Multilayer separator exhibiting improved strength and stability

摘要

A multi-layer microporous battery separator which comprises: a high molecular weight polypropylene layer having a melt flow index of <=1.2 measured at layer; a polyethylene layer; and a high molecular weight polypropylene layer having a melt flow index of <=1.2 measured at layer. The resulting microporous battery separator which is formed by a dry stretch process produces the microporous battery separator which has a porosity of <=37% while maintaining a gurley from 13-25 seconds and a thickness of <=25 microns.