TlSnF, a SnF-based solid electrolyte with high ionic conductivity and electrochemical stability for all-solid-state fluoride ion batteries.

Fluoride-ion batteries (FIBs) offer better theoretical energy densities and temperature stability, making them suitable alternatives to expensive Li-ion batteries. Major studies on FIBs operating at room temperature focus mainly on MSnF (M: Ba and Pb) solid electrolytes due to their favourable ionic conductivity values. PbSnF is the best fluoride ionic conductor known to date. However, it exhibits poor electrochemical stability. The present work demonstrates the development of TlSnF through a single-step mechanical milling method. TlSnF exhibits a better ionic conductivity value compared to the earlier reported various solid electrolytes, such as BaSnF, KSnF, and LaBaF, commonly considered for FIBs. Ionic transport number measurement using the dc polarization method indicates that TlSnF is an ionic conductor. Furthermore, F NMR spectra measured at various temperatures demonstrate that the rise in conductivity with temperature is attributed to the rapid transport of fluoride ions. The present study indicates that TlSnF can be utilized as a potential solid electrolyte for fabricating FIBs.