Microporous PVDF-HFP-based polymer membranes formed from supercritical CO2 induced phase separation

Microporous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes following supercritical CO2 induced phase separation process were prepared using four solvents. The solid electrolytes of PVDF-HFP were formed by microporous PVDF-HFP membranes filled and swollen by a liquid electrolyte. The effect of the solvents on the morphology and structure, electrolyte absorptions and lithium ionic conductivity of the activated membranes were investigated. It was approved that all the membrane had the similar sponge-like and asymmetric structure when different solvent was used. As the mutual affinity between solvent and supercritical CO2 decreased, the membrane porosity and the average pore diameter increased. The PVDF-HFP membrane with porosity at 88% and pore size at 10 mu m were successfully prepared. The uptake of electrolyte solution and lithium ionic conductivity could reach 487 wt% and 3.09 x 10(-3) S/cm respectively for obtained membrane.