Two-Dimensional Imide-Based Covalent Organic Frameworks with Tailored Pore Functionality as Separators for High-Performance Li–S Batteries

Modifying the separator of lithium-sulfur batteries (LSBs) is considered to be one of the most effective strategies for relieving the notorious polysulfide shuttle effect. Constructing a stable, lightweight, and effective LSB separator is still a big challenge but highly desirable. Herein, a stable and lightweight imide-based covalent organic framework (COF-TpPa) is facilely fabricated on reduced graphene oxide (rGO) through an oxygen-free solvothermal technique. With the directing effect of rGO and changing the side functional group of the monomer, the morphology and the pore tailoring of COF-TpPa can be simultaneously achieved and two-dimensional (2D) COF nanosheets with different functionalities (such as -SO3H and -Cl) are successfully constructed on rGO films. The specific functional groups inside the COF's pore channels and the narrowed pore size result in efficient absorption and restriction of Li2Sn for weakening the "shuttle effect". Meanwhile, the 2D COF nanosheets on the rGO is a favorable morphology for better exploiting pores inside the COF materials. As a result, the COF-SO3H-modified separator, consisting of rGO and COF-TpPa-SO3H, exhibits a high specific capacity (1163.4 mA h/g at 0.2 C) and a desirable cyclic performance (60.2% retention rate after 1000 cycles at 2.0 C) for LSBs. Our study provides a feasible strategy to rationally design functional COFs and boosts their applications in various energy storage systems.