Abstract: A battery separator is a microporous membrane. The membrane has a major volume of a thermoplastic polymer and a minor volume of an inert particulate filler. The filler is dispersed throughout the polymer. The membrane exhibits a maximum Z-direction compression of 95% of the original membrane thickness. Alternatively, the battery separator is a microporous membrane having a TMA compression curve with a first substantially horizontal slope between ambient temperature and 125° C., a second substantially horizontal slope at greater than 225° C. The curve of the first slope has a lower % compression than the curve of the second slope. The curve of the second slope is not less than 5% compression. The TMA compression curve is graphed so that the Y-axis represents % compression from original thickness and the X-axis represents temperature.

Abstract: A battery separator is a microporous membrane. The membrane has a major volume of a thermoplastic polymer and a minor volume of an inert particulate filler. The filler is dispersed throughout the polymer. The membrane exhibits a maximum Z-direction compression of 95% of the original membrane thickness. Alternatively, the battery separator is a microporous membrane having a TMA compression curve with a first substantially horizontal slope between ambient temperature and 125° C., a second substantially horizontal slope at greater than 225° C. The curve of the first slope has a lower % compression than the curve of the second slope. The curve of the second slope is not less than 5% compression. The TMA compression curve is graphed so that the Y-axis represents % compression from original thickness and the X-axis represents temperature.

Abstract: A battery separator comprising: a microporous polyolefin film having from 0.1% to 50% by weight of a block copolymer including a polyetheresteramide monomer. In this battery separator the polyolefin is selected from the group consisting of: polyethylene, polypropylene, polybutylene, polymethylpentene, mixtures thereof, and copolymers thereof. Preferably the polyolefin is polyethylene, mixtures of polyethylene and copolymers of polyethylene, or polypropylene, mixtures of polypropylene and copolymers of polypropylene and has less than or equal to 5% by weight of the block copolymer. In the battery separator of the invention, the microporous film generally has a thickness of no greater than 200 microns, a porosity in the range of 10 to 90%, and a pore size in the range of 0.005 micron to 1.5 micron.

Abstract: A method of making a composite microporous membrane includes the steps of: coating a nonporous precursor film with a polymer composition, and then stretching the coated nonporous precursor. Stretching includes a first stretching conducted at a first temperature and a first stretching rate and a second stretching conducted at a second temperature and a second stretching rate. The first stretching rate and the second stretching rate are different.