Synthesis of Na2FePO4F/C and its electrochemical performance

Using NaF as the only Na precursor, fluorophosphate Na 2 FePO 4 F/C materials have been synthesized via the solid-state reaction. Na 2 FePO 4 F starts to form at 300   °C, becomes the sole crystalline form between 400 and 600   °C, and decomposes at 650   °C. Comparing with the theoretical capacity of 124   mAh   g −1 , the sample prepared at 600   °C delivered a discharge capacity of 118   mAh   g −1 . The outstanding electrochemical performance is believed to result from the good crystallization and high purity of the synthesized materials . The capacity retentions at 0.5   C and 2   C are 95.8% and 89.8%, respectively, of that at 0.05   C. Furthermore, a discharge capacity of 122   mAh   g −1 is maintained under the cycling between 2.0 and 5.2   V vs. Li/Li + , indicating that the second Na + is not extracted from the Na 2 FePO 4 F lattice.