Mass-Balancing of Electrodes as a Strategy to Widen the Operating Voltage Window of Carbon/Carbon Supercapacitors in Neutral Aqueous Electrolytes

Abstract

In the present study, the effect of mass-balancing electrodes with respect to electrochemical performance of carbon-based supercapacitors (SCs) is investigated. It was found that by adjusting the mass ratio of positive and negative electrodes in SCs using the same active material in both electrodes (Pica activated carbon) one can extend the operating voltage of the SC beyond the typical window of stability for aqueous electrolyte systems. After studying the electrochemical stability window of single electrodes using cyclic voltammetry, symmetric (positive and negative electrode with the same mass) and asymmetric SCs (mass ratio of 2.46 positive/negative electrodes) are assembled and characterized.The results confirm that the asymmetric carbon-based SCs with mass ratio of 2.46 and a cycling history of 2000 cycles at 1.6 V and 5000 cycles more at 1.8 V, is able to retain over 75% of the initial capacitance after 7000 additional charge-discharge cycles at 2 V. On the contrary, a decreasing performance of the symmetric system losing more than 90% of the initial capacitance is detected under the same experimental conditions. Moreover, some insights about the electrochemical processes which occur during cycling of EDLCs are given. In particular, infrared spectroscopy experiments indicate that the loss of performance of symmetric carbon-based SC is dominated by the aging of the positive electrode.