Synergistic\nEffect of Carbon Encapsulation and Iron\nDoping Based on Metal–Organic Framework Precursor Enhances\nNaVPO<sub>4</sub>F Electrochemical Performance for Sodium-Ion Batteries

Sodium fluorovanadium phosphate (NaVPO<sub>4</sub>F) has long been\nrecognized as a promising cathode material for sodium-ion batteries.\nHowever, its low conductivity has limited its practical application\ndue to its poor rate performance and long-term stability. The study\nintroduces a method to enhance the electrochemical performance of\nNaVPO<sub>4</sub>F by using the metal–organic framework (MOF)\nas a precursor. This method involves the incorporation of Fe-doping\nand MOF-derived carbon encapsulation. The synthesized NaV<sub>0.94</sub>Fe<sub>0.06</sub>PO<sub>4</sub>F/MC samples (NVPF-Fe/MC) exhibit\nextraordinary qualities as cathode material for sodium-ion batteries:\na high capability (123.1 mAh/g at 1C), outstanding ultralong cyclability\n(remaining 83.0% of its capacity even after 1000 cycles at a high\ncycling rate of 5 C), and significantly improved rate performance.\nThe NVPF-Fe/MC||HC full cell also exhibits excellent reversible capacity\n(retaining 87.7% sodium storage capacity after 100 cycles). The mesoporous\ncarbon nanonetwork shortens the ion-electron diffusion pathway, promoting\nionic-electronic conductivity and reaction kinetics. Additionally,\nFe<sup>3+</sup> doping increases the cell volume to enlarge the diffusion\nchannel, while activating part of the V<sup>5+</sup>/V<sup>4+</sup> (4.0 V vs Na<sup>+</sup>/Na) due to the induced effect of Fe<sup>3+</sup>, thereby improving the specific capacity and cycling stability.