Nitrile-functionalized covalent organic framework aerogels: dual-role components for high-performance lithium-sulfur batteries

Lithium-sulfur batteries have garnered substantial attention in the energy field owing to the remarkably high theoretical capacity of sulfur. Nevertheless, several inherent drawbacks, including the poor electrical conductivity of sulfur, its significant volumetric expansion during cycling, and the notorious shuttling effect caused by the dissolution of lithium polysulfides, have severely restricted their widespread practical application. In this research endeavor, nitrile-functionalized covalent organic framework (COF-CN) aerogels and their corresponding functionalized polypropylene separators were successfully synthesized and applied to lithium-sulfur batteries. The Boc protection synthesis strategy played a pivotal role in the preparation of COF-CN aerogels. These aerogels demonstrated remarkable ability to efficiently load sulfur while still maintaining their characteristic porous structure. Electrochemical tests further revealed that the lithium-sulfur battery equipped with the COF-CN modified separator exhibited distinct advantages over the unmodified version in terms of rate performance (595 mA h g^–1 at 2.0 C) and cycling stability (656 mA h g^–1 after 200 cycles at 0.5 C). This enhanced performance can be mainly attributed to the strong interaction between the nitrile functional groups present in the COF-CN aerogels and the polysulfides, which effectively suppressed the polysulfide shuttling effect.