Chemo‑Electrochemical Tandem Catalysis Unlocking Sulfur Reaction in Practical Lithium-Sulfur Batteries

As next-generation high-energy batteries, lithium-sulfur (Li-S) batteries are promising solutions for long-range electric vehicles due to their ultrahigh theoretical energy density. However, they face fundamental challenges from low sulfur utilization, particularly under electrolyte-starved practical conditions that polysulfides are unable to dissolve. Here, we propose a chemo-electrochemical tandem catalyst, Li_xTiS₂, which chemically catalyzes the transformation of S₈/Li₂S₈ to Li₂S₄ and subsequently catalyzes electrochemical reduction to lithium sulfide (Li₂S). This tandem mechanism fundamentally alters the reaction kinetics from conventional first-order to zero-order behavior, overcoming the limitation imposed by the solubility of sulfur species. It thus enables efficient sulfur conversion and an ultralow activation energy of ∼0.3 eV (a 50% reduction compared to without catalysts) under a low electrolyte-to-sulfur (E/S) ratio (5 µL mg_s ^-1), significantly improving battery performance in practical conditions. The coin cell shows an ultralow capacity decay of 0.028% per cycle over 1500 cycles, and a 2.0 Ah pouch cell achieves the high energy density of 550 Wh kg^-1 with good stability.