Enhancing the Lithium Storage Performance of the NbO Anode via Synergistic Engineering of Phase and Cu Doping.

NbO has been viewed as a promising anode material for lithium-ion batteries by virtue of its appropriate redox potential and high theoretical capacity. However, it suffers from poor electric conductivity and low ion diffusivity. Herein, we demonstrate the controllable fabrication of Cu-doped NbO with orthorhombic (T-NbO) and monoclinic (H-NbO) phases through annealing the solvothermally presynthesized NbO precursor under different temperatures in air, and the Cu doping amount can be readily controlled by the concentration of the precursor solution, whose effect on the lithium storage behaviors of the Cu-doped NbO is thoroughly investigated. H-NbO shows obvious redox peaks (Nb/Nb and Nb/Nb) with much higher capacity and better cycling stability than those for the widely investigated T-NbO. When introducing appropriate Cu doping, the optimized H-Cu-NbO electrode shows greatly enhanced conductivity and lower diffusion barrier as revealed by the theoretical calculations and electrochemical characterizations, delivering a high reversible capacity of 203.6 mAh g and a high capacity retention of 140.8 mAh g after 5000 cycles at 1 A g, with a high initial Coulombic efficiency of 91% and a high rate capacity of 144.2 mAh g at 4 A g. As a demonstration for full-cell application, the H-Cu-NbO||LiFePO cell displays good cycling performance, exhibiting a reversible capacity of 135 mAh g after 200 cycles at 0.2 A g. More importantly, this work offers a new synthesis protocol of the monoclinic NbO phase with high capacity retention and improved reaction kinetics.