Patent ID: 7402539

Claim:
A battery separator consisting essentially of a nonwoven fabric having a substantially unilayered structure, wherein an apparent total surface area of fibers per a surface density of said nonwoven fabric is 20 m 2 or more, a thickness of said nonwoven fabric is 0.1 mm or less, a uniformity index of said nonwoven fabric is 0.15 or less, said nonwoven fabric consists essentially of non-fibrillated fibers, said nonwoven fabric contains fine fibers having a fiber diameter of 4 μm or less and high-modulus fibers having a Young's modulus of 50 cN/dtex or more, the fibers forming the nonwoven fabric are fixed substantially only by fusing the fibers to each other, the high-modulus fibers are composed of ultra-high-molecular-weight polyethylene, and the fine fibers are formed from island components remaining after removing a sea component from islands-in-sea composite fibers, wherein an average fiber diameter of the high-modulus fibers is 5 times or more an average fiber diameter of the fine fibers.