Patent ID: 8709640

Claim:
A multi-layer, microporous polyolefin membrane, comprising: a first layer material and a second layer material, the first and second layer materials comprising polyethylene and polypropylene, wherein (i) the first layer material contains polyethylene in a first amount of at least 80 wt. %, based on the weight of the first material; (ii) the second layer material contains polyethylene in a second amount of at least 50 wt. %, based on the weight of the second material; (iii) the first amount is greater than the second amount on a weight percent basis, (iv) the multi-layer, microporous polyolefin membrane contains polyethylene in a total amount of at least 61 wt. %, based on the combined weight of the first and second layer materials, and (v) a content of polypropylene in the first layer material is less than a content of polypropylene in the second layer material on a weight percent basis, and wherein the polypropylene is a propylene homopolymer, and wherein the multi-layer membrane comprises: a first microporous layer containing the first layer material, a third microporous layer containing the first layer material, and a second microporous layer containing the second layer material, the second microporous layer being located between the first and third microporous layers.