The unexpected discovery of the Mg(HMDS)2/MgCl2 complex as a magnesium electrolyte for rechargeable magnesium batteries

Abstract

We developed a unique class of non-Grignard, aluminum-free magnesium electrolytes based on a simple mixture of magnesium compounds: magnesium hexamethyldisilazide (Mg(HMDS)₂) and magnesium chloride (MgCl₂). Through a reverse Schlenk equilibrium, a concentrated THF solution of Mg(HMDS)₂–4MgCl₂ was prepared to achieve reversible Mg deposition/dissolution, a wide electrochemical window, and a coulombic efficiency of 99%. High reversible capacities and good rate capabilities were obtained in Mg–Mo₆S₈ cells using these new electrolytes in tests with different rates. The unexpected high solubility of MgCl₂ in the solvent of THF with the help from Mg(HMDS)₂ provides a new way to develop magnesium electrolytes.