One of the greatest challenges toward rechargeable magnesium batteries is the development of noncorrosive electrolyte solutions with high anodic stability that can support reversible Mg deposition/dissolution. In the last few years, magnesium electrolyte solutions based on Cl-free fluorinated alkoxyborates were investigated for Mg batteries due to their high anodic stability and ionic conductivity and the possibility of reversible deposition/dissolution in ethereal solvents. Here, the electrochemical performance of Mg[B(hexafluoroisopropanol)4]2/dimethoxyethane (Mg[B(HFIP)4]2/DME) solutions was examined. These electrolyte solutions require a special "conditioning" pretreatment that removes undesirable active moieties. Such a process was developed and explored, and basic scientific issues related to the mechanism by which it affects Mg deposition/dissolution were addressed. The chemical changes that occur during the conditioning process were examined. Mg[B(HFIP)4]2/DME solutions were found to enable reversible Mg deposition, albeit with a relatively low Coulombic efficiency of 95% during the first cycles. Prolonged deposition/dissolution cycling tests demonstrate a stable behavior of magnesium electrodes. Overall, this system presents a reasonable electrolyte solution and can serve as a basis for future efforts to develop chlorine-free alternatives for secondary magnesium batteries. It is clear that such a conditioning process is mandatory, as it removes reactive contaminants that lead to unavoidable passivation and deactivation of Mg electrodes from the solution.
Keywords: corrosion; electrochemical conditioning process; halogen-free electrolyte solutions; magnesium anodes; rechargeable magnesium batteries.