Synergistic control of nucleation and crystallinity in Prussian blue cathodes for enhanced sodium-ion batteries

Abstract Prussian blue (PB) and its analogues are promising cathode materials for sodium-ion batteries due to their open framework and favorable ion transport properties. However, their electrochemical performance is often limited by structural defects, poor crystallinity, and unstable cycling behavior. In this study, a synergistic strategy combining polyvinylpyrrolidone (PVP), sodium citrate (NC), and low-temperature synthesis is employed to regulate nucleation kinetics and crystallinity of PB particles. PB samples were synthesized via a co-precipitation method by varying sodium citrate content (0–7.35 g) and synthesis temperature (25 °C and 0 °C). The optimized sample, prepared with 7.35 g NC at 0 °C (NPB-3), exhibits enhanced crystallinity and improved electrochemical performance. Increasing NC content at 25 °C improves reversible specific capacity from 81 to 97 mAh g⁻¹ at 1 C, while low-temperature synthesis further enhances capacity retention from 68 to 76 mAh g⁻¹ after 150 cycles. The improved performance is attributed to the chelating effect of sodium citrate, which slows nucleation and reduces structural defects, and the low-temperature condition, which promotes controlled crystal growth and structural stability. This synergistic control of nucleation and crystallinity mitigates lattice degradation during cycling and enhances Na⁺ storage performance. The findings provide a simple and scalable approach for improving PB-based cathodes, contributing to the development of cost-effective and durable sodium-ion batteries.