Direct hydrofluorothermal synthesis of sodium transition metal fluorosulfates as possible Na-ion battery cathode materials

Synthesis under hydrofluorothermal conditions produces new iron, manganese and vanadium fluorosulfates; these include the isomorphous (Na3MF2)-F-III(SO4)(2), M = V, Mn, Fe, with a sheet-like structure formed of linked (MF2O4)-F-III and SO4 polyhedra separated by sodium ions which may be extracted electrochemically at potentials of >3.5 V.