Patent ID: 8039140

Claim:
An absorbent battery separator comprising a substantially homogeneous blend of a thermoplastic polymer and of at least one inert filler, the inert filler being chosen from the group consisting of pyrogenic silica, precipitated silica, titanium dioxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, and mixtures thereof, the separator having a volume porosity of at least 75% and a bimodal pore size distribution comprising between 30 and 70% of fine pores having a diameter of less than 1 μm and between 30 and 70% of extraction pores having a diameter of greater than 2 μm, wherein the separator contains less than 18% pyrogenic silica by volume, wherein the fine pores and the extraction pores include a geometry defined by solvent particles from two solvents that are absorbed by and then removed from the separator.