The relation between the structure and electrochemical performance of sodiated iron phosphate in sodium-ion batteries

Abstract The structure and electrochemical performance of sodiated iron phosphate were investigated by means of X-ray diffraction, high-resolution transmission electron microscopy and electrochemical measurements. The results indicate that after the sodiation process, all FePO 4 samples transform into the amorphous sodium iron phosphate and crystallite NaFePO 4 , namely triphylite NaFePO 4 for amorphous FePO 4 and maricite NaFePO 4 for trigonal FePO 4 , respectively. The amorphous FePO 4 samples show excellent electrochemical performance in terms of cyclic stability and discharge capacity, while trigonal FePO 4 displays poor electrochemical performance. The outstanding electrochemical performance of amorphous FePO 4 was attributed to the amorphous and triphylite NaFePO 4 with high electrochemical activity. Those findings indicate that amorphous FePO 4 can be transformed into active NaFePO 4 , which may have great potential as an electrode material for sodium-ion batteries.