Dual‐Halide Electrode–Electrolyte Interphase for High‐Voltage Potassium‐Ion Batteries

Abstract In potassium‐ion batteries (PIBs), the electrode–electrolyte interphase (EEI) formed in conventional electrolytes often suffers from uneven thickness, poor compactness, and severe dissolution, which fails to provide long‐term protection for electrodes, leading to rapid capacity decay and reduced cycling durability. To address these issues, this work proposes a chlorine (Cl)‐substitution strategy for ether‐based electrolytes, promoting the formation of a dual‐halide EEI (enriched with KCl and KF), which significantly enhances the dissolution resistance of the interphase. Furthermore, the strong electron‐withdrawing effect of the –Cl functional group effectively lowers the highest occupied molecular orbital (HOMO) energy level of the solvent molecules, thereby broadening the electrochemical oxidation stability window of the electrolyte. Benefiting from the robust and stable dual‐halide EEI, the Prussian blue (PB) cathode exhibits exceptional cycling stability (over 2500 cycles at 4.5 V), and the graphite anode achieves an average Coulombic efficiency of up to 99.63%. Meanwhile, the PB||graphite full cell achieves a high energy density of ≈380 Wh kg −1 (based on the mass of PB cathode) and remarkable cycling stability under high‐voltage operation. This work provides new insights into the rational design of dissolution‐resistant EEI and advanced high‐voltage PIBs.