Synergistic Effect of Dual-Functional Groups in MOF-Modified Separators for Efficient Lithium-Ion Transport and Polysulfide Management of Lithium-Sulfur Batteries.

Abstract

Lithium-sulfur batteries (LSBs) have been regarded as an attractive candidate for future energy storage systems owing to their exceptionally high energy density. However, the further application of LSBs is faced with critical challenges such as the intrinsic insulation of sulfur and the shuttle effect of soluble lithium polysulfides (LiPS). To overcome these problems, a dual functional metal-organic framework (UIO-66-NH₂-HSO₃) modified separator is proposed, strategically implemented to examine the dual functionality in anchoring LiPS and facilitating Li⁺ transport. Theoretical calculations indicated that the Li⁺ diffusion kinetics and LiPS adsorption ability are synergistically boosted by the dual-functional groups in the framework. The -HSO₃ demonstrates high affinity for capturing LiPS species while simultaneously repulsing polysulfide anions. Conversely, -NH₂ effectively immobilizes these anionic species. Additionally, the lower LUMO energy level of NH₂-H₂BDC and the higher HOMO energy level of HSO₃-H₂BDC significantly accelerate the reaction kinetics of LSBs. Electrochemical assessments revealed that the UIO-66-NH₂-HSO₃@PP composite delivers ultra-high rate capability and long-term cycling durability, surpassing most of the reported results. In situ spectroscopic analysis established that the UIO-66-NH₂-HSO₃@PP facilitates homogeneous lithium-ion migration while mitigating polysulfide shuttling. This study provides a theoretical foundation for the rational design of multifunctional MOFs membranes as advanced separators for high-performance LSBs.