A novel composite micro-porous polymer electrolyte membrane based on optimized composition of PVdF-co-HFP-ZrO2 was prepared by a preferential polymer dissolution process. The effect of porosity on the electrochemical properties of polymer electrolyte membranes, such as ionic conductivity and lithium transference number was studied by electrochemical AC-impedance spectroscopy and steady state current method, respectively. The results show that the formation of micro-porous by the removal of poly vinyl alcohol in the PVdF-HFP-ZrO2 matrix can enhance the ionic conductivity and lithium transference number when polymer membrane is soaked in 1 M LiClO4 electrolyte solution containing 1:1 (v/v) ratio of EC and DEC It is also found that the ionic conductivity data follows the Arrhenius equation. Finally, the charge-discharge studies were carried out by fabricating a cell with carbon as the anode and LiMg0.10Mn1.90O4 as the cathode and composite micro-porous polymer electrolyte membrane as the separator. The excellent performance, such as high ionic conductivity, high lithium transference number, good compatibility with electrode materials and higher discharge capacity of PVdF-co-HFP-ZrO2 based polymer electrolyte membrane suggest that the polymer electrolyte can be used as the best candidate for high performance lithium-ion batteries. (C) 2007 Elsevier B.V. All rights reserved.