Battery diaphragm

Abstract

A battery diaphragm having superior chemical resistance, low resistance, superior ion selective permeability and high mechanical strength is provided. The battery diaphragm is formed of a composite film including a complex of a porous base substrate (A) with a crosslinked polymer (B1) containing repeated units of a vinyl heterocyclic compound having at least two hydrophilic groups. Alternatively, the battery diaphragm is formed of a composite film including a complex of a porous base substrate (A) with a crosslinked polymer (B2) containing repeated units of a vinyl compound each having a functional group, and thereafter decomposing part of the functional groups. Alternatively, the battery diaphragm is formed of a composite film including a complex of a porous base substrate (A) with a crosslinked polymer (B3) containing repeated units of a vinyl compound each having a functional group, wherein the complex of the porous base substrate (A) with the crosslinked polymer is prepared by impregnating a porous structure of the porous base substrate (A) with a monomer mixture containing a crosslinking momomer and the vinyl compound having functional groups, and thereafter causing photopolymerization to generate the crosslinked polymer (B3) in the porous structure.

Dependencies are inferred from the claim text.