High electrochemical performance and phase evolution of magnetron sputtered MoO2 thin films with hierarchical structure for Li-ion battery electrodes

Abstract

MoO₂ thin films with hierarchical structure were magnetron-sputtering deposited on copper foils by using a metal molybdenum target. The microstructure, electrochemical performance and phase evolution of the MoO₂ thin films were investigated. The novel structure contributes to the high specific capacity of 860 mA h g⁻¹ at a current rate of 400 mA g⁻¹, high reversible capacity of 760 mA h g⁻¹ after 100 cycles and high rate capability (370 mA h g⁻¹ at 3200 mA g⁻¹). The electrochemical mechanism was studied by investigating the microstructures and phase evolution of the MoO₂ thin film electrodes by using transmission electron microscopy (TEM) after being electrochemically induced at various stages in the first charge–discharge cycle and in the 12^th cycle, respectively. The TEM investigations reveal that the MoO₂ thin film electrodes undergo a conversion reaction such as MoO₂ + xLi⁺ ↔ Li_xMoO₂ ↔ Mo + xLi₂O, which is kinetically infeasible under normal conditions.