Abstract: A battery separator composed of a microporous sheet product having first and second major surfaces and a thickness of less than about 50 mils, formed from a uniform mixture of a polysulfone polymer and a filler or polysulfone polymer and structure enhancing agent, said sheet product having a fibrous sheet embedded within said mixture and between the first and second major surfaces. The porosity of the sheet product is at least about 60 volume percent composed of pores such that the average pore diameter increases from each major surface toward the interior of the sheet product's thickness.

Abstract: A battery separator composed of a microporous sheet product having first and second major surfaces and a thickness of less than about 50 mils, formed from a uniform mixture of a polymer and a filler or a polymer and a structure enhancing agent and having a porous sheet embedded between the first and second major surface. The porosity of the sheet product is at least about 50 volume percent having a pore distribution such that the nominal pore diameter increases from each major surface towards the interior central portion of the sheet product's thickness.