| abstract |
A flexible polymeric film useful as an interelectrode separator or electrolyte member (45) in electrolytic devices, such as rechargeable batteries, comprises a copolymer of vinylidene fluoride with 8 to 25 % hexafluoropropylene. The film may be cast or formed as a self-supporting layer retaining about 20 to 70 % of a high-boiling solvent or solvent mixture plasticizer comprising such compounds as ethylene carbonate, propylene carbonate, dimethyl carbonate, and dibutyl phthalate. The film may be used in such form or after leaching of the retained plasticizer with a film-inert low-boiling solvent to provide a separator member into which a solution of electrolytic salt is subsequently imbibed to displace retained plasticizer or replace plasticizer previously leached from the polymeric matrix. |