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

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.