Synergistic Site Engineering in Trimetallic Spinel Sulfides for High-Loading Lithium-Sulfur Batteries

The performance of lithium-sulfur batteries is severely limited by polysulfide shuttling and sluggish redox kinetics, underscoring the need for efficient catalysts to mediate polysulfide adsorption and conversion. Achieving precise control over active sites and understanding their mechanistic roles are central to the rational design of efficient catalysts. In this work, we systematically unravel the distinct roles of octahedral and tetrahedral sites in spinel sulfides, establishing a dual-site cooperative mechanism governing polysulfide adsorption and conversion. X-ray absorption spectroscopy confirms engineered site-selective doping within spinel sulfides, enabling controlled occupation of octahedral and tetrahedral sites. Symmetric cells with tailored electrolyte systems, together with galvanostatic intermittent titration technique analysis, reveal that controlled site occupation enables stage-resolved differentiation of catalytic roles toward long- and short-chain polysulfides. Further theoretical calculations reveal that octahedral sites preferentially stabilize long-chain polysulfides through enhanced 3p orbital overlap with ligand sulfur, whereas tetrahedral sites facilitate short-chain polysulfide conversion by weakening terminal S-S bonds. Guided by these insights, we rationally design Fe-Co-Ni trimetallic spinel sulfides with tunable site distributions. The optimized cathode delivers an initial capacity of 1347.3 mAh g^-1 at 0.1 C and retains 81.6% capacity after 300 cycles at 0.2 C, even at a high sulfur loading of 7.5 mg cm^-2. These findings reveal a dual-site adsorption-conversion mechanism in spinel sulfides and provide design guidance for efficient lithium-sulfur catalysts.