Modulation of Potential-Limiting Steps in Lithium-Sulfur Batteries by Catalyst Synergy.

Electrocatalysis is considered to be an effective method to solve the sluggish kinetics of lithium-sulfur batteries. However, a single catalyst cannot simultaneously catalyze multi-step sulfur reductions. And once the catalyst surface is covered by the initially deposited solid products, the subsequent catalytic activity will significantly deteriorate. Here, microporous ZIF-67 and its derivative nano-metallic Co 0 are used as dual-catalyst aiming to address these drawbacks. The dual catalytic center effectively cooperates the adsorption and electron transfer for multi-steps of sulfur reductions, transforming the potential-limited step (Li 2 S 4 →Li 2 S 2 /Li 2 S) into a thermodynamic spontaneous reaction. ZIF-67 first adsorbs soluble Li 2 S 4 to form a coordination structure of ZIF-Li 2 S 4 . Then nano-metallic Co 0 attracts uncoordinated S atoms in ZIF-Li 2 S 4 and facilitates the breaking of S-S bonds to form transient reductive ZIF-Li 2 S 2 and Co-S 2 via. spontaneous electron transfer. These intermediates facilitate continuous conversion to Li 2 S with reduced formation energy, which is beneficial to the regeneration of the catalyst. As a result, the cathode with ZIF@CNTs/Co@CNFs synergetic catalyst achieves initial areal capacity of 4.7 mAh cm -2 and maintains 3.5 mAh cm -2 at low electrolyte/sulfur ratio (E/S) of 5 µL mg -1 . This study provides valuable guidance for improving the electrochemical performance of lithium-sulfur batteries through catalyst synergistic strategies for multi-step reactions.