Solvating magnesium polysulfides enables low–barrier speciation for magnesium sulfur batteries

Magnesium–sulfur batteries offer high theoretical energy density but suffer from low sulfur utilization and rapid capacity fading. This work identifies the strong Mg2+–polysulfide Coulombic interaction as responsible for sluggish kinetics. We demonstrate that the solvation of magnesium polysulfides fundamentally governs their behavior, relaxing Mg2+–polysulfide coupling to facilitate polysulfide speciation and conversion kinetics. Our findings reveal that solvation with high shielding ability effectively modifies the binding configuration of magnesium polysulfides, which lowers the energy barrier for their stepwise conversion, thus improving reaction reversibility. Furthermore, under solvation modulation, magnesium sulfide deposition exhibits a three-dimensional nucleation morphology, providing more active sites for redox. Consequently, the developed cells achieve the equilibrium potential ~1.1 V (vs. Mg/Mg2+) and extended cycle life (0.1 C over 120 cycles,1 C (60 min) = 1675 mA g-1), with pouch cells showing high discharge capacity (940.80 mAh g−1 in the 1st cycle; > 600 mAh g-1 after 18 cycles). Magnesium–sulfur batteries promise high energy density but face slow kinetics. Here, authors tailor electrolyte solvation to weaken magnesium-polysulfide binding, enabling improved cycling both coin and pouch cells.