Unveiling Aqueous Potassium‐Ion Batteries with Prussian Blue Analogue Cathodes

Abstract Aqueous rechargeable potassium‐ion batteries have considerable advantages and potentials in the application of large‐scale energy storage systems, owing to its high safety, abundant potassium resources, and environmental friendliness. However, the practical applications are fraught with numerous challenges. Identification of suitable cathode materials and potassium storage mechanisms are of great significance. Herein, an aqueous potassium‐ion battery comprising Prussian blue analogs cathode (K 1.15 Fe[Fe(CN) 6 ]·1.36H 2 O) and perylene‐3,4,9,10‐tetracarboxylic anode is designed, which delivers a high energy density of 52.0 Wh kg −1 and excellent cycling stability with high capacity retention of 84.5% after 4000 cycles. Importantly, a synergistic study of the relationships among crystal structure, spin state, kinetics, and electrochemical performances is thoroughly conducted. By employing in situ and ex situ characterizations, the potassium storage mechanism is comprehensively elucidated from multiple perspectives.