The study explores the use of Prussian blue analogues (PBAs) as cathode materials in lithium-ion batteries, addressing the challenges of slow kinetics and valence state inactivation in organic and aqueous electrolytes. The researchers developed a polymeric cathode electrolyte interphase (CEI) layer through a ring-opening reaction of ethylene carbonate triggered by OH− radicals from structural water. This approach significantly improves the electrochemical kinetics and stability of iron hexacyanoferrate (FeHCFe), achieving a specific capacity of 125 mAh g−1 with over 500 cycles. The CEI layer enhances structural integrity, activates Fe low-spin states, and prevents water and hydronium ions from penetrating the structure, preserving active sites and improving the activation of Fe2+. The study demonstrates the potential of PBAs as viable, durable, and efficient cathode materials for commercial use in lithium-ion batteries.The study explores the use of Prussian blue analogues (PBAs) as cathode materials in lithium-ion batteries, addressing the challenges of slow kinetics and valence state inactivation in organic and aqueous electrolytes. The researchers developed a polymeric cathode electrolyte interphase (CEI) layer through a ring-opening reaction of ethylene carbonate triggered by OH− radicals from structural water. This approach significantly improves the electrochemical kinetics and stability of iron hexacyanoferrate (FeHCFe), achieving a specific capacity of 125 mAh g−1 with over 500 cycles. The CEI layer enhances structural integrity, activates Fe low-spin states, and prevents water and hydronium ions from penetrating the structure, preserving active sites and improving the activation of Fe2+. The study demonstrates the potential of PBAs as viable, durable, and efficient cathode materials for commercial use in lithium-ion batteries.