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

Abstract

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 Mg 2+ transport. The optimized TU content (0.05–0.2 g) added to 1.5 g of Mg(NO 3 ) 2 ·6H 2 O 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.