Effect of Electrolytic Properties of a Magnesium Organohaloaluminate Electrolyte on Magnesium Deposition

Complex magnesium organohaloaluminate electrolytes were studied by electrochemical transport measurements and in-situ electrochemical/X-ray absorption spectroscopy. Cyclic voltammetry was employed to examine the reversibility of electrochemical magnesium deposition. To better understand the role of this electrolyte system, ionic transport properties such as transference number, ionic conductivity, and diffusion coefficient of Mg-ion species were measured at different concentrations. Transference number was determined by atomic absorption spectroscopy by quantifying the amount of potentiometric Mg deposition on Pt electrode. Despite exhibiting 100% Coulombic efficiency for Mg deposition and dissolution, the electrolyte showed low ionic conductivity and transference number at moderate and higher concentrations. To further investigate the observed transport properties, electrochemical deposition of magnesium from [Mg2(μ-Cl)3·6(OC4H8)]+ was monitored with in-situ/in-operando X-ray absorption spectroscopy of the Mg K-edge. Extended X-ray absorption fine structure (EXAFS) analysis revealed the presence of a nondimeric and interfacial Mg intermediate at potentials below Mg plating. From a combination of the electrochemical transport results and in-situ/in-operando X-ray absorption measurements, a mechanism for Mg deposition in organohaloaluminate electrolyte is proposed.