Microporous membranes, methods for making such membranes, and the use of such membranes as battery separator film

摘要

The present invention relates to microporous membranes comprising polymer and having well-balanced permeability and heat shrinkage, especially heat shrinkage at elevated temperature. The invention also relates to methods for making such membranes, and the use of such membranes as battery separator film in, e.g., lithium ion secondary batteries.

主权项

1. A microporous membrane comprising at least one layer, the layer comprising polymethylpentene having an MFR of 22.0 dg/min to 28.0 dg/min and a Tm of 223.0° C. to 230.0° C. in an amount of 22.0 wt. % to 40.0 wt. % based on the weight of the layer, wherein the membrane further comprises polyethylene having an Mw of 1.0×105 to 2.0×106 and a Tm ≧130.0° C., the membrane having an air permeability ≦1.0×103 seconds/100 cm3/20 μm, a TD heat shrinkage at 105° C. ≦2.1%, and a TD heat shrinkage at 130° C. <25.0%.