Cobalt Ditelluride Meets Tellurium Vacancy: An Efficient Catalyst as a Multifunctional Polysulfide Mediator toward Robust Lithium–Sulfur Batteries

The commercialization of lithium-sulfur batteries (LSBs) faces significant challenges due to persistent issues, such as the shuttle effect of lithium polysulfides (LiPSs) and the slow kinetics of cathodic reactions. To address these limitations, this study proposes a vacancy-engineered cobalt ditelluride catalyst (v-CoTe₂) supported on nitrogen-doped carbon as a sulfur host at the cathode. Density functional theory calculations and experimental results indicate that the electron configuration modulation of v-CoTe₂ enhances the chemical affinity and catalytic activity toward LiPS. Specifically, v-CoTe₂ can strongly interact with PSs through multisite coordination, effectively facilitating the kinetics of the LiPS redox reaction. Furthermore, the introduction of Te vacancies generates a large number of spin-polarized electrons, further enhancing the reaction kinetics of LiPS. As a result, the v-CoTe₂@S cathode demonstrates high initial capacity and excellent cyclic stability, maintaining 80.4% capacity after 500 cycles at a high current rate of 3 C. Even under a high sulfur load of 6.7 mg cm^-2, a high areal capacity of 6.1 mA h cm^-2 is retained after 50 cycles. These findings highlight the significant potential of Te vacancies in CoTe₂ as a sulfur host material for LSBs.