In Situ Sulfurized Carbon-Confined Cobalt for Long-Life Mg/S Batteries

Magnesium (Mg) batteries have attracted growing attention because of their low cost and high volumetric capacity. Mg/S batteries are of particular interest because of the high capacities of Mg and sulfur, which cooperatively enable high energy densities. However, the shuttling polysulfides during the S0/S2– conversion impair the cathode stability and corrode the Mg anode. This work reports the in situ sulfurization of carbon-confined cobalt in a mesoporous matrix (MesoCo@C) through sulfur melt impregnation and its effectiveness in uplifting the cathode stability and alleviating the Mg anode corrosion (i.e., formation of magnesium sulfides/sulfates). The CoSx species play important roles in binding with polysulfides and regulating the notorious polysulfide shuttle. Both the carbon matrix and the preserved cobalt are excellent electron conductors and allow fast charge transfer to the CoSx species, which become the active sites that facilitate the interaction with magnesium polysulfides and improve the cathode kinetics. These combined effects collectively give rise to the stable capacity of 280 mAh/g at 0.2 C (1 C = 1675 mA/g) for at least 400 cycles.