Synthesis, Structural, and Transport Properties of Novel Bihydrated Fluorosulphates NaMSO4F•2H2O (M = Fe, Co, and Ni)

3d-metal fluorosulphates that have a tavorite-type structure (e.g., LiFeSO4F) were recently reported as attractive positive electrode candidates for future Li-ion batteries aimed at large volume markets. These new fluorosulphates had to be synthesized via ionothermal synthesis owing to both their thermal instability at temperatures greater than 300 degrees C and their water solubility. In an attempt to depart from ionothermal synthesis, low-temperature solid-state reactions and solvothermal processes were successfully tried. The latter technique, which is reported herein, proceeds with water as the solvent and has led to a new family of fluorosulphates NaMSO4F center dot 2H(2)O that crystallize in a monoclinic unit cell (SG = P2(1)/m) similar to the uklonskovite-type structure earlier proposed for NaMgSO4F center dot 2H(2)O. These new phases show no electrochemical activity with either Li or Na metal and have room temperature ionic conductivities on the order of 1 x 10(-9) S cm(-1). Additionally, we have discovered the feasibility, upon controlled dehydration of the NaMSO4F center dot 2H(2)O phases, to prepare NaMSO4F phases adopting a derived tavoritetype structure and displaying ionic conductivities around 10(-7) S cm(-1). Finally, this finding opens the possibility to achieve Li-based fluorosulphates via two-step synthetic pathways.