High energy and high power density electrochemical capacitors

High energy density electrochemical capacitors were built with a newly discovered electrode material (amorphous RuO₂ · xH₂O). Energy densities as high as 96 J/g (26 Wh/kg) were obtained based on the RuO₂ · xH₂O electrode material alone. However, the power density of the capacitor is low. By mixing RuO₂ · xH₂O powders with about 20% weight of carbon black, power densities greater than 10 kW/kg could be achieved at a delivered energy density of about 72 J/g (20 Wh/kg). Capacitance as a function of cycle life was studied for up to 60 000 cycles. The temperature dependence of capacitance and resistance of the capacitor are also reported in this paper.