Physical and electrochemical characterizations of poly(vinylidene fluoride-co-hexafluoropropylene)/SiO2-based polymer electrolytes prepared by the phase-inversion technique

Abstract

Highly porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF–HFP)-based polymer membranes filled with fumed silica (SiO2) were prepared by a phase-inversion technique, and films were also cast by a conventional casting method for comparison. N-Methyl-2-pyrrolidone as a solvent was used to dissolve the polymer and to make the slurry with SiO2. Phase inversion occurred just after the impregnation of the applied slurry on a glass plate into flowing water as a nonsolvent, and then a highly porous structure developed by mutual diffusion between the solvent and nonsolvent components. The PVdF–HFP/SiO2 cast films and phase-inversion membranes were then characterized by an examination of the morphology, thermal and crystalline properties, absorption ability of an electrolyte solution, ionic conductivity, electrochemical stability, and interfacial resistance with a lithium electrode. LiPF6 (1M) dissolved in a liquid mixture of ethylene carbonate and dimethyl carbonate (1:1 w/w) was used as the electrolyte solution. Through these characterizations, the phase-inversion polymer electrolytes were proved to be superior to the cast-film electrolytes for application to rechargeable lithium batteries. In particular, phase-inversion PVdF–HFP/SiO2 (30–40 wt %) electrolytes could be recommended to have optimum properties for the application. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 140–148, 2006