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

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, PbSnF solid electrolytes in different phases (β- and γ-PbSnF) are successfully synthesized and characterized. The ASSFIBs composed of β-PbSnF electrolytes, a BiF 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 BiF/β-PbSnF/Sn battery. The optimized battery delivers a high initial discharge capacity of 181.3 mAh g at 8 mA g and can be reversibly cycled at 40 mA g with a high discharge capacity of over 100.0 mAh g after 120 cycles at room temperature. Additionally, it displays high discharge capacities over 90.0 mAh g 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.