POLYMERIC MESOPOROUS SEPARATOR ELEMENTS FOR LAMINATED LITHIUM-ION RECHARGEABLE BATTERIES

摘要

A mesoporous polymeric membrane for use as an ionically-conductive inter-electrode separator in a rechargeable battery cell is prepared from a coatable composition comprising a polymeric material, a volatile fluid solvent for the polymeric material, and a second fluid miscible with and of lesser volatility than the solvent, the second fluid being a nonsolvent exhibiting no significant solvency for the polymeric material. A layer is cast from the composition to form a layer which is gelled and solidified to a self-supporting membrane by volatilizing the solvent and nonsolvent coating vehicle fluids under conditions in which the solvent volatilizes at a rate substantially faster than that of the nonsolvent. As a result the polymeric material initially gells in the more nonsolvent-predominant regions of the layer and isolates the nonsolvent as droplets substantially uniformly distributed throughout a matrix of polymeric material. The nonsolvent is subsequently volatilized from the droplets to yield a like distribution of mesopore voids throughout said membrane matrix. The porous membrane is capable of absorbing significant amounts of electrolyte solution to provide suitable ionic conductivity for use in rechargeable battery cells. The addition of inert particulate filler to the coating composition provides further strength in the body of the membrane and, due to preferential accumulation of particles in the dispersed nonsolvent droplets, provides particulate support within the membrane mesopores which prevents collapse of the voids at cell fabrication laminating temperatures and thus maintains electrolyte absorption capability.