Nonaqueous electrolyte secondary battery separator, nonaqueous electrolyte secondary battery member, and nonaqueous electrolyte secondary battery

Abstract

Provided is a nonaqueous electrolyte secondary battery separator capable of satisfactorily maintaining ion permeability even after being compressed. The nonaqueous electrolyte secondary battery separator includes a polyolefin porous film in which an average of inclination angles of major axes of voids extracted from a two-dimensional image of a cross section of the polyolefin porous film is not less than 7.0, the inclination angles being calculated from respective circumscribed rectangles of the voids, the two-dimensional image being obtained by use of SEM, and the cross section being formed by cutting the polyolefin porous film (i) along a straight line that passes a center of a surface of the polyolefin porous film and is parallel to an MD or a TD and (ii) in a direction perpendicular to the surface.

Dependencies are inferred from the claim text.