Ion‐Exchange Synthesis of Low‐Water Prussian Blue Analogs for Enhanced Sodium Storage

ABSTRACT Iron hexacyanoferrate (FeHCF) is a promising cathode material for sodium‐ion batteries (SIBs) due to its high theoretical capacity and low cost. Nevertheless, water in FeHCF is likely to take up Na + sites leading to the reductions in capacity and rate capability. Herein, an ion‐exchange method is proposed to synthesize low‐water potassium‐sodium mixed iron hexacyanoferrate (KNaFeHCF). The ion‐exchange method can preserve the lattice structure with low vacancies and K + with larger ionic radii can reduce the water content in FeHCF and improve Na + reaction kinetics. Compared with the NaFeHCF synthesized by co‐precipitation method, the water content of optimal sample KNaFeHCF‐12 h can be decreased by 21.2%. The sample exhibits excellent electrochemical performance, with a discharge capacity of 130.33 at 0.1 and 99.49 mAh g −1 at 30 C. With a full‐cell configuration with a hard carbon anode, the discharge capacity reaches 115.3 mAh g −1 at 0.1 C. This study demonstrates a viable method for producing Prussian blue cathode materials with low water content, high specific capacity, and exceptional cycling stability. image