Multifunctional covalent organic framework 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 mA h 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.