Regulating Interfacial Kinetics of Mg Metal Anode by Introducing Thiourea Additives to Halogen-Free Electrolyte

Regulating interfacial kinetics at the Mg metal anode is crucial to advancing the performance of magnesium-sulfur (Mg-S) batteries. In this study, we present a novel strategy by introducing thiourea (TU) additives to a halogen-free electrolyte (HFE), aiming to stabilize the Mg-electrolyte interface and enhance Mg²⁺ transport. The optimized TU content (0.05-0.2 g) added to 1.5 g of Mg(NO₃)₂·6H₂O improves ion mobility, increases the transference number to 0.81, and enhances ionic conductivity. Coin cells assembled with TU-modified electrolytes exhibit an initial discharge capacity of 880 mAh g^-1 and more stable electrochemical behavior over the early cycles, along with reduced polysulfide diffusion compared to that of the pristine system. Comprehensive characterizations (X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS)) confirm that the TU additive facilitates the formation of a more uniform and stable interfacial layer on the Mg anode surface. These findings demonstrate that interfacial kinetics can be effectively regulated through simple electrolyte engineering, offering a promising route to enhance the electrochemical performance of Mg-S batteries.