Scalable synthesis of Na2MVF7 (M = Mn, Fe, and Co) as high-performance cathode materials for sodium-ion batteries.

We demonstrate an economical polytetrafluoroethylene-assisted fluorination method to synthesize three binary sodium-rich fluorides Na2MVF7 (M = Mn, Fe, and Co). The optimal Na2FeVF7 cathode delivers a high reversible capacity of 146.5 mA h g-1 based on active Fe2+/Fe3+ and V3+/V4+ redox reactions in sodium-ion batteries. A steady cycling performance with a high capacity retention of 95% over 200 cycles is achieved owing to the negligible structural change during Na+ insertion/extraction.