Study on the influence of Cu/F dual-doping on the Fe–Mn based compound as cathode material for sodium ion batteries

This work focuses on the improvement on the electrochemical performances of Fe–Mn based oxides as cathode for sodium ion batteries by doping Cu and F elements. The synthesized doped-compounds exhibit extremely excellent electrochemical performance. For instance, it's initial discharge capacity can reach 195.6 mAh g−1 at a current density of 10 mA g−1. Meanwhile, after 200 cycles at 200 mA g−1, it still remains a capacity of 124.1 mAh g−1, 87.8% of the initial capacity of 141.3 mAh g−1. More significantly, it can deliver a high capacity of 106.4 mAh g−1 at a high current density of 1000 mA g−1. It is found that F/Cu co-substitution obviously improve the discharge capacity and cycle stability of Fe–Mn based oxide especially at higher current densities. Doping Cu and F elements has influence on the structure and morphology of the material, which results in the improvement of charge-discharge characteristics.