Highly Reversible and Stable Sulfur‐Containing Cathodes for Magnesium Batteries with Two‐Plateau Redox Reactions Enabled by Kinetically Favored Mg─S Decomposition

Abstract Rechargeable magnesium sulfur batteries (MSBs) face issues like polysulfide shuttling, sluggish redox kinetics, and high cost, leading to dissatisfied practical demonstrations. Herein, simple battery configurations utilizing 100% sulfur are proposed on nine collectors and a low‐cost phenolate‐based magnesium complex (PMC) electrolyte to address these problems. Comprehensive studies indicate that the Cu collector is the most conducive to improving battery performance, not only facilitating the generation of magnesium sulfides during discharging but also effectively dissociating Mg─S bonds during charging. Moreover, Cu surfaces can effectively adsorb magnesium polysulfides (MgSx) and induce an insulator‐to‐metal transition of MgS, leading to a more effective suppression of the shuttle effect and the transfer of electrons. MXene interlayers are further introduced between electrodes to inhibit MgSx shuttling and enhance the interfacial electronic conductivity, as reflected by the reinforced high discharge voltage plateau at ≈1.7 V and stable long discharge voltage plateau at ≈1.2 V. The assembled MSBs exhibit the highest reported capacity of 1260 mAh g−1S and an energy density of 1230 Wh kg−1S with a cycle life of over 1000 cycles. This research contributes to the fundamental understanding of rechargeable MSBs and marks a significant advancement in optimizing cell designs for better performance.