Nb(2)O(5) Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density

[Image: see text] 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-Nb(2)O(5) nanoparticles/N-doped graphene hybrid anode (T-Nb(2)O(5)/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl(5) at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb(2)O(5) 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-Nb(2)O(5)/NG were improved by doping nitrogen. The T-Nb(2)O(5)/NG anode showed superior rate capability (68 mA h g(–1) even at 2 A g(–1)) and good cycling life (106 mA h g(–1) at 0.2 A g(–1) for 200 cycles and 83 mA h g(–1) at 1 A g(–1) for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb(2)O(5)/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg(–1) at a power density of 100 W kg(–1) and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g(–1)) and showed a promising application for highly efficient energy storage systems.