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 × 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.