Conditioning–Free Electrolytes for Magnesium Batteries Using Sulfone–Ether Mixtures with Increased Thermal Stability

2018-05-16T14:14:59Z (GMT) by Laura C. Merrill Jennifer Schaefer
We report an investigation of electrochemical properties and speciation of electrolytes composed of magnesium bis(hexamethyldisilazide) (Mg(HMDS)<sub>2</sub>) and magnesium chloride in sulfone-ether mixtures. The inclusion of sulfones dramatically increased the thermal stability of the electrolytes to 80 °C. The addition of ether was necessary to form an electrochemically active species. Electrochemical reversibility was maintained above 90% for 50 cycles for equivolume mixtures of butyl sulfone and THF. Sulfolane based solutions demonstrated low reversibilities and mass spectrometry measurements showed the preferential formation of an MgCl<sup>+</sup> cation over the Mg<sub>2</sub>Cl<sub>3</sub><sup>+</sup> cation. Greater amounts of Mg<sub>2</sub>Cl<sub>3</sub><sup>+</sup> compared to MgCl<sup>+</sup> is linked with higher performing electrolytes. Spectroscopic measurements showed co-solvation of the active magnesium cation with both solvents.