Scalable synthesis of processable high performance O3-NaNi0.4Mn0.4Fe0.2O2: A methodological investigation and electrochemical insights

The O3-NaNi 0.4 Mn 0.4 Fe 0.2 O 2 (NaNMF442) cathode material was synthesised using a scalable coprecipitation and calcination process, yielding a high-purity and crystalline material well-suited for sodium ion batteries. Electrochemical properties were investigated using sodium metal anode counter electrodes and the cells were found to give a capacity of 140.5 mAh g -1 , an average voltage of 3.17 V vs. Na + /Na, and an energy density of 445.4 Wh Kg -1 at a (dis)charge rate of 24 mA g -1 , and 118.8 mAh g -1 , 3.1 V vs. Na + /Na, and 316.8 Wh Kg -1 at 240 mA g -1 . Further testing in proof-of-concept full cells against commercial hard carbon counter electrodes, followed by a comprehensive post-cycling analysis, revealed that the half cell performance had been limited by electrolyte decomposition. This was attributed to side reaction with the sodium metal, highlighting the importance of a holistic analysis of all cell components, from synthesis to post-cycling, in order to ensure a comprehensive understanding of material performance. These results demonstrate the promising nature of the sodium nickel-manganese-iron layered oxide family, in particular those based on the NaNMF442 stoichiometry, as high-performance cathode materials with good rate capability for sodium ion batteries.