Porous poly(vinylidene fluoride-co-hexafluoropropylene) polymer membrane with sandwich-like architecture for highly safe lithium ion batteries

Porous polymer membrane with a sandwich-like architecture has been prepared by coating poly(methyl methacrylate) (PMMA) on poly(vinylidene fluoride-co-hexafluoropylene) (PVDF-HFP) porous membranes. Field emission scanning electron microscopy analysis identified that the PMMA/PVDF-HFP porous polymer membrane consists of the stacking of several porous layers with one layer of large pores in the middle of the membrane. This unique sandwich-like structure provides large porosity and good affinity towards a liquid organic electrolyte, leading to a high electrolyte uptake of 342wt%, excellent electrolyte retention, and enhanced tolerance towards high temperature and fire. The gel polymer electrolyte membrane achieved a high ionic conductivity of 1.31mScm-1 with similar activation energy as the conventional Celgard 2400 separator in liquid electrolyte. The porous polymer electrolyte membrane also has an outstanding thermal and electrochemical stability. When applied in lithium ion batteries with LiFePO4 cathode and lithium metal anode, the PMMA/PVDF-HFP electrolyte membrane demonstrated high discharge capacity, enhanced high rate capability, and extended cycle life. The PMMA/PVDF-HFP porous polymer membrane could be employed as an integrated separator and electrolyte for lithium ion batteries with high safety.