Ionic liquid-based electrolytes are encountering a great interest for the development of alkali metal (Li, Na, Mg, …) batteries. The use of magnesium metal as a negative electrode is of particular interest in post-lithium batteries as it has higher theoretical volumetric capacities and is more abundant in the earth’s crust than lithium. The first prototype system for a magnesium rechargeable battery included electrolytes based on magnesium organohaloaluminate salts, such as Mg(AlCl₃R)₂ and Mg(AlCl₂RR′)₂, in organic solvents such as tetrahydrofuran and glymes.¹ These systems are based on the combination of a Lewis acid and Lewis base, to produce salts with active Mg species that promote facile and reversible Mg deposition. Recent advances include the development of so-called non-nucleophilic salts, which are less corrosive than the original strongly nucleophilic versions.² However, these electrolytes are not stable in air and water, thus still present safety risks. Electrolytes containing air and water stable salts, e.g. Mg(TFSI)₂, have significant advantages not only in terms of safety, but also in terms of chemical and electrochemical stability. Incorporating air and water stable salts into ionic liquids can result in electrolytes which, unlike those containing organic solvents, have low volatility and flammability.

Understanding Mg²⁺ solvation in ILs is one key step in the development of stable electrolyte systems which promote facile Mg²⁺ desolvation at the electrode surface. In this study, the intermolecular interactions between Mg²⁺ ands the IL anions and the impact of these interactions on the physical properties are examined. Furthermore, the transport mechanism of the Mg²⁺ in ionic liquid electrolytes is explored.

References

1.         Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature 2000, 407, 724-727.

2.         Zhao-Karger, Z.; Zhao, X.; Wang, D.; Diemant, T.; Behm, R. J.; Fichtner, M. Adv. Energy Mater. 2015, 5, 1401155.