Sodium-Rich Prussian Blue Analogs Synthesized with Reducing Sodium Salt for Enhanced Rate and Cycling Stability Sodium-Ion Storage

Prussian blue analogs (PBAs) as cathode material for sodium-ion batteries have attracted widespread attention due to their affordability, simple synthesis, and high theoretical capacity. Nevertheless, the oxidation of Fe²⁺ and sodium loss lead to poor electrochemical properties which restrict the practical use of PBAs. Herein, a simple coprecipitation approach based on sodium salt-reduction-assisted synthesis was proposed to construct high-sodium PBAs. The sodium bisulfite (NaHSO₃) not only effectively inhibits the oxidation of Fe²⁺ but also increases the mole ratio of Na⁺ in the resulting products. The optimized sample exhibits excellent specific capacity (131.1 mAh g^-1 at 0.1C), high rate performance (103.9 mAh g^-1 at 10C), and good cyclic performance (94.8% capacity retention after 200 cycles). Experimental results reveal that the sample synthesized with sodium bisulfite possesses improved sodium-ion diffusion kinetics and stable crystal structure. In this study, a scalable method is introduced for the synthesis of PBAs with excellent electrochemical properties and further applications.