Vanadium nitride encapsulated carbon fibre networks with furrowed porous surfaces for ultrafast asymmetric supercapacitors with robust cycle life

Transition metal nitrides have received significant attention in view of their application as pseudocapacitive electrodes in high performance supercapacitors owing to their high capacitance, excellent electrical conductivity, high electrochemical selectivity, and low environmental impact. Nevertheless, the utilization of transition metal nitrides still encounters serious challenges due to the chemical instability of these materials during cycling in the presence of oxygen and/or water containing electrolytes, which leads to rapid capacitance fading. Here, we propose a novel structure comprising vanadium nitride encapsulated carbon fibre networks with furrowed porous surfaces prepared by electrospinning followed by an optimal stabilization and carbonization treatments. The resultant electrode shows a high energy density of 53.1-36.0 W h kg^-1 at high power densities in the range from 2700-54 000 W kg^-1. This performance is superior to previously reported results on other asymmetric supercapacitors. Moreover, an excellent cycling stability of 92.9% at a current density of 80 A g^-1 after 10 000 cycles, and a superb electrode flexibility have been recorded. Our original synthesis strategy provides a useful methodology to increase the chemical stability of vanadium nitride by carbon encapsulation, which also leads to shorter diffusion pathways due to the furrowed porous surfaces and the advanced network structure consisting of 1-dimensional fibres.