Trimming the π bridge of microporous frameworks for bidentate anchoring of polysulfides to stabilize lithium-sulfur batteries

Microporous frameworks with pi-conjugated blocks and tunable electronic structures present enormous potential as energy-storage materials. However, the role of the pi-bridge and structure-activity relationship have not been explored in lithium-sulfur (Li-S) batteries. Here, we report a pi bridge trimming strategy for a semiconducting microporous framework (SMF) with tunable molecular polarity in redox-enhanced and dendrite-free Li-S batteries. The results demonstrate that the pi bridge of SMFs plays an important role in polysulfide anchoring and anion immobilization, including the binding energy, charge transfer, redox kinetics, and cyclability, which can be finely regulated by molecular engineering. As a result, SMF-2 with a thiophene bridge achieves bidentate anchoring of lithium polysulfides, which delivers an ultralow capacity-fading rate of 0.033% per cycle for 1000 cycles at 1C and stable Li plating/stripping performance for 300 h. Our work may shed light on the molecular design of pi-conjugated materials for advanced Li-S batteries.