High performance MnO thin-film anodes grown by radio-frequency sputtering for lithium ion batteries

Abstract

Thin films of manganese oxides have been deposited on Cu foils by radio-frequency (RF) sputtering under different conditions. Crystalline MnO films cannot be obtained but Mn3+/M4+ oxides are formed when the growth proceeds under the Ar atmosphere, due to the oxidation of MnO. While they can be obtained under the Ar:H2 (95:5 vol%) reduction atmosphere at both room temperature and 500 °C. The latter films in thickness of ∼0.5 μm exhibit an initial coulombic efficiency of 75%, reversible capacities of 380 μAh cm−2 μm−1 (∼700 mAh g−1) at 4 μA cm−2 (∼0.05 C) after 100 cycles, and 230 μAh cm−2 μm−1 (∼428 mAh g−1) at 20 C. These values demonstrate that the sputtering-grown MnO films here exhibit excellent cyclability and rate performance in comparison to the reported data of MnO anodes. Pure phase with low oxidation state and certain porosity could be favorable factors accounting for such improved electrochemical performance.