Enhancing the Lithium Storage Performance of the Nb 2 O 5 Anode via Synergistic Engineering of Phase and Cu Doping.

Nb 2 O 5 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 Nb 2 O 5 with orthorhombic (T-Nb 2 O 5 ) and monoclinic (H-Nb 2 O 5 ) phases through annealing the solvothermally presynthesized Nb 2 O 5 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 Nb 2 O 5 is thoroughly investigated. H-Nb 2 O 5 shows obvious redox peaks (Nb 5+ /Nb 4+ and Nb 4+ /Nb 3+ ) with much higher capacity and better cycling stability than those for the widely investigated T-Nb 2 O 5 . When introducing appropriate Cu doping, the optimized H-Cu 0.1 -Nb 2 O 5 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 -1 and a high capacity retention of 140.8 mAh g -1 after 5000 cycles at 1 A g -1 , with a high initial Coulombic efficiency of 91% and a high rate capacity of 144.2 mAh g -1 at 4 A g -1 . As a demonstration for full-cell application, the H-Cu 0.1 -Nb 2 O 5 ||LiFePO 4 cell displays good cycling performance, exhibiting a reversible capacity of 135 mAh g -1 after 200 cycles at 0.2 A g -1 . More importantly, this work offers a new synthesis protocol of the monoclinic Nb 2 O 5 phase with high capacity retention and improved reaction kinetics.