Self-Assembled Nb 2 O 5 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 (Nb 2 O 5 ) and peanut shell carbon (PSC) as the anode and cathode materials, respectively. The advanced architecture of self-assembled Nb 2 O 5 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 three-dimensional nanocubes, and further to two-dimensional nanosheets. The resulting Nb 2 O 5 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: ∼80% at 1280 mA g –1 after 3000 cycles).