Tailoring Covalent Organic Frameworks as Functionalized Molecular Traps to Enable Sulfur Conversion and Li ⁺ Desolvation for Durable Lithium–Sulfur Batteries

ABSTRACT

Suppressing polysulfid shuttling and enhancing Li ⁺ desolvation kinetics are crucial for high‐performance lithium–sulfur (Li─S) batteries. Herein, we propose an elaborate molecular trap design strategy based on functional‐group decoupling and synergistic enhancement in covalent organic frameworks (COFs) to resolve the aforementioned issues. A cyano‐containing COF (CN‐COF) and its amidoxime derivative (COF‐AO) serve as cooperative dual‐sided separator coatings. CN‐COF contributes a well‐ordered porous structure for confining sulfur species; its C≡N sites interact with polysulfides to reduce the reaction energy barrier of sulfur conversion. On the anode side, ─NH ₂ /─OH groups in COF‐AO promote Li ⁺ desolvation and modulate Li ⁺ transport by capturing solvent molecules via hydrogen bonding, which suppresses parasitic reactions and ensures rapid Li ⁺ migration. Besides, the regular topological structure and size‐exclusion effect of COF restrict migration of large‐sized solvent molecules and polysulfides, enabling homogeneous Li ⁺ flux and smooth Li deposition. Benefiting from these advantages, Li||Li symmetrical cells achieve stable cycling for 7000 h at 5 mA cm ⁻² /5 mAh cm ⁻² . The Li─S battery delivers an initial capacity of 820 mAh g ⁻¹ with an ultralow decay rate of 0.024% per cycle over 900 cycles at 5 C.The pouch cell exhibits a high initial capacity of 1020 mAh g ⁻¹ at 0.2 C and stable operation for 150 cycles.