Non-aqueous-secondary-battery separator and non-aqueous secondary battery

A non-aqueous-secondary-battery separator comprising:

• a composite membrane including
• a polyolefin microporous membrane;
• and
• a heat-resistant porous layer provided on one or both surfaces of the polyolefin microporous membrane and containing a particulate organic binder and an inorganic filler, wherein the tortuosity rate of the composite membrane is from 1.5 to 2.0, the particulate organic binder contains at least a polyvinylidene fluoride type resin that is selected from the group consisting of a mixture of polyvinylidene fluoride and an acrylic polymer, a mixture of a polyvinylidene fluoride copolymer and an acrylic polymer, and a copolymer of vinylidene fluoride with a monomer component that is selected from the group consisting of an acrylic acid, a methacrylic acid, an acrylic ester and a methacrylic ester, -and the heat-resistant porous layer has a porous structure in which the particulate organic binder and the inorganic filler are connected to each other, and
• the difference between the membrane resistance of the composite membrane and the membrane resistance of the polyolefin microporous membrane is equal to or smaller than 0.58Ω·cm2.