Supramolecular channels via crown ether functionalized covalent organic frameworks for boosting polysulfides conversion in Li−S batteries

Lithium−sulfur (Li−S) batteries are promising for next-generation high-energy-density systems. However, the sluggish sulfur conversion and shuttle of polysulfides severely restrict their commercial applications. Herein, a crown ether functionalized COF (BPTA-CE-COF) is in situ synthesized on the surface of carbon nanotubes (CNTs), which is called CE-COF@CNT, for modifying the separator in Li−S batteries. The CE-COF@CNT possesses high conductive property and abundant supramolecular channels formed by crown ether functional groups, which can catalytically accelerate diffusion/conversion of polysulfides and composition/decomposition of Li2S through the crown ether-Li+ interaction. It is further verified by density functional theory (DFT) calculations, X-ray photoelectron spectroscopy, and ex situ Fourier transform infrared analysis. Notably, the modified separator enables the Li−S cell with a high initial discharge capacity of 1618.1 mAh g−1 at 0.1 C, excellent rate performance, and good cyclic stability with an ultralow capacity decay of 0.040% per cycle over 1000 cycles at 1 C. Besides, even with a high-sulfur mass loading (8.04 mg cm−2) and lean electrolyte (4.0 μL mg−1), the targeted Li−S cell still delivers a high capacity retention of 92.9% over 100 cycles. This work provides a new strategy for the development of high-performance Li−S batteries with COF materials.