Characterization of Na-based phosphate as electrode materials for electrochemical cells

We report the electrochemical properties of submicron-sized particles of NaFePO4. Two materials have been studied and characterized by XRD, SEM, EDX, EIS and Raman experiments: the maricite phase synthesized by hydrothermal method and the olivine phase obtained from delithiation of LiFePO4. NaFePO4 materials have an electrochemical activity in Na cell using NaPF6–EC–DEC electrolyte, but only in the heterosite phase, and the capacity is reduced already in the second cycle. The two-phase system at intermediate compositions has also been analyzed.

► Electrochemical features of both maricite and olivine NaFePO4.
► Full insertion of Na achieved at 1.7 V, capacity retention of 147 mAh g−1 in olivine.
► Na insertion/de-insertion operates in a two-phase process.
► XRD and EDX analysis of intermediate compositions.