Rational design of N-doped carbon coated NiNb2O6 hollow nanoparticles as anode for Li-ion capacitor

Searching for anode materials with fast Li+ intercalation kinetics to mitigate the dynamic imbalance with the rapid capacitive cathode is the fundamental strategy to achieve high energy-power density of Li-ion capacitors (LICs). Hence, NiNb2O6 hollow nanoparticles are first synthesized by hydrothermal method and then sealed with a protective N-doped carbon shell to achieve the target NiNb2O6@NC composite. As the anode of LICs, the NiNb2O6@NC sample exhibits a high capacity of 435.8 mAh g at 50 mA g(-1) and excellent rate performance of 47.8% capacity retention with the current density increased to 2 A g(-1). The lithium storage mechanism of NiNb2O6 is proposed as a combined conversion reaction and an intercalation reaction, which the NiNb2O6 decomposes into Ni metal and LixNb2O5 during the 1st discharge/charge process. The irreversible Ni would not contribute to the reversible capacity and will improve the electric conductivity for fast transport of electrons and the LixNb2O5 will act as the host for lithium ions by means of the intercalation mechanism. Furthermore, the assembled NiNb2O6@NC//activated carbon LICs exhibit a maximum energy density of 123.9 Wh kg(-1) and the capacity retention reaches 86.1% after 5000 cycles. The superior electrochemical performances indicate that the rationally-designed NiNb2O6@NC is expected to be a potential anode material for LICs.