High‐Entropy Prussian Blue Analogs via a Solid‐Solution Storage Mechanism for Long Cycle Sodium‐Ion Batteries Cathodes

The open‐framework characteristics of Prussian blue analogs (PBAs) have been recognized as advantages for cathode application in Sodium‐ion batteries (SIBs). Nevertheless, lattice distortions during charge‐discharge cycles critically compromise their cyclability. Recent advancements in high‐entropy design strategies have significantly improved structural stability and energy storage efficiency within functional materials. In this study, we developed the high‐entropy PBAs, K1.68Mn0.21Cu0.20Ni0.20Co0.19Fe0.20[Fe(CN)6]0.87□0.13·0.66H2O, via a cost‐effective aqueous coprecipitation protocol. Notably, this approach facilitates the concurrent incorporation of five transition metals (Mn, Cu, Ni, Co, and Fe), thereby establishing a stable crystalline framework. Electrochemical characterization demonstrates that the cathode achieves a specific capacity of 124.9 mAh g−1 at 0.025 A g−1. At various current densities (0.025‐1 A g−1), the cathode maintains a particular capacity retention of 62.1% during rate testing. Furthermore, the cathode exhibits exceptional cyclability, preserving 78.7% capacity at 1 A g−1 after 3000 cycles. Operando X‐ray diffraction (XRD) analysis confirms the formation of a reversible solid‐solution intercalation/extraction mechanism process, which prevents phase transitions and enhances cyclability. This high‐entropy material holds significant potential as a cathode for SIBs, offering high specific capacity and outstanding long‐term cycling stability. These superior properties position it as a competitive candidate for advanced energy storage systems.