Novel electrospun poly(vinylidene fluoride-co-hexafluoropropylene)-in situ SiO₂ composite membrane-based polymer electrolyte for lithium batteries

Composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} and different composition of silica have been prepared by electrospinning polymer solution containing in situ generated silica. These membranes are made up of fibers of 1-2μm diameters. These fibers are stacked in layers to produce fully interconnected pores that results in high porosity. Polymer electrolytes were prepared by immobilizing 1MLiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC) in the membranes. The composite membranes exhibit a high electrolyte uptake of 550-600%. The optimum electrochemical properties have been observed for the polymer electrolyte containing 6% in situ silica to show ionic conductivity of 8.06 mS cm ^-1 at 20°C, electrolyte retention ratio of 0.85, anodic stability up to 4.6V versus Li/Li⁺, and a good compatibility with lithium metal resulting in lowinterfacial resistance. A first cycle specific capacity of 170 mAhg^-1 was obtained when the polymer electrolytewas evaluated in a Li/lithium iron phosphate (LiFePO⁴) cell at 0.1 C-rate at 25°C, corresponding to 100% utilization of the cathode material. The properties of composite membrane prepared with in situ silica were observed to be comparatively better than the one prepared by direct addition of silica.