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.