Triple-Site Integrated Redox-Active Metal–Organic Cages Enable Complementary Acceleration Mechanisms for Serially Enhancing Sulfur Redox Kinetics

Abstract

The development of lithium–sulfur batteries (LSBs) is hindered by the shuttle effect of lithium polysulfides (LiPSs) and sluggish sulfur redox reaction (SRR) kinetics. Herein, we integrate multiple functional units (−SH, −NH₂, Zr) into metal–organic cages (MOCs) to construct a triple-site integrated MOC (TSI-MOC), synergistically suppress the shuttle effect, and promote the SRR. The −SH-decorated ligand forms a sulfur oligomer with LiPSs, promoting faster reaction pathways. The exposed Zr-based clusters catalyze the conversion of LiPSs, while the −NH₂-functionalized ligand adjacent to the metal clusters aids in aggregating LiPSs, further enhancing the catalytic and confinement effects. LSBs with TSI-MOCs deliver a higher discharge capacity (949.7 mAh g^–1) and a lower capacity decay rate (only 0.018% at 1 C) compared to those with single-site MOCs (S-MOCs) and dual-site integrated MOCs (DSI-MOCs). The TSI-MOC also enables LSBs with a high areal capacity of 9.08 mAh cm^–2 under a high sulfur loading of 9.1 mg cm^–2, as well as the stable operation of Li–S pouch cells with a high energy density of 307 Wh kg^–1. This work demonstrated the importance of integrating multiple functional sites to improve the chemical interactions between hosts and redox-active intermediates, facilitating the thoughtful design of MOCs for high-performance LSBs.