In-situ grown Ti3C2T @CoSe2 heterostructure as trapping-electrocatalyst for accelerating polysulfides conversion in lithium-sulfur battery

Lithium-sulfur (Li-S) batteries are considered the desirable candidate for the next generation energy storage system, owing to their significant advantages in high theoretical energy density (2600 Wh kg−1) and environmental friendliness. Nevertheless, the notorious shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPSs) limit the application of Li-S batteries. Herein, heterostructure with CoSe2 nanoparticles strongly anchored on Ti3C2Tx substrate are prepared by a universal, simple, and non-hazardous preparation method, with Lewis acidic molten salt etching and subsequent in-situ selenization processes. The fabricated Ti3C2Tx@CoSe2 heterostructure exhibits high electrical conductivity and acts as electrocatalyst to facilitate the fast conversion of LiPSs. With Ti3C2Tx@CoSe2 heterostructure coated separator, the assembled Li-S cells deliver high initial capacity of 1183 mAh/g and well maintain at 788 mAh/g after 100 cycles at 0.5C. Besides, excellent rate performance (713 mAh/g at 3C) and long-term cycling performance (capacity fading rate of 0.059% per cycle at 0.5C and 0.041% per cycle at 1C) are achieved. The cells exhibited impressive performances even under the condition of lean electrolyte, high sulfur loading and practical shape (pouch cell). Additionally, Co atom was proved to serve as the catalytic site in the redox reaction of LiPSs by ex-situ XPS. Consequently, this work provides a new insight for the regulation of polysulfides conversion in Li-S batteries.