ZIF-8/ZIF-67 derived ZnS@Co-N-C hollow core-shell composite and its application in lithium‑sulfur battery

Lithium‑sulfur batteries are energy conversion devices that possess much higher energy densities than traditional lithium-ion batteries. However, the shuttle effect of the chemical reaction in the positive electrode of lithium‑sulfur batteries significantly reduces their specific capacity and charge retention characteristics. Therefore, we fabricated a novel hollow core-shell structure to serve as a separator modification layer and inhibit the shuttle effect. A ZIF-8/ZIF-67 core-shell precursor was first prepared by a room temperature solution reaction. This precursor was then treated by a vulcanization and calcination process to form the end product, in which ZnS was the core active site and CoN doped carbon nanocages were the outer shell. The discharge capacity and the cycling durability of a lithium‑sulfur battery were significantly improved by coating this novel structure on a polyethylene (PE) separator. Electrochemical measurements and microstructural analysis demonstrated that the unique hollow structure served as a polysulfide reservoir. Moreover, the Co-N-C shell and ZnS core of this structure also chemically interacted with and had a catalytic effect on the polysulfides, which enhanced the cycle and rate performance of the battery. Therefore, the lithium‑sulfur battery prepared using a ZnS@Co-N-C core-shell composite-coated PE separator showed excellent electrochemical performance.