Highly Efficient Non-Nucleophilic Mg(CF3SO3)2-Based Electrolyte for High-Power Mg/S Battery

The application of high-energy Mg/S batteries was obstructed by the insufficiency of low-cost and non-nucleophilic electrolyte. In this work, a non-nucleophilic electrolyte was prepared by facilely dissolving Mg(CF3SO3)2, MgCl2, and AlCl3 in 1,2-dimethoxyethane (DME). The equilibrium species of the MTB electrolyte mainly comprise [Mg2(μ-Cl)2(DME)4]2+ and [(CF3SO3)AlCl3]-, which are generated by dehalodimerization reaction and Lewis acid-base reaction, respectively. The electrolyte exhibits a highly efficient reversible Mg deposition/dissolution, low overpotential of around 250 mV, and good oxidative stability up to 3.5 V after conditioning. The conditioning process that the active [Mg2(μ-Cl)2(DME)4]2+ species transforms into [Mg3(μ3-Cl)(μ2-Cl)2(DME)7]3+ was demonstrated, owing to the irreversible deposition of Al3+ on Mg foil. More importantly, this electrolyte exhibited good compatibility and kinetics for reversible Mg/MgSx redox, resulting in a high specific capacity of 866 mAh g-1 at 200 mA g-1 and high power density of 550 W kg-1. This work offers a new direction for low-cost, non-nucleophilic electrolyte and paves the way to explore high-power Mg/S batteries.