Synergistic engineering of oxygen-doping and sulfur vacancies on VS₂ microflower enables reversible multielectron redox reaction for high-performance Mg-based hybrid batteries

Vanadium-based materials with multiple valence states are considered as promising cathodes for rechargeable Mg-Li hybrid ion batteries (MLIBs) on account of their high theoretical capacity and unique crystal structure. Nevertheless, it still faces great challenges involving sluggish reaction kinetics and limited redox couples, resulting in unsatisfactory cycle stability and inadequate energy density. Herein, a synergistic engineering strategy of O-doping and sulfur vacancies is rationally designed for the construction of hierarchical VS₂ microflower (denoted as S_v-VS₂-O), serving as a high-performance cathode for MLIBs. The multielectron redox reactions triggered by the multiple valence states of V endow the S_v-VS₂-O with enhanced redox voltage, delivering great superiority in reversible capacity (292.6 mAh g⁻¹ at 50 mA g⁻¹) and energy density (323.9 Wh kg⁻¹). Systematic theoretical calculations together with electrochemical results reveal that the synergistic benefits of O-doping and sulfur vacancies simultaneously improve ion adsorption ability, facilitate rapid charge transfer, and lower ion migration barrier, thereby achieving the optimization of reaction reversibility and kinetics. Additionally, the buffering effect of microflower structure with sufficient space on volume changes promotes cycling stability. Consequently, these features ensure the S_v-VS₂-O cathode with exceptional long cycle lifespan (98.6 % capacity retention after 2000 cycles at 2000 mA g⁻¹). To verify practical applicability, the assembled pouch-type cell maintains a relatively good cycling stability for 120 cycles. This work highlights the importance of an appealing synergistic strategy of doping and vacancy engineering for achieving multielectron redox reactions of advanced cathodes for metal-ions batteries.