POROUS FILM AND SEPARATOR FOR NONAQUEOUS ELECTROLYTE CELL OR BATTERY

摘要

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous electrolyte cell or battery, hardly causing internal short-circuiting due to the penetration or the like of electroconductive particles and having a high surface hardness and to obtain a porous film suitable for composing the separator. SOLUTION: This porous film having a surface protecting layer is obtained by using a polyolefin porous film such as polyethylene or polypropylene as a substrate, coating at least one surface of the substrate with a mixture containing inorganic fine particles such as aluminum oxide or silicon dioxide and a resin to be a binder and then ultrasonically treating the resultant coated substrate in ethanol.