Hollow Stair-Stepping Spherical High-Entropy Prussian Blue Analogue for High-Rate Sodium Ion Batteries

Prussian blue analogues (PBAs) are considered to be one of the most suitable sodium storage materials, especially with the introduction of the high-entropy (HE) concept into their structure to further improve their various abilities. However, severe agglomeration of the HEPBA particles still limits the fast charging capabilities. Here, an HEPBA (Na_x(FeMnCoNiCu)[Fe(CN)₆]_y□_1-y·nH₂O) with a hollow stair-stepping spherical structure has been prepared through the chemical etching process of the traditional cubic structure of HEPBA. Electrochemical characterization (sodium ion battery), kinetic analysis, and COMSOL Multiphysics simulations reveal that the nature of the high-entropy and the hollow stair-stepping spherical structure can greatly improve the diffusion behavior of Na⁺ ions. Moreover, the hollow structure effectively mitigates the volume change of HEPBA during SIBs operation, ultimately extending the lifespan. Consequently, the as-prepared HEPBA cathode exhibits excellent rate performance (126.5 and 76.4 mAh g^-1 at 0.1 and 4.0 A g^-1, respectively) and stable long-term capability (maintaining its 75.6% capacity after 1000 cycles) due to its unique structure. Furthermore, the waste of the etching process can easily be recycled to prepare more HEPBA product. This processing method holds great promise for designing nanostructures of advanced high-entropy Prussian blue analogues for sodium ion batteries.