Selective chemisorption of polysulfides by porous molecular crystal: Cathode host materials for lean-electrolyte lithium-sulfur cells with high electrochemical stability

Abstract

The development of high-energy-density lithium-sulfur batteries with porous substrate materials often meets the compromise between the facile accommodation of polysulfides and the fast electrolyte absorption. Porous molecular crystals (PMCs), a new class of organic porous materials assembled by discrete small molecules via weak intermolecular interactions, recently show their potential in energy storage. Cyclobenzoin ester (CE), as one of PMCs, features a high abundance of carbonyl groups as a porous molecule. In this study, we utilize the unique adsorption characteristics of CE as an effective sulfur host to design lean-electrolyte lithium-sulfur cells with excellent electrochemical stability. The porosity and polar carbonyl groups of CE provide an excellent chemisorption platform for polysulfides, while also enabling smooth electrolyte penetration. As a result, our sulfur-cyclobenzoin ester (sulfur-CE) energy storage material attains rigorous cell-design parameters with a low electrolyte-to-sulfur ratio (4 μL mg−1) and a high sulfur loading/content (4 mg cm−2 and 80 wt%), yet exhibits excellent electrochemical characteristics, including an outstanding discharge capacity of 907 mA h g−1, cyclability of 200 cycles, and a high rate performance from C/20 to 1C. This research opens a new strategy of selective chemisorption for simultaneously optimizing lean-electrolyte lithium-sulfur cells with both high active-material loadings and high cell stability.