Engineering Catalytic CoSe-ZnSe Heterojunctions Anchored on Graphene Aerogels for Bidirectional Sulfur Conversion Reactions.

Sluggish sulfur reduction and lithium sulfide (Li2 S) oxidation prevent the widespread use of lithium-sulfur (Li-S) batteries, which are attractive alternatives to Li-ion batteries. The authors propose that a transition metal selenide heterojunction (CoSe-ZnSe) catalytically accelerates bidirectional sulfur conversion reactions. A combination of synchrotron X-ray absorption spectroscopy and density functional theory calculations show that a highly active heterointerface with charge redistribution and structure distortion effectively immobilizes sulfur species, facilitates Li ion diffusion, and decreases the sulfur reduction and Li2 S oxidation energy barriers. The CoSe-ZnSe catalytic cathode exhibits high areal capacities, good rate capability, and superior cycling stability with capacity fading rate of 0.027% per cycle over 1700 cycles. Furthermore, CoSe-ZnSe heterojunctions anchored on graphene aerogels (CoSe-ZnSe@G) enhance ionic transport and catalytic activity under high sulfur loading and lean electrolyte conditions. A high areal capacity of 8.0 mAh cm-2 is achieved at an electrolyte/sulfur ratio of 3 µL mg-1 . This study demonstrates the importance of bidirectional catalytic heterojunctions and structure engineering in boosting Li-S battery performances.