Transition metal oxides and sulfides have been intensively investigated as host materials for the S cathode in lithium-sulfur (Li-S) batteries; however, the distinctions between them in battery operation have remained unclear. In this study, VO2 and VS2 nanosheets were systematically studied as host materials for Li-S batteries through theoretical calculations and experimental testing. First-principles calculations demonstrated that VS2 showed more favorable properties, including the inherent semi-metallic conductivity of VS2 , moderate adsorption strength for Li2 Sn , fast Li+ transport with a low diffusion barrier, and accelerated surface redox reactions with a low Li2 S decomposition barrier. In comparison, the low electronic conductivity and strong adsorption strength of VO2 increased Li+ diffusion as well as Li2 S decomposition barriers of the electrode, resulting in relatively poor rate capability and cycle stability. In experiments, the VS2 @S electrode exhibited superior electrochemical performance compared with VO2 @S, giving a large capacity of 713 mAh g-1 at 5 C and a low capacity fading rate of 0.13 % per cycle over 200 cycles at 1 C. The constructed relationships between S cathode and host materials could guide the future design of high-performance S cathodes for Li-S batteries.
Keywords: Li-S batteries; electrochemical properties; first-principles calculations; vanadium dioxide; vanadium disulfide.
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