MULTILAYER SEPARATOR AND LITHIUM ION SECONDARY BATTERY USING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a multilayer separator with heat resistance high enough to prevent shrinkage of the separator even under a high temperature condition while ensuring a permeation characteristic as a lithium ion secondary battery.SOLUTION: The multilayer separator has a first porous film on a major surface of a second porous film and the first porous film is constructed by repeatedly forming a layer with high density and a layer with low density along the major surface of the second porous film.