Exploring the structural and conductivity behaviours of mechanochemically and hydrothermally synthesized Ce3+-doped BaSnF4 solid electrolytes for all-solid-state fluoride-ion batteries

Recent studies on batteries have drawn significant attention to all-solid-state fluoride-ion batteries (FIBs) as potential alternatives to the conventional Li-ion batteries because of their higher theoretical energy densities. On the solid electrolyte side, efforts are being made to develop a suitable material with improved ionic conductivity (∼ 10⁻³ S/cm) and enhanced electrochemical stability. SnF₂-based solid electrolyte, BaSnF₄ crystallizes in the PbSnF₄ structure and is frequently considered as a potential solid electrolyte for FIBs operating at room temperature (RT). In this study, the conductivity results of BaSnF₄ are influenced by doping with rare-earth ions (Ce³⁺) at different concentrations and by the synthesis methodology. The structural and transport behaviours of Ce³⁺-doped BaSnF₄ solid electrolytes, prepared by mechanical milling and hydrothermal methods, are compared. The formation of the doped materials, which exhibit a tetragonal phase, is confirmed by X-ray diffraction. The presence of Ce³⁺ in the doped materials prepared by both methods is confirmed by their photoluminescence characteristics. Among the materials investigated in this study, 2 mol% Ce³⁺-doped BaSnF₄, prepared by mechanical milling (Ba_0.98Ce_0.02SnF_4.02-MM) exhibits the highest ionic conductivity and electrochemical stability. The conductivity (RT) exhibited by Ba_0.98Ce_0.02SnF_4.02-MM is higher compared to earlier reports on different rare-earth ion-doped BaSnF₄, which were primarily prepared by solution-based methods. Ion transport number measurement using dc polarization technique revealed that the conductivity exhibited by Ba_0.98Ce_0.02SnF_4.02-MM is mainly due to ionic conduction. The observation of a higher ionic conductivity value in Ba_0.98Ce_0.02SnF_4.02-MM highlights its great potential for use as a solid electrolyte in the fabrication of FIBs.