Regulating Coordination Environment in Metal–Organic Frameworks for Adsorption and Redox Conversion of Polysulfides in Lithium–Sulfur Batteries

Metal–organic frameworks (MOFs) have shown potential for trapping and catalyzing lithium polysulfides (LiPSs) in lithium–sulfur batteries (LSBs), which is, however, challenging, because their catalytic metal centers are usually fully coordinated with ligands and inactivated. To understand the design principle of such MOFs, herein, three task-specific Bi-MOFs (Bi-MOF-1, Bi-MOF-2, and Bi-MOF-3) were designed to regulate the catalytic sites and systematically study the mechanism for trapping and catalyzing LiPSs. Specifically, the catalytic function of Bi-MOFs can be artificially activated or locked by exposing Bi3+ clusters or coordinating Bi3+ with organic molecules. A series of ex situ/in situ electrochemical tests and theoretical calculations demonstrated the key role of both the open metal sites on Bi3+ clusters and Bi3+-S interaction within Bi-MOF-1 for adsorbing and catalyzing LiPSs. Moreover, Bi-MOF-1 can improve the specific capacity of LSBs by 50% and decrease the decay rate by 80% after 1000 cycles at 1 C, compared with the LSBs without catalytic interlayer, showing the great potential of catalytic MOFs for high-performance LSBs.