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 Na(3)M(III)F(2)(SO(4))(2), M = V, Mn, Fe, with a sheet-like structure formed of linked M(III)F(2)O(4) and SO(4) polyhedra separated by sodium ions which may be extracted electrochemically at potentials of >3.5 V.