Ion conductive film and precursor film thereof

Details Ion conductive film and precursor film thereof Ion conductive film and precursor film thereof

1997-02-26

1998-11-10

Kiliman, Leszek

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

428 354, 428 366, 4284744, 4284755, B32B 516, B32B 2708

Patent

active

058341129

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to an ion conductive film capable of being used as a solid electrolyte for use in electrochemical applications such as an alkali secondary battery or the like. More precisely it relates to an ion conductive film having an excellent properties of resistance to heat and mechanical properties as well as a reduced deterioration of these properties under aging or heating and a reduced morphological change.


BACKGROUND OF THE INVENTION

Heretofore, there have been used micro-porous membrane and nonwovens fabrics of aliphatic polyamides, polypropylene, polyethylene, polysulfone have been used as materials for separators for an alkali secondary battery. Since a battery using these kinds of materials may encounter problems of resistance to oxidation and lacks of resistance to heat, other problems may occur such as minute short circuits causing a separator to melt due to the heat generated thereby, triggering successively greater short circuits causing further violent heat generation; ejection of the electrolytic solution or decomposed product thereof from the container of a battery forcibly heated by the heat resulting in break-down of an appliance in which the battery is loaded.
In order to solve these problems, attempts to use aromatic polyamides having no glass transition temperature and properties of resistance to heat and chemicals have been disclosed in Japanese Unexamined Patent Publication No. 58-147956, No. 5-290822 and No. 5-335005. However, the separators disclosed in these publications are laminations with fibers or fibrillated pulp-like materials because they need to have gas permeable fine pores for maintaining conductivity of electrolyte. The laminations are formed forcibly by melting the structural components by means of an ultrasonic or heat welding technique since a mere lamination of the layers lacks mechanical strength. It is difficult to obtain a laminate with sufficient mechanical strength since an aromatic polyamide is hard to bond by a melt-bonding technique because the polymeric material does not exhibits melting point. When these laminates are reinforced by means of a thermo-bonding technique with addition of another thermoplastic polymeric substance, the amount of pores becomes reduced in reinforced laminates so that the ultimately required characteristic of ion conductivity cannot be ensured. For this reason, such laminates have a disadvantage in that sufficient discharge capacity cannot be obtained due to an increased internal resistance.
There are known electrically conductive films which incorporated carbon or the like. Such films are electron conductive by nature, but not ion conductive as intended in the present invention.
Research and development work directed to utility of ion conductive film has been carried out as reported by J. V. Wright showing that an alkali metal-polyethylene oxide complex exhibits ion conductivity (British Polymer Journal, P319, Vol.2, 1975). A problem, however, is that the ion conductive film has poor ion conductivity as compared with a liquid type electrolyte. The film must be made smaller in thickness to improve ion conductivity. A satisfactory mechanical strength has not been attained simultaneously with the requirement for thickness. It is also required that a polymer needs to have a lower glass transition point in view of ion mobility. Consequently, an ion conductive film of the polymer produces a greater change in shape and a greater reduction in mechanical strength when the material is under heat.
In the meantime, Japanese Unexamined Patent Publication Nos. 1-309205, 2-86658 and 3-37268, proposed gel-like ion conductive films prepared from a non-ion conductive matrix such as a polysulfone and polyparabane acid or the like as carriers to which an electrolyte, is added, if necessary, with addion of a solvent. The ion-conductive film disclosed in these publications can be prepared by dissolving electrolyte and matrix polymer in a solvent followed by removal of the solvent. However, it is difficult to use

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