Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1994-09-30
1997-01-07
Gorgos, Kathryn
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429249, 429254, 20415715, 521 505, 521 50, 521905, 522 2, 526252, 526255, 4284111, H01M 618
Patent
active
055915426
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This is a 371 of PCT/JP94/00182 filed Feb. 8, 1994, and published as WO94/18711 Aug. 18, 1994.
The present invention relates to a battery or separator diaphragm and a battery, and more particularly, it relates to a battery with such a diaphragm which has excellent battery characteristics and safety features. The terms "diaphragm" and separator are used as synonyms herein.
Background Information
In recent years, capacities and outputs of batteries have been increased in primary and secondary batteries such as an alkaline manganese battery, a nickel-cadmium battery, a nickel-hydrogen battery, and a lithium battery. The range of use for such batteries has been greatly widened.
However, a safety hazard in an abnormal battery state has been highlighted. Particularly in the lithium battery which is widely applied in electronics or the like, the temperature of the battery may abruptly rise and thereby increase the internal pressure if an overcharge or an external short circuit that is caused by improper handling, leading to spouting of the electrolyte.
In order to prevent occurrence of an abnormal state caused by such an external short or the like, a method has been studied for increasing the resistance of a diaphragm for suppressing a short-circuit current, thereby inhibiting heat generation. As a concrete example of such a method, there has been developed a technique of insulating the diaphragm at a temperature of not more than 180.degree. C., which is the melting point of lithium. Such insulating greatly increases the internal resistance of the battery, thereby suppressing a short-circuit current and inhibiting heat generation as described below, for example.
Japanese Patent Publication No. 5-16139 (Japanese Patent Laying-Open No. 60-52) discloses a diaphragm consisting of polypropylene nonwoven fabric having a surface which has been impregnated with polyethylene fine powder. When a battery employing such a diaphragm is heated, polyethylene is melted to block pores of the diaphragm. Consequently, the ion permeability of the diaphragm is extremely reduced, whereby a temperature rise in the battery is suppressed.
On the other hand, Japanese Patent Laying-Open No. 3-283259 discloses a battery employing a diaphragm comprising a synthetic resin fine porous film having at least one surface covered with a polymer powder aggregate such as a polyethylene powder aggregate, for example, having a softening temperature of 95.degree. to 160.degree. C.
Further, Japanese Patent Laying-Open No. 3-291848 also discloses a battery employing a diaphragm comprising a synthetic resin fine porous film which is covered with a resin porous powder aggregate. This powder aggregate has a softening point of 95.degree. to 160.degree. C., and contains 1 to 50 wt. % of particles of 0.01 to 1 .mu.m in particle size.
In addition to such a diaphragm carrying resin particles, a diaphragm of a multilayer structure consisting of a first layer which enters a non-porous state at 80.degree. to 150.degree. C. and a second layer maintaining its shape at a temperature which is 10.degree. C. higher than 150.degree. C. is disclosed in Japanese Patent Publication No. 4-38101, for example.
In addition, a lithium battery employing a polyolefin porous film as the diaphragm is also developed. When a short-circuit test is made as to this battery, pores are blocked by shape change of the diaphragm. Consequently, ion permeability of the diaphragm is remarkably reduced and temperature rise of the battery is suppressed.
However, it has been found that the aforementioned conventional safety features have the following problems, although the good effects thereof are certainly recognized:
Namely, in the lithium battery employing a polyolefin porous film as the diaphragm, for example, a temperature rise is suppressed by a shape change of the diaphragm in a short-circuit test. However, heating may be caused anyway since the diaphragm may be broken due to a reduction in strength when a base material of which the diaphragm itself is made undergoe
Hara Koji
Harada Akira
Sakamoto Takeshi
Fasse W. F.
Fasse W. G.
Gorgos Kathryn
Sumitomo Electric Industries Ltd.
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