Anion vacancy engineering in carbon coating VS₄ microspheres assembled by nanorod arrays for high-performance rechargeable Mg-Li hybrid batteries

Transition metal sulfides (TMSs) stand out as promising cathodes for rechargeable Mg-Li hybrid ion batteries (MLIBs) owing to their high theoretical capacity and rich redox chemistry. Nevertheless, it still faces great challenges involving the sluggish reaction kinetics and insufficient active sites, resulting in unsatisfactory stability and limited rate capability. And the role of anion vacancies on improving electrochemical properties of TMSs is still unclear. Herein, we have successfully designed an anion defect engineering strategy for the construction of carbon coating VS₄ microspheres assembled by nanorod arrays (S_v-VS₄@C-300) as the high-performance cathode for MLIBs. The systematic electrochemical tests together with theoretical calculations reveal that the sulfur vacancies simultaneously improve ion adsorption ability, facilitate charge transfer rate and boost reaction kinetics. Additionally, the open microsphere structure together with rich sulfur vacancies cooperatively provide more active sites and release the internal stress during cycling, thereby realizing the enhancement of capacity and structural stability. Consequently, these features enable S_v-VS₄@C-300 with impressively high reversible capacity (485.1 mAh/g at 50 mA g⁻¹) and exceptional long cycle lifespan (128.3 mAh/g at 2000 mA g⁻¹ after 5000 cycles). This work implements an innovative strategy represented by anion vacancy engineering in the design of high-performance TMSs-based cathodes for rechargeable batteries.