High electrochemical performance and lithiation-delithiation phase evolution in CuO thin films for Li-ion storage

Magnetron sputtered CuO thin films with a hierarchical structure and large specific surface were prepared, and their electrochemical properties and reaction characteristics as the Li-ion storage electrodes were investigated. The nanostructured CuO thin film showed a high capacity, good cycling stability and excellent rate performance and exhibited discharge capacities of 703 mA h g(-1) at 100 mA g(-1) and 465 mA h g(-1) at 1000 mA g(-1) even after 100 electrochemical cycles. Transmission electron microscopy was applied to investigate the phase evolution of the CuO thin film after being electrochemically induced at various stages in the 3rd lithiation-delithiation cycle. An intermediate phase of Cu4O3, besides Cu and Cu2O products, was identified in the CuO electrode during the electrochemical process. The investigation of phase evolution revealed that the CuO active materials were partially reduced to Cu4O3, followed by being reduced to Cu2O and Cu during the discharge process, whereas the reversible electrochemical reactions Cu -> Cu2O -> Cu4O3 -> CuO took place during the charging process.