Unraveling the intricacies of surface salt formation on Mg(0001): Implications for chloride-ion batteries

We present a density functional theory study of the initial steps of chlorine deposition on the Mg(0001) surface. Such processes occur in chloride-ion batteries in which lithium and magnesium are used as anode materials. In addition, it is also of fundamental interest, as halide adsorption on metal electrodes is an important process in interfacial electrochemistry. We discuss the adsorption properties and determine the stable adsorption structures, both with respect to the free chlorine molecule but also as a function of the electrode potential. We find indications of the immediate formation of the ${\mathrm{MgCl}}_2$ surface salt structure upon exposure of Cl to a Mg surface. These findings are discussed with respect to the conversion of the Mg anode to a ${\mathrm{MgCl}}_2$ configuration which provides the thermodynamical driving force for the discharge of a Cl-ion battery.