Potassium Nickel Hexacyanoferrate as a High-Performance Cathode: Structural Enhancements via Potassium Ferrocyanide in AAIBs

Potassium nickel hexacyanoferrate (KNHCF) has emerged as a promising cathode material for aqueous aluminum-ion batteries (AAIBs) due to its tunable structural and electrochemical properties. In this study, a variant of K₄[Fe(CN)₆] [KNHCF (K4)] as compared to the pristine K₃[Fe(CN)₆] [KNHCF (K3)], is used. Structural characterization revealed that KNHCF (K4) possesses a denser crystal structure, a smaller particle size, a higher nickel content (closer to the theoretical formula), and fewer structural defects than KNHCF (K3). These attributes facilitate efficient ion transport, improved intercalation kinetics, and enhanced cycling stability. Electrochemical tests demonstrated that KNHCF (K4) achieved a discharge plateau at approximately 1.3 V with a specific capacity of ∼120 mAh/g, retained over 100 mAh/g after 450 cycles, and maintained superior rate capability, with ∼95 mAh/g at a current density of 0.5 A/g. The findings underscore the critical role of structural optimization in enhancing the performance of PBAs for energy storage applications, highlighting the potential of the KNHCF (K4) label as a high-performance cathode material for next-generation rechargeable batteries.