Electrochemical and Thermal Properties of α-NaFeO₂Cathode for Na-Ion Batteries

α-NaFeO 2 is promising as minor-metal free cathode materials for low cost sodium-ion batteries. It has a flat voltage plateau at 3.3 V vs. Na metal and a stable reversible capacity of 85 mAh g −1 . Fe 3+ /Fe 4+ redox reaction on charge/discharge cycle was confirmed by 57 Fe Mössbauer spectrometer. The thermal stability of NaFeO 2 cathodes with/without 1 mol dm −3 NaClO 4 /EC-DMC electrolyte was investigated by DSC measurements. The fully-charged Na 0.58 FeO 2 powder decomposed thermally at a temperature higher than 300°C, with Fe 2 O 3 as a possible product. On the other hand, the mixture of Na 0.58 FeO 2 powder and electrolyte showed exothermic heat in a temperature range of 220–300°C. However, NaFeO 2 showed better thermal stability in the electrolyte than LiCoO 2 counterparts in Li ion battery systems, including less heat generation and higher exothermic onset temperature. This indicated that the Na-ion batteries might have comparable thermal stability with Li-ion batteries.