Highly Crystalline Prussian Blue for Kinetics Enhanced Potassium Storage

Abstract Prussian blue analogs (PBAs) are promising cathode materials for potassium‐ion batteries (KIBs) owing to their large open framework structure. As the K + migration rate and storage sites rely highly on the periodic lattice arrangement, it is rather important to guarantee the high crystallinity of PBAs. Herein, highly crystalline K 2 Fe[Fe(CN) 6 ] (KFeHCF‐E) is synthesized by coprecipitation, adopting the ethylenediaminetetraacetic acid dipotassium salt as a chelating agent. As a result, an excellent rate capability and ultra‐long lifespan (5000 cycles at 100 mA g −1 with 61.3% capacity maintenance) are achieved when tested in KIBs. The highest K + migration rate of 10 −9 cm 2 s −1 in the bulk phase is determined by the galvanostatic intermittent titration technique. Remarkably, the robust lattice structure and reversible solid‐phase K + storage mechanism of KFeHCF‐E are proved by in situ XRD. This work offers a simple crystallinity optimization method for developing high‐performance PBAs cathode materials in advanced KIBs.