Pressure Tuning and Sn Particle Size Optimization for Enhanced Performance in PbSnF4‐Based All‐Solid‐State Fluoride Ion Batteries

Abstract 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 4 solid electrolytes in different phases ( β ‐ and γ ‐PbSnF 4 ) are successfully synthesized and characterized. The ASSFIBs composed of β ‐PbSnF 4 electrolytes, a BiF 3 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 3 / β ‐PbSnF 4 /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.