Understanding supercapacitive performance of a N-doped vanadium carbide/carbon composite as an anode material in an all pseudocapacitive asymmetric cell

Abstract

Pseudocapacitive asymmetric supercapacitors (ASCs) have captivated huge attention in electrochemical energy storage applications owing to their wide operating voltage window and high energy/power densities as compared to carbon-based double layer capacitors. Yet it is challenging to achieve electrochemical performance compatibility between negative and positive electrodes for optimum ASC performance. Herein, we have fabricated an all pseudocapacitive asymmetric supercapacitor using a N-doped V₄C₃/C nano-heterostructure with a porous layered structure as the negative electrode and a VO₂/VSe₂ hybrid composite with flower-like morphology as the positive electrode material. A N-doped V₄C₃/C nano heterostructure is realized using a novel in situ reduction/carbonization method with V₂O₅ and dicyandiamide as precursors. The porous layered structure thus produced provides abundant reaction sites and facilitates fast ion transport, resulting in a specific capacitance of 118 F g⁻¹ at a current density of 0.75 A g⁻¹ with an outstanding rate capability up to 20 A g⁻¹ current density and good cycling stability after 10 000 cycles. The partially selenized vanadium oxide (VO₂/VSe₂ hybrid) positive electrode also exhibits a specific capacitance of 108.9 F g⁻¹ at 0.25 A g⁻¹ current density, along with an ultrahigh cycling stability of 97% after 10 000 cycles. The assembled N-doped V₄C₃/C//VO₂/VSe₂ ASC displays a 1.8 V stable voltage window in 1 M sodium sulfate aqueous electrolyte and can deliver an energy density of 21.4 W h kg⁻¹ and a power density of 4.5 kW kg⁻¹, which surpasses those of many aqueous-based symmetric and asymmetric supercapacitors, and thus substantiates the prospect of vanadium-based materials for high-performance electrochemical energy storage systems.