Patent ID: 7923143

Claim:
A battery separator comprising a nonwoven fabric, wherein said nonwoven fabric contains: (1) superfine fibers having a fiber diameter of 3 μm or less, (2) noncircular fine fibers having a noncircular cross-sectional shape and having a fiber diameter of 3 to 5 μm (excluding 3 μm), said fiber diameter meaning a diameter of a circle having an area the same as that of the noncircular cross-sectional shape, and (3) polypropylene based high-strength composite fibers containing a fusible component on the surface thereof and having a tensile strength of 4.5 cN/dtex or more, and the fusible components contained in the polypropylene based high-strength composite fibers are fused; wherein said battery separator has a maximum pore size of 25 μm or less and a ratio of maintained thickness of at least 85%.