A Key concept in Magnesium Secondary Battery Electrolytes.

A critical roadblock toward practical Mg-based energy storage technologies is the lack of reversible electrolytes that are safe and electrochemically stable. Here, we report on high-performance electrolytes based on 1-ethyl-3-methylimidazolium chloride (EMImCl) doped with AlCl3 and highly amorphous δ-MgCl2 . The phase diagram of the electrolytes reveals the presence of four thermal transitions that strongly depend on salt content. High-level density functional theory (DFT)-based electronic structure calculations substantiate the structural and vibrational assignment of the coordination complexes. A 3D chloride-concatenated dynamic network model accounts for the outstanding redox behaviour and the electric and magnetic properties, providing insight into the conduction mechanism of the electrolytes. Mg anode cells assembled using the electrolytes were cyclically discharged at a high rate (35 mA g(-1) ), exhibiting an initial capacity of 80 mA h g(-1) and a steady-state voltage of 2.3 V.