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, K_1.68 Mn_0.21 Cu_0.20 Ni_0.20 Co_0.19 Fe_0.20[Fe(CN)₆]_0.87□_0.13·0.66H₂O, via a cost-effective aqueous co-precipitation method. 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.