Hollow nanocages of vanadium nitride-based electrode material designed for superior charging/discharging stability supercapacitors

Abstract

As an emerging high-power density energy storage device, supercapacitors are limited in their development by electrode materials. Transition metal nitrides have attracted widespread attention in supercapacitors due to their high electrical conductivity and considerable capacity. Among them, vanadium nitride features a high theoretical capacity and excellent electrical conductivity, nevertheless, its solubility problem in alkaline electrolytes has always hindered the practical application of vanadium nitride. Herein, a universal method is reported for the preparation of vanadium nitride quantum dot composites by solvothermal methods and in situ substitution. Using the stable ZIF-8 dodecahedral structure, vanadium ions are riveted to the structure of the metal–organic framework by in situ substitution; after high-temperature annealing, it retains the dodecahedral structure of ZIF-8 and forms hollow nanocages. This hollow structure generates more active sites and ameliorates the reaction kinetics of the vanadium nitride material. It has a capacity of 278 F g⁻¹ at a current density of 0.5 A g⁻¹. Interestingly, a capacity retention rate of 82.23% can be achieved after 20 000 cycles at a current density of 3 A g⁻¹. In addition, the assembled device exhibits a coulombic efficiency of 97.35%, a power density of 775 W Kg⁻¹, and an energy density of 49.8 W h kg⁻¹. This good electrochemical performance, especially the enhanced cycling stability, should be attributed to the effective solution to solve the dissolution problem of vanadium nitride in electrolytes. In conclusion, the proposed method is simple and easy to implement and has a broad utilization value and application prospects in energy conversion and storage systems.