Dynamic Defect‐Healing Electrolyte Enabling 220000‐Cycle Life for Aqueous Potassium‐Ion Batteries

ABSTRACT Aqueous potassium‐ion batteries (AKIBs) offer a sustainable solution for grid‐scale energy storage. Yet, the structural dissolution of metal hexacyanoferrates (MHCFs) in aqueous electrolytes remains a critical bottleneck limiting cycle life. Herein, we report a dynamic defect‐healing electrolyte by coupling a high‐entropy MHCF (HE‐HCF‐80) cathode with a Fe 3+ ‐functionalized ethylene glycol (EG)‐based modified electrolyte (ME), redefining electrolytes as active repair reservoirs rather than passive ionic conductors. This electrolyte strategy leverages ethylene glycol to disrupt the hydrogen‐bonding network of water, effectively suppressing free‐water activity. Concurrently, the Fe 3+ additive serves as a dynamic cation reservoir, enabling in situ healing of lattice vacancies and mitigating Jahn–Teller distortions during cycling. Consequently, the system delivers ≥135 mAh g − 1 at 2000 mA g − 1 , retaining 98.97% of its capacity over 48000 cycles and achieving an ultralong lifespan of up to 220000 cycles at 10000 mA g − 1 . Additionally, the electrolyte confers reduced flammability and retains fluidity at low temperatures. This versatile strategy is readily applicable to commercial Prussian blue, which exhibits 84.75% capacity retention after 35000 cycles. It enables a full cell to deliver 96.14% retention over 100000 cycles, providing a scalable blueprint for inherently safe, grid‐scale energy storage where extreme cycle life is paramount.