| abstract |
A separator composed of a composite film including a porous base material containing a thermoplastic resin and a heat-resistant porous layer provided on one surface of the porous base material and containing an organic binder and an inorganic filler, wherein the organic binder is a particulate polyvinylidene fluoride type resin, the heat-resistant porous layer has a porous structure in which the particulate polyvinylidene fluoride type resin and the inorganic filler are connected to each other, the ratio of the thickness Ta of the heat-resistant porous layer to the thickness Tb of the composite film (Ta/Tb) is 0.10 to 0.40, the content of the inorganic filler in the heat-resistant porous layer is 85 to 99 mass % relative to the total mass of the organic binder and the inorganic filler, and the curl amounts of the composite film in the longitudinal direction and the width direction are both 0.5 mm or less. |