Highly Connected Three-Dimensional Covalent Organic Framework with Flu Topology for High-Performance Li-S Batteries

Lithium-sulfur batteries (LSBs) have been consid-ered as a promising candidate for next-generation energy storage devices, which however still suffer from the shuttle effect of the intermediate lithium polysulfides (LiPSs). Covalent-organic frame-works (COFs) have exhibited great potential as sulfur hosts for LSBs to solve such a problem. Herein, a pentiptycene-based D2h symmetrical octatopic polyaldehyde, 6,13-dimethoxy-2,3,9,10,18,19,24,25-octa(4 '-formylphenyl)pentiptycene (DMOPTP), was prepared and utilized as a building block toward preparing COFs. Condensation of DMOPTP with 4-connected tetrakis(4-aminophenyl)methane affords an expanded [8 + 4] connected network 3D-flu-COF, with a flu topology. The non-interpenetrated nature of the flu topology endows 3D-flu-COF with a high Brunauer-Emmett-Teller surface area of 2860 m2 g-1, large octahedral cavities, and cross-linked tunnels in the framework, enabling a high loading capacity of sulfur (similar to 70 wt %), strong LiPS adsorption capability, and facile ion diffusion. Remarkably, when used as a sulfur host for LSBs, 3D-flu-COF delivers a high capacity of 1249 mA h g-1 at 0.2 C (1.0 C = 1675 mA g-1), outstanding rate capability (764 mA h g-1 at 5.0 C), and excellent stability, representing one of the best results among the thus far reported COF-based sulfur host materials for LSBs and being competitive with the state-of-the-art inorganic host materials.

Automated summary

Covalent-organic frameworks (COFs) show great potential as sulfur hosts for lithium-sulfur batteries (LSBs) to solve the shuttle effect of intermediate lithium polysulfides (LiPSs). In this study, a pentiptycene-based D2h symmetrical octatopic polyaldehyde was synthesized as a building block for preparing a 3D-flu-COF with a high loading capacity of sulfur, strong LiPS adsorption capability, and facile ion diffusion. When used as a sulfur host for LSBs, 3D-flu-COF exhibits high capacity, outstanding rate capability, and excellent stability, making it one of the best COF-based sulfur host materials for LSBs.