Patent attributes
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.
