SnF2-Assisted Interface Engineering for High-Performance All-Solid-State Fluoride-Ion Batteries.

All-solid-state fluoride-ion batteries (ASSFIBs) offer compelling advantages in energydensity and safety, but their practical application is hindered by poor interfacial stability andsluggish fluoride-ion kinetics, particularly at the anode. Herein, we report an interfaceengineering strategy, specifically incorporating SnF2 into a Sn-based composite anode, thatsignificantly enhances the performance and durability of ASSFIBs with a β-PbSnF4 solidelectrolyte and a BiF3 cathode. The introduction of SnF2 pre-constructs internal Sn/SnF2interfaces, which facilitate ion diffusion, mitigate volume changes, and promote morereversible fluorination/defluorination reactions. As a result, the SnSnF2 composite anodeendows ASSFIBs with higher capacity, improved rate performance, and superior cyclingstability compared to a pristine Sn composite anode. The ASSFIB with a SnSnF2composite anode operates stably for 60 cycles at room temperature with a capacity retentionof nearly 100%. Furthermore, the temperature-dependent performance of ASSFIBs with aSnSnF2 anode (–20 °C to 60 °C) is investigated. Combined analyses using distribution ofrelaxation times, stack pressure measurements, and morphological characterization revealthat while elevated temperatures boost initial capacity via enhanced kinetics, they alsotrigger interfacial porosity and mechanical degradation, leading to accelerated capacityfading. In contrast, operation at low temperatures preserves solid–solid contact andinterfacial integrity, enabling stable cycling. This work demonstrates a highly effectiveinterface engineering approach to enhance the electrochemical performance of ASSFIBsand provides deep insight into their thermomechanical failure mechanisms.