Synergistic Coating‐Replenishment Engineering Stabilizes Prussian Blue Analogues Cathodes for Long‐Life Aqueous K‐Ion Batteries

Abstract Prussian blue analogues (PBAs), particularly potassium iron hexacyanoferrate (KFeHCF), have emerged as promising cathodes for aqueous K‐ion batteries (AKIBs). However, their practical application is hindered by the issues of Fe dissolution during electrochemical cycling and the newly identified K loss during synthesis, which jointly accelerate structural degradation. Here, a synergistic strategy combining PEDOT:PSS encapsulation with KCl‐mediated potassium replenishment is proposed, simultaneously suppressing Fe dissolution and mitigating water intrusion through surface coating and bulk‐phase stabilization. The optimized cathode delivers 124 mAh g −1 with 85.3% capacity retention after 200 cycles at 0.2 A g −1 , nearly tripling the performance of uncoated counterparts. Paired with a PTCDI anode in 30 mol kg −1 KFSI electrolyte, the full cell shows excellent capacity (121 mAh g −1 ) and remarkable durability, retaining 80.3% capacity after 2000 cycles at 4 C. This work not only resolves the long‐neglected K loss issue in PBAs cathodes but also establishes a universal paradigm of defect‐compensated surface engineering for next‐generation aqueous batteries.