Lewis Acid-Base Synergistically Enhancing Practical Composite Electrolyte for Fluoride-ion Batteries at Room Temperature.

Fluoride-ion batteries (FIBs) represent a potential "next-generation" electrochemical storage device, offering high energy density. However, the practical implementation of FIBs at room temperature is impeded by the limitations of currently available ceramic electrolytes. Here, a composite NH(4)HF(2)@PEO@β-PbSnF(4) electrolyte with both high conductivity of 10(-4) S cm(-1) and wide electrochemical stability window (4.59 V vs Pb/PbF(2)) at room temperature is fabricated. Field emission transmission electron microscope (FETEM) demonstrates the presence of a space charge region, which enhances the conductivity. Furthermore, (19)F NMR and density functional theory (DFT) calculations elucidate that the interaction between Sn(2+) (Lewis acid) and HF(2) (-) (Lewis base) induces significant modifications to the electronic structure, which critically contribute to the enhanced electrochemical stability window of the composite electrolyte. Integrating this promising electrolyte with high-voltage CuF(2) cathodes and Pb/PbF(2) anodes, a reversible coin cell with a discharge capacity of 143 mAh g(-1) up to 50 cycles is demonstrated. The rational design of such composite electrolytes offers a pathway toward the practical application of FIBs at room temperature.