Nonaqueous secondary battery separator and process for its fabrication

Abstract

This invention provides a separator for a nonaqueous rechargeable battery comprising a composite porous membrane that has both a shutdown function and heat resistance good enough to be effective for the suppression of meltdown, desired in a high-performance nonaqueous rechargeable battery having increased energy density, increased output, and increased size, and can realize a separator for a nonaqueous rechargeable battery having excellent handling properties and ion permeability. The composite porous membrane comprises a polyolefin microporous membrane having an air permeability per thickness of not less than 15 sec/100 cc·μm and not more than 50 sec/100 cc·μm (JIS P 8117) and a membrane thickness of not less than 5 μm and not more than 25 μm and a porous layer formed of poly-m-phenylene isophthalamide covering and integrated with both sides of the polyolefin microporous membrane. The composite porous membrane is characterized in that the composite porous membrane has a thickness of not less than 6 μm and not more than 35 μm and an air permeability (JIS P 8117) of not less than 1.01 times and not more than 2.00 times that of the polyolefine microporous membrane, and the coverage of poly-m-phenylene isophthalamide is not less than 1.0 g/m2 and not more than 4.0 g/m2.

Dependencies are inferred from the claim text.