Cathode Properties of Perovskite-type NaMF3 (M = Fe, Mn, and Co) Prepared by Mechanical Ball Milling for Sodium-ion Battery

NaFeF3 and NaMnF3 are promising cathode materials for sodium-ion batteries due to their low cost, low environmental impact and large theoretical capacity. NaCoF3 also has attracted attention as the high voltage cathode material for sodium-ion batteries. But, these ionic NaMF3 (M = Fe, Mn and Co) compounds have insulating character. To improve the lower electronic conductivity, two-step ball-milling with carbon was performed to obtain a uniform NaMF3 and carbon composite. The rechargeable capacity of NaFeF3 was 169 mAh g−1, and its energy density was over 500 Wh kg−1, which is the highest among the reported iron-based cathode materials for sodium-ion batteries. In addition, the experimental voltage for NaMnF3 was ca. 3.4 V, and the voltages for NaMF3 (M = Fe and Mn) calculated by the DFT method corresponded well with the experimental results for NaFeF3 and NaMnF3.