Development of all-solid-state fluoride ion battery with enhanced electrochemical stability

Fluoride ion solid-state batteries are featured as the next-generation energy storage devices with high energy density and improved thermal stability. In this investigation, the solid fluoride ion conductor BaSnF4 is synthesized via hydrothermal reaction for the first time to achieve a high ionic conductive phase, unlike conventional mechanochemical reaction followed by thermal treatment. The ionic conductivity of synthesized tetragonal BaSnF4 is found to be 5.3 x 10-5 S/cm at room temperature with an activation energy of 0.32 eV. Further, the potential fluoride ion-conductor PbF2 synthesized via a facile sonochemical reaction is utilized as a composite cathode comprising PbF2.rGO (5 wt%). An all-solid-state electrochemical cell with configuration Sn/ BaSnF4/PbF2.rGO is subjected to linear sweep voltammetry measurement inferred an electrochemical stability window between 0.8 V to 2.1 V, which is significantly larger than the reported values for BaSnF4 so far. The charge-discharge characteristics of the cell have exhibited a discharge capacity of 172 mAh/g, demonstrating the feasibility of the architecture of fluoride ion battery systems operating at ambient conditions. Thus, for the first time, the synergetic effect of the composite cathode PbF2. rGO has proven to have high conduction pathways for fluoride ions in energy storage applications.