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

α-NaFeO2 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. Fe3+/Fe4+ redox reaction on charge/discharge cycle was confirmed by 57Fe Mössbauer spectrometer. The thermal stability of NaFeO2 cathodes with/without 1 mol dm−3 NaClO4/EC-DMC electrolyte was investigated by DSC measurements. The fully-charged Na0.58FeO2 powder decomposed thermally at a temperature higher than 300°C, with Fe2O3 as a possible product. On the other hand, the mixture of Na0.58FeO2 powder and electrolyte showed exothermic heat in a temperature range of 220–300°C. However, NaFeO2 showed better thermal stability in the electrolyte than LiCoO2 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.