Optimization of filler type within poly(vinylidene fluoride-co-trifluoroethylene) composite separator membranes for improved lithium-ion battery performance

Porous poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) based composite membranes filled with clays (montmorillonite, MMT), zeolites (Y zeolite, NaY), ceramics (barium titanate, BaTiO3) and carbonaceous (multiwalled-carbon nanotubes, MWCNT) fillers were prepared by solvent casting at room temperature. It is shown that, the thermal, mechanical and electrochemical properties of the membranes are not significantly affected by the presence of the fillers. On the other hand, the overall electrochemical behavior of the separator membranes improves with the inclusion of fillers, with respect to the pure polymer, as shown by the increase of the room temperature ionic conductivity for the composite membranes. Furthermore, cathodic half-cells based on composite membranes showed higher capacity retention and rate performance after 50 cycles than pristine polymer membranes. It is thus concluded that filler type deeply affects membrane separator performance in lithium-ion batteries, the P(VDF-TrFE) membrane with MMT filler being the one with the best performance among the evaluated fillers.