Controllable Formation of Niobium Nitride/Nitrogen-Doped Graphene Nanocomposites as Anode Materials for Lithium-Ion Capacitors

Niobium nitride/nitrogen-doped graphene nanosheet hybrid materials are prepared by a simple hydrothermal method combined with ammonia annealing and their electrochemical performance is reported. It is found by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the as-obtained niobium nitride nanoparticles are about 10-15 nm in size and homogeneously anchored on graphene. A non-aqueous lithium-ion capacitor is fabricated with an optimized mass loading of activated carbon cathode and the niobium nitride/nitrogen-doped graphene nanosheet anode, which delivers high energy densities of 122.7-98.4 W h kg(-1) at power densities of 100-2000 W kg(-1), respectively. The capacity retention is 81.7% after 1000 cycles at a current density of 500 mA g(-1). The high energy and power of this hybrid capacitor bridges the gap between conventional high specific energy lithium-ion batteries and high specific power electrochemical capacitors, which holds great potential applications in energy storage for hybrid electric vehicles.