Multi-Layer Microporous Membrane, Battery Separator And Battery

[0170]Preparation of First Polyolefin Solution

[0171]A first polyolefin composition comprising (a) 50% first polyethylene resin having a weight average molecular weight of 3.0×105 and a molecular weight distribution of 8.6, (b) 37.5% first polypropylene resin having a weight average molecular weight of 1.1×106, a heat of fusion of 114 J / g and a molecular weight distribution of 5, (c) 12.5% second polypropylene resin having a weight average molecular weight of 6.6×105, a heat of fusion of 103.3 J / g and a molecular weight distribution of 11.4, and (a′) no added second polyethylene resin, is prepared by dry-blending, percentages by weight of the first polyolefin composition. The polyethylene resin in the composition has a melting point of 135° C. and a crystal dispersion temperature of 100° C.

[0172]The Mw and Mw / Mn of polyethylene for all examples are measured by a gel permeation chromatography (GPC) method under the following conditions.

[0173]Measurement apparatus: GPC-150 C availab

[0187]Example 1 is repeated except the first and second microporous polyolefin membranes were laminated in an order of first microporous membrane / second microporous membrane / first microporous membrane at a layer thickness ratio of 25 / 50 / 25.

[0188]Example 1 is repeated except the first polyolefin composition of the first polyolefin solution comprises 25% first polypropylene resin and 25% second polypropylene resin along with the 50% first polyethylene resin, percentages by weight of the first polyolefin composition.