Synthesis of Low-Defect Iron-Based Prussian Blue with Low Water Content for High-Stability Sodium-Ion Batteries

This study proposes an innovative two-step synthesis strategy to significantly enhance the performance of sodium-ion batteries by developing low-defect, low-water-content iron-based Prussian blue (PB) materials. Addressing the limitations of traditional co-precipitation methods—such as rapid reaction rates leading to excessive crystal defects and interstitial water content—the research team introduced a synergistic approach combining non-aqueous phase precursor synthesis and controlled water-concentration secondary crystallization. The process involves preparing a PB precursor in a glycerol system, followed by secondary crystallization in a water/ethanol mixed solvent with precisely regulated water content, achieving dual objectives of water-content reduction and crystal morphology optimization. Systematic characterization revealed that water concentration during secondary synthesis critically influences the materials crystal structure, morphological features, and water content. The optimized PB50-24 material exhibited a highly regular cubic morphology with a sodium content of 9.2% and a remarkably low interstitial water content of 2.1%. Electrochemical tests demonstrated outstanding performance: an initial charge-discharge capacity of 120 mAh g⁻¹ at 1C rate, retention of 105 mAh g⁻¹ after 100 cycles, and a high-rate capability of 86 mAh g⁻¹ at 10C, representing significant improvements in cycling stability and rate performance over conventional methods. This work not only establishes a cost-effective, scalable synthesis pathway for Prussian blue materials but also provides theoretical guidance for developing other metal-based Prussian blue analogs, offering substantial value for advancing the industrial application of sodium-ion batteries in next-generation energy storage systems.