Heterojunction of Vanadium Oxide Nanobelts for Aqueous Magnesium-Ion Batteries

Aqueous magnesium-ion batteries (AMIBs) have garnered a lot of interest in future energy storage due to their high energy density, easy preparation, and excellent safety. Yet, the lack of a proper electrode material with high-capacity performance hinders its development. In this work, a facile heterojunction of VO2·xH2O@V2O5 (VOx) electrode with a nanobelt structure was synthesized by an electrochemical deposition process for AMIBs for the first time. The specific structure combines the advantages of layered V2O5 and tunnel-like VO2·xH2O, which shows excellent storage capacity and cycle stability. It shows high rate performances of 510 and 195.5 mAh g–1 at 0.05 and 5 A g–1, respectively, as well as a cycle performance of 100 mAh g–1 after 1000 cycles at 1 A g–1. Combining experimental characterization and theoretical calculations, we can show that the structured water in VOX can improve the conductivity and diffusion rate of Mg2+. The mechanism study reveals that VOX undergoes a cointercalation reaction of H+ and Mg2+ during the discharge process. This study not only highlights the role of structural water and heterogeneous design in enhancing Mg2+ diffusion in VOX materials but also offers a novel approach for preparing a high-performance AMIB system.