NbO Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-NbO nanoparticles/N-doped graphene hybrid anode (T-NbO/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-NbO nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-NbO/NG were improved by doping nitrogen. The T-NbO/NG anode showed superior rate capability (68 mA h g even at 2 A g) and good cycling life (106 mA h g at 0.2 A g for 200 cycles and 83 mA h g at 1 A g for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-NbO/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg at a power density of 100 W kg and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g) and showed a promising application for highly efficient energy storage systems.