JP2002124298A - Nonaqueous electrolytic solution and lithium secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having excellent battery characteristics such as a cycle characteristic, electric capacity and a shelf life characteristic of the battery. SOLUTION: In this nonaqueous electrolytic solution wherein an electrolyte is dissolved in a nonaqueous solvent, the nonaqueous electrolytic solution is characterized by including 0.001-0.8 wt.% of one or more kinds of heterocyclic compounds such as 3-chlorothiophene in the nonaqueous electrolytic solution. This lithium secondary battery uses the nonaqueous electrolytic solution.

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 capable of providing a lithium secondary battery having excellent battery characteristics such as cycle characteristics, electric capacity and storage characteristics of a battery, and lithium using the same. Related to secondary batteries.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power sources for driving small electronic devices and the like. Lithium secondary batteries are mainly composed of a positive electrode, a non-aqueous electrolyte, and a negative electrode. In particular, a lithium secondary battery using a lithium composite oxide such as LiCoO ₂ as a positive electrode and a carbon material or lithium metal as a negative electrode has been developed. It is preferably used. And as the non-aqueous solvent of the non-aqueous electrolyte for the lithium secondary battery,
Carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC) are suitably used.

[0003] However, there is a demand for a secondary battery having more excellent battery characteristics such as cycle characteristics and electric capacity. In a lithium secondary battery using, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, or the like as a positive electrode, charge and discharge are repeated until a maximum operating voltage that normally exceeds 4.1 V. However, there is a serious problem that the capacity of this battery gradually decreases when charge and discharge are repeated over a long period of time. This phenomenon occurs because the solvent in the non-aqueous electrolyte partially oxidizes and decomposes when charged to a maximum operating voltage exceeding 4.1 V, and the decomposition product hinders the desired electrochemical reaction of the battery. Battery performance is degraded. This is thought to be due to electrochemical oxidation of the solvent at the interface between the positive electrode material and the non-aqueous electrolyte. For this reason, at present, the battery characteristics such as the cycle characteristics and the electric capacity of the batteries that repeatedly charge and discharge up to the maximum operating voltage exceeding 4.1 V are not always satisfactory.

Japanese Patent Application Laid-Open No. 9-106835 discloses 3-
About 1 to 4 chlorothiophene, thiophene, furan, etc.
A technique has been disclosed for protecting a battery by increasing the resistance of an electrolyte by electrochemically polymerizing at an unusually high voltage when overcharging occurs by adding volume%. But,
In JP-A-11-162512, when these compounds are added in an amount of about 1 to 4% by volume, the cycle is repeated up to the upper limit of the voltage exceeding 4.1 V, or the composition is exposed to a long-term high temperature of 40 ° C. or more. Such as high voltage and / or
Alternatively, it is described that battery characteristics such as cycle characteristics tend to deteriorate in charge / discharge in a high-temperature state, and the tendency becomes more pronounced as the amount of addition increases. For this reason,
At present, battery characteristics such as battery cycle characteristics and electric capacity are not always satisfactory.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a non-aqueous electrolyte for a lithium secondary battery, which causes a decrease in cycle characteristics in charging and discharging at a voltage higher than 4.1 V and / or at a high temperature of 40 ° C. or more as described above. Solves the problems related to liquids and has excellent cycle characteristics of batteries when charged and discharged in a high voltage state where the upper limit voltage is higher than 4.1 V and / or a high temperature state of 40 ° C. or higher, and furthermore, the batteries have excellent electric capacity and storage characteristics in a charged state. An object of the present invention is to provide a lithium secondary battery capable of forming a lithium secondary battery having excellent characteristics, and a non-aqueous electrolyte thereof.

[0006]

According to the present invention, there is provided a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following general formulas (I), (II) and (III): ),
(IV), (V), (VI), (VII),

[0007]

Embedded image

[0008]

Embedded image

[0009]

Embedded image

[0010]

Embedded image

[0011]

Embedded image

[0012]

Embedded image

[0013]

Embedded image

Wherein Y ^{1 to} Y ¹⁰ are each an oxygen atom,
X ^{1 to} X ¹⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms,
It represents an aralkyl group having 7 to 15 carbon atoms, a halogen atom, and an alkylsilyl group having 1 to 12 carbon atoms. X ¹ and X ² ,
X ² and X ³ , X ³ and X ⁴ , X ⁵ and X ⁶ , X ⁷ and X ⁸ , X ⁹ and X ¹⁰ , X ¹¹ and X ¹² are bonded to each other to form a straight or branched chain having 3 to 12 carbon atoms. A branched alkylene group or a linear or branched alkylenedioxy group having 1 to 6 carbon atoms may be shown. m and n each represent an integer of 0 to 2. The present invention relates to a non-aqueous electrolyte characterized in that at least one of the heterocyclic compounds represented by the formula (1) is contained in an amount of 0.001 to 0.8% by weight based on the non-aqueous electrolyte. Further, the present invention provides a lithium secondary battery using a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the general formula (I), (I) II), (I
At least one of the heterocyclic compounds represented by II), (IV), (V), (VI), and (VII) is contained in an amount of 0.001 to 0.8% by weight based on the nonaqueous electrolyte. And a lithium secondary battery.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The non-aqueous electrolyte of the present invention is used as a component of a lithium secondary battery. The constituent members other than the non-aqueous electrolyte constituting the secondary battery are not particularly limited, and various constituent members conventionally used can be used.

The above formulas (I), (II) and (II) contained in a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent
In the heterocyclic compounds represented by I), (IV), (V), (VI), and (VII), Y ^{1 to} Y ¹⁰ represent an oxygen atom, a sulfur atom, and a nitrogen atom. Substituents for the nitrogen atom include straight-chain alkyl groups such as methyl, ethyl, propyl and butyl, branched alkyl groups such as isopropyl and isobutyl, cyclopropyl and cyclohexyl. Alkyl groups and aralkyl groups containing such cycloalkyl groups are preferred. X ^{1 to} X ¹⁴ are each independently an alkyl group having 1 to 12 carbon atoms [methyl group,
A linear alkyl group such as an ethyl group, a propyl group or a butyl group; a branched alkyl group such as an isopropyl group or an isobutyl group; a cyclopropyl group or a cyclohexyl group (hereinafter referred to as cyclo-Hex). Such as a cycloalkyl group], an aralkyl group having 7 to 15 carbon atoms (such as a benzyl group or a phenethyl group), a halogen atom (a fluorine atom,
A chlorine atom, a bromine atom, an iodine atom) and an alkylsilyl group having 3 to 15 carbon atoms (such as a trimethylsilyl group, a triethylsilyl group, a tributylsilyl group, and a butyldimethylsilyl group) are preferable. Further, X ¹ and X ² , X ² and X ³ , X ³
And X ⁴ , X ⁵ and X ⁶ , X ⁷ and X ⁸ , X ⁹ and X ¹⁰ , X ¹¹ and X ¹² are bonded to each other to form a trimethylene group, a tetramethylene group,
A straight-chain or branched alkylene group having 3 to 12 carbon atoms such as a methyltrimethylene group, a methylenedioxy group, an ethylenedioxy group, a trimethylenedioxy group, a propylenedioxy group or the like having 1 to 6 carbon atoms; It may represent a linear or branched alkylenedioxy group. Here, m and n each represent an integer of 0 to 2.

Heterocyclic compound represented by formula (I)
As a specific example of, for example, Y¹If = O, franc
[X¹= X^Two= X^Three= X^Four= H], 2-methylfuran [X¹
= Me, X^Two= X^Three= X^Four= H], 3-methylfuran [X^Two
= Me, X¹= X^Three= X^Four= H], 2,5-dimethylfura
[X¹= X^Four= Me, X^Two= X^Three= H], 3,4-dimethyl
Lefran [X^Two= X^Three= Me, X¹= X^Four= H], 2, 3,
4-trimethylfuran [X¹= X^Two= X^Three= Me, X^Four=
H], 2,3,4,5-tetramethylfuran [X¹= X^Two
= X^Three= X^Four= Me], 2-cyclohexylfuran [X¹
= Cyclo-Hex, X ^Two= X^Three= X^Four= H], 2-ethynyl
Franc [X¹= CCH, X^Two= X^Three= X^Four= H], 3-black
Lofran [X^Two= Cl, X¹= X^Three= X^Four= H], 3-bro
Mofuran [X ^Two= Br, X¹= X^Three= X^Four= H], 2-tri
Methylsilylfuran [X¹= SiMe_Three, X^Two= X^Three= X^Four
= H], 3,4-ethylenedioxyfuran [X^TwoAnd X^ThreeBut
OCH_TwoCH_TwoJoin with O, X¹= X^Four= H], 4, 5, 6,
7-tetrahydroisobenzofuran [X^TwoAnd X^ThreeIs (CH
_Two)_Four, X¹= X^Four= H] and the like. Y¹=
In the case of S, thiophene [X¹= X^Two= X^Three= X^Four= H], 2
-Methylthiophene [X ¹= Me, X^Two= X^Three= X^Four=
H], 3-methylthiophene [X^Two= Me, X¹= X^Three=
X^Four= H], 2,5-dimethylthiophene [X¹= X^Four=
Me, X^Two= X^Three= H], 3,4-dimethylthiophene
[X^Two= X^Three= Me, X¹= X^Four= H], 2,3,4-tri
Methylthiophene [X¹= X^Two= X^Three= Me, X^Four= H],
2,3,4,5-tetramethylthiophene [X¹= X^Two=
X^Three= X^Four= Me], 3-cyclohexylthiophene [X
^Two= Cyclo-Hex, X¹= X^Three= X^Four= H], 2-ethenyl
Thiophene [X¹= CHCH_Two, X^Two= X^Three= X^Four= H],
3-ethenylthiophene [X^Two= CHCH_Two, X¹= X^Three=
X^Four= H], 2-ethynylthiophene [X¹= CCH, X
^Two= X ^Three= X^Four= H], 3-ethynylthiophene [X^Two= C
CH, X¹= X^Three= X^Four= H], 3-chlorothiophene
[X^Two= Cl, X¹= X^Three= X^Four= H], 3-bromothiophene
[X^Two= Br, X¹= X^Three= X^Four= H], 3-fluoro
Thiophene [X^Two= F, X¹= X^Three= X^Four= H], 3-Yaw
Dothiophene [X^Two= I, X¹= X^Three= X^Four= H], 2-t
Limethylsilylthiophene [X¹= SiMe_Three, X^Two= X^Three
= X^Four= H], 3,4-ethylenedioxythiophene
[X^TwoAnd X^ThreeIs OCH_TwoCH_TwoJoin with O, X¹= X^Four= H],
4,5,6,7-tetrahydrobenzo [c] thiophene
[X^TwoAnd X^ThreeIs (CH_Two)_Four, X¹= X^Four= H]
No. Y¹= N-methylpyrrole when NMe
[X¹= X^Two= X^Three= X^Four= H], 2-methyl-N-methyl
Pyrrole [X¹= Me, X^Two= X^Three= X^Four= H], 3-methyl
Ru-N-methylpyrrole [X^Two= Me, X¹= X^Three= X^Four=
H], 2,5-dimethyl-N-methylpyrrole [X¹=
X^Four= Me, X^Two= X^Three= H], 3,4-dimethyl-N-
Methylpyrrole [X^Two= X^Three= Me, X¹= X^Four= H],
2,3,4-trimethyl-N-methylpyrrole [X¹=
X^Two= X^Three= Me, X^Four= H], 2,3,4,5-tetra
Methyl-N-methylpyrrole [X¹= X^Two= X^Three= X^Four= M
e], 3-cyclohexyl-N-methylpyrrole [X^Two
= Cyclo-Hex, X¹= X^Three= X^Four= H], 1, 2, 3,
4,5,6,7,8-octahydro-9-methylcarba
Zol [X¹And X^TwoIs (CH_Two)_Four, X^ThreeAnd X^FourIs (C
H_Two)_FourAnd bonding]. However, the present invention
It is not limited to these compounds.

Heterocyclic compound represented by formula (II)
As a specific example of the object, for example, Y^Two= 0, 2, 2 '
-Bifran [X^Five= X⁶= X⁹= X^Ten= H, m = 0], 4
-Methyl-2,2'-bifuran [X^Five= Me, X⁶= X⁹
= X^Ten= H, m = 0], 3,4'-dimethyl-2,2 '
-Bifran [X^Five= X⁹= Me, X⁶= X^Ten= H, m =
0], 2, 2 ': 5', 2 ''-tarfuran [X^Five= X⁶=
X⁷= X⁸= X⁹= X^Ten= H, m = 1], 2, 2 ':
5 ', 2' ': 5' ', 2' ''-quarter franc [X^Five= X
⁶= X⁷= X⁸= X⁹= X^Ten= H, m = 2].
You. Y^Two= S, 2,2'-bithiophene [X^Five= X
⁶= X⁹= X^Ten= H, m = 0], 4-methyl-2,2'-
Bithiophene [X^Five= Me, X⁶= X⁹= X^Ten= H, m =
0], 4,4'-dimethyl-2,2'-bithiophene
[X^Five= X^Ten= Me, X⁶= X⁹= H, m = 0], 3,
3 ', 4,4'-tetramethyl-2,2'-bithiofe
[X^Five= X⁶= X⁹= X^Ten= Me, m = 0], 2,
2 ': 5', 2 ''-terthiophene [X ^Five= X⁶= X⁷=
X⁸= X⁹= X^Ten= H, m = 1], 3-methyl-2,
2 ': 5', 2 ''-terthiophene [X⁶= Me, X^Five=
X⁷= X⁸= X⁹= X^Ten= H, m = 1], 3'-methyl-
2,2 ': 5', 2 ''-terthiophene [X⁷= Me,
X^Five= X ⁶= X⁸= X⁹= X^Ten= H, m = 1], 4,3 ″ −
Dimethyl-2,2 ': 5', 2 ''-terthiophene [X
^Five= X⁹= Me, X⁶= X⁷= X⁸= X^Ten= H, m = 1],
4,4 "-dimethyl-2,2 ': 5', 2" -terthio
Fen [X^Five= X^Ten= Me, X⁶= X⁷= X⁸= X⁹= H,
m = 1], 3,3 ', 3 ", 4,4', 4" -hexame
Cyl-2,2 ': 5', 2 ''-terthiophene [X^Five=
X⁶= X⁷= X⁸= X⁹= X^Ten= Me, m = 1], 2,
2 ': 5', 2 '': 5 '', 2 '' '-quarter thiophene
[X^Five= X⁶= X⁷= X⁸= X⁹= X^Ten= H, m = 2]
And so on. Y^Two= NMe, 1,1'-dimension
Chill-2,2'-bipyrrole [X^Five= X⁶= X⁹= X^Ten=
H, m = 0], 1,1 ', 1 "-trimethyl-2,
2 ': 5', 2 ''-ter-1H-pyrrole [X^Five= X⁶=
X⁷= X⁸= X⁹= X^Ten= H, m = 1].
You. However, the present invention is limited to these compounds
is not.

Specific examples of the heterocyclic compound represented by the general formula (III) include, for example, 2,2'-dithiobisfuran [Y ³ = S, Y ⁴ = S, n = 0], 2- [ [(2-thienylmethyl) dithio] methyl] furan [Y ³ = 0, Y ⁴ =
S, n = 1], furfuryl disulfide [Y ³ = 0, Y ⁴
ＯO, n = 1]. However, the present invention is not limited to these compounds.

Specific examples of the heterocyclic compound represented by the general formula (IV) include, for example, furo [2,3-b] furan [Y ⁵ = Y ⁶ = 0, X ¹¹ = X ¹² = H], Thieno [2,3-
b] Thiophene [Y ⁵ = Y ⁶ = S, X ¹¹ = X ¹² = H], thieno [2,3-b] furan [Y ⁵ = 0, Y ⁶ = S, X ¹¹ =
X ¹² = H], 3-methylthieno [2,3-b] thiophene [Y ⁵ = Y ⁶ = S, X ¹¹ = Me, X ¹² = H], 3,4-
Dimethylthieno [2,3-b] thiophene [Y ⁵ = Y ⁶ =
S, X ¹¹ = X ¹² = Me]. However, the present invention is not limited to these compounds.

Heterocyclic compound represented by formula (V)
As a specific example of, for example, flow [3,2-b] furan
[Y⁷= Y⁸= O, X¹³= X¹⁴= H], thieno [3,2-
b] thiophene [Y⁷= Y⁸= S, X¹³= X¹⁴= H],
Eno [3,2-b] furan [Y ⁷= O, Y⁸= S, X¹³=
X¹⁴= H], 3-methylthieno [3,2-b] thiophene
[Y⁷= Y⁸= S, X¹³= Me, X¹⁴= H], 3,6-
Dimethylthieno [3,2-b] thiophene [Y⁷= Y⁸=
S, X¹³= X¹⁴= Me]. However, the book
The invention is not limited to these compounds.

Specific examples of the heterocyclic compound represented by the general formula (VI) include, for example, dithieno [3,2-b:
2 ′, 3′-d] thiophene [Y ⁹ = S]. However, the present invention is not limited to this compound.

Specific examples of the heterocyclic compound represented by the general formula (VII) include, for example, thieno [3,2-b] thieno [2 ′, 3 ′, 4,5] thieno [2,3-d Thiophene [Y ¹⁰ = S]. However, the present invention is not limited to this compound.

As the heterocyclic compound contained in the non-aqueous electrolyte, the compounds represented by the general formulas (I), (II), (III) and (I)
When the heterocyclic compound represented by V), (V), (VI) or (VII) is contained, if the content is excessively high, the voltage is higher than 4.1 V and / or a high temperature state of 40 ° C. or higher. Sufficient battery performance cannot be obtained in charging / discharging. Further, even if the amount is excessively small, the expected sufficient battery performance cannot be obtained.
Therefore, the content is preferably in the range of 0.001 to 0.8% by weight, more preferably 0.005 to 0.5% by weight, and most preferably 0.01 to 0.8% by weight based on the weight of the non-aqueous electrolyte. The range of 0.3% by weight may improve the cycle characteristics.

The heterocyclic compound of the present invention is used in an amount of 0.001 to 0.
The non-aqueous electrolyte containing 8% by weight has an upper limit voltage of 4.1 compared to an electrolyte containing no heterocyclic compound at all or an electrolyte containing more than 0.8% by weight of heterocyclic compound.
It has been found that in charging / discharging at a voltage higher than V and / or at a high temperature of 40 ° C. or more, a unique and unexpected effect of dramatically improving cycle characteristics is exhibited. This mechanism of action does not deviate from the guesswork, but is believed to be due to electrochemical polymerization at a battery voltage below the maximum operating voltage to form a good thin conductive coating. That is, 0.8% by weight
If the amount is excessively exceeded, the amount of the additive that electrochemically polymerizes increases at a battery voltage equal to or lower than the maximum operating voltage, and a thick conductive film that impairs the reversibility of the battery is formed. It is considered that battery characteristics such as cycle characteristics are worse than those of the electrolyte solution to which no heterocyclic compound is added. As described above, when the additive of the present invention is added in an amount of 0.001 to 0.8% by weight based on the nonaqueous electrolyte, the cycle characteristics are significantly improved.

Examples of the non-aqueous solvent used in the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), and γ-butyrolactone. Lactones such as dimethyl carbonate (DMC), methyl ethyl carbonate (M
EC), chain carbonates such as diethyl carbonate (DEC), tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane Ethers, such as acetonitrile, esters such as methyl propionate, methyl pivalate and octyl pivalate, and amides such as dimethylformamide.

These non-aqueous solvents may be used alone or in combination of two or more.
The combination of the non-aqueous solvent is not particularly limited, for example,
A combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a lactone,
Various combinations such as a combination of three types of cyclic carbonates and chain carbonates are exemplified.

As the electrolyte used in the present invention, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (S
O ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂
CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ )
₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C
_{3 F 7) 3, LiPF 5} (iso-C 3 F 7) , and the like. These electrolytes may be used alone or in combination of two or more. These electrolytes are
The non-aqueous solvent is usually 0.1 to 3 M, preferably 0.5 to 3 M.
It is used after being dissolved at a concentration of ~ 1.5M.

The non-aqueous electrolyte of the present invention is prepared by, for example, mixing the above-mentioned non-aqueous solvent, dissolving the above-mentioned electrolyte therein, and mixing the above-mentioned formulas (I), (II), (III), (IV), (V),
It is obtained by dissolving at least one of the heterocyclic compounds represented by (VI) and (VII).

For example, a composite metal oxide of lithium and at least one metal selected from the group consisting of cobalt, manganese, nickel, chromium, iron and vanadium is used as the positive electrode active material. Examples of such a composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ ,
LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <
1) and the like. LiCoO ₂ and LiMn ₂
O ₄ , LiCoO ₂ and LiNiO ₂ , LiMn ₂ O ₄ and Li
_They may be appropriately mixed and used like NiO ₂ .

For the positive electrode, a conductive agent such as acetylene black or carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or a copolymer of styrene and butadiene (SB) is used.
R), a copolymer of acrylonitrile and butadiene (NB
R), a binder such as carboxymethylcellulose (CMC) and a solvent are kneaded to form a positive electrode mixture, and the positive electrode material is applied to an aluminum foil or a stainless steel lath plate as a current collector, dried, and dried. After pressure molding, 50 ° C ~ 250
It is produced by performing a heat treatment under vacuum at a temperature of about 2 ° C. for about 2 hours.

As the negative electrode active material, lithium metal, lithium alloy, or a carbon material capable of occluding and releasing lithium (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion) Body, carbon fiber], or a composite tin oxide.
In particular, the spacing (d ₀₀₂ ) between the lattice planes ( ₀₀₂ ) is 0.33.
It is preferable to use a carbon material having a graphite type crystal structure of 5 to 0.340 nm (nanometer). In addition,
Powder materials such as carbon materials include ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),
It is kneaded with a binder such as a copolymer of styrene and butadiene (SBR), a copolymer of acrylonitrile and butadiene (NBR), and carboxymethyl cellulose (CMC) to be used as a negative electrode mixture.

The structure of the lithium secondary battery is not particularly limited, and may be a coin-type battery or a polymer battery having a single or multiple layers of a positive electrode, a negative electrode, a separator, a roll-shaped positive electrode, a negative electrode, and a roll-shaped battery. Examples include a cylindrical battery and a prismatic battery having a separator. As the separator, a known microporous polyolefin membrane, woven fabric, nonwoven fabric, or the like is used.

The voltage range of the charge / discharge cycle of the lithium secondary battery in the present invention is preferably such that the maximum operating voltage is greater than 4.1 V, more preferably 4.2 V or more, and most preferably 4.3 V or more. Is obtained. The cutoff voltage is preferably 2.0 V or higher, and more preferably 2.5 V or higher. Although the current value is not particularly limited, it is usually used at a constant current discharge of 0.1 to 2C. The temperature range of the charge / discharge cycle is 0 to 100.
C. is preferable, and more preferably 40 to 80 C., a large effect is obtained.

[0035]

Next, the present invention will be specifically described with reference to examples and comparative examples. Example 1 [Preparation of non-aqueous electrolyte] EC / DEC (volume ratio) = 3/7
Was prepared and a non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 M in the non-aqueous solvent.
-Chlorothiophene [in the general formula (I), Y ¹ = S, X ² =
Cl, X ¹ = X ³ = X ⁴ = H] with respect to the non-aqueous electrolyte.
1% by weight was added.

[Preparation of Lithium Secondary Battery and Measurement of Battery Characteristics] LiCoO ₂ (positive electrode active material): 80% by weight, acetylene black (conductive agent): 10% by weight, polyvinylidene fluoride (binder): 10% by weight % Of the mixture, a 1-methyl-2-pyrrolidone solvent was added to the mixture, and the mixture was applied onto an aluminum foil, dried, press-molded, and heat-treated to prepare a positive electrode. 90% by weight of natural graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) were added, and a 1-methyl-2-pyrrolidone solvent was added thereto. Applied, dried,
A negative electrode was prepared by pressure molding and heat treatment. Then, using a separator made of a polypropylene microporous film, the above non-aqueous electrolyte was injected, and a coin battery (20 mm in diameter,
(Thickness: 3.2 mm). Using this coin battery, 4.3 V at a constant current of 0.8 mA under high temperature (40 ° C.)
After charging to a final voltage of 4.3 V, the battery was charged at a constant voltage for a total of 6 hours. Next, the battery was discharged to a final voltage of 2.7 V under a constant current of 0.8 mA, and the charging and discharging were repeated. The initial discharge capacity was 1.03 as a relative ratio when the ratio of 1M LiPF ₆ + EC / DEC (capacity ratio) = １ ／ to the non-aqueous electrolyte (Comparative Example 1) was set to 1. In addition, the initial discharge capacity is 10
The discharge capacity retention rate after 100 cycles when the value was 0% was 90.7%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Comparative Example 1 A non-aqueous solvent having EC / DEC (volume ratio) = 1/2 was prepared.
LiPF ₆ was dissolved therein to a concentration of 1M.
At this time, no heterocyclic compound was added. Using this non-aqueous electrolyte, a coin battery was produced in the same manner as in Example 1, and the battery characteristics were measured. 100 for the initial discharge capacity
The discharge capacity retention after the cycle was 63.8%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Comparative Examples 2 to 5 Comparative Example 1 was repeated except that the end-of-charge voltage, the temperature during charging and discharging, and the amount of 3-chlorothiophene were changed as shown in Table 1.
In the same manner as in the above, a coin battery was prepared, and the battery performance was measured. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

[0039]

[Table 1]

Example 2 A non-aqueous solvent having EC / DEC (volume ratio) = 1/2 was prepared.
LiPF₆Dissolved to a concentration of 1M
After preparing the aqueous electrolyte, as a heterocyclic compound 3,
4-ethylenedioxythiophene [in the general formula (I), Y
¹= S, X^TwoAnd X ^ThreeIs OCH_TwoCH_TwoJoin with O, X¹= X^Four=
H] was used in the same manner as in Example 1 except that 0.05% by weight was used.
A coin battery was prepared, and the battery performance was measured. Initial discharge volume
The discharge capacity retention rate after 100 cycles was 92.
4%. Coin battery manufacturing conditions and battery characteristics
It is shown in Table 2.

Examples 3 to 5 Coin batteries were fabricated in the same manner as in Example 2 except that the amount of 3,4-ethylenedioxythiophene was changed, and the battery performance was measured. Table 2
Shown in

[0042]

[Table 2]

Example 6 A non-aqueous solvent having EC / MEC (volume ratio) = 1/2 was prepared.
LiPF₆Dissolved to a concentration of 1M
After preparing the aqueous electrolyte solution, 2,2 was further added as a heterocyclic compound.
2'-bithiophene [Y in the general formula (II)^Two= S, X^Five
= X⁶= X⁹= X ^Ten= H, m = 0] in an amount of 0.1% by weight.
Otherwise, a coin battery was manufactured in the same manner as in Example 1, and the battery characteristics were changed.
The properties were measured. 100 cycles after initial discharge capacity
Of the battery was 91.8%. Coin cell battery
Table 3 shows manufacturing conditions and battery characteristics.

Example 7 3-Methylthiophene as a heterocyclic compound [in the formula (I), Y ¹ = S, X ² = Me, X ¹ = X ³ = X ⁴ = H]
Was prepared in the same manner as in Example 6 except that 0.1% by weight was added, and the battery characteristics were measured. The discharge capacity retention rate after 100 cycles with respect to the initial discharge capacity was 92.0%. Table 3 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 8 As a heterocyclic compound, N-methylpyrrole [general formula (I)
Where Y ¹ = NMe, X ¹ = X ² = X ³ = X ⁴ = H]
A coin battery was prepared in the same manner as in Example 6 except that the weight% was added, and the battery characteristics were measured. 10 to the initial discharge capacity
The discharge capacity retention rate after 0 cycles was 91.3%.
Table 3 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 9 As a heterocyclic compound, 3-bromofuran [general formula (I)
Where Y ¹ = O, X ² = Br, X ¹ = X ³ = X ⁴ = H].
A coin battery was prepared in the same manner as in Example 6 except that 1% by weight was added, and the battery characteristics were measured. 1 for the initial discharge capacity
The discharge capacity retention rate after 00 cycles was 90.7%. Table 3 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 10 The same as Example 6 except that furfuryl disulfide [in the formula (III), Y ³ ＯO, Y ⁴ ＯO, n = 1] was added as a heterocyclic compound in an amount of 0.1% by weight. Was prepared and the battery characteristics were measured. 100 for the initial discharge capacity
The discharge capacity retention after the cycle was 92.6%. Table 3 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 11 As a heterocyclic compound, 0.1% by weight of thieno [3,2-b] thiophene [Y ⁷ = Y ⁸ = S, X ¹³ = X ¹⁴ = H] in the general formula (V) was added. A coin battery was manufactured in the same manner as in Example 6, except that the battery characteristics were measured. The discharge capacity retention ratio after 100 cycles with respect to the initial discharge capacity was 91.4%. Table 3 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 12 As a heterocyclic compound, dithieno [3,2-b: 2 ′, 3 ′
-D] A coin battery was prepared in the same manner as in Example 6 except that 0.1% by weight of thiophene [Y ⁹ = S in the general formula (VI)] was added, and the battery characteristics were measured. The discharge capacity retention rate after 100 cycles with respect to the initial discharge capacity was 91.2%. Table 3 shows the manufacturing conditions and battery characteristics of the coin battery.

[0050]

[Table 3]

Example 13 A coin battery was fabricated in the same manner as in Example 2 except that artificial graphite was used instead of natural graphite as the negative electrode active material, and 0.1% by weight of 3,4-ethylenedioxythiophene was added. Then, the battery characteristics were measured. 100 for the initial discharge capacity
The discharge capacity retention after the cycle was 93.7%. Table 4 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 14 As a positive electrode active material, LiNi _0.8 C was used in place of LiCoO _2.
A coin battery was prepared in the same manner as in Example 13 except that o _0.2 O ₂ was used, and the battery characteristics were measured. The discharge capacity retention ratio after 100 cycles with respect to the initial discharge capacity was 91.9%. Table 4 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 15 LiMn ₂ O ₄ was used instead of LiCoO ₂ as the positive electrode active material.
A coin battery was prepared in the same manner as in Example 13 except that the above was used, and the battery characteristics were measured. 100 for the initial discharge capacity
The discharge capacity retention after the cycle was 93.3%. Table 4 shows the manufacturing conditions and battery characteristics of the coin battery.

[0054]

[Table 4]

As described above, the amount of the heterocyclic compound is 0.001.
When the addition of .about.0.8% by weight, the upper limit of the voltage is higher than that of a non-aqueous electrolyte containing more than 0.8% by weight of a heterocyclic compound or a non-aqueous electrolyte containing no heterocyclic compound at all.
It was found that the cycle characteristics were clearly superior in charging and discharging at a voltage higher than 1 V and / or at a high temperature of 40 ° C. or higher.

It should be noted that the present invention is not limited to the embodiments described above, and various combinations that can be easily inferred from the gist of the invention are possible. In particular, the combinations of the solvents in the above examples are not limited. Further, while the above embodiments relate to coin batteries, the present invention relates to cylindrical, prismatic,
Also applies to batteries for polymers.

[0057]

According to the present invention, the cycle characteristics of the battery,
A lithium secondary battery having excellent battery characteristics such as electric capacity and storage characteristics can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Matsumori 10-figure, 1978 Kogushi, Obe City, Ube City, Yamaguchi Prefecture F-term in the Ube Chemical Plant Ube Chemical Plant 5H029 AJ05 AK03 AL02 AL06 AL07 AL08 AM02 AM03 AM04 AM05 AM07 DJ09 HJ02

Claims (2)

[Claims] 1. A non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following general formulas (I), (II), (III), (IV), and (V) ),
(VI), (VII), Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image (Wherein, Y ^{1 to} Y ¹⁰ each represent an oxygen atom, a sulfur atom, or an alkylamino group; X ^{1 to} X ¹⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms,
5 represents an aralkyl group, a halogen atom, and an alkylsilyl group having 1 to 12 carbon atoms. X ¹ and X ² , X ² and X ³ , X
³ and X ⁴ , X ⁵ and X ⁶ , X ⁷ and X ⁸ , X ⁹ and X ¹⁰ , X ¹¹ and X ¹²
May be bonded to each other to represent a linear or branched alkylene group having 3 to 12 carbon atoms, or a linear or branched alkylenedioxy group having 1 to 6 carbon atoms. m and n each represent an integer of 0 to 2. ) At least one of the heterocyclic compounds represented by the formula (1)
A non-aqueous electrolyte solution containing from 0.1 to 0.8% by weight. 2. A lithium secondary battery using a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following general formulas (I) and (I).
I), (III), (IV), (V), (VI), (V
II), embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image (Wherein, Y ^{1 to} Y ¹⁰ each represent an oxygen atom, a sulfur atom, or an alkylamino group; X ^{1 to} X ¹⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms,
5 represents an aralkyl group, a halogen atom, and an alkylsilyl group having 1 to 12 carbon atoms. X ¹ and X ² , X ² and X ³ , X
³ and X ⁴ , X ⁵ and X ⁶ , X ⁷ and X ⁸ , X ⁹ and X ¹⁰ , X ¹¹ and X ¹²
May be bonded to each other to represent a linear or branched alkylene group having 3 to 12 carbon atoms, or a linear or branched alkylenedioxy group having 1 to 6 carbon atoms. m and n each represent an integer of 0 to 2. ) At least one of the heterocyclic compounds represented by the formula (1)
A lithium secondary battery characterized by being contained in an amount of from 0.01 to 0.8% by weight.