Functionalized Hydrated Eutectic‐Like Electrolyte Boosting Interfacial Compatibility for Ultra‐Stable Aqueous Potassium‐Ion Batteries

Aqueous potassium‐ion batteries (AKIBs) are promising for low‐cost and safe energy storage yet hindered by the narrow electrochemical stability window (ESW) of aqueous electrolytes and severe electrode destabilization. Herein, a high‐performance AKIBs is successfully established by combining rational electrolyte design with electrode optimization. We engineered an optimized hydrated eutectic‐like electrolyte (HEE132) that restructures the K + solvation sheath using acetamide and acetate anions, expanding its electrochemical stability window to 2.36 V while suppressing electrode dissolution. By incorporating Fe/Co co‐coordination at the low‐spin sites, a dual‐metal Prussian blue cathode (D‐MFC) with enhanced structural stability and redox activity is coupled with a PTCDI organic anode for efficient K + storage. The resulting PTCDI//D‐MFC full batteries within HEE132 electrolyte achieve superior electrochemical performance including stable voltage output, outstanding rate capability maintaining 83.6 mAh g −1 at high current density of 2.0 A g −1 , and exceptional cycling stability with 95.1% capacity retention over 1000 cycles. The demonstrated electrolyte‐dominated regulation approach provides an effective strategy for developing practical aqueous potassium‐ion batteries toward large‐scale energy storage applications.