Regulating Electronic Structure and Confinement-Induced Site Densification in Defective MOF for Boosted Polysulfide Catalysis in Lithium-Sulfur Batteries.

Lithium-sulfur batteries are poised as next-generation energy storage systems but remain constrained by sluggish redox kinetics and severe polysulfide shuttling. The liquid-solid Li2S4-to-Li2S conversion governs the reaction rate, underscoring the importance of electrocatalysts in accelerating polysulfide conversion. Here, we report a defective ZIF-67 catalyst, designed through controlled ligand removal, to simultaneously regulate the electronic structure and induce confinement-driven active site densification. The partial removal of ligands exposed unsaturated Co sites, forming "enzyme-like catalytic pockets" to immobilize polysulfides. The remaining ligands surrounding the metal centers tuned the local electronic environment, optimizing intermediate stabilization and catalytic activity. This synergistic regulation enhanced polysulfide adsorption, reduced steric hindrance, and accelerated the critical Li2S deposition/dissolution processes. Consequently, the sulfur cathode incorporating defective ZIF-67 exhibited improved cycling stability, delivering a capacity fade rate of 0.11 % per cycle over 200 cycles at 5 C, and maintaining a fade rate of 0.075 % per cycle over 150 cycles at 1 C with a sulfur loading of 4 mg cm-2. Our findings highlight the pivotal role of defect engineering in tailoring both site density and electronic structure within MOFs, offering a rational strategy for boosting polysulfide catalysis and advancing the practical application of lithium-sulfur batteries.