JPH03295178A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To improve the cycle property and high-rate discharge characteristic by using specific Lewis acid double salt for the electrolyte of an organic electrolytic solution, and using a mixed solvent of cyclic ester carbonate and chain ester for the solvent. CONSTITUTION:The Lewis acid double salt expressed by a general formula (I) LiXFn is used for the electrolyte of the organic electrolytic solution of a nonaqueous secondary battery, where X indicates B, P, As, Sb and (n) indicates 4 when X is B and 6 when X is P, As, Sb, and a mixed solvent of cyclic ester carbonate and chain ester is used for the solvent. LiBF4, LiPF6, LiAsF6, LiSbF6 are practical examples for the Lewis acid double salt. The cyclic ester carbonate is expressed by a general formula (II). The chain ester is expressed by a general formula (III). A secondary battery with excellent safety, cycle property and high-rate discharge characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novel secondary battery with excellent cyclic high rate discharge characteristics.

[Conventional technology]

In recent years, secondary batteries using organic electrolytes have attracted attention because they have high energy density.

Hitherto, perchlorate-based electrolytes have been mainly studied as electrolytes for such organic electrolytes. Perchlorate-based electrolytes have high electrical conductivity and excellent properties, but secondary batteries using them are susceptible to high temperature storage, overcharging,
Under harsh environments such as short circuits, performance may deteriorate, internal pressure may increase,
Furthermore, it had the major drawback of exhibiting phenomena such as explosions.

On the other hand, as a solution to improve this drawback, LiBF4L
Lewis acid double salt type electrolytes such as iPFb are also known. However, when such a Lewis acid double salt type electrolyte is used, the basic performance as a secondary battery, such as cycle characteristics, self-discharge, etc., is not always satisfactory. Of course, attempts have already been made to improve these shortcomings; for example, Japanese Patent Application Laid-Open No. 61-2143
In Publication No. 77, an attempt was made to improve the electrolyte by adding an amine compound, but although improvements were seen in aspects such as the stability of the electrolyte, the performance in terms of high rate discharge characteristics was still satisfactory. It wasn't. Also, JP-A-63-1140
No. 76 discloses an electrolytic solution in which a Lewis acid double salt type electrolyte such as LiAsFh is dissolved in a mixed solvent of an ester solvent and an ether solvent.

Although this improvement has been found to improve the performance of metallic lithium negative electrodes, and is a major advance, ether solvents have poor oxidation resistance, as is well known, and the problem remains that the electrolyte deteriorates, especially on the positive electrode side. Ta. Especially in recent years, LiCo
4■ such as 0z, LiNiO2, LiCoyNiz02, etc.
Lithium-containing composite oxide-based positive electrode materials having the above electromotive force are attracting attention, but when such materials are used, the use of the above-mentioned ether-based solvents causes fatal problems.

[Problem to be solved by the invention]

The present inventors have made extensive efforts to improve the performance of organic electrolytes using LiXF as an electrolyte, particularly their cycleability and high rate discharge characteristics.
It has been found that when used as an electrolyte, there is a significant improvement not only when a specific solvent is mixed, but also when a specific solvent is mixed.

[Means to solve the problem]

According to the present invention, there is provided a secondary battery basically comprising a positive electrode, a negative electrode, and an organic electrolyte, in which the electrolyte of the organic electrolyte has the general formula (I) LiXF, (I) (wherein X is B , P, As, Sb, n is 4 when X is B, and 6 when P, Δs, sb.), and the solvent is a cyclic carbonate and a chain The present invention provides a non-aqueous secondary battery characterized in that the solvent is a mixed solvent with a ester.

The electrolyte LiXFn in the present invention is a Lewis acid double salt represented by LiF + XF, 1-+→ LiXF, l, and specific examples include LiBF4. tt
ppi, LiAsF6. Examples include Li5bP6.

Margin below The cyclic carbonate ester in the present invention is General formula (II) R.

5CzHC CI(CH3 H,C,HC CH2 Hydrogen or any alkyl group. ) The following are specific examples.

H,C-CO2 3CHC C.O.

Carbonate H, CHC CHCH: 1 5C2HC CH2 Brobylene carbonate The chain ester as used in the present invention refers to the general formula (III) R,
-c-o-Rx (III)1 (In the formula, R is hydrogen or an arbitrary alkyl group, and Rz is an arbitrary alkyl group.) For example, methyl formate, ethyl formate, propyl formate, formic acid isobutyl, pentyl formate, methyl acetate,
Examples include ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl acetate, and ethyl acetate.

In the present invention, the mixing ratio of the solvent is preferably cyclic carbonate/chain ester = 10/90 to 9515 by weight, more preferably cyclic carbonate/chain ester = 15785 to 80/20, and Particularly preferably, cyclic carbonate/chain ester = 30/70~
It is 65/35.

Although the positive electrode and negative electrode used in the present invention are not particularly limited, examples of the positive electrode include TiS, TiS, and the like.

Metal sulfides such as MoS, Pe5t; Ll
(+-x) COO2゜Li(I-x+NiO2,L
i++-x) MnOz, NaCo0z.

Li (I-X)CoySnzOz, Li (+-X)
Co, N1zO1゜Li (I-0Co, FezO□
Alkali metal-containing composite oxides such as V2O3, V
Examples include metal oxides such as 6O13 and Mo0=. Examples of negative electrodes include lithium metal, lithium alloys, carbonate materials, and conductive polymers. Particularly remarkable effects are found when a carbonaceous material is used as the negative electrode.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Commercially available petroleum needle coke (manufactured by Koa Oil Co., Ltd., KOA
-SJ Coke) was ground to an average particle size of 10 μm using a ball mill. In addition, the BET surface area of this needle coke,
True density, interplane melting d0゜2゜Lc obtained from X-ray diffraction
<oat> is 11 back/g and 2.13 g/, respectively.
d, 3.44 people, and 52 people. To 1 part by weight of this powder, 0.05 parts by weight of polyvinylidene fluoride was added as a binder, made into a paste using dimethylformamide, and coated on one side of a 1 cm x 2 10 μm copper foil to form a film with a thickness of 130 μm. A film was formed, and this was sandwiched between SUS nets to form the negative electrode of the battery shown in FIG.

On the other hand, after pulverizing LiCoO2 to an average particle size of 3 μm using a ball mill, 0.00% of graphite was added to 1 part by weight of this powder.
025 parts by weight, 0.025 parts by weight of acetylene black,
Add 0.02 parts by weight of polyvinylidene fluoride as a binder, make a paste using dimethylformamide, and apply 100% of the paste to one side of 15 μm aluminum foil 1 ct 11 x 21.
A film was formed to a thickness of 0 μm and sandwiched between SUS nets to form a positive electrode. The electrolyte is LiBF in a mixed solvent of propylene carbonate and methyl acetate.

1 mojl! As shown in Table 1, batteries B-F were assembled using an electrolytic solution dissolved so as to give /f. Note that a microporous polyethylene membrane was used as the separator.

For these batteries B-F, charge/discharge cycles at a constant current of 2 mA (end-of-charge voltage 4.OOV, end-of-discharge voltage 2.7
0V) 10 times, then constant current 2mA charging once,
Perform constant current 10mA discharge once, then constant current 2m
A charge/discharge cycle was repeated. The results are shown in Table 1.

Comparative Example 1 Battery A was assembled in exactly the same manner as in Example 1, except that propylene carbonate alone was used as the electrolyte solvent in Example 1, and the same measurements as in Example 1 were performed on the battery A. The results are shown in Table 1.

Comparative Example 2 Battery G was assembled in the same manner as in Comparative Example 1, except that methyl acetate was used instead of the electrolyte solvent propylene carbonate in Comparative Example 1, and the same measurements as in Comparative Example 1 were performed on the battery G. Ta. The results are shown in Table 1.

Example 2 with blank space below: Battery H-J was assembled in exactly the same manner as in Example 1, except that the electrolyte solvent was a mixed solvent of propylene carbonate, ethylene carbonate, and methyl acetate. The same measurements as in Example 1 were carried out. The results are shown in Table 2.

Margin: 4° [Effects of the Invention] According to the present invention, it is possible to obtain a secondary battery that is excellent in safety, cycleability, and high rate discharge characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a configuration example of a secondary battery of the present invention. In Fig. 1, 1 is a positive electrode, 2 is a negative electrode, 3°3' is a current collector, 4.4' is an SUS net, 5, 5' are external electrode terminals,
6 is a battery case, 7 is a separator, and 8 is an electrolyte.

Claims (1)

[Claims] A secondary battery basically comprising a positive electrode, a negative electrode, and an organic electrolyte, wherein the electrolyte of the organic electrolyte has the general formula (I) LiXF_n(I) (wherein X is B, P, As, Sb, n is 4 when X is B, and 6 when X is P, As, Sb.), and the solvent is a cyclic carbonate ester and a chain carbonate. A non-aqueous secondary battery characterized by being a mixed solvent with ester.