Nitrogen and oxygen co-doped mesoporous carbon spheres as capacitive anode for high performance sodium-ion capacitors

Abstract The poor rate capability of battery-type anode is usually the bottleneck of the power-energy outputs of a hybrid alkaline metal ion capacitor. In this work, nitrogen and oxygen co-doped mesoporous carbon spheres with excellent rate performance and cycle stability are used as anode materials of sodium ion capacitors (SICs). The high N and O element doping levels as well as the amorphous and mesoporous structure have enabled prominent capacitive Na ion storage behavior, which in turn match well with the capacitive cathode in the hybrid device. Under optimum conditions, the SIC delivers a high energy density of 103.1 Wh kg−1 at a power density of 205.6 W kg−1. Even at a high power density of 7520 W kg−1, an energy density of 23.5 Wh kg−1 is still maintained. Moreover, a robust cycle stability with capacity retention of 84.6 % after 2500 cycles at 1 A g-1 is maintained. Such excellent electrochemical performances convincingly demonstrate that the all-carbon based SICs with the highly capacitive N and O co-doped mesoporous carbon anode can be promising Na ion-based energy storage devices alternative to their Li ion-based counterparts.