Continuing Quest for High Temperature Electrochemical Capacitors

Progress is described in the development of small electrochemical capacitors that would be capable of high current pulses when in parallel with high energy density primary batteries used at present in oil and gas drilling operations. Difficulties were experienced initially in passivation of electrode substrate materials in presence of minute amounts of water related impurities and with an unacceptable leakage current at full charge at maximum temperature of up to 150 degrees C prevailing in most oil services applications. While the problem of electrode substrate passivation has been successfully resolved by choice of material and of a surface pre-treatment in preparation of electrodes the excessive leakage current has only recently been sufficiently reduced to consider hybrid power sources with batteries and electrochemical capacitors practical. A tentative conclusion has been reached that the electrolyte components, otherwise stable alone or in rechargeable batteries, are subject to decomposition in presence of high surface area carbon creating an internal electrochemical shuttle responsible for self-discharge.