Performance enhancement of rechargeable magnesium–sulfur batteries based on a sulfurized poly(acrylonitrile) composite and a lithium salt

Research on magnesium-sulfur (Mg–S) batteries has gained great attention due to the high theoretical gravimetric and volumetric energy densities (1700 Wh kg−1 and 3200 Wh L−1), as well as because of their economic, ecologic and safety advantages. In this study, we present room-temperature Mg–S batteries with a sulfurized poly(acrylonitrile) composite (SPAN) cathode and a Mg2+/Li+ hybrid electrolyte (magnesium trifluoromethanesulfonate, (CF3SO3)2Mg), lithium trifluoromethanesulfonate, MgCl2 and AlCl3 in 1,2-dimethoxyethane (DME)). These cells deliver high discharge capacities and energy densities of 1100 mAh gs−1 and 700 Wh kgs−1 at 1 C, respectively, with >99.9% Coulombic efficiency. Electrochemical and kinetic measurements as well as post-mortem analysis revealed that utilization of SPAN and a lithium salt in the electrolyte is crucial and beneficial for the prevention of the polysulfide shuttle. It also dramatically reduces the cell resistance and the overpotential via the formation of MgLiSx species. Concomitantly, this system supports the formation of a solid electrolyte interface (SEI) layer, which greatly improves the reaction kinetics of the Mg2+ ions and the cycle performance.