Development of electrochemical capacitors incorporating processable polymer gel electrolytes

The behavioural characteristics of two classes of electrochemical supercapacitors, based respectively on porous (ie activated) carbon electrodes and polypyrrole-coated carbon electrodes, have been compared by cyclic voltammetry in order to identify the electrode/electrolyte combinations suitable for high power density applications. It is shown that the large specific capacitances of activated carbon electrodes (in Fg(-1)) are not accessible during high rates of charge/discharge because ions from the electrolyte are slow to reach the internal surfaces of the carbon electrodes. Much larger charge/discharge rates (and hence power densities) are achievable with polypyrrole-coated carbon electrode/polymer electrolyte combinations. These concepts are now being incorporated into working prototypes for ultimate scaleup to meet the needs of electric vehicle applications. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.