SEPARATOR FOR ELECTRIC POWER STORAGE DEVICE

PROBLEM TO BE SOLVED: To provide a separator for an electric power storage device which includes a microporous film formed by melting, mixing and kneading raw material constituents mainly consisting of a polyolefin-based resin, inorganic powder, and a plasticizer into a film, and then removing, by extraction, part or all of the plasticizer from it, and which serves to prevent a detection failure in detecting a defect and the like with an image-detection type inspection apparatus even in a case where the film is arranged so as to contain an adequate amount of carbon black for imparting weather resistance thereto.SOLUTION: The separator for an electric power storage device comprises: a microporous film which contains 20-80 wt.% of a polyolefin-based resin, 20-80 wt.% of inorganic powder, and 0-30 wt.% of a plasticizer, and which has an average pore diameter of 1 μm or less, a porosity of 50-95%, and a base thickness of 10-500 μm. The raw material constituents of the film include carbon black having an average primary particle diameter of 100-500 nm. The microporous film contains 0.5-5 wt.% of the carbon black, and has a luminosity of 5-8.