Multifunctional covalent organic frameworks with extended π-d conjugated structure for lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries hold great promise for the next generation of high energy density systems. However, sluggish sulfur conversion and the shuttle effect of polysulfides severely limit their commercial applications. Herein, a multifunctional covalent organic framework (Ni-COF) with extended π-d conjugated structure was synthesized and used for separator modification to overcome the obstacles in Li-S batteries. Ni-COF inherits the advantages of both COFs and conductive metal-organic frameworks, while compensating for their respective disadvantages. The abundant oxygen-containing groups in Ni-COF act as chemical adsorption sites to inhibit the shuttle effect of polysulfides. The designed π-d conjugated structure enhances electrical conductivity and provides high-density metal catalytic sites, thereby facilitating the conversion of polysulfides and enhancing the reaction kinetics of Li-S batteries. Consequently, the Li-S batteries with Ni-COF@PP separator exhibit remarkable rate performance of 719 mAh g-1 at 4 C, along with a low attenuation rate of 0.087% per cycle over 300 cycles at 1 C. This study proposes a novel strategy for the rational design of COFs in Li-S batteries.