| abstract |
A battery separator for a lithium battery comprising a microporous film both calendered and dry-stretched; or a dry-stretched microporous membrane having pores different from circular The micropore group, for example, the hole group is slit-shaped, trapezoidal or rectangular. The holes are openings or gaps between adjacent sheets, which are adjoined on one or both sides by fibrils or bridging structures between adjacent sheets. The present invention can reduce the porosity and/or improve the transverse tensile strength of the multilayer microporous membrane in a controlled manner. The multilayer microporous membranes of the present invention are readily coated with polymer ceramic coatings. The thickness ratio of the polypropylene layer and the polyethylene layer in the multilayer microporous film of the present invention can be tailored to balance mechanical strength and thermal shutdown performance. |