Poly(vinylidene fluoride) (PVDF)/poly(vinylidene fluoridehexafluoropylene) (PVDF-HFP) monolayer nanofibrous membrane and PVDF/PVDF-HFP/Al2O3 multilayer composite nanofibrous membranes were successfully prepared by the electrospinning method.The surface morphology

crystallinity

dimensional thermal stability

and electrochemical properties of the composite nanofibrous membranes were characterized by scanning electron microscopy (SEM)

differential scanning calorimetry (DSC)

thermal shrinkage and alternating current (AC) impedance.The smooth surface and uniform distribution fibers morphology were obtained for the PVDF/PVDF-HFP monolayer nanofibrous membrane.This membrane are made of fibers of 2 m diameter.The coarse surface and thinner fiber diameter were observed for the composite membrane.Moreover

the composite membrane exhibits lower crystallinity and higher electrolyte uptake than PVDF/PVDF-HFP monolayer nanofibrous membrane.The dimensional shrinkage of PVDF/PVDF-HFP/Al2O3 bilayer composite membrane is 3% at 170 ℃ for 1 h.Polymer electrolytes were prepared by immobilizing 1 mol/L LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl carbonate(DEC) in the membranes.The PVDF/PVDF-HFP/Al2O3 bilayer composite membranes exhibit a high electrolyte uptake of 497 wt%.The ion conductivity of the bilayer composite polymer electrolyte is 5.0410-3 S/cm at 25 ℃.Meanwhile

it has electrochemical stability at potentials higher than 4.6 V versus Li/Li+.The three types of membranes were assembled with lithium iron phosphate (LiFePO4)/Li coin cells.The cell based on the PVDF/PVDF-HFP/Al2O3 bilayer composite electrolyte presents good rate capabilities over various discharge current densities.The PVDF/PVDF-HFP/Al2O3 bilayer composite electrolyte has better compatibility and interface stability with lithium metal.