Nanograin tungsten oxide with excess oxygen as a highly reversible anode material for high-performance Li-ion batteries

Nanogranular tungsten oxide (WO₃) with excess oxygen is synthesized and its battery performance is evaluated as an anode material for the Li-ion battery (LIB). The formation of a monoclinic WO₃ phase is confirmed using X-ray diffraction (XRD) and micro (µ)-Raman spectroscopy analyses. The Rutherford back scattering results confirm the existence of excess oxygen in the film. The charge discharge processes are associated with the conversion of the WO₃ from the oxide state to the metallic state, and vice versa, and it shows a maximum specific capacity of 778.8 mAh g⁻¹ at a current density of 0.1 Ag⁻¹ in the first discharge. Even at a very high current density of 1 Ag⁻¹, the sample retains the capacity of 228.6 mAh g⁻¹. It shows excellent rate capability and a long-term cycling stability over 500 charge–discharge cycles, with capacity retention of 217%. The observed high discharge capacity and superior long-term cyclability of the nanograin WO₃ anode are attributable to the synergetic effect of the excess-oxygen induced increased donor density and enhanced electrical conductivity.