Recrystallization-Driven Quasi-Spherical Prussian Blue Analogs with High Tap Density and Crystallinity for Sodium-Ion Batteries

Abstract

Prussian blue analogs (PBAs) are widely applicable as cathode materials due to their straightforward synthesis procedures, low cost, and considerable theoretical capacity. However, structural defects and low tap density pose substantial challenges to their commercial application. Herein, we propose a recrystallization-driven strategy to synthesize monoclinic binary hexacyanoferrate (CFHCF) with high crystallinity and a remarkably high tap density of 0.992 g cm^–3. Moreover, the detailed process of quasi-spherical morphology evolution and defect repair is systematically investigated during recrystallization. Furthermore, various in situ and ex situ techniques are employed to reveal the origin of the high specific capacity and the structural evolution mechanism. Additionally, the designed CFHCF//HC pouch cell demonstrates satisfactory capacity retention over 250 cycles and successfully powers a toy platform for flag raising and lowering. Notably, this recrystallization-driven strategy offers valuable insights into the synthesis and commercial applications of highly crystallized PBAs.