Catalytic multivariable metal-organic frameworks for lithium-sulfur batteries

Metal-organic frameworks (MOFs) hold potential for promoting the redox reaction of sulfur species (RRS) and suppressing the shuttle effect in lithium–sulfur batteries (LSBs). However, except for a limited number of frameworks, most MOFs are found to be inert in accelerating RRS, which is largely related to the fact that their design principles and mechanism of catalysis have not been fully understood. Systematic density functional theory (DFT) calculations and experimental results reveal that the lack of exposed polar catalytic sites restricts MOF's potential in promoting RRS. Herein, based on a series of multivariable MOFs containing ligands with different thermal stability, selective ligand removal and ligand exchange (LE) strategies were applied successively to expose the catalytic metal clusters and introduce extra adsorption sites, rendering inert MOFs into catalytic ones. Such post-modified multivariable MOFs were shown to yield LSBs with remarkably improved specific capacity and cycling stability realizing 7.9 mAh cm−2 of capacity after 100 cycles at high sulfur loading of 8.1 mg·cm−2 under a lean electrolyte condition. The universal strategy proposed in this work will guide the design of catalytic MOFs for RRS and promote the development of advanced catalysts for high-performance LSBs.