Mechanochemical synthesis of NaMF₃ (M = Fe, Mn, Ni) and their electrochemical properties as positive electrode materials for sodium batteries

Mechanical treatment was used as a nonconventional solid-state process for large-scale preparation of fluoride materials as an alternative to the hazardous high-pressure fluorination route. Sodium fluoroperovskites of Fe, Mn, and Ni were achieved by mechanical grinding of NaF and binary metal fluorides for different periods of time under Ar. The obtained monophases were characterized by XRD measurements, AAS, ICP-OES, and IC. The electrochemical performance of the achieved materials was tested in a Na half-cell under different operating conditions. It was revealed that mechanochemically inserted sodium is electrochemically active for the NaFeF₃ positive electrode composition. In this pilot study, NaFeF₃ showed an initial discharge capacity of 130 mA h g^-1 at 0.2 mA cm^-2.