Covalent Organic Frameworks for Separator Modification of Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries are regarded as one of the promising energy storage systems. However, rapid capacity attenuation caused by shuttle effect of soluble polysulfides is major challenge in practical application. The separator modification is regarded as one countermeasure besides the construction of sulfur host materials. Covalent organic frameworks (COFs) are one type of outstanding candidates for suppressing shuttle effect of polysulfides. Herein, recent advances of COFs in the application as commercial separator modifiers are summarized. COFs serve as ionic sieves, the importance of porous size and surface environments in inhibiting soluble polysulfides shuttling and promoting lithium ions conduction is highlighted. The superiority of charge-neutral COFs, ionic COFs, and the composites of COFs with conductive materials for improving reversible capacity and cycling stability is demonstrated. Some new strategies for the design of COF-based separator modifiers are proposed to achieving high energy density. The review provides new perspectives for future development of high-performance Li-S batteries.