Active Macromolecular Network Reconstruction of Electrolytes for High-Voltage Aqueous Potassium-Ion Batteries

Abstract Aqueous potassium-ion batteries (AKIBs) are promising for grid-scale energy storage owing to their intrinsic safety and low cost, but their practical application is limited by the narrow electrochemical stability window of water and interfacial water decomposition. Here we report a hydroxyl-terminated poly(ethylene glycol) (PEG)-based electrolyte that achieves a 3.6 V electrochemical stability window when combined with 2 M potassium trifluoromethanesulfonate. The hydroxyl-terminated PEG matrix simultaneously coordinates K+ through its ether oxygen atoms and modulates water via terminal hydroxyl groups, thereby reconstructing the polymer–water hydrogen-bond network. This synergistic interaction disrupts the bulk water structure, suppresses the incorporation of free water into the primary K+ solvation sheath, and consequently reshapes the local solvation environment. The electrolyte decreases the first-shell water coordination number to below 0.5 and increases the contact ion-pair fraction to 65%. Full cells employing a potassium iron manganese hexacyanoferrate cathode and a perylene-3,4,9,10-tetracarboxylic diimide anode deliver 72 mA h g–1 at 4C, retain 62.5% capacity after 2500 cycles, and sustain 45 mA h g–1 at 10C. This work establishes active macromolecular-network restructuring as an effective strategy for designing high-voltage aqueous electrolytes.