PVdF-HFP/metal oxide nanocomposites: The matrices for high-conducting, low-leakage porous polymer electrolytes

Highly conducting porous polymer electrolytes comprised of poly(vinylidene-fluoride-co-hexafluoropropylene) (PVdF-HFP), metal oxide (TiO2, MgO, ZnO)/or mesoporous zeolite (MCM-41, SBA-15), ethylene carbonate (EC), propylene carbonate (PC), and LiClO4 were fabricated with a simple direct evaporation method. It was found that when metal oxide or mesoporous zeolite was mixed with PVdF-HFP, the impedance spectroscopy showed that the room temperature conductivity increased from 1.2 × 10−3 S cm−1 (for pure PVdF-HFP) to 2.1 × 10−3 S cm−1. SEM micrographs showed that the pore size of the composite membrane was similar to that of pure PVdF-HFP membrane but the porosity decreased, nevertheless the solution uptake increased. The increasing in solution uptake is not related directly to the surface area or dielectric constant of the oxides. It may be due to the affinity of the metal oxide toward the electrolyte solution. Furthermore, the solution leakage of PVdF-HFP/MgO and PVdF-HFP/SBA-15 composite electrolytes also decreased compared to pure PVdF-HFP electrolyte. These polymer composite electrolytes were stable up to 5.5 V (versus Li/Li+) and the lithium ion cells assembled with these polymer electrolyte show a good performance at a discharge rate below C/2.