Pressure Tuning and Sn Particle Size Optimization for Enhanced Performance in PbSnF4-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 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.
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