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

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.