Steering Yolk-Shell Nanostructures of 1D Unit-Based Covalent Organic Frameworks as Binder Modulators.

Abstract

Induced by their weak chain interactions, 1D unit-based covalent organic frameworks (1D COFs) are favorable in molecular assembly, yet their exploration in morphology engineering and related energy storage applications are still rare. Here, a series of 1D COFs based nano-structures (i.e. yolk-shell spheres (YS-COF), hollow spheres (HS-COF) and solid spheres (SS-COF)) is prepared via a solvent-induced strategy that can be applied as binder modulators for Li-S batteries. Specifically, they can impart enhanced mechanical properties, more adaptability to volume change, and better ability in adsorbing/catalyzing lithium polysulfide intermediates (LiPSs) to traditional PVDF binder. Remarkably, the thus-assembled YS-COF-based cell displays an initial specific capacity of up to 1011 mAh g-1 at 0.5 C, which is much higher than that of HS-COF, SS-COF, and PVDF-based Li-S batteries. Even at 4 C, it still maintains a discharge specific capacity of 962 mAh g-1 and can cycle for >600 cycles. DFT calculations and finite element simulation reveal the important roles of nanomorphology and functional groups of YS-COF in promoting electrochemical redox kinetics to boost battery performances. This strategy might provide in-depth insights in the morphology engineering and performance optimization of 1D COFs for Li-S batteries.