Fe-doped VS_y (y = 2 or 4) for magnesium energy storage: improved conductivity, stability, and electrochemical performance

High-performance magnesium (Mg) batteries require advanced electrode materials with improved conductivity, stability, and ion transport. In this study, iron (Fe)-doped vanadium disulfide (VSy@Fe) is synthesized via a one-step in-situ hydrothermal method with 5 at% Fe incorporation. Fe doping reduces the bandgap from 1.85 eV to 1.42 eV, enhances electrical conductivity by ~ 35%, and modifies the layered structure, promoting efficient Mg²⁺ diffusion. VSy@Fe delivers an initial discharge capacity of 210 mAh g⁻¹ at 50 mA g⁻¹, compared to 145 mAh g⁻¹ for pristine VSy, and retains 82% capacity after 100 cycles. Cyclic voltammetry and electrochemical impedance spectroscopy reveal a decrease in charge transfer resistance from 78 Ω (VSy) to 32 Ω (VSy@Fe), confirming improved kinetics. Thermal stability is enhanced, with a 20 °C increase in decomposition temperature. In halogen-free electrolytes, VSy@Fe shows superior initial capacity retention, although prolonged cycling indicates partial ion transport limitations, suggesting further optimization is required. These findings highlight VSy@Fe as a promising cathode material for next-generation Mg-ion batteries with improved performance and stability.