Mg, Al, Cl, and F Walk into a Coin-Cell… Electrolyte Solutions and Strategies for Rechargeable Magnesium-ion Batteries

Abstract

Effective grid-level collection of renewable resources such as wind or solar will require energy storage systems with high capacity, affordable, and safe battery electrochemistries. Research into novel battery technologies may ultimately prove rewarding in the ability to successfully combat both the variable availability of energy resources as well as the variable geographic and temporal demand for power. Magnesium-ion batteries (MIBs) offer a high volumetric energy density, and could supplement existing technologies. To this end, a series of magnesium dialkoxides were synthesized and characterized for use in magnesium ion electrolytes. We found a series of compounds that display considerably improved characteristics compared to previously investigated dialkoxides on the basis of Coulombic efficiency, anodic stability limit, conductivity, and solubility. Electrolyte performance is dependent on various electrolyte properties such as Lewis acid concentration, solvent environment, electrolytic conditioning, and ligand electrochemical characteristics. The electrodeposited magnesium from these systems was analyzed for both morphology and purity. Magnesium dialkoxides are extremely promising candidates for magnesium-ion technologies. Indeed, as proof of principle, the compounds investigated were shown to be compatible with a Mo6S8 cathode in a functioning MIB. The easy manipulation of these dialkoxide precursor compounds, compared to commonly investigated Grignard reagents, is a practical benefit. Our improved understanding of ligand and environment modification and their effects on the resulting electrochemistry is integral for the development of novel magnesium-ion electrolytes. The strategies employed in this work to increase the electrochemical properties of these electrolytes could prove useful in the improvement of other classes of magnesium electrolytes. The development of a highly efficient electrolyte system for the creation of an environmentally friendly and affordable MIB could revolutionize the applications of large-capacity rechargeable energy storage.