Abstract: Provide is a separator for a power storage device, which reliably prevents short circuits between positive and negative electrode layers while maintaining the permeating ions function, and effectively suppresses shrinkage, and a power storage device using the separator. The separator is composed of a composite material including inorganic microparticles and an organic binder, the composite material has a pigment volume concentration of 55% or more, and the inorganic microparticles have an average particle size in the range of 0.2 to 3.0 ?m, and a general particle shape index in the range of 0.50 to 0.85. The composite material can have a pigment volume concentration in the range of 55 to 80%, or 55 to 65%.

Abstract: Provide is a separator for a power storage device, which reliably prevents short circuits between positive and negative electrode layers while maintaining the permeating ions function, and effectively suppresses shrinkage, and a power storage device using the separator. The separator is composed of a composite material including inorganic microparticles and an organic binder, the composite material has a pigment volume concentration of 55% or more, and the inorganic microparticles have an average particle size in the range of 0.2 to 3.0 ?m, and a general particle shape index in the range of 0.50 to 0.85. The composite material can have a pigment volume concentration in the range of 55 to 80%, or 55 to 65%.