Synthesis, Crystal Structure, and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)6][AlCl4]2 was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm−1). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface. Simple but effective: A simple magnesium salt [Mg(THF)6][AlCl4]2 can be used as a magnesium electrolyte that possesses a highly reversible Mg cycling efficiency, good anodic stability, and good ionic conductivity. Mg/S batteries containing the electrolyte could be cycled over 20 cycles, thus indicating electrochemically reversible conversion of sulfur into MgS.