Carbon/PbO2 asymmetric electrochemical capacitor based on methanesulfonic acid electrolyte

A new hybrid electrochemical capacitor based on an activated carbon negative electrode, lead dioxide thin film and nanowire array positive electrode with an electrolyte made of a lead salt dissolved in methanesulfonic acid was investigated. It is shown that the maximum energy density and specific capacity of the C/PbO₂ nanowire system increase during the first 50 cycles before reaching their maximum values, which are 29 Wh kg⁻¹ and 34 F g⁻¹, respectively, at a current density of 10 mA cm⁻² and a depth of discharge (positive active electrode material) of 3.8%, that corresponds to a 22C rate. This is 7–8 times higher than the corresponding maximum values reached with a C/PbO₂ thin film cell operated in the same conditions. After an initial activation period, the performances of the C/PbO₂ nanowire system stay constant and do not show any sign of degradation during more than 5000 cycles. For comparison, the C/PbO₂ thin film system exhibits a 50% decrease of its performances in similar conditions.