SEPARATOR FOR POWER STORAGE DEVICE

The purpose of the present invention is to provide a separator which is for a power storage device, and which has high strength and can be thinned. The separator for a power storage device has a microporous membrane containing polyolefin as a main component, wherein the melt tension of the microporous membrane as measured at a temperature of 230°C is 30 mN or less, and the melt flow rate (MFR) of the microporous membrane as measured under a load of 2.16 kg and at a temperature of 230°C is 0.9 g/10 min or less.