphate, octamethylenehexafluoroisopropyl phosphate, octamethyleneheptafluorobutyl phosphate and the like can be mentioned. Among them, ethylene trifluoroethyl phosphate is preferred.

The proportion of the phosphate ester in the non-aqueous solvent used in the present invention is usually 9 to 50% by volume, preferably 15 to 40% by volume. In the present invention, the non-aqueous solvent containing a phosphate ester preferably contains at least one organic solvent selected from carbonates, lactones, ethers, sulfolanes and dioxolanes. Carbonates, lactones, ethers,
In both sulfolane and dioxolane,
The compounds are not limited, and known compounds can be used.

For example, carbonates include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, vinylene carbonate and the like. Among these, ethylene carbonate, propylene carbonate, dimethyl carbonate,
Diethyl carbonate and methyl ethyl carbonate are preferred.

Examples of the lactones include γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ
-Octanolactone, β-butyrolactone, δ-valerolactone, ε-caprolactone and the like. Among these, γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone are preferred.

Examples of the ethers include tetrahydrofuran, 2-methyltetrahydrofuran and 1,4-dioxane. Examples of the sulfolane include sulfolane. As dioxolanes,
1,3-dioxolan can be mentioned. Non-aqueous solvents used in the present invention include bisphosphonic esters and / or
Alternatively, a host acid ester is contained.

The type of the bisphosphonic acid ester is not particularly limited, but is preferably a compound represented by the following general formula (I).

[0027]

Embedded image

(Wherein, R ₁ , R ₂ , R ₄ and R ₅ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom, and R ₃ represents an alkylene having 1 to ₃ carbon atoms. In the general formula (I), R ₁ , R ₂ , R ₄ and R ₅ are each independently substituted by a linear or branched C ₁ -C 4 fluorine atom. A good alkyl group,
R ₃ represents an alkylene group having 1 to ₃ carbon atoms. R ₁ ,
When R ₂ , R ₄ and R ₅ are an alkyl group having 1 to 4 carbon atoms, specific examples thereof include a methyl group, an ethyl group, and an n-
Propyl group, i-propyl group, n-butyl group, sec-
Examples thereof include a linear or branched alkyl group such as a butyl group and a t-butyl group. Examples of the alkyl group substituted with a fluorine atom include a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a pentafluoroethyl group, and a hexafluoroisopropyl group. Of these, a methyl group and an ethyl group are preferred. In formula (I), examples of the alkylene group having 1 to 3 carbon atoms represented by R ₃ include a methylene group, an ethylene group, and a propylene group.

Specific examples of the bisphosphonate represented by the general formula (I) include tetramethylmethylenebisphosphonate, tetramethylethylenebisphosphonate, tetramethylpropylenebisphosphonate, tetraethylmethylenebisphosphonate, tetraethylethylenebisphosphonate, and tetraethylethylenebisphosphonate. Propylene bisphosphonate, tetrakis (2,2,2-trifluoroethyl) methylenebisphosphonate, tetrakis (2,2,2-trifluoroethyl) ethylenebisphosphonate and the like can be given.

Among them, tetraethylmethylenebisphosphonate and tetraethylethylenebisphosphonate are preferred. These may be used in combination of two or more. The host acid ester is an ester of a host acid (phosphonic acid) which is a monocyclic ester of a phosphonic acid, and the kind thereof is not particularly limited, but is a compound represented by the following general formula (II). preferable.

[0031]

Embedded image

Wherein R ₆ represents an alkylene group having 2 to 4 carbon atoms, and R ₇ represents an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom. , R ₆ represents an alkylene group having 2 to 4 carbon atoms, and R ₇ represents a linear or branched alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom. Specific examples of such a host acid ester represented by the general formula (II) include methyl propane host acid,
Ethyl propane host, 1,1,1-trifluoroethyl propane host, methylbutane host, ethylbutane host, 1,1,1-trifluoroethyl butane host, and the like.

Of these, methyl propane host and ethyl propane host are preferred. These may be used in combination of two or more. The total content of the bisphosphonic acid ester and the host acid ester used in the present invention is preferably 1 to 30% by weight, and particularly preferably 2 to 20% by weight, based on the non-aqueous electrolyte.

The addition of such a bisphosphonic acid ester or host acid ester to the non-aqueous solvent has the effect of improving the charge / discharge characteristics (charge / discharge efficiency, charge / discharge capacity) of the battery generated when the non-aqueous solvent is used. is there. Type of lithium salt solute dissolved in the nonaqueous solvent is not particularly limited, but a known lithium salt used in the non-aqueous lithium secondary battery can be used, preferably LiPF _6, Li
A lithium salt of an inorganic acid such as BF ₄ or a lithium salt of an organic acid represented by the following general formula (V) can be used.

[0035]

Embedded image

Wherein m and n are integers of 1 to 4, respectively.
The organic acid lithium salt of the general formula (V) includes LiN (S
O_TwoCF_Three)_Two, LiN (SO_TwoC_TwoF_Five)_Two, LiN
(SO_TwoC_ThreeF₇)_Two, LiN (SO_TwoC_FourF ₉)_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_Two
F_Five) ・ (SO_TwoC_ThreeF₇), LiN (SO_TwoC
_TwoF_Five) ・ (SO_TwoC_FourF₉), LiN (SO_TwoC_ThreeF
₇) ・ (SO_TwoC_FourF₉). these
Medium, LiN (SO_TwoCF_Three)_Two, LiN (SO_TwoC_TwoF
_Five)_Two, LiN (SO_TwoCF_Three) ・ (SO_TwoC_FourF₉)
Is preferred.

The lithium salt 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 .
１．５1.5 mol / dm ³ is used. 0.
If it is less than 5 mol / dm ³ or more than 2 mol / dm ³ , the conductivity of the electrolyte tends to decrease. (Lithium Secondary Battery) The lithium secondary battery of the present invention comprises the above-mentioned non-aqueous electrolyte, a negative electrode and a positive electrode.

The negative electrode material constituting the battery is not particularly limited as long as it contains a material capable of inserting and extracting lithium, but is preferably a known carbonaceous material, specifically, for example, coke, glassy carbon or the like. , Artificial graphite, natural graphite, non-graphitizable carbon, pyrolytic carbon, carbon fiber and the like can be used. Or as other negative electrode material preferably lithium metal and lithium and aluminum, tin, zinc,
An alloy with a metal such as silver or lead can be used. A known negative electrode material such as a conductive polymer can be used as the negative electrode material. These negative electrode materials may be used as a mixture of two or more kinds.

As the shape of the negative electrode, a sheet electrode applied to a current collector after mixing with a binder and a conductive agent, if necessary, and a pellet electrode 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 from the viewpoint of easy processing into a thin film and cost. As the positive electrode material constituting the battery, various materials capable of inserting and extracting lithium, such as a lithium transition metal composite oxide material such as lithium manganese oxide, lithium cobalt oxide, and lithium nickel oxide, can be used. The above-mentioned lithium transition metal composite oxide is preferable.

The shape of the positive electrode is not particularly limited, and examples thereof include a sheet electrode applied to a current collector after mixing with a binder and a conductive agent, if necessary, and a pellet electrode subjected to press molding. 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.

[0042]

EXAMPLES Hereinafter, the embodiments of 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 and the battery performance were evaluated by the following methods. 1. Evaluation of self-extinguishing property of electrolyte: width 15 mm, length 300
mm, a glass fiber filter paper with a thickness of 0.19 mm,
The glass fiber filter paper was sufficiently impregnated with the electrolytic solution by immersing it in a beaker containing the electrolytic solution for 10 minutes or more. 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. The lower end was heated with a small gas flame of lighters for about 3 seconds, and the 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 charge / discharge cycle characteristics: For measurement of charge / discharge cycle characteristics, a coin-type battery having a diameter of 20 mm and a thickness of 1.6 mm was manufactured, and 0.2 mA / cm in a voltage range of 0 to 1.5 V.
Charge / discharge was performed at a current density of ² . As for the battery capacity, the discharge capacity (dedoping capacity) after three cycles was obtained.

In the battery, a positive electrode (working electrode) and a negative electrode (counter electrode) are accommodated in a stainless steel case also serving as a positive electrode terminal via a separator made of a porous polypropylene film impregnated with an electrolytic solution, and then put through a gasket made of polypropylene. It was manufactured by sealing with a stainless steel sealing plate also serving as the negative electrode terminal. As a working electrode, a carbon material as an active material, a fluororesin as a binder were mixed at a weight ratio of 90:10, and this was dispersed in a solvent (N-methylpyrrolidone) to form a slurry. After coating and drying on copper foil as a current collector,
A working electrode having a diameter of 12.5 mm was produced. As the counter electrode, a lithium metal sheet having a diameter of 12.5 mm and a thickness of 1.0 mm was used.

Examples 1 to 7 and Comparative Examples 1 and 2 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. did. Using this electrolytic solution, self-extinguishing properties (flame retardancy) and electrical conductivity were measured. Also, the discharge (dedoping) capacity of a coin-type battery using natural graphite for the working electrode was measured.
Table 2 shows the results.

FIG. 1 shows the results of the charging and discharging efficiency characteristics of the coin batteries of Examples 1, 2, 5 and Comparative Example 2. In addition, the symbol in a table | surface shows the following. EC: ethylene carbonate PC: propylene carbonate GBL: γ-butyrolactone TMP: trimethyl phosphate EDMP: dimethylethyl phosphate PrDMP: dimethylpropyl phosphate TEMDP: tetraethylmethylene diphosphonate TEEDP: tetraethylethylene diphosphonate MPt: methylpropane hostnate

[0047]

[Table 1]

[0048]

[Table 2]

As shown in Table 2, the electrolytic solution of Comparative Example 1 has a high capacity in the test cell, but has no self-extinguishing property. In Comparative Example 2, the addition of the phosphoric acid ester has a self-extinguishing property and a high flame-retardant effect, and the conductivity is improved, but the discharge capacity is very low. In contrast, Examples 1 to 7
In the electrolyte solution to which the additive was added, self-extinguishing properties were exhibited and the discharge capacity was greatly improved.

As shown in FIG. 1, the comparative example has low charge / discharge efficiency, whereas the example maintains high charge / discharge efficiency and has excellent cycle characteristics.

[0051]

The electrolytic solution for a lithium secondary battery of the present invention comprises:
It has flame retardancy (self-extinguishing), good charge / discharge characteristics, and high safety and reliability.

[Brief description of the drawings]

FIG. 1 is a diagram showing the cycle characteristics of charge and discharge efficiency of coin batteries manufactured using an electrolyte solution of an example and an electrolyte solution of a comparative example.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Asato Kominato 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Prefecture Mitsubishi Chemical Corporation Tsukuba Research Laboratory F-term (reference) AM00 AM02 AM03 AM04 AM07 HJ01 HJ02

Claims (9)

[Claims] 1. A non-aqueous electrolyte for a lithium secondary battery comprising a lithium salt dissolved in a non-aqueous solvent, wherein the non-aqueous solvent contains a phosphate ester, a bisphosphonate ester and / or
Or a non-aqueous electrolyte solution containing a host acid ester. 2. A bisphosphonate having the general formula (I): (Wherein, R ₁ , R ₂ , R ₄ and R ₅ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom, and R ₃ represents an alkylene group having 1 to ₃ carbon atoms. The non-aqueous electrolyte solution according to claim 1, which is a compound represented by the formula: 3. The method according to claim 1, wherein the host acid ester has the general formula (II): (Wherein, R ₆ represents an alkylene group having 2 to 4 carbon atoms;
₇ is a compound having 1 to 4 carbon atoms which may be substituted by a fluorine atom).
Or the non-aqueous electrolyte according to 2. 4. The phosphoric ester of the general formula (III): (Wherein, R ₁₃ , R ₁₄ and R ₁₅ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom.
However, the total number of carbon atoms of R ₁₃ , R ₁₄ and R ₁₅ is 3 to 12
Or a compound represented by the general formula (IV): (Wherein, R ₁₆ represents an alkyl group having 1 to 4 carbon atoms which may be substituted by a fluorine atom, and R ₁₇ represents an alkylene group having 2 to 8 carbon atoms). Item 1
4. The non-aqueous electrolyte according to any one of claims 1 to 3. 5. The non-aqueous solvent according to claim 1, wherein the non-aqueous solvent contains at least one organic solvent selected from the group consisting of carbonates, lactones, ethers, sulfolane and dioxolane. Non-aqueous electrolyte. 6. The lithium salt is LiPF ₆ , LiBF ₄
Or an organic acid lithium salt represented by the general formula (V):
The non-aqueous electrolyte according to claim 1. Embedded image (Wherein, m and n each represent an integer of 1 to 4) 7. The non-aqueous electrolyte according to claim 1, wherein the content of the phosphate in the non-aqueous solvent is 9 to 50% by volume. 8. The non-aqueous electrolyte according to claim 1, wherein the total content of the bisphosphonate and the host ester in the non-aqueous electrolyte is 1 to 30% by weight. 9. A positive electrode containing a compound capable of occluding and releasing lithium, a negative electrode containing at least one selected from a carbonaceous material capable of occluding and releasing lithium, a lithium metal or a lithium alloy, and a lithium salt containing a nonaqueous solvent. A non-aqueous electrolytic solution dissolved in a lithium secondary battery, wherein the non-aqueous electrolytic solution is the non-aqueous electrolytic solution according to any one of claims 1 to 8. Next battery.