3D Interconnected\nPorous Sodium Super Ionic Conductor-Structured\nNa<sub>4</sub>Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(P<sub>2</sub>O<sub>7</sub>)/C as a Cathode Material fo

Na<sub>4</sub>Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>P<sub>2</sub>O<sub>7</sub> (NFPP), with a high theoretical specific\ncapacity of\n129 mAh g<sup>–1</sup>, is regarded as a promising cathode\nmaterial for sodium-ion batteries. However, its practical application\nin sodium-ion batteries is severely constrained by its intrinsic low\nelectronic conductivity and the presence of NaFePO<sub>4</sub> impurities.\nIn this study, a sol–gel method combined with solid-state calcination\nis successfully employed to synthesize NFPP/C, a sodium super ionic\nconductor, with a three-dimensional interconnected porous structure.\nThe NFPP/C material exhibits a uniform surface carbon coating and\na continuous mesoporous structure. After annealing at 550 °C\nfor 10 h, NFPP/C demonstrates excellent electrochemical performance,\nincluding a high discharge capacity of 104.6 mAh g<sup>–1</sup> at 0.1 C, superior long-term cycling stability (79.3% capacity retention\nafter 2000 cycles at 10 C), and outstanding rate capability (71.4\nmAh g<sup>–1</sup> at 20 C). This method provides a universal\nsynthesis strategy for high-performance phosphate cathode materials\nwith three-dimensional interconnected porous architectures for sodium-ion\nbatteries.