Improvement of electrochemical performance of Mn-Fe based compound Na0.69Mn(0.92−x)Fe0.08MgxO2

This work focused on the improvement on the electrochemical properties of the Mn-Fe based layered oxide materials as cathode for sodium ion batteries. The strategy of substituting Mn by cheap Mg element is studied in detail. The influences of Mg content on the crystal structure and electrochemical properties are investigated by XRD and charge-discharge tests, respectively. The composition with the most optimum Mg content is determined as Na0.69Mn0.82Fe0.08Mg0.1O2. It exhibits improved performance compared with previously reported literature. Its initial discharge capacity reached 175.8 mAh g-1 at a current density of 20 mA g-1. Meanwhile, it displays much better rate capabilities with a capacity retention as high as 71.6% after 100 cycles at a higher current rate of 100 mA g-1. More significantly, it can deliver high discharge capacities of 121, 102, and 91 mAh g−1 at high current densities of 400, 1000, and 2000 mA g-1, respectively.