Effect of calcination temperature on the microstructure of vanadium nitride/nitrogen-doped graphene nanocomposites as anode materials in electrochemical capacitors

Abstract

Hybrid vanadium nitride/N-doped graphene (VN/N-Gr) nanocomposites have been recently used as anode materials in electrochemical capacitors. The electrochemical performances of electrode materials are dependent on their microstructures, which in turn are dependent on the fabrication methods and conditions. In this study, VN/N-Gr nanocomposites were fabricated by an in situ method by pyrolysis of a mixture of dicyandiamide, glucose, and vanadium(IV) oxide sulfate hydrate under a N₂ atmosphere. The effect of calcination temperature on the microstructure of the as-prepared products was systematically investigated. It is found that calcination temperature can greatly influence the structure, VN_xO_y and doping N content of VN/N-Gr, as well as the corresponding electrochemical performance. As an electrochemical capacitor electrode, the VN/N-Gr nanocomposite prepared at 700 °C exhibits a high specific capacitance of 342.1 F g⁻¹ at 0.5 A g⁻¹ in a 2 M KOH aqueous electrolyte with a wide operation window from −1.0 to 0.2 V. Furthermore, the assembled symmetrical device delivers an energy density of 10.3 W h kg⁻¹ at a power density of 276.3 W kg⁻¹ and remains 7.6 W h kg⁻¹ at a power density of 5484.2 W kg⁻¹. The findings in this work suggest that a judicious choice of calcination temperature during the pyrolysis process could improve the performances of electrode materials and the corresponding devices.