CROSS-LINKED MULTILAYER POROUS POLYMER MEMBRANE BATTERY SEPARATORS

摘要

A cross-linkable polyolefin composition (polyethylene, polypropylene or an ethylene-propylene copolymer) is coextruded with ultrahigh molecular weight polyethylene to form two-layer separator membranes, or three-layer separator membranes, for lithium-ion battery cells. In three-layer separator membranes, the cross-linkable polyolefin is formed as the outer faces of the separator for placement against facing surfaces of cell electrodes. The polymer materials initially contain plasticizer oil, which is removed from the extruded membranes, and the extruded membranes are also stretched to obtain a suitable open pore structure in the layered membranes to provide for suitable infiltration with a liquid electrolyte. The cross-linked polyolefin layer provides strength at elevated temperatures and the lower-melting, ultrahigh molecular weight polyethylene layer provides the separator membrane with a thermal shutdown capability.

主权项

1. A separator membrane structure for separation of electrodes in an electrochemical cell, the separator membrane structure being in the form of a flat, but foldable or rollable micro-porous layer having a thickness no greater than about fifty micrometers, the separator comprising a two-layer structure of co-extruded, coextensive layers of (i) a cross-linked polyolefin and (ii) a ultrahigh molecular weight polyethylene or a coextensive, three-layer structure of two outer layers of cross-linked polyolefin and a central layer of ultrahigh molecular weight polyethylene, the separator structure having a pore volume that is 20% to 70% of the external outline volume of the separator structure, the cross-linked polyolefin providing the membrane structure with resistance to shrinkage when heated to temperatures up to about 150° C., and the ultrahigh molecular weight polyethylene serving to melt and plug the pores of the separator if it is overheated.