Rational Understanding of the Catalytic Mechanism of Molybdenum Carbide on Polysulfide Conversion in Lithium-Sulfur Battery
Lithium-sulfur (Li-S) batteries are promising candidates for next-generation energy storage devices due to its high theoretical energy density, whose practical applications are mainly hampered by the shuttle effect of intermediate polysulfides (LiPSs). Anchoring materials, such β-Mo2C, with strong chemical interaction have been proposed to improve the electrochemical performance of Li-S batteries. However, the chemical bonding and conversion reaction of LiPSs on Mo2C surface are not well studied. Here, we report on the discovery that the superior performance of Mo2C is originated from the sulfur termination. By combining X-ray spectroscopy measurements and theoretical calculations, we reveal sulfur should passivate Mo2C (101) surface that not only offers moderate chemical interaction with LiPSs but also facilitate the conversion reactions during both the discharge and charge processes. Our results suggest that it is important to consider the sulfurization of catalysts with metal surfaces when they are used to accelerate the conversion of polysulfides.