Ascorbic acid regulates the dissolution kinetics of Fe3(PO4)2 to prepare prussian blue cathodes for sodium-ion batteries

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Conventional co-precipitation synthesis of Fe-based Prussian Blue cathodes relies on controlled precursor feeding, chelating agents, sodium-compensating salts, and inert atmospheres to regulate crystallization and suppress defects. Here, a simplified one-pot strategy is developed in which ascorbic acid regulates ferrous phosphate (Fe 3 (PO 4 ) 2 ) dissolution and enables gradual Fe-ion release. Studies of reaction time and ascorbic acid dosage indicate that mild acidity, reducing conditions, and possible Fe-ascorbate coordination jointly moderate dissolution and the subsequent reaction with sodium ferrocyanide. This method produces Fe-based Prussian Blue with high sodium content, low vacancy concentration, and low water content, without slow precursor feeding, inert-atmosphere protection, or additional chelating and sodium-compensating agents. Thermally activated PBA-044 delivers an initial discharge capacity of 104.6 mAh g −1 at 0.2 C and retains 84.5 % of its capacity after 500 cycles at 5 C. Tests using various acidic media and iron-based precursors demonstrate the broader feasibility of dissolution-regulated synthesis, although product quality depends on acid strength, coordination ability, precursor solubility, and particle characteristics. This work provides a practical strategy for simplifying the synthesis of Fe-based Prussian Blue cathodes.