JPH06150970A - Secondary battery - Google Patents

Abstract

PURPOSE:To provide a new secondary battery excellent in the cycle property and preservation characteristic and having high safety. CONSTITUTION:A negative electrode of a secondary battery is made of a carbon material, the electrolyte of an electrolytic solution is Lewis acid double salt expressed by LiXFn, a main solvent is a mixed solvent of cyclic ester carbonate and cyclic ester at 10:90 to 80:20wt.%, and aromatic hydrocarbon of 5 to 60wt.% is contained in the mixed solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel secondary battery having excellent cycleability and storage characteristics and high stability.

[0002]

2. Description of the Related Art In recent years, secondary batteries using organic electrolytes are
It has attracted attention because of its high energy density.

Conventionally, as an electrolyte of such an organic electrolyte,
Perchlorate type has been mainly studied. While perchlorate-based electrolytes have high electrical conductivity and excellent properties, secondary batteries using them suffer from performance deterioration under severe conditions such as high temperature storage, overcharge and short circuits. However, there was a big drawback that it showed a phenomenon such as an increase in internal pressure and further an explosion.

On the other hand, in order to improve such a defect,
Lewis acid double salt type electrolytes such as LiBF ₄ and LiPF ₆ 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 and self-discharge, is not always satisfactory. Of course, attempts have been made to improve these drawbacks. For example, JP-A-61-214377 has attempted to improve these performances by adding an amine-based additive, but the improvement has not yet been made. I was not satisfied.

Further, Japanese Patent Application Laid-Open No. 2-215059 proposes a new electrolytic solution system comprising a cyclic carbonic acid ester, a cyclic ester, and a Lewis acid double salt, and shows a remarkable improvement in performance, particularly a negative electrode active material. It is disclosed that it is particularly useful for a battery system using a carbonaceous material.

[0006] The discovery of such an electrolytic solution not only improves the performance but also the safety, but it is not always satisfactory.

[0007]

DISCLOSURE OF THE INVENTION The present invention is directed to the safety of a battery using the above-mentioned electrolytic solution system, in particular, to the destruction of a can due to an increase in internal pressure during abnormal conditions such as high temperature heating and throwing into a fire. This was done to prevent the phenomenon.

[0008]

According to the present invention, there is provided a secondary battery having a positive electrode, a negative electrode, and an organic electrolyte as a basic structure, wherein the negative electrode is made of a carbonaceous material, and the electrolyte of the organic electrolyte is Formula (I) LiXF _n (I) (wherein X is B, P, As, Sb, n is 4 when X is B, and is 6 when P, As, Sb) Is a Lewis acid double salt, and the main solvent is a mixed solvent of cyclic carbonic acid ester / cyclic ester = 10/90 to 80/20 in a weight ratio, and aromatic hydrocarbon is 5 to 6 with respect to the mixed solvent.
A secondary battery containing 0% by weight is provided.

By adding an aromatic hydrocarbon to the mixed solvent system, the gas ejection behavior associated with an increase in internal pressure is remarkably improved during abnormalities such as high temperature heating and charging into a fire as described above.
The reason for this is not yet clear, but it is presumed that this aromatic hydrocarbon may be due to the internal cooling effect by removing the latent heat of vaporization when the gas is ejected.

The electrolyte LiXF _{n in the} present invention is a Lewis acid double salt represented by LiF + XF _{n -1} → LiXF _n , and specific examples include LiB.
_{F 4, LiPF 6, LiAsF 6} , LiSbF 6 , and the like.

The cyclic carbonic acid ester referred to in the present invention is represented by the general formula (II)

[0012]

[Chemical 1]

(N = 2, 3, 4, R ₁ and R ₂ are each represented by hydrogen or any alkyl group, and specific examples include the following.)

[0014]

[Chemical 2]

[0015]

[Chemical 3]

The cyclic ester as used in the present invention is represented by the general formula (III)

[0017]

[Chemical 4]

(N = 2 to 5 R ₁ and R ₂ are represented by hydrogen or an arbitrary alkyl group, and examples thereof include the following.)

[0019]

[Chemical 5]

In the present invention, the solvent is mixed in a weight ratio of cyclic carbonic acid ester / cyclic ester = 10/90 to 8
0/20 is good. Cyclic carbonic acid ester / cyclic ester = 20/80 to 70/30 is preferable. More preferably, cyclic carbonic acid ester / cyclic ester = 20/80 to 60
/ 40. 80 cyclic carbonate / cyclic ester
If it is larger than / 20, self-discharge increases, which is not preferable. Cyclic carbonate / cyclic ester 10/90
If it is smaller than the above range, the cycle property is deteriorated, which is not preferable.

This aromatic hydrocarbon has a total carbon number of 6 to 15
Is preferred. When the total carbon number exceeds 15, the effect of improving the gas ejection behavior is insufficient, which is not preferable. The amount added should be 5 to 60% by weight based on the mixed solvent. Preferably 5 to 45% by weight, more preferably 10
~ 35% by weight.

If the amount is less than 5% by weight, the effect of improving the gas ejection behavior is insufficient, which is not preferable. If it exceeds 60% by weight, the battery performance is adversely affected, which is not preferable.

Specific examples of such aromatic hydrocarbons include benzene, toluene, xylene, ethylbenzene, cumene, anisole, chlorobenzene, tetralin, cyclohexylbenzene, nonylbenzene and diethylbenzene.

The carbonaceous material used as the negative electrode in the present invention is not particularly limited, but organic polymer compounds,
Examples thereof include those obtained by firing and carbonizing pitch, coal, wood, etc., those obtained by a vapor phase carbonization growth reaction of organic substances, and naturally occurring carbonaceous materials such as natural graphite.

For example, carbonaceous materials such as activated carbon and graphite described in JP-A-58-35881, JP-A-59-173979 and JP-A-59-207568,
Examples include calcined carbides such as phenolic resins described in JP-A-59-173979, and carbonaceous materials having a specific structure disclosed in JP-A-62-122066, that is, hydrogen. / Atomic ratio of carbon is 0.1
Less than 5 and determined by X-ray diffraction (002)
A carbonaceous material that satisfies the condition range in which the surface spacing is 3.37 Å or more and the crystallite size in the C-axis direction is 150 Å or less can be given. Furthermore, the carbonaceous material having a specific structure disclosed in Japanese Examined Patent Publication No. 4-24831, that is, the values of the crystal thickness Lc (i) and the true density ρ (g / cm ³ ) in X-ray diffraction are conditions.

1.80 <ρ <2.18, 15 <Lc and 120ρ−227 <Lc <120ρ−189 Preferably 1.80 <ρ <2.18, 15 <Lc and 120ρ−227 <Lc <120ρ− 196 More preferably, the effect of the present invention is further exerted by using a carbonaceous material in the range of 1.96 <ρ <2.16, 15 <Lc and 120ρ-227 <Lc <120ρ-196.

The positive electrode is not particularly limited, but examples thereof include metal sulfides such as TiS ₂ , TiS ₃ , MoS ₂ and FeS ₂ , and metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ and MoO _3. Thing, Li _(1-X) MnO ₂ , Li _(1-X) CoO ₂ , Li _{(1-X)
Examples} thereof include alkali metals such as NiO ₂ and Li _(ix) Co _y Sn _z O _{2 and} particularly lithium-containing composite metal oxides.

A separator is further mentioned as a basic constituent element in assembling the non-aqueous secondary battery of the present invention. The separator is not particularly limited, but a woven fabric,
Nonwoven fabrics, glass woven fabrics, synthetic resin microporous membranes, and the like can be mentioned. For example, the synthetic resin microporous membrane disclosed in JP-A-58-59072, particularly a polyolefin-based microporous membrane, can be used for its thickness, strength and membrane resistance. It is preferable from the aspect.

Further, if necessary, a battery is constructed by using components such as a current collector, a terminal and an insulating plate. Further, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, and further, if necessary, a paper type battery having a single layer or a multi-layer separator, a laminated type battery, or a positive electrode, a negative electrode, and further required. For example, a form of a cylindrical battery or the like in which a separator is wound in a roll shape can be mentioned.

[0030]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

Example 1 LiCoO ₂ was used as a positive electrode active material, graphite and acetylene black were used as conductive agents, and fluororubber was used as a binder. LiCoO ₂ : graphite: acetylene black: fluorine rubber = 88: 7.5: 2. A mixture of 5: 2 weight ratio was used as a dimethylformamide paste,
A sheet obtained by coating and drying on an Al foil was used as a positive electrode, needle coke powder was used as a negative electrode active material, fluororubber was used as a binder, and a mixture of needle coke and fluororubber was mixed at a weight ratio of 95: 5 to form a dimethylformamide paste.
The sheet coated and dried on the foil was used as a negative electrode, and the polyethylene microporous membrane was used as a separator. The rupture structure of the can bottom engraved type shown in FIG. 1 and FIG.
A C-type battery having 0 kg / cm ² setting) was produced. In addition, as the electrolytic solution, propylene carbonate and γ
-Mixed solvent of butyrolactone (weight ratio = 50:50)
To this, add 30% by weight of toluene and add 1 m of LiBF ₄ .
An electrolyte solution was used which was dissolved so as to be ol / l.

As a safety test of this battery, a constant voltage of 4.
The battery was fully charged at 2 V and a heating test was performed on a hot plate at 250 ° C. to observe the gas ejection behavior. The results are shown in Table 2.

A charge / discharge cycle test (charge: 4.2 V constant voltage, 250 mA discharge: 2.7 V final voltage, 250 mA) was performed as a performance test, and the capacity retention rate after 100 cycles is shown in Table 3.

Example 2 et seq. The same operation as in Example 1 was carried out except that the aromatic hydrocarbon and its addition amount were changed as shown in Table 1.

COMPARATIVE EXAMPLE 1 Hereinafter, the aromatic hydrocarbons and their addition amounts in Example 1 are shown in Table 1.
Exactly the same operation was performed except that it was changed as shown in.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

As described above, according to the present invention,
It is possible to obtain a novel secondary battery having excellent cycleability and storage characteristics and high safety.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of secondary batteries used in Examples and Comparative Examples.

FIG. 2 is a bottom view of the battery.

[Explanation of symbols]

 1 Positive Electrode 2 Negative Electrode 3 Separator 4 Battery Can 5 Sealing Lid 6 Positive Terminal for Hermetic Seal 7 Insulating Glass 8 Straight Cutout Groove 9 Branch Cutout Groove

Front Page Continuation (72) Inventor Akira Koyama 1-3-1 Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa Asahi Kasei Corporation (72) Inventor Yoshiaki Asami 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Toshiba Battery Co., Ltd. In-house (72) Inventor Hirose Nobuyoshi Toshiba Battery Co., Ltd. 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo

Claims (1)

[Claims] 1. A secondary battery comprising a positive electrode, a negative electrode, and an organic electrolytic solution as a basic component, wherein the negative electrode is made of a carbonaceous material, and the electrolyte of the organic electrolytic solution is represented by the general formula (I) LiXF _n (I ) (Wherein X is B, P, As, Sb, n is 4 when X is B, and is 6 when P, As, Sb is 6), and a Lewis acid double salt The main solvent is a mixed solvent of cyclic carbonate / cyclic ester = 10/90 to 80/20 in weight ratio, and aromatic hydrocarbon is 5 to 6 with respect to the mixed solvent.
A secondary battery containing 0% by weight.