A novel sandwiched membrane as polymer electrolyte for lithium ion battery

A novel kind of sandwiched polymer membrane was prepared by coating three layers of poly(vinyl difluoride) (PVDF), poly(methyl methacrylate) (PMMA) and PVDF, separately. Its characteristics were investigated by scanning electron microscopy, FT-IR, X-ray diffraction, and differential thermal analysis. It consists of two phases. The outer PVDF layers are porous, and the inner PMMA layer is solid. Since the PMMA has a good compatibility with the carbonate-based liquid electrolyte, the membrane can easily absorb the electrolyte to form a gelled polymer electrolyte (GPE). As a result, the evaporation peak of the liquid electrolyte is increased to 160 °C. Due to very low evaporation of the liquid electrolyte, LiCoO₂ shows good cycling behavior in the range of 4.4-3.0 V when this GPE is used as the separator and polymer electrolyte, and lithium as the counter and reference electrode. This unique sandwiched membrane is promising for application in scale-up lithium ion batteries with high safety and high energy density.