Reversible S0/MgSx Redox Chemistry in MgTFSI2-MgCl2 Electrolyte for Rechargeable Mg/S Battery

Magnesium redox chemistries are attracting growing attentions for rechargeable Mg batteries due to the unique benefits of Mg metal electrode: high reversibility without dendrite, low reduction potential and high specific capacity. Mg/S couple is of particular interest due to its high energy density (1700 Wh/kg and 3200 Wh/L) and low cost. Previous reports have justified the feasibility of a rechargeable Mg/S battery; however, only limited cycling stability was achieved, and the complicated preparation procedure of the electrolytes have significantly compromised the benefits of Mg/S chemistry, and hindered the development of Mg/S battery. Herein, we report the first rechargeable Mg/S battery using MgTFSI2-MgCl2-DME electrolyte and demonstrate the best cycling stability among all reported Mg/S batteries by suppressing polysulfide dissolution. Mechanistic study shows the battery works via S0/MgSx redox and the large voltage hysteresis mainly origins from Mg anode overpotential.