VSe2/V2C heterocatalyst with built-in electric field for efficient lithium-sulfur batteries: Remedies polysulfide shuttle and conversion kinetics

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Lithium sulfur (Li-S) battery is a kind of burgeoning energy storage system with high energy density. However, the electrolyte-soluble intermediate lithium polysulfides (LiPSs) undergo notorious shuttle effect, which seriously hinders the commercialization of Li-S batteries. Herein, a unique VSe2/V2C heterostructure with local built-in electric field was rationally engineered from V2C parent via a facile thermal selenization process. It exquisitely synergizes the strong affinity of V2C with the effective electrocatalytic activity of VSe2. More importantly, the local built-in electric field at the heterointerface can sufficiently promote the electron/ion transport ability and eventually boost the conversion kinetics of sulfur species. The Li-S battery equipped with VSe2/V2C-CNTs-PP separator achieved an outstanding initial specific capacity of 1439.1 mA h g−1 with a high capacity retention of 73% after 100 cycles at 0.1 C. More impressively, a wonderful capacity of 571.6 mA h g−1 was effectively maintained after 600 cycles at 2 C with a capacity decay rate of 0.07%. Even under a sulfur loading of 4.8 mg cm−2, areal capacity still can be up to 5.6 mA h cm−2. In-situ Raman tests explicitly illustrate the effectiveness of VSe2/V2C-CNTs modifier in restricting LiPSs shuttle. Combined with density functional theory calculations, the underlying mechanism of VSe2/V2C heterostructure for remedying LiPSs shuttling and conversion kinetics was deciphered. The strategy of constructing VSe2/V2C heterocatalyst in this work proposes a universal protocol to design metal selenide-based separator modifier for Li-S battery. Besides, it opens an efficient avenue for the separator engineering of Li-S batteries.