Abstract: An electrochemical capacitor includes a polymer thin film, a liquid electrolyte absorbed in the polymer thin film, and thin flexible active electrode layers constituting anode and cathode composed of energy dense material of high intrinsic surface area positioned at either side of the electrolyte-retaining polymer thin film to tightly sandwich it between the electrode layers. In one embodiment, the capacitor includes a polymer electrolyte in which a polymer thin film is cast from the base polymer and impregnated with the electrolyte solution, which contains a salt for ionic conduction. In another embodiment, the base polymer material includes an ionically conducting polymer, a perfluorocarbon polymer backbone to which sulfonic acid sites are permanently anchored. The energy dense material of the electrode layers may be physically mixed with battery active material to enhance the capacity and discharge time of the capacitor.