Conductive metal-metal phase and built-in electric field of 1T-VSe2-MXene hetero-structure to accelerate dual-directional sulfur conversion for high-performance Li-S batteries

The shuttle effect and tardy redox kinetics of lithium-polysulfides (LiPSs) seriously restrict the electrochemical performance of lithium-sulfur batteries (LSBs). Here, 1T-VSe2-MXene hetero-structure catalysts with conductive metal-metal phase and built-in electric field (BIEF) as sulfur hosts are developed to accelerate the catalytic conversion of sulfur species. Theoretical and experimental analysis verify that because the difference of energy-level structure between conductive MXene and 1T-VSe2 drives the electron flow through the hetero-interface to construct the interfacial BIEF of metal-metal phase. In the effect of interfacial BIEF, more electrons are accu-mulated on Se surface sites, so enhancing Li-Se bonding for strong adsorption with LiPSs/Li2S. Meanwhile, the strengthened Li-Se bonding weakens the competing Li-S bonds in LiPSs/Li2S captured on the heterostructure, thus accelerating the dissociation of Li-S bonds yet reducing Li2S nucleation/decomposition energy barrier. Furthermore, abundant Li+ are quickly propelled at the BIEF of the hetero-interface with metal-metal phase, thereby offering a rapid Li+ transfer and boosting the redox kinetics of sulfur species. As expected, the S/1T-VSe2- MXene cathode displays a high reversible capacity of 1321 mAh g-1 at 0.1C, a superb long cyclic stability with a capacity decay of 0.058% per cycle for over 550 cycles at 0.5C, and a high initials areal capacity of 6.42 mAh cm-2 (sulfur loading: 6.9 mg cm-2) at 0.2C. This work reveals its absorption and catalytic conversion mechanism and offers an effective way to design conductively dual-directional Li-S catalysts for high-performance LSBs.