Pressure Tuning and Sn Particle Size Optimization for Enhanced Performance in PbSnF₄-Based All-Solid-State Fluoride...

All-solid-state fluoride ion batteries (ASSFIBs) show remarkable potential as energy storage devices due to their low cost, superior safety, and high energy density. However, the poor ionic conductivity of F^- conductor, large volume expansion, and the lack of a suitable anode inhibit their development. In this work, PbSnF₄ solid electrolytes in different phases (β- and γ-PbSnF₄) are successfully synthesized and characterized. The ASSFIBs composed of β-PbSnF₄ electrolytes, a BiF₃ cathode, and micrometer/nanometer size (µ-/n-) Sn anodes, exhibit substantial capacities. Compared to the μ-Sn anode, the n-Sn anode with nanostructure exhibits superior battery performance in the BiF₃/β-PbSnF₄/Sn battery. The optimized battery delivers a high initial discharge capacity of 181.3 mAh g^-1 at 8 mA g^-1 and can be reversibly cycled at 40 mA g^-1 with a high discharge capacity of over 100.0 mAh g^-1 after 120 cycles at room temperature. Additionally, it displays high discharge capacities over 90.0 mAh g^-1 with excellent cyclability over 100 cycles under -20 °C. Detailed characterization has confirmed that reducing Sn particle size and boosting external pressure are crucial for achieving good defluorination/fluorination behaviors in the Sn anode. These findings pave the way to designing ASSFIBs with high capacities and superior cyclability under different operating temperatures.