Regulating the synergy coefficient of composite materials for alleviating self-discharge of supercapacitors

Supercapacitor is an efficient energy storage device, yet its wider application is still limited by self-discharge. Currently, various composite materials have been reported to have improved inhibition on self-discharge, while the evaluation of the synergistic effect in composite materials is challenging. Herein, pairs of intercalation type pseudocapacitive niobium oxides are pre-lithiated and coupled to construct conjugatedly configured supercapacitors, within which the cathode and anode experience identical reaction environment with single type of charge carrier, thus providing ideal platform to quantify the synergistic effect of composite materials on the self-discharge process. By using titanium dioxide as the stabilizer, we have compared how the modes of forming composite would influence the self-discharge performance of the active composite materials with similar ratio of the constituent materials. Specifically, core@shell Nb2O5@TiO2 composite using TiO2 as the shell shows significantly higher synergy coefficient (µ = 0.61, defined as the value that evaluates the synergistic effect between composite materials, and can be quantified using the overall performance of the composite, performance of individual component as well as the ratio of the component.) than other control group samples, which corresponds to the highest retained energy of 63% at 100 h. This work is expected to provide a general method for quantifying the synergistic effect and guide the design of composite materials with specific mode of forming the composite.