JP2000348763A - Nonaqueous electrolytic solution for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the decomposition of an electrolytic solution and to prevent the swelling of a battery due to the production of carbonic acid gas or the like by including specific phenyl sulfone or its derivative in a nonaqueous electrolytic solution usable for a secondary battery having a negative electrode formed of a carbon material capable of doping and dedoping Li and containing a nonaqueous solvent and a Li compound as an electrolyte. SOLUTION: This nonaqueous electrolytic solution for a secondary battery contains phenyl sulfone expressed by the formula or its derivative (in the formula, R1 and R2 each are a hydrogen atom, alkyl group or halogen group and may be the same or different). Preferably, the concentration of the phenyl sulfone or the derivative is 0.1-10 wt.% in the nonaqueous electrolytic solution. Thereby, the charge-discharge characteristic of the electrolytic solution in a Li secondary battery containing a nonaqueous solvent can be improved so that the charge-discharge cycle characteristic thereof can be improved. Additionally, the nonaqueous solvent can be used which is considered to be hard to use for a secondary battery having a negative electrode formed of a carbon material because of causing decomposition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving a non-aqueous electrolyte for a secondary battery, and more particularly, to a non-aqueous solvent-based lithium compound as an electrolyte in a secondary battery having a negative electrode made of a carbon material. The present invention relates to a technique for improving a nonaqueous electrolyte for a secondary battery.

[0002]

2. Description of the Related Art In recent years, camera-integrated video tape recorders have been developed.
As a new portable power source such as a VTR, a mobile phone, a laptop computer, etc., in particular, lithium which is lighter, has a higher capacity and a higher energy density than conventional nickel-cadmium (Ni-Cd) secondary batteries or lead secondary batteries. Secondary batteries are attracting attention. An example of the configuration of a lithium secondary battery is
A carbon material capable of doping and undoping Li is used for the negative electrode, and lithium is used as the negative electrode active material.

Conventionally, LiPF ₆ or the like has been used as an electrolyte of a non-aqueous electrolyte of a lithium secondary battery, and propylene carbonate (PC), ethylene carbonate (E) has been used as a non-aqueous solvent.
C), dimethyl carbonate (DMC), ethyl methyl carbonate (M
EC), diethyl carbonate (DEC), γ-butyrolactone (GBL), ethyl acetate (EA), methyl propionate (MPR), 1,2-dimethoxyethane (DME), 2,
-Methyltetrahydrofuran (2-MeTHF) or the like is used.

However, lithium, which is a negative electrode active material in a lithium secondary battery, is highly reactive and reacts with the above-mentioned electrolyte, and the reaction product adheres to the electrode surface as a film, and the film is formed. Greatly affect the battery characteristics. In addition, carbonates in a non-aqueous solvent react with lithium to form a film of a carbonate having ion conductivity, so that adverse effects on battery characteristics, such as an increase in battery internal resistance, are small. Since it becomes a protective film on the surface of the negative electrode and improves the storage characteristics and the like of the battery, it has conventionally been the main component of the nonaqueous electrolyte for a lithium secondary battery of a negative electrode made of a carbon material. Some of them have disadvantages such as relatively high melting point and high viscosity, and linear carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC) are: The dielectric constant is low, the conductivity of the electrolyte when used as an electrolyte solvent is low, and there is a problem that sufficient fast charging characteristics or low-temperature discharging characteristics required for a high-output secondary battery cannot be obtained. Furthermore, carbonates generate carbon dioxide gas or olefin gas by decomposition during charge / discharge of the secondary battery or during storage at a high temperature, so that the internal pressure increases and the battery swells.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of solving the drawbacks of the prior art. The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0006]

The present invention can be used for a secondary battery having a negative electrode made of a carbon material capable of doping and dedoping Li, and comprises a non-aqueous solvent and an electrolyte. In a non-aqueous electrolyte for a secondary battery containing a lithium compound, phenyl sulfone or a derivative thereof represented by the following formula 1

(Equation 1) [However, R ₁ and R ₂ in the above formula are a hydrogen atom, an alkyl group or a halogen group, and may be the same or different. ], Which relates to a non-aqueous electrolyte solution for a secondary battery. In a preferred embodiment, the concentration of the phenylsulfone or a derivative thereof in the nonaqueous electrolyte for a secondary battery is 0.1 to 10% by weight. It is related.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

According to the present invention, various non-aqueous solvents can be used regardless of carbonates. Examples of the non-aqueous solvent used in the present invention include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), and γ-butyrolactone (GBL). ), Ethyl acetate (EA), methyl propionate (MPR), ethyl propionate (EPR), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE),
-Various solvents such as methyltetrahydrofuran (2-MeTHF), tetrahydrofuran (THF), sulfolane (SL), and methylsulfolane (MeSL) which are conventionally used in nonaqueous electrolytes for secondary batteries can be used. These may be used in combination of two or more.

In the non-aqueous electrolyte for a secondary battery according to the present invention, a lithium compound is used as an electrolyte. This makes the present electrolyte particularly useful as an electrolyte for a lithium secondary battery. As such a lithium compound, those used in a conventional lithium secondary battery can be used. For example, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , L
iN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like can be used. The concentration of the lithium compound as an electrolyte in the non-aqueous electrolyte for a secondary battery is 0.1 to 0.1 from the viewpoint of conductivity.
3.0 mol / liter, preferably 0.3 to 2.0 m
ol / liter.

In the present invention, R ₁ and R
₂ is a hydrogen atom, phenyl sulfone, and R ₁ and R
₂ can also use a derivative of an alkyl group or a halogen group. Examples of the alkyl group include a methyl group and an ethyl group. Examples of the halogen group include a chloro group,
A bromo group; R ₁ and R in Formula 1
₂ may be both a hydrogen atom, an alkyl group or a halogen group, or may be different from each other, for example, one is an alkyl group and the other is a hydrogen atom.

The concentration of the phenyl sulfone or a derivative thereof in the non-aqueous electrolyte is preferably from 0.1 to 10% by weight, and more preferably from 0.5 to 5% by weight. 0.1% by weight
If it is less than 10%, the effect of suppressing gas generation due to decomposition of the nonaqueous electrolyte under high-temperature storage and the effect of improving the charge / discharge characteristics are not sufficient. Conversely, battery capacity tends to decrease.

The non-aqueous electrolyte for a secondary battery according to the present invention is prepared, for example, by adding a lithium compound as an electrolyte to a non-aqueous solvent while stirring the same, dissolving the same, and adding the above phenyl sulfone or a derivative thereof. It can be produced by dissolving.

The nonaqueous electrolyte for a secondary battery of the present invention can be applied to various secondary batteries using a lithium compound as an electrolyte.
The present invention can also be applied to a secondary battery having a negative electrode made of a carbon material capable of doping and dedoping Li.
The doping and dedoping of Li can be performed by, for example, lithium metal, lithium alloy or lithium ion. Here, as the lithium alloy, a lithium-aluminum alloy can be exemplified. Examples of the carbon material constituting the negative electrode include pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, and organic polymer compound fired bodies (phenol resin, furan resin, etc.) at an appropriate temperature. Fired and carbonized), carbon fiber, activated carbon and the like. The carbon material may be graphitized or may have a carbon-carbon correlation distance of 3.4 ° (angstrom) or less.

On the other hand, the positive electrode can be formed from various chargeable / dischargeable materials. For example, LiCoO ₂ , L
Li such as iNiO ₂ , LiMn ₂ O ₄ , LiMnO _2
x MO ₂ (where M is one or more transition metals, x
Varies depending on the charge / discharge state of the battery, usually 0.05 ≦ x
≦ 1.20), a composite oxide of lithium and one or more transition metals, FeS ₂ , TiS ₂ , V ₂
A transition element such as chalcogenite such as O ₅ , MoO ₃ or MoS ₂ or a polymer such as polyacetylene or polypyrrole can be used.

The shape of a secondary battery using the non-aqueous electrolyte for a secondary battery of the present invention is not particularly limited.
Various shapes such as a button type, a cylindrical type, a square type, and a coin type can be used.

[0016]

The present invention will be further described below with reference to examples.

Embodiment 1 FIG. The non-aqueous electrolyte secondary battery used in this example has a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, a button-type battery container, a positive electrode current collector, a negative electrode current collector, and a gasket. Wherein the positive electrode is LiCo
A molded product obtained by pressing a mixture containing O ₂ as a positive electrode active material into a pellet is used. A molded product obtained by pressing a mixture containing graphite as a negative electrode active material carrier into a pellet is used as a negative electrode. used. The non-aqueous electrolyte includes ethylene carbonate (E
C) and a mixed solvent of diethyl carbonate (DEC) (volume ratio 2: 3) with an electrolyte composed of LiPF ₆ at a concentration of 1 mol.
Per liter, and a solution containing 1% by weight of phenyl sulfone. Furthermore, a separator made of a nonwoven fabric made of polypropylene is used as the separator, and the positive electrode current collector is made of stainless steel.
On the other hand, the negative electrode side current collector was made of nickel expanded metal, and the battery case was made of stainless steel, and the positive electrode can and the negative electrode can were fixed with a polypropylene gasket. The charge / discharge cycle characteristics of the battery fabricated as described above were examined. Note that charging is performed by a constant current method, the upper limit voltage is set to 4.2 V, the current density at a constant current is set to 0.5 C, and the discharge is set to a current density of 0.5 C, and the final voltage is set to 2.7 V. did. Normal charge / discharge was performed at 25 ° C. for 50 cycles, and evaluation was made by comparing the battery capacities at 50 cycles.

Embodiment 2 FIG. Non-aqueous electrolyte 5 in Example 1
Is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1), and the amount of phenyl sulfone is 3% by weight. A battery was manufactured, and charge and discharge cycle characteristics were examined under the same conditions as in Example 1.

Comparative Example 1 A button-type battery was produced in the same manner as in Example 1 except that phenylsulfone was not added in Example 1, and under the same conditions as in Example 1,
The charge / discharge cycle characteristics were examined.

Comparative Example 2 A button-type battery was prepared in the same manner as in Example 2 except that phenylsulfone was not added in Example 2, and the charge / discharge cycle characteristics were examined under the same conditions as in Example 1.

FIG. 1 shows the above results.

As shown in FIG. 1, the electrolyte solution to which phenylsulfone was added (Examples 1 and 2) showed a decrease in the battery capacity during normal charge / discharge, low temperature discharge and high temperature discharge at a discharge capacity of 50 cycles. In all cases, the battery capacity cycle deterioration was not observed as compared with the electrolyte solution to which the phenyl sulfone was not added (Comparative Examples 1 and 2), indicating that the electrolyte solution was effective.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the invention. Needless to say, For example,
In the above embodiment, the shape of the battery is described as a button type, but the shape is not limited to this, and similar effects can be obtained even with other square, cylindrical, coin type, etc. .

[0024]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows. That is, according to the present invention, the decomposition of the electrolytic solution is suppressed, and the battery is prevented from swelling due to an increase in the internal pressure of the battery due to generation of carbon dioxide gas or olefin gas.
The charge / discharge characteristics of the electrolyte in the lithium secondary battery containing the non-aqueous solvent can be improved, and the charge / discharge cycle characteristics can be improved.Moreover, in the negative electrode secondary battery made of a carbon material, decomposition occurs, Non-aqueous solvents that are considered difficult to use can be made available.

[Brief description of the drawings]

FIG. 1 is a graph illustrating the operation and effect of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Example 1 2 ... Example 2 3 ... Comparative example 1 4 ... Comparative example 2

Continued on the front page (72) Inventor Takahiro Hexagon 3-1-1-1, Mizutani Higashi, Fujimi-shi, Saitama Toyama Pharmaceutical Co., Ltd. Shiki Plant (72) Inventor Tetsuo Kojima 3-1-1-1, Mizutani-Higashi, Fujimi-shi, Saitama Toyama (72) Inventor Sadao Ueda 3-1-1 Mizutani Higashi, Fujimi City, Saitama Prefecture Toyama Pharmaceutical Co., Ltd. (72) Minoru Nakano Minoru Higashi Mizutani, Fujimi City, Saitama Prefecture 11-1 Toyama Pharmaceutical Co., Ltd. Shiki Plant F-term (reference) 5H029 AJ02 AJ04 AJ07 AK02 AK03 AK05 AK16 AL06 AL07 AL12 AM02 AM03 AM04 AM05 AM07 BJ02 BJ03 DJ09 EJ11 HJ01 HJ10

Claims (2)

[Claims] Claims: 1. A secondary battery having a negative electrode made of a carbon material capable of doping and undoping Li,
In a non-aqueous solvent for a secondary battery containing a non-aqueous solvent and a lithium compound as an electrolyte, phenyl sulfone represented by the following formula 1 or a derivative thereof: [However, R ₁ and R ₂ in the above formula are a hydrogen atom, an alkyl group or a halogen group, and may be the same or different. ], A non-aqueous electrolyte for a secondary battery. 2. The concentration of the phenyl sulfone or a derivative thereof according to claim 1 in the non-aqueous electrolyte for a secondary battery is from 0.1 to 0.1.
The non-aqueous electrolyte for a secondary battery according to claim 1, wherein the amount is 10% by weight.