Facile design and synthesis of Co-free layered O3-type NaNi0.2Mn0.2Fe0.6O2 as promising cathode material for sodium-ion batteries

O3-type layered oxides have received extensive attention as a class of battery layered materials. However, problems such as rate capability, stable period difference, and voltage deviation of these oxides hinder their practical application. The method of orthogonal experiment was adopted, and the reaction temperature, raw material concentration, reaction time and ammonia concentration were regarded as single factors. Finally, the optimal conditions for synthesizing cathode materials were obtained as follows: the reaction temperature was 50 °C, the raw material concentration was 0.2 mol·L-1, the reaction time was 16 h, and the ammonia concentration was 1 mol·L-1. A layered oxide cathode material Co-free NaNi0.2Mn0.2Fe0.6O2 with high iron content was synthesized by co-precipitation method. When the charging voltage is greater than 4 V, the higher the utilization rate of sodium ions, the higher the energy density. But the higher the cut-off voltage, the worse the cycle stability. Due to the low manganese content and the high iron content, the average oxidation state of manganese is low. 57Fe-Mo¨ssbauer spectroscopy showed that the synthesized samples had high spin Fe3+. Under the control of the optimal synthesis conditions, the specific discharge capacity of the reaction increased from 105 mAhּ·g−1 to 112.5 mAhּ·g−1 at 0.1C.