JP2002158035A - Non-aqueous electrolyte and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte that suppresses reduction decomposition of electrolyte at storage in high temperature and restrains deterioration of battery property and that gives superior load characteristics and low temperature property to the battery, and a secondary battery containing this non- aqueous electrolyte. SOLUTION: In an electrochemical cell which uses the basal face of high orientation pyrolytic graphite(HOPG) as a working electrode and metal lithium as a counter electrode for a reference electrode, and a non-aqueous electrolyte as an electrolyte, a non-aqueous electrolyte made of non-aqueous solvent and electrolyte having a strength of 200 uA/cm2 or less of reduction peak appearing between 0.6 V-0.3 V at the first cycle that sweeps potential of the working electrode at the room temperature at a speed of 10 mV/sec. at 3.0 V-0 V-3.0 V is used and a non-aqueous electrolyte secondary battery using this electrolyte is provided. The desirable manner of the non-aqueous electrolyte is that vinylene carbonate and an additive that suppresses specific reduction decomposition reaction of the electrolyte happening on the negative electrolyte are contained.

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 having excellent charge / discharge characteristics and a secondary battery using the same. More specifically, the present invention relates to a non-aqueous electrolyte solution containing vinylene carbonate and an additive that suppresses a specific reductive decomposition reaction of an electrolyte solution occurring on a negative electrode, and a secondary battery using the same.

[0002]

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

As such a battery, there is a non-aqueous electrolyte secondary battery, a typical example of which is a lithium ion secondary battery.
Carbonate compounds having a high dielectric constant are known as non-aqueous solvents used for such a purpose, and the use of various carbonate compounds has been proposed. As an electrolytic solution, LiBF ₄ , LiPF ₆ , LiCl can be used in a mixed solvent of the above-mentioned high dielectric constant carbonate compound solvent such as propylene carbonate and ethylene carbonate and a low viscosity solvent such as diethyl carbonate.
A solution in which an electrolyte such as O ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , or Li ₂ SiF ₆ is mixed is used.

[0004] On the other hand, research on electrodes has been promoted with the aim of increasing the capacity of batteries, and carbon materials capable of occluding and releasing lithium are used as negative electrodes of lithium ion secondary batteries. In particular, highly crystalline carbon such as graphite has characteristics such as a flat discharge potential, and is therefore used as most negative electrodes of currently commercially available lithium ion secondary batteries.

When a highly crystalline carbon such as graphite is used for the negative electrode, if propylene carbonate or 1,2-butylene carbonate is used as a non-aqueous solvent having a high dielectric constant for the electrolytic solution, the solvent will not be present on the edge surface of the graphite during the first charge. , And the insertion reaction of lithium ions, which is an active material, into graphite hardly progresses. As a result, it is known that the initial charge / discharge efficiency decreases. (Electroc
hem.Soc., 146 (5) 1664-1671 (1999) etc.)

For this reason, as a non-aqueous solvent having a high dielectric constant used in the electrolytic solution, ethylene carbonate which is solid at ordinary temperature but hardly undergoes a reductive decomposition reaction is mixed with propylene carbonate, and the propylene in the electrolytic solution is mixed. Attempts have been made to suppress the reductive decomposition reaction of non-aqueous solvents by limiting the content of carbonate. It has been proposed to include vinylene carbonate in an electrolyte as an additive for suppressing the reductive decomposition reaction of a solvent on a negative electrode. By including vinylene carbonate,
It has been shown that the storage characteristics of the battery are improved (Japanese Patent Application Laid-Open No. 7-192756). It has been reported that by adding vinylene carbonate, the cycle life of the battery is improved (Japanese Unexamined Patent Publication (Kokai) No. 7-192760), and that propylene carbonate which undergoes reductive decomposition at the edge surface of a graphite negative electrode can be used (10 times). International Conference on Lithium Batteries, Abstract No. 286). Since vinylene carbonate makes propylene carbonate usable, it is suggested that vinylene carbonate acts on the edge surface of the graphite negative electrode.

[0007] These measures have improved the charge and discharge characteristics of the battery. However, when the battery is repeatedly stored at a high temperature and repeated charge and discharge cycles, the electrolytic capacity is further improved to reduce the load characteristics and the battery capacity of the battery. Liquid is needed.

The graphite material has a structure in which highly developed carbon-condensed ring planes are stacked, and the plane in which the end faces of the carbon-condensed rings are oriented is the edge face, and the plane in which the carbon-condensed ring planes are oriented is the basal plane. We call it plane. Both the edge surface and the basal surface have electron conductivity, and both sides can electrochemically reduce and decompose the electrolytic solution. Some reports have begun on the reductive decomposition of the electrolyte on the basal surface (Electrochemistry Communicationm2 (2000) 436-
440, Proceedings of the 2000 Autumn Meeting of the Institute of Electrical Chemistry, 2A17, 21 pages), and no additives for electrolytes that suppress reductive decomposition on the basal surface have been reported.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic solution which suppresses reductive decomposition of an electrolytic solution during storage at a high temperature and suppresses deterioration of battery characteristics in order to meet the above-mentioned demand. It is another object of the present invention to provide a non-aqueous electrolyte that gives a battery excellent load characteristics and low-temperature characteristics.
It is another object of the present invention to provide a secondary battery including the non-aqueous electrolyte.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and found that reductive decomposition of the electrolytic solution on both the edge surface and the basal surface on the graphite negative electrode is suppressed. In addition, high temperature storage test of the battery,
It has been found that life characteristics such as a cycle test can be improved.

That is, the present invention provides an electrochemical cell using a basal surface of highly oriented pyrolytic graphite (HOPG) as a working electrode, lithium metal as a reference electrode and a counter electrode, and a non-aqueous electrolyte as an electrolyte. 25
° C), the potential of the working electrode is 3.0 V to 0 V to 3.0 V
In the first cycle in which the potential is swept at a speed of 10 mV / sec, the intensity of the reduction peak appearing between 0.6 V and 0.3 V is less than 200 uA / cm ² , Provide liquid.

A non-aqueous electrolyte according to the present invention is characterized in that the intensity of the reduction peak appearing between 0.6 V and 0.3 V is 150 uA / cm ² or less.

The non-aqueous electrolyte according to the present invention is characterized in that the intensity of the reduction peak appearing between 0.6 V and 0.3 V is 100 uA / cm ² or less.

The non-aqueous electrolyte contains as an additive at least one compound selected from a compound having a norbornene skeleton and a benzenesulfonic acid derivative.
Is a preferred embodiment of the present invention. .

The non-aqueous electrolyte may be vinyl ethylene carbonate, divinyl ethylene carbonate, divinyl sulfone, dimethipin, norbornene dicarboxylic anhydride, maleic anhydride, diglycolic anhydride, sulfobenzene carboxylic anhydride, sulfobenzene carboxylic acid. At least one selected from acid esters, dilithium benzenedisulfonate, and benzenedisulfonates.
The non-aqueous electrolyte according to any one of the above items, which contains a kind of compound as an additive, is a preferred embodiment of the present invention.

The nonaqueous electrolyte according to any one of the above items, wherein the nonaqueous electrolyte further contains vinylene carbonate, is also a preferred embodiment of the present invention.

The non-aqueous solvent according to any one of the above-mentioned, wherein the non-aqueous solvent is a non-aqueous solvent containing an ester solvent, is also a preferred embodiment of the present invention.

The non-aqueous electrolyte described in that the ester solvent is a cyclic ester and / or a chain carbonate is also a preferred embodiment of the present invention.

The preferred embodiment of the present invention is also the nonaqueous electrolyte according to any one of the above, wherein the electrolyte is a lithium salt.

Further, the present invention provides a battery containing the above-mentioned non-aqueous electrolyte.

Further, the present invention provides a negative electrode active material comprising any of lithium metal, a lithium-containing alloy, a carbon material capable of doping and undoping lithium ions, and a metal oxide capable of doping and undoping lithium ions. A negative electrode including a transition metal oxide, a transition metal sulfide, a composite oxide of lithium and a transition metal, a conductive polymer material, a carbon material, or a mixture thereof as a positive electrode active material; Provided is a lithium secondary battery including a water electrolyte.

The negative electrode active material is a carbon material capable of doping / dedoping lithium ions, and the distance between planes (d002) on the (002) plane of the carbon material measured by X-ray analysis is 0.340 nm or less. Is a preferred embodiment of the present invention.

[0023]

Next, the nonaqueous electrolyte according to the present invention and a nonaqueous electrolyte secondary battery using the nonaqueous electrolyte will be described in detail.

The electrolytic solution of the present invention is an electrochemical cell using a basal surface of highly oriented pyrolytic graphite (HOPG) as a working electrode, metallic lithium as a reference electrode and a counter electrode, and a non-aqueous electrolytic solution as an electrolytic solution. At room temperature (25 ° C.), at the first cycle in which the potential of the working electrode is swept from 3.0 V to 0 V to 3.0 V at a rate of 10 mV / se, 0.6 V due to the basal surface on the HOPG electrode is applied. A non-aqueous electrolytic solution comprising a non-aqueous solvent and an electrolyte having a reduction peak appearing at ~ 0.3 V of 200 uA / cm ² or less. The present invention also provides a battery, preferably a lithium secondary battery, containing the non-aqueous electrolyte.

In order to evaluate the reductive decomposition characteristics of the electrolyte solution on the edge surface and the basal surface on the negative electrode, a current potential (CV) using a highly oriented pyrolytic graphite (abbreviated HOPG) electrode as a working electrode was used.
Perform the measurement. In the present invention, in the CV measurement using the HOPG electrode, a battery having more excellent life characteristics can be obtained by using an electrolytic solution that suppresses both the reduction peak caused by the edge surface and the reduction peak caused by the basal surface. Can be. When reductive decomposition occurs in the electrolyte on the edge surface and the basal surface on the negative electrode, the energy of the battery decreases, and the decomposition product accumulates on the electrode surface, and the load characteristics and low-temperature characteristics of the battery deteriorate.

In the electrolyte of the present invention, the reduction peak appearing between 0.6 V and 0.3 V attributable to the basal plane on the HOPG electrode is preferably 200 uA / cm ² or less, more preferably. is a 150uA / cm ² or less, more preferably 100uA / cm ² or less.

The non-aqueous electrolyte of the present invention is a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte. As the non-aqueous solvent, a known non-aqueous solvent used for a battery can be appropriately selected and used. However, the non-aqueous solvent is 0.6 V to 0.3 V due to the above-described basal surface on the HOPG electrode. In order to satisfy the requirement of the reduction peak appearing in the above, the selection of an appropriate non-aqueous solvent, electrolyte and additive is required.

In the present invention, the above-mentioned HO
0.6 V to 0.3 V due to the basal surface on the PG electrode
It is preferred to use the selected additives in order to satisfy the requirements of the reduction peak appearing between.

Preferred examples of the non-aqueous solvent include cyclic carbonates and chain carbonates described below. Specific examples of ethylene carbonate and methyl ethyl carbonate are as follows:
Using a mixture having a weight ratio of 6 and further describing an electrolytic solution in which LiPF ₆ is dissolved at 1 mol / l as a specific example of the electrolyte, the intensity of the reduction peak appearing between 0.6 V and 0.3 V under the above-described conditions is as follows. About 250uA at peak top
/ Cm ² .

Therefore, it is preferable to add to the electrolyte an additive that suppresses the reduction pea that appears between 0.6 V and 0.3 V due to the basal surface on the HOPG electrode.

Additives According to the present invention, the amount of 0.1% originated from the basal surface on the HOPG electrode.
Examples of the additive capable of suppressing the reduction peak appearing between 6 V and 0.3 V include the following compounds.

(1) Compound having a norbornene skeleton

Embedded image (Wherein at least one of R ^{1 and} R ² is a substituent containing a cyclic carbonate or a cyclic carboxylic anhydride, and R ^{3 to} R ⁸ may be the same or different from each other, and may be hydrogen, halogen, carbon It is selected from organic groups represented by Formulas 1 to 10.) More specifically, examples of the compound represented by the general formula (1) include those having the following structures.

[0033]

Embedded image

Examples of the organic group having 1 to 10 carbon atoms include a hydrocarbon group, a halogenated hydrocarbon group, a hydrocarbon group containing a hetero atom, and a halogenated hydrocarbon group containing a hetero atom. Heteroatoms include oxygen, nitrogen,
Examples include sulfur, phosphorus, and boron. Examples of the halogen include fluorine and chlorine.

Specific examples of the organic group having 1 to 10 carbon atoms include a trifluoromethyl group, a trifluoromethoxy group,
Trifluoroethyl group, trifluoroethoxy group, pentafluoroethyl group, pentafluoroethoxy group, methyl group, methoxy group, ethyl group, ethoxy group, vinyl group,
Vinyloxy, ethynyl, propyl, propyloxy, isopropyl, 1-propenyl, 2-propenyl, 1-propynyl, 2-propynyl, allyloxy,
Propargyloxy group, butyl group, butoxy group, sec-butyl group, t-butyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 2-methyl-2-propenyl group, 1-methylenepropyl group, 1 -Methyl-2-propenyl group, 1,2-dimethylvinyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, butenyloxy group, butynyloxy group, pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2-methylpropyl group, 2,2-dimethylpropyl group,
Phenyl group, phenoxy group, methylphenyl group, ethylphenyl group, vinylphenyl group, ethynylphenyl group,
Fluorovinylphenyl group, fluoroethynylphenyl group, fluorophenyl group, difluorophenyl group, trifluoromethylphenyl group, chlorophenyl group, fluoromethoxyphenyl group, difluoromethoxyphenyl group, methoxycarbonyl group, ethoxycarbonyl group, trifluoroethoxycarbonyl group And a trifluoromethylcarbonyl group.

Among the substituents exemplified above, the number of carbon atoms of the substituent is 3 or less from the viewpoint of solubility of the norbornene derivative having a cyclic carbonate or a cyclic dicarboxylic anhydride as a substituent in an electrolytic solution. It is desirable.

Specific examples of the norbornene derivative having a cyclic carbonate or a cyclic dicarboxylic anhydride as a substituent include the following compounds.

Embedded image

As the compound having a norbornene skeleton other than the general formula (1), the following compounds are exemplified.

[0039]

Embedded image

(2) Benzenesulfonic acid derivative

Embedded image (R ⁹ is an alkyl group or a metal. R ^{10 to} R ¹⁴ may be the same or different and may be bonded to each other, and may be hydrogen, halogen, a sulfonic acid ester group, a sulfonic acid metal group, or a carboxylic acid ester. Group, carboxylic acid metal group,
It is selected from organic groups having 1 to 10 carbon atoms. )

In the formula (2), examples of the metal include an alkali metal and an alkaline earth metal, and an alkali metal is particularly desirable. Specific examples of the alkali metal include lithium, sodium, and potassium, with lithium being most desirable.

Examples of the organic group having 1 to 10 carbon atoms include a hydrocarbon group, a halogenated hydrocarbon group, a hydrocarbon group containing a hetero atom, and a halogenated hydrocarbon group containing a hetero atom. Heteroatoms include oxygen, nitrogen,
Examples include sulfur, phosphorus, and boron. Examples of the halogen include fluorine and chlorine.

Specific examples of the organic group having 1 to 10 carbon atoms include a trifluoromethyl group, a trifluoromethoxy group,
Trifluoroethyl group, trifluoroethoxy group, pentafluoroethyl group, pentafluoroethoxy group, methyl group, methoxy group, ethyl group, ethoxy group, vinyl group,
Vinyloxy, ethynyl, propyl, propyloxy, isopropyl, 1-propenyl, 2-propenyl, 1-propynyl, 2-propynyl, allyloxy,
Propargyloxy group, butyl group, butoxy group, sec-butyl group, t-butyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 2-methyl-2-propenyl group, 1-methylenepropyl group, 1 -Methyl-2-propenyl group, 1,2-dimethylvinyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, butenyloxy group, butynyloxy group, pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2-methylpropyl group, 2,2-dimethylpropyl group,
Phenyl group, phenoxy group, methylphenyl group, ethylphenyl group, vinylphenyl group, ethynylphenyl group,
Fluorovinylphenyl group, fluoroethynylphenyl group, fluorophenyl group, difluorophenyl group, trifluoromethylphenyl group, chlorophenyl group, fluoromethoxyphenyl group, difluoromethoxyphenyl group, methoxycarbonyl group, ethoxycarbonyl group, trifluoroethoxycarbonyl group And a trifluoromethylcarbonyl group.

Of the substituents of R ^{10 to} R ¹⁴ exemplified above,
From the viewpoint of the solubility of phenylsulfonic acid or phenylsulfonic acid metal in the electrolytic solution, the substituent preferably has 3 or less carbon atoms.

In the present invention, it is particularly desirable that at least one of R ^{10 to} R ¹⁴ is a sulfonic acid ester group or a sulfonic acid metal group.

Specific examples of the above-mentioned phenylsulfonic acids include the following compounds. Hereinafter, the term "ester" means any of methyl ester, ethyl ester, propyl ester, butyl ester, phenyl ester, trifluoromethyl ester, and pentafluoropropyl ester.

Sulfobenzoic anhydride, naphthalenesulfonic acid ester, benzenesulfonic acid ester, benzenedi (sulfonic acid ester), benzenetri (sulfonic acid ester), sulfobenzoic acid diester, toluenesulfonic acid ester, toluenedi (sulfonic acid ester) ,
Toluent (sulfonic acid ester), (methyl) (sulfo) benzoic acid diester, trifluoromethylbenzene (sulfonic acid ester), trifluoromethylbenzenedi (sulfonic acid ester), trifluoromethylbenzenetri (sulfonic acid ester), (Sulfo) (trifluoromethyl) benzoic acid diester, lithium naphthalenesulfonate, lithium benzenesulfonate, lithium trifluoromethylbenzenesulfonate, dilithium benzenedisulfonate, dilithium trifluoromethylbenzenedisulfonate, benzenetri Trilithium sulfonate, dilithium sulfobenzoate, lithium methoxycarbonylbenzenesulfonate, lithium ethoxycarbonylsulfonate, vinyloxycarbonylsulfonic acid Lithium salt, lithium allyloxycarbonylsulfonic acid salt, lithium ethynyloxycarbonylsulfonic acid salt, lithium propargyloxycarbonylbenzenesulfonic acid salt, lithium trifluoroethyloxycarbonylbenzenesulfonic acid salt, lithium toluenesulfonic acid salt, dilithium toluenedisulfonic acid salt Of the phenylsulfonic acid derivatives exemplified above, benzenedisulfonic acids and sulfobenzoic acids are particularly desirable.

(3) Others In addition to the compounds exemplified in the above (1) and (2), vinyl ethylene carbonate, divinyl ethylene carbonate, propenyl ethylene carbonate, butenyl ethylene carbonate, methyl vinyl ethylene carbonate,
Examples include dipropenyl ethylene carbonate, divinyl sulfone, dimethipin, maleic anhydride, diglycolic anhydride, and the like.

Among the additives which can suppress the reduction peak appearing between 0.6 V and 0.3 V caused by the basal surface on the HOPG electrode, vinyl ethylene carbonate, divinyl ethylene carbonate, divinyl sulfone, dimethipin, Norbornene dicarboxylic anhydride,
Sulfobenzenecarboxylic acid anhydrides, sulfobenzenecarboxylic acid diesters, benzenedisulfonic acid dilithium salts, and benzenedisulfonic acid diesters are preferred.

The amount of the additive that suppresses the reduction peak that appears between 0.6 V and 0.3 V due to the basal surface on the HOPG electrode is 0.001 to 0.001% with respect to the entire electrolyte.
It is desirable that the content be 5% by weight, preferably 0.01 to 2% by weight, and more preferably 0.05 to 1% by weight.

In the present invention, vinylene carbonate can be added in addition to the additive that suppresses the reduction peak appearing between 0.6 V and 0.3 V caused by the basal plane on the HOPG electrode. In the first measurement cycle under the same conditions, HOPG was added to vinylene carbonate.
This has the effect of suppressing the reduction peak appearing between 0.9 V and 0.6 V due to the edge surface on the electrode. When only vinylene carbonate is added without using the above-described additives, it is difficult to suppress a reduction peak due to a basal plane appearing between 0.6 V and 0.3 V. In order to suppress the reduction peak appearing between 0.9 V and 0.6 V due to the basal plane and the edge plane, it is more effective and preferable to use both vinylene carbonate and the above-mentioned additives in the present invention. .

The amount of vinylene carbonate to be added in the above additive is 0.01 to 0.01% based on the whole electrolyte.
It is desirably 10% by weight, preferably 0.05 to 5% by weight, more preferably 0.1 to 2% by weight.

Nonaqueous Solvent Desirable nonaqueous solvents in the present invention include cyclic carbonates and / or chain carbonates. Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate,
Examples thereof include 2-pentylene carbonate, 2,3-pentylene carbonate, γ-butyrolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone, and 1,4-butane sultone. In particular, ethylene carbonate and propylene carbonate having a high dielectric constant are preferably used. When the improvement of the battery life is particularly intended, ethylene carbonate is particularly preferable.

These cyclic esters may be used as a mixture of two or more. As specific combinations, ethylene carbonate and propylene carbonate, ethylene carbonate and butylene carbonate, ethylene carbonate and γ-butyrolactone, ethylene carbonate and propylene carbonate and γ-butyrolactone, ethylene carbonate and 1,4-butane sultone, ethylene carbonate and propylene carbonate and 1 , 4-butane sultone, ethylene carbonate, γ-butyrolactone and 1,4-butane sultone.

When the electrolytic solution of the present invention is also provided with an improvement in low-temperature characteristics, it is desirable that the non-aqueous solvent contains a chain carbonate. Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, methyl trifluoroethyl carbonate and the like. No. In particular, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate having low viscosity are preferably used. These chain carbonates may be used as a mixture of two or more.

Specific examples of the combination of the cyclic carbonate and the chain carbonate of the non-aqueous solvent include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate and dimethyl carbonate. , Ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl Carbonate, ethylene carbonate Boneto propylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate and methyl ethyl carbonate and diethyl carbonate.

When the cyclic ester and the chain carbonate are mixed, the ratio thereof is represented by a weight ratio, and the ratio of the cyclic ester to the chain ester is 5:95 to 80:20, preferably 10:90 to 70:30. , More preferably 15:85
55:45. With such a ratio, the increase in the viscosity of the electrolyte is suppressed, and the degree of dissociation of the electrolyte is not reduced, so that the conductivity of the electrolyte relating to the charge / discharge characteristics of the battery can be increased. Therefore, it is possible to improve the load characteristics of the battery at a high load at normal temperature and the load characteristics of the battery at a low temperature.

Preferred non-aqueous solvents according to the present invention are those containing a cyclic ester and / or a linear ester. In addition to these, a solvent widely used as a non-aqueous solvent for batteries can be further mixed and used.

The non-aqueous electrolyte according to the present invention may contain, as the non-aqueous solvent, other solvents other than those described above. Specific examples of the other solvents include methyl formate, ethyl formate and propyl formate. , Methyl acetate, ethyl acetate, propyl acetate,
Chain esters such as methyl propionate, ethyl propionate, methyl butyrate, methyl valerate, ethyl trifluoroacetate, methyl pentafluoroacetate, trifluoroethyl acetate, trifluoroethyl propionate; trimethyl phosphate, triethyl phosphate, etc. Phosphate ester; 1,
2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether,
Chain ethers such as dipropyl ether; 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolan, 2-
Cyclic ethers such as methyl-1,3-dioxolane; amides such as dimethylformamide and diethylformamide;
Chain carbamates such as methyl-N, N-dimethylcarbamate and trifluoroethyl-N, N-diethylcarbamate; cyclic sulfones such as sulfolane; cyclic carbamates such as N-methyloxazolidinone; cyclic amides such as N-methylpyrrolidone; Cyclic urea such as N, N-dimethylimidazolidinone, sulfur-containing compounds such as divinylsulfone, sulfolane, dimethyl sulfate; boron-containing compounds such as trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, tritrimethylsilyl borate

In the present invention, as a preferable combination of the non-aqueous solvent in the case of improving the low temperature characteristics of the battery, a combination containing at least one of the cyclic esters and the chain carbonate is proposed. When improving the flash point of the solvent rather than improving the low-temperature properties, it is better to reduce the content of the chain-like ester. Specific combinations of solvents include ethylene carbonate and propylene carbonate, ethylene carbonate and butylene carbonate, ethylene carbonate and γ-butyrolactone, ethylene carbonate and propylene carbonate and γ-butyrolactone, ethylene carbonate and 1,4-butane sultone, ethylene carbonate and propylene carbonate And 1,4-butane sultone, ethylene carbonate and γ butyrolactone and 1,4-butane sultone, ethylene carbonate and sulfolane, ethylene carbonate and trimethyl phosphate, ethylene carbonate and γ butyrolactone and phosphate triester, ethylene carbonate and γ
Examples include butyrolactone and sulfolane, ethylene carbonate, γ-butyrolactone, sulfolane, and phosphoric acid triester. In this case, it is desirable to limit the addition of the chain carbonate to 20% or less by weight.

Non-aqueous Electrolyte The non-aqueous electrolyte of the present invention has a non-aqueous solvent, vinylene carbonate and 0.6 V-based on the basal surface on the HOPG electrode.
And an additive for suppressing the reduction peak appearing between 0.3 V.

As specific examples of the electrolyte, LiPF ₆ , Li
PF ₃ (C _n F _{2n + 1} ) ₃ , LiBF ₄ , LiClO ₄ , LiAs
Lithium salts such as F ₆ , LI ₂ SiF ₆ , LiC ₄ F ₉ SO ₃ , and LiC ₈ F ₁₇ SO ₃ are exemplified. Further, a lithium salt represented by the following general formula can also be used. LiOSO ₂ R
₈ , LiN (SO ₂ R ₉ ) (SO ₂ R ₁₀ ), LiC (SO ₂ R _1)
1 ) (SO ₂ R ₁₂ ) (SO ₂ R ₁₃ ), LiN (SO ₂ O
R ₁₄ ) (SO ₂ OR ₁₅ ) (here, R _{8 to} R ₁₅ may be the same or different from each other and are perfluoroalkyl groups having 1 to 6 carbon atoms). These lithium salts may be used alone or as a mixture of two or more.

Among these, in particular, LiPF ₆ , LiPF ₃
(C _n F _{2n + 1} ) ₃ , LiBF ₄ , LiOSO ₂ R ₈ , LiN (S
O ₂ R ₉ ) (SO ₂ R ₁₀ ), LiC (SO ₂ R ₁₁ ) (SO ₂ R
₁₂ ) (SO ₂ R ₁₃ ), LiN (SO ₂ OR ₁₄ ) (SO ₂ OR
₁₅ ) is preferred. Further, LiPF ₆ and LiBF ₄ are desirable.

It is desirable that such an electrolyte is contained in the non-aqueous electrolyte at a concentration of 0.1 to 3 mol / l, preferably 0.5 to 2 mol / l.

The non-aqueous electrolyte according to the present invention as described above
Not only is it suitable as a non-aqueous electrolyte for lithium ion secondary batteries, but it can also be used as a non-aqueous electrolyte for primary batteries.

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

Examples of the negative electrode active material constituting the negative electrode include metallic lithium, lithium alloys, carbon materials capable of doping and undoping lithium ions, and metal oxides capable of doping and undoping lithium ions. Is mentioned. Among these, a carbon material capable of doving / de-doping lithium ions is preferable. Such a carbon material may be graphite or amorphous carbon, and activated carbon, carbon fiber, carbon black, mesocarbon microbeads, natural graphite and the like are used.

As the negative electrode active material, the (002) plane spacing (d002) measured by X-ray analysis was 0.340 nm.
The following carbon materials are preferable, and the density is 1.70 g / cm ³
The graphite described above or a highly crystalline carbon material having properties similar thereto is desirable. When such a carbon material is used, the energy density of the battery can be increased.

As the positive electrode active material constituting the positive electrode, Mo is used.
Transition metal oxide or transition metal sulfide such as S ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , L
Conductive oxides such as iMnO ₄ , LiNiO ₂ , LiNi _x Co _(1-x) O _2, composite oxides composed of lithium and transition metals, polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole / polyaniline composites Polymer materials and the like can be mentioned.
Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is a lithium metal or lithium alloy, a carbon material can be used as the positive electrode. Further, as the positive electrode, a mixture of a composite oxide of lithium and a transition metal and a carbon material can be used.

The separator is a film that electrically insulates the positive electrode and the negative electrode and allows lithium ions to pass therethrough, and examples thereof include a porous film and a polymer electrolyte. A microporous polymer film is suitably used as the porous film, and examples of the material include polyolefin, polyimide, and polyvinylidene fluoride. In particular, a porous polyolefin film is preferable, and specific examples thereof include a porous polyethylene film, a porous polypropylene film, and a multilayer film of a porous polyethylene film and polypropylene. Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, a polymer swelled with an electrolytic solution, and the like. The electrolyte of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer.

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

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

The non-aqueous electrolyte secondary battery according to the present invention can be applied to a coin-type non-aqueous electrolyte secondary battery. In a coin-type battery, a disc-shaped negative electrode, a separator, a disc-shaped positive electrode, and a stainless steel or aluminum plate are housed in a coin-shaped battery can in a state of being stacked in this order.

[0074]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited by these Examples.

In the present invention, CV measurement using a highly oriented pyrolytic graphite (abbreviated as HOPG) electrode as a working electrode was performed by the following method. CV Measurement Using HOPG Electrode CV measurement is performed by using a cleavage plane (Φ5 mm) of HOPG (using STM-1 grade manufactured by Advanced Ceramic Corporation) as a working electrode, lithium metal as a counter electrode, and electrolytic lithium. 1.5 ml of the solution was used. This cell was used for CV measurement (solartoron1286 electrochemic
al interface), and the current potential was measured at room temperature (25 ° C.). The measurement voltage range was a potential sweep cycle that turned back from 3.0 V to 0.0 V to 3.0 V based on the potential of Li / Li ⁺ . This potential sweep cycle was performed at a speed of 10 mV / sec, and the flowing reduction current was measured.

Comparative Example 1 Ethylene carbonate (E
C) was measured in the first cycle of an electrolyte solution (hereinafter referred to as a blank electrolyte solution) in which 1 mol / l of LiPF ₆ was dissolved in a mixed solvent having a weight ratio (4: 6) of C) and ethyl methyl carbonate (EMC). . FIG. 1 shows the result. In this CV measurement diagram, the reduction peak appearing at 0.9 to 0.6 V is a peak due to the edge of HOPG, and the reduction peak appearing at 0.6 to 0.3 V is HOPG.
This is a peak due to G basal.

(Comparative Example 2) The CV measurement of the first cycle of an electrolyte obtained by adding 2% by weight of vinylene carbonate (VC) to a blank electrolyte was performed. FIG. 2 shows the result. In this CV measurement diagram, 0.9 to 0.6
It can be seen that the reduction peak appearing at V is small and suppressed, but the reduction peak appearing at 0.6-0.3 V is not suppressed at all.

Example 1 A first cycle CV measurement of an electrolyte obtained by adding 0.5% by weight of sulfobenzoic anhydride to a blank electrolyte was carried out. FIG. 3 shows the result.

Example 2 A first cycle CV measurement of an electrolyte obtained by adding 0.5% by weight of m-benzenedisulfonic acid dimethyl ester to a blank electrolyte was performed. FIG. 4 shows the result.

Example 3 The first cycle CV measurement of an electrolyte obtained by adding 0.5% by weight of dipotassium benzenesulfonate to a blank electrolyte was carried out. FIG. 5 shows the result. (Example 4) Norbornene-5,6-
The CV measurement of the first cycle of the electrolytic solution to which 1% by weight of dicarboxylic anhydride was added was performed. FIG. 6 shows the results. (Example 5) The CV measurement in the first cycle of an electrolyte obtained by adding 1% by weight of spiro-type norbornylsuccinic anhydride represented by the following formula to a blank electrolyte was performed. FIG. 7 shows the results.

Embedded image (Example 6) CV of the first cycle of an electrolyte obtained by adding 1% by weight of vinyl ethylene carbonate to a blank electrolyte
A measurement was made. FIG. 8 shows the results. 4 to 9, the reduction peaks appearing at 0.6 to 0.3 V are all suppressed to 100 uA / cm ² or less, and when used together with vinylene carbonate, both reductions related to the edge surface and the basal surface are reduced. It can be seen that the peak can be suppressed.

(Examples 7 to 10) <Preparation of non-aqueous electrolyte> Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed with EC: MEC.
= 4: 6 (weight ratio), and then LiPF ₆ as an electrolyte was dissolved in a non-aqueous solvent to prepare a non-aqueous electrolyte so that the electrolyte concentration was 1.0 mol / L. Next, predetermined amounts of the additives shown in Table 1 were added to the non-aqueous solvent.

<Preparation of Negative Electrode> Natural graphite (LF made of Chuetsu graphite)
-18A) 87 parts by weight and 13 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed and dispersed in N-methylpyrrolidinone as a solvent to prepare a natural graphite mixture slurry. Next, this negative electrode mixture slurry was applied to a 18 μm-thick negative electrode current collector made of strip-shaped copper foil, dried, compression-molded, and punched into a 14 mm disk shape to form a coin-shaped natural graphite. An electrode was obtained. The thickness of this natural graphite electrode mixture is 1
10 microns, weight 20mg / Φ14mm.

<Preparation of LiCoO ₂ Electrode>
₂ (HLC-2 manufactured by Honjo FMC Energy Systems Co., Ltd.)
2) 84 parts by weight, 9.5 parts by weight of graphite as a conductive agent, 0.5 parts by weight of acetylene black and 3 parts by weight of polyvinylidene fluoride as a binder were mixed, and dispersed in N-methylpyrrolidone as a solvent. _Two mixture slurries were prepared. This LiCoO ₂ mixture slurry is applied to an aluminum foil having a thickness of 20 μm, dried, compression-molded, and Φ13 mm
First, a LiCoO ₂ electrode is prepared. This LiC
The thickness of the oO ₂ mixture is 90 microns and the weight is 40 mg / Φ
13 mm.

<Production of Battery> A natural graphite electrode having a diameter of 14 mm, a LiCoO ₂ electrode having a diameter of 13 mm, a thickness of 25 μm,
A separator made of a microporous polypropylene film having a diameter of 16 mm is laminated in a stainless steel 2032 size battery can in the order of a natural graphite electrode separator and a LiCoO ₂ electrode. Thereafter, 0.03 ml of the non-aqueous electrolyte was poured into the separator, and an aluminum plate (thickness: 1.2 mm, diameter: 16 mm, and a spring was housed. Finally, a battery can lid was inserted via a polypropylene gasket. By caulking, a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was produced while maintaining the airtightness in the battery.

<Measurement of Self-Discharge Rate During High-Temperature Storage> Using the coin battery prepared as described above,
Under the condition of a constant current of 4.2 mA and a constant voltage of 4.2 mA, the battery was charged until the current value at the time of the constant voltage of 4.2 V became 0.05 mA.
The battery was discharged under the condition of a constant current of 1 mA and a constant voltage of 3.0 V until the current value at a constant voltage of 3.0 V became 0.05 mA. Next, this battery was charged under the condition of a constant current of 3.85 V and a constant current of 3.85 V until the current value at a constant voltage of 3.85 V became 0.05 mA. Thereafter, the battery was stored in a thermostat at 45 ° C. for 7 days.

After aging, the battery was discharged to 3.0 V and the remaining capacity was measured. At this time, a self-discharge capacity (= charge capacity-remaining capacity) was determined as an index indicating the self-discharge property of the battery. The ratio of the non-added electrolyte to the amount of self-discharge was defined as the self-discharge ratio. This self-discharge capacity is an index that reflects the amount of reductive decomposition of the electrolytic solution at the negative electrode.

<Measurement Results of Self-Discharge Amount> Table 1 shows the electrolytic solutions used in the examples and the measurement results of the self-discharge amount. (Comparative Example 3) A battery was prepared and the self-discharge amount was measured in the same manner as in Example 7 except that the preparation of the non-aqueous electrolyte was performed without adding the additive. The results are shown in Table 1. (Comparative Example 4) In Example 7, when preparing a non-aqueous electrolyte solution, vinylene carbonate was added at 1.5 watts.
A battery was prepared in the same manner except that t% was added, and the self-discharge amount was measured. The results are shown in Table 1.

[Table 1]

From the above results, it was found that the electrolytic solution of the present invention exhibited a more excellent self-discharge suppressing effect than vinylene carbonate alone, and the electrolysis of the electrolytic solution on the negative electrode was further suppressed.

[0089]

By using the non-aqueous electrolyte of the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery in which the reductive decomposition reaction of the electrolyte during high-temperature storage is suppressed, and the battery has an excellent load. A non-aqueous electrolyte solution having properties and low-temperature properties is obtained. Further, a secondary battery including the non-aqueous electrolyte and having improved load characteristics and low-temperature characteristics is provided.

[Brief description of the drawings]

FIG. 1 is a view showing a CV measurement result in a first cycle for a blank electrolyte solution of Comparative Example 1.

FIG. 2 is a diagram showing a CV measurement result in a first cycle for a blank electrolyte solution of Comparative Example 2.

FIG. 3 is a diagram showing a CV measurement result in a first cycle for the electrolyte solution of Example 1.

FIG. 4 is a diagram showing a CV measurement result in a first cycle for the electrolyte solution of Example 2.

FIG. 5 is a diagram showing a CV measurement result of a first cycle for the electrolyte solution of Example 3.

FIG. 6 is a diagram showing a CV measurement result of a first cycle for the electrolyte solution of Example 4.

FIG. 7 is a diagram showing a first cycle CV measurement result of the electrolyte solution of Example 5.

FIG. 8 is a diagram showing a CV measurement result in a first cycle for the electrolyte solution of Example 6.

Continued on the front page F-term (reference) CA03 CA04 CA05 CA07 CA11 CA14 CA15 CA20 CA29 CB02 CB07 CB08 CB12 DA09 EA21 EA25 EA26 FA19 HA01 HA04 HA13 HA14 HA16 HA17 HA18 HA20

Claims (18)

[Claims] In an electrochemical cell using a basal surface of highly oriented pyrolytic graphite (HOPG) as a working electrode, metallic lithium as a reference electrode and a counter electrode, and a non-aqueous electrolyte as an electrolyte, room temperature (25 ° C.) At a potential of 3.0 V to 0
In the first cycle in which the potential is swept from V to 3.0 V at a rate of 10 mV / sec, the intensity of the reduction peak appearing between 0.6 V and 0.3 V is 200 uA / cm ² or less. A non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte. 2. The non-aqueous electrolyte according to claim 1, wherein the intensity of a reduction peak appearing between 0.6 V and 0.3 V is 150 uA / cm ² or less. 3. The non-aqueous electrolyte according to claim 1, wherein the intensity of the reduction peak appearing between 0.6 V and 0.3 V is 100 uA / cm ² or less. 4. The method according to claim 1, wherein the non-aqueous electrolyte contains at least one compound selected from a compound having a norbornene skeleton and a benzenesulfonic acid derivative as an additive. The non-aqueous electrolyte according to the above. 5. The method according to claim 1, wherein the non-aqueous electrolyte comprises vinyl ethylene carbonate, divinyl ethylene carbonate, divinyl sulfone, dimethipin, norbornene dicarboxylic anhydride, maleic anhydride, diglycolic anhydride, sulfobenzene carboxylic anhydride, sulfobenzene carboxylic anhydride, At least one selected from benzenecarboxylic acid esters, benzenedisulfonic acid dilithium salt, and benzenedisulfonic acid esters
The non-aqueous electrolyte according to any one of claims 1 to 3, comprising a kind of compound as an additive. 6. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous electrolyte further contains vinylene carbonate. 7. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent is a non-aqueous solvent containing an ester solvent. 8. The non-aqueous electrolysis according to claim 4, wherein the amount of the additive is 0.01 to 2% by weight based on the whole non-aqueous electrolyte. liquid. 9. The non-aqueous electrolyte according to claim 6, wherein the amount of vinylene carbonate is 0.05 to 5% by weight based on the whole non-aqueous electrolyte. . 10. The non-aqueous electrolyte according to claim 7, wherein the ester solvent is a cyclic ester and / or a chain carbonate. 11. The method according to claim 1, wherein the cyclic ester is any one of ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, 1,4-butane sultone or a mixture thereof.
0 non-aqueous electrolyte. 12. The non-aqueous electrolyte according to claim 10, wherein the chain carbonate is any one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate or a mixture thereof. 13. The weight ratio of said cyclic carbonate to said chain carbonate in a non-aqueous solvent is 15:85 to 55:45.
The non-aqueous electrolyte according to any one of claims 10 to 12, wherein 14. The non-aqueous electrolyte according to claim 1, wherein the electrolyte is a lithium salt. 15. The non-aqueous electrolyte according to claim 14, wherein the lithium salt is LiPF ₆ . 16. A battery comprising the non-aqueous electrolyte according to claim 1. 17. A negative electrode containing, as a negative electrode active material, one of lithium metal, a lithium-containing alloy, a carbon material capable of doping / undoping lithium ions, and a metal oxide capable of doping / dedoping lithium ions. 17. A positive electrode comprising any one of a transition metal oxide, a transition metal sulfide, a composite oxide of lithium and a transition metal, a conductive polymer material, a carbon material, or a mixture thereof as a positive electrode active material. And a non-aqueous electrolyte. 18. The negative electrode active material is a carbon material capable of doping / dedoping lithium ions, and a distance between planes (d002) on the (002) plane of the carbon material measured by X-ray analysis is 0.340 nm. The lithium secondary battery according to claim 17, wherein: