Acid-etched iron-based Prussian blue derivatives as high-performance cathode materials for sodium-ion batteries

Iron-based Prussian blue (Fe-PB) materials have been widely investigated as cathode materials for sodium-ion batteries owing to their unique open framework structure. However, the enhancement of electrical conductivity and the reduction of structural defects in Prussian blue analogues remain challenging. In this study, hollow layered Fe-PB materials with gradually inward-etched centers were successfully synthesized through a phthalic acid (PA)-assisted chelation and etching process. Compared to conventionally hydrothermally synthesized materials, the prepared Fe-PB was characterized by an increased specific surface area, shortened sodium-ion diffusion pathways, and reduced lattice water content, leading to significantly improved electrochemical properties. When evaluated as a cathode material for sodium-ion batteries, the etched Fe-PB demonstrated an initial specific capacity of 106.4 mAh g⁻¹ at a current density of 100 mA g⁻¹. After 500 charge/discharge cycles, a specific capacity of 78.8 mAh g⁻¹ was maintained, corresponding to a capacity retention rate of 74.1 % and a remarkably low capacity decay rate of 0.05 % per cycle. This work not only provides an effective strategy for improving the sodium storage performance of Fe-PB materials but also offers valuable insights into the hydrothermal synthesis of high-performance Prussian blue analogues with reduced lattice water content and enhanced electrochemical properties.