Controlled Electrochemical Charge Injection to Maximize the Energy Density of Supercapacitors

摘要

To increase the energy density of supercapacitors (SCs), numerous attempts are focused on developing high-capacity electrode materials and high-voltage electrolytes. However, a common but very important problem that has not been solved is that the high specific capacity of electrode materials and the voltage window of electrolytes cannot always be fully used when assembled into SC devices. In early studies it was found that this problem results from the unsuitable electrode potential window (EPW) in SC devices. In fact, both the working voltage and the specific capacity of SCs rely significantly on the EPW of individual electrodes. Therefore, the EPW must be optimized to maximize the energy density of SCs. Up to date, however, the unsuitable EPW can be moderated only by balancing the electrode mass141 (as illustrated in Figure 1 a) or by using different materials as electrodes to assemble asymmetric SCs. The balancing of the electrode mass will increase the working voltage but not increase the specific capacity.161 It is difficult and time consuming to find appropriate materials matching each other which can be used for the electrodes of an asymmetric SC. For Li-ion capacitors, prelithiating anodes can be used to enlarge the positive EPW for an increasing capacity, but they are inapplicable to conventional SCs. Therefore, we consider that the adjustment of the electrode potential (EP) is the general key to optimizing the EPW.