COFs-confined multifunctional Sulfur-host design towards High-performance Lithium-sulfur batteries

Abstract

Herein, a covalent organic framework (COF) confined multifunctional sulfur-host design strategy, with built-in porous catalyst and external microporous COF layer, is proposed to deal with the notorious lithium polysulfides (LiPSs) shuttle effect in lithium-sulfur (Li-S) batteries. The built-in hollow catalyst, consists of carbon supported cobalt nanodots (Co-NC) derived from ZIF-67 metal–organic framework, servers as sulfur accommodation and catalytic center for LiPSs trapping and conversion. The Co-NC is wrapped by a thin microporous TpBD-Me2 COF layer with polar functional groups, providing additional physical and chemical confinement for polysulfides shuttling. With these merits, the cell with S/Co-NC@TpBD-Me2 cathode exhibits a high initial capacity of 1178.15 mAh g−1 at 0.2C, and average 0.04% decay per cycle at 1C in 500 cycles. The cell also delivers a high rate performance (543.13 mAh g−1) up to 5C. Even at raised sulfur loading (5.71 mg cm−2) and lean electrolyte condition (E/S ratio 6.10 μL mg−1), a 4.53 mAh cm−2 high area capacity is achieved after 50 cycles. The Li-S pouch cell also achieves a specific capacity of 860.35 mAh g−1 at 0.1C after 50 cycles. This COF-confined multifunctional composite design provides an alternative strategy for the fabrication of high-performance Li-S batteries.