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.