Abstract: Microporous polymer membranes of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) were prepared through the inclusion-followed-by-extraction method using the plasticizer/non-solvent dibutyl phthalate (DBP). The optimum content of DBP was found to be 400 wt% with respect to the polymer for achieving the highest ionic conductivity. Microporous polymer electrolytes (MPEs) were prepared by incorporating liquid electrolytes in the membrane. A maximum ionic conductivity of 1.5횞10-3 (S/cm) was obtained at room temperature when using 1 M LiBF4 and 1 M LiPF6 solutions in TEGDME/EC (1 : 1). The MPEs were evaluated for the first discharge capacity in Li/S cells, which exhibited a single plateau at ca. 2.6 V, with a maximum discharge capacity of 900 mAh/g for LiPF6 in TEGDME/EC electrolyte. The binary
solvent TEGDME/EC was found to be more suitable than PC/EC for Li/S cells in terms of the first discharge capacity. The active material utilization of the sulfur cathode was found to be better for 40 wt% sulfur, relative to higher sulfur contents; we attribute this phenomenon to the effectiveness of the conductive carbon coating on sulfur present at this composition.
Keywords: microporous polymer electrolyte, PVdF-HFP, lithium/sulfur battery, TEGDME/EC