Multi-heterostructured MXene/NiS/CoS with S-Vacancies to Promote Polysulfide Conversion in Lithium-Sulfur Batteries.

The severe shuttle effect of polysulfides (LiPSs) and the slow liquid-solid phase conversion are the main obstacles hindering the practical application of lithium-sulfur (Li-S) batteries. Separator modification with a high-activity catalyst can boost LiPSs conversion and suppress their shuttle effect. In this work, multi-heterostructured MXene/NiS/CoS with rich S-vacancies was constructed facilely with a hydrothermal and high-temperature annealing strategy for separator modification. The MXene sheet not only provides a physical barrier but also ensures a high conductivity and adsorption capacity of the catalyst; the dual active centers of NiS and CoS catalyze LiPSs conversion. In addition, the vacancies and heterostructures can modulate the electronic structure of the catalyst, improve its intrinsic activity, and reduce the polysulfides reaction barrier, thus facilitating ion/electron transport and inhibiting the shuttle effect. Benefiting from these advantages, the Li-S battery with MXene/NiS/CoS modified separator exhibits exciting discharge capacities (1495.4 mAh g at 0.1C and 549.0 mAh g at 6C) and an excellent ultra-long cycle life (average capacity decay rate of 0.026% for 2000 cycles at 2C); at a high sulfur loading of 10.0 mg cm, the battery operates for nearly 80 cycles at 0.2C, giving a capacity retention rate of 75.76%. This work provides a high-activity catalyst for Li-S batteries.