Long‐Durable Potassium Ion Batteries Enabled by Medium‐Entropy Lattice Engineering on Prussian Blue Analogues Cathodes

Abstract Given their structural merits and electrochemical benefits, Prussian blue analogues (PBAs) hold great promise as cathode materials for potassium ion batteries (PIBs). However, these cathodes face formidable hurdles by structural failure and poor rate capability, primarily resulting from significant volumetric changes and sluggish kinetics during repeated intercalation/deintercalation of bulky K + ions. Theoretically, the study reveals explicitly that quaternary medium‐entropy PBAs (Q‐ME‐PBAs), composed of Fe, Ni, Co, and Cu, demonstrate minimal lattice volume variations and low diffusion barriers during K + ion interactions. This endows Q‐ME‐PBA with favorable ability to induce significant 3D lattice distortion, enabling the material to endure structural alterations during K + ion movements and reinforce phase stability. Consequently, leveraging the structural and compositional advantages, the resultant Q‐ME‐PBAs cathode showcases exceptional cycling performance, maintaining over 90% capacity retention after 300 cycles at 0.25 C with a high initial coulombic efficiency of 94.4% and retaining 74.7% capacity even after an ultra‐long 10 000 cycles at 3.75 C over 147 days. Notably, full cells paired with hard carbon and graphite anodes show outstanding cycling stability and rate capability. This study charts fresh design directions for crafting high‐performance and durable cathodes through medium‐entropy lattice engineering for advanced PIBs.