A redox-active metal–organic framework mediator enables enhanced polysulfide confinement and streamlined reaction pathways in lithium–sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) hold significant potential for energy storage but are hindered by challenges such as the shuttle effect and the slow conversion of soluble lithium polysulfides (LiPSs). In this study, we proposed a robust strategy of constructing redox-active metal–organic framework mediators (RM-MOFs) for use as sulfur hosts and effective redox mediators (RMs) in LSBs. The RM-MOF immobilizes the redox-active dithiothreitol (DTT) molecules on the exposed metal sites of the mesoporous MOF, which can prevent the loss of DTT, arrange it uniformly in separate pores, confine LiPSs, and continuously modulate redox kinetics during long-term cycling. Notably, the RM-MOF streamlines the redox pathways through redox reactions between LiPSs and the –SH groups of the DTT units, forming short-chain organosulfur compounds and facilitating radical reactions. Leveraging these advantages, the RM-MOF significantly enhances the performance of LSBs in both discharge capacity at various C-rates and cycling stability (over 90% reduced decay rate), enabling a high areal capacity of 13.8 mA h cm⁻² at high sulfur loading and high-energy density (316.5 W h kg⁻¹) pouch cell operation. Importantly, this work provides insight into the design and functional mechanisms of the RM-MOF, paving the way for the development of more advanced porous mediators for next-generation LSBs.