Covalently introducing sulfur in a thiol-rich metal-organic framework toward advanced lithium-sulfur batteries

The severe shuttle effect and sluggish reaction kinetics have hindered the commercial application of high-energy lithium-sulfur (Li-S) batteries. In this work, a dual-thiol metal-organic framework (MOF) was in situ synthesized on carbon nanotubes, and sulfur was covalently connected to this composite (UiO-66(SH)2@CNT) to form a MOF-sulfur copolymer (S-UiO-66(SH)2@CNT). Benefiting from the strong covalent interaction between thiol groups and sulfur species, the S-UiO-66(SH)2@CNT cathode can retard the shuttle effect and simultaneously strengthen the redox kinetics of polysulfides. As a result, a discharge capacity of 791 mAh g-1 is achieved at a current density of 0.2 C, whereas the S/UiO-66@CNT cathode using the blend of UiO-66@CNT and sulfur as active materials only shows a specific capacity of 670 mAh g-1. Moreover, the S-UiO-66(SH)2@CNT cathode exhibits a higher capacity retention of 93.27 % at 0.5 C during 200 cycles compared with that of the S/UiO-66@CNT cathode (64.94 %). This work will provide significant inspiration for the design of advanced MOFs and cathodes for excellent Li-S batteries.