JP2001023690A - Nonaqueous electrolyte for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the decomposition of an electrolyte solution, to prevent swelling due to the internal pressure increase of a battery and to enhance the charge/discharge characteristics of the electrolyte solution by including an o- terphenyl in a nonaqueous solvent usable in a secondary battery having a negative electrode of a carbon material capable of doping/dedoping Li and in a nonaqueous electrolyte solution containing a lithium compound as an electrolyte. SOLUTION: The concentration of an O-terphenyl in a nonaqueous electrolyte solution is preferably 0.5-3 wt.%. A nonaqueous solvent is for example a propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate or the like, two kinds or more may be mixed for use. For an electrolyte, a lithium compound such as LiClO4, LiAsF6, LiBF4 or the like is used and a concentration is preferably 0.3-2.0 mol/l. A carbon material constituting a negative electrode is such as pyrolytic carbons, cokes, graphites, organic polymer compound sintered compacts or the like. The charge/ discharge characteristics can be improved.

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, O-terphenyl represented by the following formula 1 is used.

(Equation 1) The present invention relates to a non-aqueous electrolyte for a secondary battery, characterized by comprising: Also, as a preferred embodiment thereof,
The present invention relates to a non-aqueous electrolyte for a secondary battery, wherein the concentration of the O-terphenyl in the non-aqueous electrolyte for a secondary battery is 0.01 to 5% by weight.

[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 have been 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.

[0010] The concentration of the O-terphenyl in the non-aqueous electrolyte is preferably 0.01 to 5% by weight, more preferably 0.5 to 3% by weight. If the amount is less than 0.01% by weight, the effect of improving the charge / discharge characteristics and the like is not sufficient. On the other hand, if the amount exceeds 5% by weight, the effect is saturated and the battery capacity tends to decrease.

The non-aqueous electrolyte for a secondary battery of the present invention is dissolved, for example, by adding a lithium compound as an electrolyte into the non-aqueous solvent while stirring the non-aqueous solvent, and adding the above orthoterphenyl. It can be manufactured by the following.

The non-aqueous 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.
That is, the present invention can be applied to a secondary battery having a negative electrode made of a carbon material that precipitates Li during charging and elutes during discharging. 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. Even if the carbon material is graphitized, the carbon-to-carbon interlayer distance is 3.4 ° (angstrom).
M) The following may be used.

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 the 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.

[0015]

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 press-forming a mixture containing O ₂ as a positive electrode active material into a pellet is used. A molded product obtained by pressure-forming a mixture containing graphite as a negative electrode active material carrier is used as a negative electrode. used. The non-aqueous electrolyte includes ethylene carbonate (E
C) and diethyl carbonate (DEC) in a mixed solvent (volume ratio 2: 3) containing an electrolyte made of LiPF ₆ at a concentration of 1 mol.
Per liter, and a solution containing 1% by weight of O-terphenyl was used. Further, a separator made of polypropylene non-woven fabric is used for the separator, and the positive electrode side 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. The charging was performed by the constant current method, the upper limit voltage was set to 4.2 V, the current density at constant current was set to 0.5 C, and the discharge was set to 0.5 C at the current density, and the final voltage was 2.7 V. And Normal charge / discharge is 25 ° C
For 100 cycles. Evaluation was made by comparing the battery capacities at 100 cycles.

Embodiment 2 FIG. Except that the non-aqueous electrolyte in Example 1 was a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1), and the addition amount of O-terphenyl was 3% by weight, A button-type battery was manufactured in the same manner as in Example 1, and the charge / 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 O-terphenyl 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 O-terphenyl was not added in Example 2, and the charge / discharge cycle characteristics were examined under the same conditions as in Example 1.

The above results are shown in FIG.

As shown in FIG. 1, the electrolyte solution to which O-terphenyl was added (Examples 1 and 2) was the electrolyte solution to which O-terphenyl was not added (Comparative Example 1 and Comparative Example 2) at a discharge capacity of 100 cycles. Compared with (), the battery capacity cycle deterioration was not observed, and it was found that there was an effect.

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. .

[0023]

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 expansion of the battery due to the increase in the internal pressure of the battery due to the generation of carbon dioxide gas or olefin gas is prevented,
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

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takahiro Hexagon 3-11-1 Mizutani Higashi, Fujimi-shi, Saitama Toyama Pharmaceutical Co., Ltd. Shiki Plant (72) Inventor Tetsuo Kojima 3-11 Mizutani-Higashi, Fujimi-shi, Saitama -1 Inside the Shiki Plant of Toyama Pharmaceutical Co., Ltd. (72) Inventor Sadao Ueda 3-1-1-1 Mizutani Higashi, Fujimi City, Saitama Prefecture Inside the Shiki Plant of Toyama Pharmaceutical Co., Ltd. (72) Inventor Minoru Nakano Mizutani, Fujimi City, Saitama Prefecture 3-11-1 Toyama Pharmaceutical Co., Ltd. Shiki Plant F term (reference) 4H006 AA03 AB78 BJ50 FC54 5H029 AJ02 AJ05 AJ07 AJ12 AK02 AK03 AK05 AK16 AL06 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 BJ02 BJ03 DJ08 EJ11 HJ01 H08

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, O-terphenyl represented by the following formula 1 is used. A non-aqueous electrolyte for a secondary battery, comprising: 2. The secondary battery according to claim 1, wherein the concentration of the O-terphenyl according to claim 1 in the non-aqueous electrolyte for a secondary battery is 0.01 to 5% by weight. For non-aqueous electrolyte.