Sol-gel-driven nanoscale molecular reconstruction for the conversion of FePO4 into high-performance Na4Fe3(PO4)2P2O7 cathodes

The sol-gel method is a promising route for synthesizing Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) electrodes, owing to its mild reaction conditions, precise compositional control, and high product homogeneity. However, conventional approaches typically rely on soluble nitrate or sulfate precursors to achieve uniform elemental distribution, leading to the release of toxic nitrogen and sulfur oxides during calcination. In this context, a novel sol-gel-driven molecular reconstruction coupled with thermally induced structural transformation is first proposed for the controllable conversion of insoluble FePO 4 clusters into high-performance NFPP/C cathode materials. Alkaline etching-induced crystal weakening and the coordination effect of complexing agents synergistically promote the reconfiguration of crystalline FePO 4 agglomerates into an amorphous structure and simultaneously achieve homogeneous dispersion of all components at the nanoscale. In the subsequent pyrolysis, a Maricite-NaFePO 4 -mediated structural evolution was evidenced by advanced in-situ characterization techniques. The optimized 1.37-NFPP/C electrode demonstrates remarkable electrochemical performance, delivering an exceptional reversible capacity of 105.42 mAh g −1 at 0.1C, retaining 85.75% of its capacity at a high rate of 15.0C relative to 0.2C, and maintaining 95.76% of its initial capacity after 1000 cycles at 3.0C. This study presents a novel synthetic method for the scalable and precisely controlled fabrication of high-performance NFPP/C electrode materials and provides a new strategy for tailoring the structure of polyanionic compounds, paving the way for the development of next-generation sodium-ion batteries.