Covalently grafting conjugated porous polymers to MXene offers a two-dimensional sandwich-structured electrocatalytic sulfur host for lithium–sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries have received increasing attention due to their high energy density (2600 W h kg( -1)) as well as the low cost and nontoxicity of sulfur. However, sluggish conversion kinetics and the notorious shuttle effect of the polysulfides present in sulfur cathodes hinder the practical use of Li-S batteries. Herein, an electrocatalytic sulfur host with a two-dimensional (2D) sandwich structure is synthesized and found to display excellent properties for overcoming the noted challenges. The electrocatalytic sulfur host is prepared by covalently grafting a conjugated microporous polymer (CMP) to MXene nanosheets and denoted as CMP-M. The CMP component features triazine and benzothiophene units and thus the constituent heteroatoms endow CMP-M with a plethora of chemisorption sites to capture various polysulfides. The MXene component provides an electrocatalytic template to construct the 2D sandwich composite and can facilitate charge transfer while accelerating polysulfide conversion. Li-S cells prepared using CMP-M as sulfur hosts are found to exhibit a number of outstanding performance metrics including a high specific capacity (i.e., 1402 mA h g-1 at 0.1C), an outstanding rate capability (i.e., 610 mA h g(-1) at 4C), and a low capacity decay (from an initial value of 730 to 550 after 1000 cycles at 2C, corresponding to 0.025% per cycle). The methodology presented herein offers a universal approach for constructing electrocatalytic 2D composites that are useful not only in Li-S batteries but also in other contemporary energy technologies.