Simultaneous Modification\nof Al<sup>3+</sup>/F<sup>–</sup> Cosubstitution to Construct\na Solid Framework for\nNa<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> with High\

Challenges related to poor electronic conductivity and\ncycling\nstability have impeded the development and utilization of Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> (<i>NVP</i>).\nTherefore, this study focuses on enhancing the performance of <i>NVP</i> by employing a sol–gel method to design various\ngradients of F/Al-doped and carbon nanotube (CNT)-enwrapped <i>NVP</i> materials. The introduction of F doping replacing PO<sub>4</sub> tetrahedra reduces the occupied space, while F monomers can\nestablish stronger bonds with VO<sub>6</sub> octahedral pillars closer\nto O atoms. Additionally, Al doping introduces a new AlO<sub>6</sub> octahedral structure at the V site, strengthening the 3D framework.\nThe synergistic substitution of F and Al contributes to improving\nthe stability of the framework, which enhances the Na<sup>+</sup> migration\nchannels and overall electrochemical performance. Furthermore, the\ncoating of CNTs plays a crucial role in creating a favorable interface\ntransition layer that facilitates efficient electron transport and\nenhances electronic conductivity. Comprehensively, the modified FAl-2\nexhibits a high capacity of 115.8 mA h g<sup>–1</sup> at 0.1C.\nIt reveals 89.3 mA h g<sup>–1</sup> at 60C and maintains 83.8\nmA h g<sup>–1</sup> after 2000 cycles, indicating a capacity\nretention rate of 93.84%. Electrochemical ex situ X-ray diffraction\n(XRD) demonstrates that FAl-2 behaves at relatively low values (0.328%–1.075%)\nof volume shrinkage during the whole charge/discharge process, indicating\nits near-zero strain property. The postcycled XRD and X-ray photoelectron\nspectroscopy further verify the significantly enhanced crystal structural\nstability of FAl-2. Moreover, FAl-2 possesses a higher thermal runaway\ntemperature, indicating a superior thermal stability. The self-releasing\nheat trend observed in FAl-2 can offer valuable insights into the\ndesign of battery management systems.