Conjugated supercapacitor with suppressed self‐discharge constructed by pairs of prelithiated Nb 2 O 5 @C with optimized elemental and phase purity in the carbon shell

Abstract The realization of carbon neutralization requires further development of high‐performance supercapacitors, while their wider applications are limited by serious self‐discharge. This work proposes a conjugately configured supercapacitor, as well as the strategy for optimizing the structure of active materials specifically for such supercapacitor. The conjugated supercapacitor consists of pairs of prelithiated T‐Nb 2 O 5 @C and forms a Li x Nb 2 O 5 @C versus Li 2 − x Nb 2 O 5 @C configuration. We demonstrate that the elegant control of the coated carbon shell has a significant effect on the self‐discharge behavior. An optimized annealing temperature of 300°C is beneficial for reducing the elemental impurity while not introducing microregional phase impurity, thus leading the best resistance towards self‐discharge. When the conjugated supercapacitor is charged to an initial voltage of 1.0 V, the voltage could retain for more than 3000 min before dropping to 0.5 V. This work is expected to provide general guidance for optimizing the active materials for conjugated supercapacitors.