A highly porous polymer membrane with high affinity for electrolyte solution is prepared and characterized. In preparing this membrane, a blend of P(VdF-co-HFP) and PAN is used as a matrix polymer in order to attain high ionic conductivity and good mechanical strength. Gel polymer electrolytes are prepared by soaking the porous membranes in an electrolyte solution, and their electrochemical characteristics are investigated. A lithium-ion polymer cell is assembled with the gel polymer electrolyte prepared in the porous membrane and the charge–discharge cycling performance is evaluated.