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

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 12th cycle, respectively. The TEM investigations reveal that the MoO2 thin film electrodes undergo a conversion reaction such as MoO2 + xLi+ ↔ LixMoO2 ↔ Mo + xLi2O, which is kinetically infeasible under normal conditions.