Ultra-small V2O3 embedded N-doped porous carbon nanorods with superior cycle stability for sodium-ion capacitors

Abundant vanadium-based compounds with high theoretical capacity have attracted more attention for use as anodes in electrochemical energy storage. Herein, we report a two-step pyrolysis process on the formation of vanadium compound/N-doped porous carbon nanorods from a vanadium-based metal-organic framework. This process not only creates three different vanadium compounds (V8C7, V2O3 and VN), but also achieves the tunable N doping of carbon substrate. As anode materials for sodium storage, the optimized V2O3/N-doped porous carbon nanorods exhibit better long-term cycling performance (retention 74.4% after 3000 cycles at 1.0 A g(-1)) than others. The high cycle stability can be attributed to these superiorities in ultra-small V2O3, added N-doped porous carbon and the rich directional channels. Moreover, an asymmetric sodium-ion capacitor is assembled with a V2O3/N-doped porous carbon electrode and an activated carbon electrode, showing excellent cycling performance (retention 30.5 W h g(-1) after 5000 cycles at 1.0 A g(-1)) and also enabling a high power density of 5805 W kg(-1) with an energy density of 38.7 W h kg(-1).