BATTERY SEPARATOR, AND METHOD FOR PRODUCING SAME

Provided is a battery separator, comprising a porous membrane A comprising a polyolefin resin, and a porous membrane B laminated thereon comprising a fluororesin and inorganic particles or cross-linked polymer particles, wherein the particles are contained in an amount of 80 wt% to 97 wt% of the porous membrane B and have an average diameter being not less than 1.5 times and less than 50 times the average pore size of the porous membrane A, and a specific expression 1 and a specific expression 2 are satisfied. [0002] Provided is a battery separator having excellent heat resistance and processability (electrolyte permeability, low curling properties) and being characterized in that the air resistance increase due to lamination of a heat resistant resin is extremely small.