Provided is a technique for capturing transition metal ions, such as cobalt ions, in a secondary battery that elute from a positive electrode active material and for preventing deposition of transition metal at a negative electrode. A composition for a lithium ion secondary battery porous membrane that contains non-conductive particles and a binding material is provided. The binding material includes a polymer A including an aliphatic conjugated diene monomer unit in a proportion of greater than 85 mass % and a polymer B including a (meth)acrylic acid ester monomer unit in a proportion of at least 60 mass %. A mass basis ratio of content of the polymer A relative to content of the polymer B is at least 0.2 and no greater than 9.0.