Dehydration Conditions and Ultrafast Rehydration of\nPrussian White: Phase Transition Dynamics and Implications for Sodium-Ion\nBatteries

Prussian White (PW)\nis a strategic cathode material for sodium-ion\nbatteries, offering a high theoretical capacity and voltage. However,\nthe crystalline structure and the electrochemical performance of PW\nstrongly depend on the hydration level, which is difficult to control,\nleading to discrepancies in the results and interpretations presented\nin the literature. This work aims to provide a deeper insight into\nthe dehydration process of PW materials and a better understanding\nof the impact of their fast rehydration, upon exposure to moisture,\non their characterization. For this purpose, a Na<sub>1.87</sub>Mn[Fe(CN)<sub>6</sub>]<sub>0.99</sub>·1.99H<sub>2</sub>O sample was synthesized\nby a coprecipitation method and subsequently dehydrated to remove\nwater. After thorough characterization, our findings show that drying\nparameters, such as temperature and pressure, strongly influence the\npost-drying result. Moreover, the dehydrated samples rehydrate within\nminutes of exposure to air, which may explain some discrepancies observed\nin the literature and highlights the necessity to work under fully\nair-tight conditions.