Simultaneous Modification of Al/F Cosubstitution to Construct a Solid Framework for NaV(PO) with High Thermal Stability and Near-Zero Strain Performance.

Challenges related to poor electronic conductivity and cycling stability have impeded the development and utilization of NaV(PO) (). Therefore, this study focuses on enhancing the performance of by employing a sol-gel method to design various gradients of F/Al-doped and carbon nanotube (CNT)-enwrapped materials. The introduction of F doping replacing PO tetrahedra reduces the occupied space, while F monomers can establish stronger bonds with VO octahedral pillars closer to O atoms. Additionally, Al doping introduces a new AlO octahedral structure at the V site, strengthening the 3D framework. The synergistic substitution of F and Al contributes to improving the stability of the framework, which enhances the Na migration channels and overall electrochemical performance. Furthermore, the coating of CNTs plays a crucial role in creating a favorable interface transition layer that facilitates efficient electron transport and enhances electronic conductivity. Comprehensively, the modified FAl-2 exhibits a high capacity of 115.8 mA h g at 0.1C. It reveals 89.3 mA h g at 60C and maintains 83.8 mA h g after 2000 cycles, indicating a capacity retention rate of 93.84%. Electrochemical ex situ X-ray diffraction (XRD) demonstrates that FAl-2 behaves at relatively low values (0.328%-1.075%) of volume shrinkage during the whole charge/discharge process, indicating its near-zero strain property. The postcycled XRD and X-ray photoelectron spectroscopy further verify the significantly enhanced crystal structural stability of FAl-2. Moreover, FAl-2 possesses a higher thermal runaway temperature, indicating a superior thermal stability. The self-releasing heat trend observed in FAl-2 can offer valuable insights into the design of battery management systems.