Rechargeable magnesium batteries (RMBs) have emerged as a promising next-generation electrochemical energy storage technology due to their superiority of low price and high safety. However, the practical applications of RMBs are severely limited by immature electrode materials. Especially, the high-rate cathode materials are highly desired. Herein, we propose a dual-functional design of V₂O₅ electrode with rational honeycomb-like structure and rich oxygen vacancies to enhance the kinetics synergistically. The result demonstrates that oxygen vacancies can not only boost the intrinsic electronic conductivity of V₂O₅, but also enhance the Mg²⁺ diffusion kinetics inside the cathode, leading to the good high-rate performance. Moreover, ex-situ X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) characterizations reveal that Mg²⁺ is mainly intercalated from the (101) plane of V₂O_5−X based on the insertion-type electrochemical mechanism; meanwhile, the highly reversible structure evolution during Mg²⁺ insertion/extraction is also verified. This work proposes that the dual-functional design of electrode has a great influence in enhancing the electrochemical performance of cathode materials for RMBs.

The rechargeable magnesium batteries (RMBs) are getting more and more attention because of their high-energy density, high-security and low-cost. Nevertheless, the high charge density of Mg²⁺ makes the diffusion of Mg²⁺ in the conventional cathodes very slow, resulting in a lack of appropriate electrode materials for RMBs. In this work, we enlarge the layer spacing of V₂O₅ by introducing Na⁺ in the crystal structure to promote the diffusion kinetics of Mg²⁺. The NaV₆O₁₅ (NVO) synthesized by a facile method is studied as a cathode material for RMBs with the anhydrous pure Mg²⁺ electrolyte. As a result, the NVO not only exhibits high discharge capacity (119.2 mAh·g^-1 after 100 cycles at the current density of 20 mA·g^-1) and working voltage (above 1.6 V vs. Mg²⁺/Mg), but also expresses good rate capability. Besides, the ex-situ characterizations results reveal that the Mg²⁺ storage mechanism in NVO is based on the intercalation and de-intercalation. The density functional theory (DFT) calculation results further indicate that Mg²⁺ tends to occupy the semi-occupied sites of Na⁺ in the NVO. Moreover, the galvanostatic intermittent titration technique (GITT) demonstrates that NVO electrode has the fast diffusion kinetics of Mg²⁺ during discharge process ranging from 7.55 × 10^-13 to 2.41 × 10^-11 cm²·s^-1. Our work proves that the NVO is a potential cathode material for RMBs.