A polyolefin microporous membrane is disclosed. The membrane includes at least one microporous membrane layer, where the microporous membrane layer has an air permeability between about 100 sec/100 cc and about 220 sec/100 cc, a pin puncture strength of at least 550 gf, and a crystallization half time t1/2 of from 10 to 35 minutes when subjected to isothermal crystallization at 117° C. The air permeability and the pin puncture strength are normalized to a thickness of 16 μm.