Patent ID: 8323821

Claim:
A multi-layer microporous membrane comprising at least one first microporous membrane layer and at least one second microporous membrane layer in planar contact with the first microporous membrane layer, wherein 1) said first microporous membrane layer comprises a first polyethylene, a second polyethylene different from the first polyethylene, a first polypropylene having a weight average molecular weight of from about 0.8×10 6 to about 1.5×10 6 , a molecular weight distribution of from about 1 to about 100 and a heat of fusion of 80 J/g or higher, and a second polypropylene having a weight average molecular weight of from about 4×10 5 to about 7.5×10 5 , a molecular weight distribution of from about 5 to about 100 and a heat of fusion of 80 J/g or higher, and 2) the first and second mireroporous membrane layers are in planar contact in the following order first/second/first or first/second/first/second/first.