Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic...

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li-S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li-S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal-organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S₈ →Li₂ S₄ , while the missing cluster defects can catalyze the reaction of Li₂ S₄ →Li₂ S, so as to effectively inhibit the shuttle effect. Hence, the Li-S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g^-1 delivers a capacity of 1087 mAh g^-1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm^-2 and E/S=3.9 mL g^-1 , an areal capacity of 10.4 mAh cm^-2 for 45 cycles can still be obtained.