Efficient Magnesium Plating and Stripping in DOL/DME-Mg(HMDS)2-Based Electrolytes and Application in Mg/S Batteries

We discuss here various combinations of magnesium bis (hexamethyldisilazide) (Mg(HMDS)2) with aluminum chloride (AlCl3) or magnesium chloride (MgCl2) in a solvent mixture of 1,3-dioxalane (DOL) and 1,2-dimethoxyethane (DME) (DOL/DME) as alternative electrolytes for practical rechargeable Mg–sulfur batteries. This design strategy is contrary to the usage of the solvents tetraglyme and tetrahydrofuran (THF) commonly used with Mg(HMDS)2 to generate electrolyte formulations for Mg/S batteries. Cyclic voltammetry measurements reveal a higher current response for DOL/DME compared to tetraglyme and THF solvent-based electrolytes. Exemplary plating/stripping efficiency is obtained at room temperature and is observed to be strongly dependent on the salt concentrations. The remarkable stripping/plating reversibility (at a current density of 0.1 mA cm–2) in a Mg||Mg symmetric cell indicates the extraordinary compatibility of the electrolyte with the Mg anode. The plating of Mg on the gold working electrode is ascertained using X-ray diffraction and scanning electron microscopy. The versatility of the Mg(HMDS)2-based electrolyte in the DOL/DME solvent is further utilized in a Mg/S cell with a simple carbon nanotube–sulfur composite as the cathode and Mg-metal as the anode. The DOL/DME-Mg(HMDS)2 electrolyte-based Mg/S cell exhibited stable electrochemical performance over widely varying current densities ranging from 0.05 to 0.5 C.