Architecting Amorphous Vanadium Oxide/MXene Nanohybrid via Tunable Anodic Oxidation for High-Performance Sodium-Ion Batteries

Structural engineering and creating atomic disorder in electrodes are promising strategies for highly efficient and rapid charge storage in advanced batteries. Herein, a nanohybrid architecture is presented with amorphous vanadium oxide conformally coated on layered V₂C MXene (a-VO_x/V₂C) via tunable anodic oxidation, which exhibits a high reversible capacity of 307 mAh g^–1 at 50 mA g^–1, decent rate capability with capacity up to 96 mAh g^–1 at 2000 mA g^–1, and good cycling stability as a cathode for sodium-ion batteries. The a-VO_x layer enables reversible and fast Na⁺ insertion/extraction by providing sufficient vacancies and open pathways in the amorphous framework, unlike the irreversible phase transition in its crystalline counterpart, while layered V₂C MXene offers abundant electron/ion transfer channels, which are joined together to boost the electrochemical performance. Notably the improved reversibility and structural superiority of the a-VO_x/V₂C nanohybrid are clearly revealed by in situ Raman, in situ transmission electron microscopy, in situ synchrotron X-ray absorption spectroscopy, and density functional theory calculations, demonstrating a reversible V–O vibration and valence oscillation between V⁴⁺ and V⁵⁺ in the disordered framework, with robust structural stability and unobstructed Na⁺ diffusion. This work provides a meaningful reference for the elaborate design of MXene-based nanostructured electrodes toward advanced rechargeable batteries.