Active Sulfur-Host Material VS₄ with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting...

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium-sulfur (Li-S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS₄/rGO) composites with an ultrathin layered structure as an active sulfur-host material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS₄/rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li₂S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li-S batteries. On the one hand, the ultrathin 3%Co-VS₄/rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS₄. On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS₄/rGO cathode displays a high specific capacity of 1332.6 mA h g^-1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g^-1. Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm^-2, it still can deliver 756.2 mA h g^-1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S₈ → Li₂S → β-S₈ (first cycle) and then β-S₈ ↔ Li₂S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li-S batteries.