Amorphous Metal–OrganicFramework-Coated HalloysiteNanotubes as Efficient Sulfur Immobilizers for Lithium–SulfurBatteries

Abstract

Lithium–sulfur (Li–S) batteries, known for their high theoretical energy density, have been considered as one of the most promising candidates for next-generation batteries. However, further optimization of their electrochemical performance is often hindered by a sluggish polysulfide conversion process. Recently, amorphous metal–organic frameworks (aMOFs) with numerous unsaturated metal sites have emerged as efficient catalysts, particularly in boosting polysulfide conversion. However, the collapse of the long-range periodic porous structure makes it difficult to access the internal part of micrometer-sized aMOFs, thereby limiting the further improvement of their catalytic activity. Herein, we propose a promising core–shell structure, constructed by using a sustainable halloysite nanotube as a substrate to support aMOF. The triethylamine vapor diffusion method is applied to regulate the kinetics of aMOF growth by modulating the deprotonation of organic ligands, leading to the successful deposition of nanosized aMOF shells onto halloysite nanotubes. This aMOF/halloysite composite structure exhibits better catalytic activity toward polysulfide adsorption and conversion in the Li–S battery when compared with the pure halloysite. In addition, the composite also shows a better cycling performance, retaining a specific capacity of 510 mAh g^–1 after 350 cycles at 1.0 C. This work presents an efficient amorphous MOF shell-coating structure as a catalyst in facilitating the process of polysulfide conversion, paving the way for the development of highly active aMOF-based catalysts in the future.