Azo-Bridged Metal–Organic Frameworks with Robust Zr ₆ -Cluster Nodes: A Dual-Functional Design for Suppressing Polysulfide Shuttling in Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation energy storage devices because of their ultrahigh theoretical energy density, low cost, and environmental friendliness. However, their practical application is hindered by the shuttle effect of intermediate polysulfides and the sluggish redox kinetics of sulfur cathodes. Herein, we designed and synthesized a 3D metal-organic framework (MOF) by integrating azo-functionalized ligands with Lewis acidic zirconium (Zr)-oxo clusters (namely, Zr-MTAC) and utilized it as a cathode host material for high-performance Li-S batteries. Systematic experimental analysis and density functional theory calculations confirmed that the introduced azo groups possess highly efficient chemical adsorption ability for polysulfides and can serve as electron transport channels to accelerate the redox kinetics of sulfur cathodes. Benefiting from the synergistic effect of azo groups and Zr-oxo clusters, Zr-MTAC promotes the catalytic conversion of polysulfides, enhancing the sulfur utilization and cycling performance of Li-S batteries. Consequently, the composite sulfur cathodes based on Zr-MTAC exhibit superior cycling reversibility, exceptional cycling stability (∼700 mAh g^-1 remaining capacity after 1000 cycles), and improved rate capability. This work highlights the enormous potential of azo-functionalized MOF materials in developing energy storage devices, providing a practical and feasible solution for high-performance Li-S batteries.