PHOSPHORUS–BASED NEGATIVE ELECTRODES FOR SODIUM-ION BATTERIES
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Sodium ion batteries are promising for future use in electrified vehicles and electrical power grids. However, there exist many challenges in the development of negative electrode materials. In this work, room temperature 119Sn Mössbauer spectroscopy and X-ray diffraction were used to study the sodiation mechanism of Sn4P3. The results suggest that upon sodiation, Sn and P begin to react with sodium simultaneously and different Na-Sn phases were formed. These findings are consistent with the behavior of Sn4P3 in Li cells. This study provides an example of how Mössbauer spectroscopy can provide insight into the mechanism of metal alloying reactions in metal ion cells. Five transition metal phosphides (M-P, M=Ti, Mn, Co, Cu, Zn) were synthesized and tested in sodium ion half-cell for use as negative electrode materials. The possibility of using transition metal phosphides as negative electrode was evaluated. Conversion reactions occur during the sodiation/desodiation of the materials. It was found that even though some transition metal phosphides offer high capacities, they all suffer from high irreversible capacity, poor cycling life and high voltage hysteresis. The effects of using different binders and operating temperatures were also explored.