Patent ID: 7790320

Claim:
A method of providing a battery separator with Z-direction stability for a lithium-ion battery comprising the step of: providing a microporous membrane comprising a thermoplastic polymer being selected from the group consisting of: polyethylene, polypropylene, polybutene, polymethylpentene, ultrahigh molecular weight polyethylene, copolymers thereof, and blends of the foregoing, and 10-30 weight percent of an inert particulate filler, said inert particulate filler being selected from the group consisting of: carbon based materials, metal oxides and hydroxides, calcium and magnesium carbonates, minerals, synthetic and natural zeolites, cements, silicates, glass particles, molybdenum disulfide, zinc sulfide, barium sulfate, synthetic polymers, and mixtures thereof, and said inert particulate filler being dispersed throughout said polymer.