Self-Assembled Nb2O5 Nanosheets for High Energy-High Power Sodium Ion Capacitors

Recently, hybrid ion capacitors which combine the characteristics of batteries and supercapacitors have gained great interests for large-scale energy storage applications. Here, we demonstrated a new hybrid sodium ion capacitor configuration, utilizing the niobium pentoxide (Nb2O5) and peanut shell carbon (PSC) as the anode and cathode materials, respectively. The advanced architecture of self-assembled Nb2O5 nanosheets with exceptional sodium ion storage property was obtained by carefully controlling reaction kinetics. A key finding is that the growth mechanism is demonstrated to be a process from one-dimensional nanorods to threedimensional nanocubes, and further to two-dimensional nanosheets. The resulting Nb2O5 nanosheets//PSC hybrid capacitors deliver an exceptionally high energy density (43.2 Wh kg(-1)) and high power density (5760 W kg(-1)) based on the active materials, with a long and stable cycle life (capacity retention: similar to 80% at 1280 mA g(-1) after 3000 cycles).