High Active Magnesium Trifluoromethanesulfonate-Based Electrolytes for Magnesium-Sulfur Batteries

The shortage of high-performance and easily prepared electrolyte has hindered the progress of rechargeable magnesium-sulfur (Mg-S) batteries. In this paper, we develop a new electrolyte based on Mg(CF₃SO₃)₂-AlCl₃ dissolved in tetrahydrofuran and tetraglyme mixed solvents. Mg(SO₃CF₃)₂ as an Mg²⁺ source is nonnucleophilic, easy to handle, and much cheaper than Mg(TFSI)₂ (TFSI = bis(trifluoromethanesulfonyl)imide). After modification with anthracene (π stabilizing agent) as a coordinating ligand to stabilize the Mg²⁺ ions and MgCl₂ to improve the interface properties by accelerating the reaction of Mg(CF₃SO₃)₂ with AlCl₃, the electrolyte exhibits a low overpotential for overall Mg deposition and dissolution, moderate anodic stability (3.25 V on Pt, 2.5 V on SS, 2.0 V on Cu, and 1.85 V on Al, respectively), and a suitable ionic conductivity (1.88 mS cm^-1). More importantly, this electrolyte modulated by Li-salt additives exhibits good compatibility with S cathode and can be applicable for Mg-S batteries. The rational formulation of the new electrolyte could provide a new avenue for simply prepared Mg electrolytes of Mg-S and rechargeable magnesium batteries.