Porous polymer-coated separators with different thicknesses of coating layer have been prepared by a dip coating and phase inversion method. Polymer-coated separators soaked with electrolyte solution exhibit high ionic conductivity in the order of 10−3 Scm−1 at room temperature and are electrochemically stable up to 5.0V against Li+/Li. Lithium-ion polymer cells each composed of a mesocarbon microbead anode and a lithium–cobalt oxide cathode and separated with a polymer-coated separator, have been assembled and their charge–discharge cycling performance has been evaluated in terms of the thickness of the gelled polymer layer that is coated on the polyolefin separator.