A PF₆ ^- -Permselective Polymer Electrolyte with Anion Solvation Regulation Enabling Long-Cycle Dual-Ion Battery

Graphitic carbon that allows reversible anion (de)intercalation is a promising cathode material for cost-efficient and high-voltage dual-ion batteries (DIBs). However, one notorious but overlooked issue is the incomplete interfacial anion desolvation, which not only reduces the oxidative stability of electrolytes, but also results in solvent co-intercalation into graphite layers. Here, an "anion-permselective" polymer electrolyte with abundant cationic quaternary ammonium motif is developed to weaken the PF₆ ^- -solvent interaction and thus facilitates PF₆ ^- desolvation. This strategy significantly inhibits solvent co-intercalation as well as enhances the oxidation resistance of electrolyte, ensuring the structural integrity of graphite. As a result, the as-assembled graphite||Li cell achieves a superior cyclability with an average Coulombic efficiency of 99.0% (vs 95.7% for baseline electrolyte) and 87.1% capacity retention after 2000 cycles even at a high cutoff potential of 5.4 V versus Li⁺ /Li. Besides, this polymer also forms a robust cathode electrolyte interface, working together to enable a long-life DIB. This strategy of tuning anion coordination environment provides a promising solution to regulate solvent co-intercalation chemistry for DIBs.