POLYOLEFIN MICROPOROUS MEMBRANE, BATTERY SEPARATOR AND PRODUCTION METHOD

A battery separator includes a polyolefin microporous membrane and a porous layer placed on at least one surface of the polyolefin microporous membrane. The polyolefin microporous membrane has a variation range of an F25 value in a longitudinal direction of 1 MPa or less. The F25 value indicates a value obtained by dividing a load value measured at 25% elongation of a specimen with use of a tensile tester by a cross-sectional area of the specimen. The porous layer contains a fluorine-based resin and an inorganic particle and has an average thickness T(ave) of 1 to 5 μm.