Plasma-Induced Surface Fluorination of Metal Foils as Reliable Reference Electrodes for Fluoride-Ion Batteries

Fluoride-ion batteries (FIBs) are promising for next-generation energy storage, but their fundamental studies are limited by the rareness of stable and reproducible reference electrodes, unlike the case of lithium, sodium, and zinc chemistry, where their metal anodes can be directly leveraged as the reference electrode. Here, we report a binder-free strategy to fabricate integrated Pb/PbF₂ electrodes via CF₄ plasma-assisted fluorination of metallic Pb foils. By tuning the plasma power, temperature, and treatment time, the phase composition, morphology, and fluorination degree of resultant electrodes can be effectively controlled. The evolution mechanism between α-phase and β-phase lead(II) fluorides is established, governed by the plasma energy input and surface thermodynamics. Our proposed plasma fluorination strategy is also demonstrated to be versatile in obtaining Sn/SnF₂ electrodes with good structural integrity and tunable fluorination level. This approach avoids binder-related issues in conventional slurry-casting electrodes and provides a reliable pathway for developing reliable reference electrodes in FIB systems.