Facile Fabrication of Multivalent VOx/Graphene Nanocomposite Electrodes for High‐Energy‐Density Symmetric Supercapacitors

Abstract Supercapacitors have emerged as one of the leading energy‐storage technologies due to their short charge/discharge time and exceptional cycling stability; however, the state‐of‐the‐art energy density is relatively low. Hybrid electrodes based on transition metal oxides and carbon‐based materials are considered to be promising candidates to overcome this limitation. Herein, a rational design of graphene/VO x electrodes is proposed that incorporates vanadium oxides with multiple oxidation states onto highly conductive graphene scaffolds synthesized via a facile laser‐scribing process. The graphene/VO x electrodes exhibit a large potential window with a high three‐electrode specific capacitance of 1110 F g –1 . The aqueous graphene/VO x symmetric supercapacitors (SSCs) can reach a high energy density of 54 Wh kg –1 with virtually no capacitance loss after 20 000 cycles. Moreover, the flexible quasi‐solid‐state graphene/VO x SSCs can reach a very high energy density of 72 Wh kg –1 , or 7.7 mWh cm –3 , outperforming many commercial devices. With R ct < 0.02 Ω and Coulombic efficiency close to 100%, these gel graphene/VO x SSCs can retain 92% of their capacitance after 20 000 cycles. The process enables the direct fabrication of redox‐active electrodes that can be integrated with essentially any substrate including silicon wafers and flexible substrates, showing great promise for next‐generation large‐area flexible displays and wearable electronic devices.