In Situ Zn‐Doped Prussian Blue Analogues as High‐Rate Cathodes for Wide‐Temperature Sodium‐Ion Batteries

Despite progress in sodium‐ion batteries, developing cathodes with high stability and performance under harsh conditions remains a critical challenge. Herein, a sustainable in‐situ Zn substitution method to partially replace Fe in sodium iron hexacyanoferrate (FeHCF) using ZnO as the precursor under acidic media. The resulting Zn‐FeHCF‐2 exhibits a lower amount of coordinated water (∼10.75%), effectively alleviating lattice strain during repeated Na + insertion/extraction. As a result, the material delivers highly reversible electrochemical behavior with minimal volume variation according to in‐situ XRD. Structural analyses reveal uniform cubic particles with high crystallinity, contributing to mechanical stability and improved charge‐transfer kinetics. Electrochemically, the cathode achieves a specific capacity of ∼158.98 mAh g −1 at 0.1 C and maintains excellent rate capability up to 50 C. Moreover, a full cell assembled with Zn‐FeHCF‐2||hard carbon anode retains 96.5% of its initial capacity (88.34mAh g −1 ) after 6000 cycles at −20°C. Additionally, density functional theory (DFT) calculations indicate that zinc incorporation lowers the energy barriers for sodium‐ion diffusion, thereby facilitating faster reaction kinetics.