Effects of the starting materials of Na0.44MnO2 cathode materials on their electrochemical properties for Na-ion batteries

Na0.44MnO2 is one of the most promising cathode materials in the development of sodium ion batteries (SIBs). Here, a solid-state method is described for the synthesis of regular Na0.44MnO2 nanorods about 200 nm in size at a low temperature without further annealing being required. In this work, we have investigated effects of different precursors on preparation of Na0.44MnO2 and found that the size and width of the Na0.44MnO2 nanorods were influenced by the MnCO3 precursors. The electrochemical properties for SIBs of Na0.44MnO2 nanorods synthesized from three different preparation methods were thoroughly researched. Na0.44MnO2 nanorods prepared by hydrothermal synthesis of MnCO3 (HS-Na0.44MnO2) produced a superior cathode material than other Na0.44MnO2 which uses commercial MnCO3 (C-Na0.44MnO2) and co-precipitation synthesis of MnCO3 (CP-Na0.44MnO2) as precursors. The HS-Na0.44MnO2 exhibits high discharge capacity (about 139.6 mAh g−1), good cycling stability (98.2% after 40 cycles at the current density of 20 mA g−1) and excellent rate performance, which is a much better performance than those in previous reports. The superior electrochemical performance of HS-Na0.44MnO2 is mainly due to the relatively smaller size, uniform morphology and excellent crystallinity. Furthermore, the electrochemical impedance spectroscopy (EIS) showed that the surface film resistance and charge transfer resistance of the HS-Na0.44MnO2 is smaller than others, which leading to the better electrochemical performance.