Al₂O₃/PVFM/Al₂O₃ trilayer membranes are prepared by means of simple coating of PVA-Al₂O₃ solution onto both sides of PVFM thin membranes, which is prepared via phase inversion method. The characteristics of the trilayer membranes and gel polymer electrolytes are investigated using FESEM, tensile testing apparatus, thermal shrinkage test, EIS and charge-discharge test. When inorganic Al₂O₃ particles are used to coat the PVFM membrane, drawbacks associated with gel-type membranes, namely, poor mechanical strength and thermal stability are greatly improved. Lithium ion cell with the Al₂O₃/PVFM/Al₂O₃ based GPE matched with LiFePO₄ shows excellent electrochemical performance.