Catalytic oxidation of Li ₂ S on the surface of metal sulfides for Li−S batteries

Polysulfide binding and trapping to prevent dissolution into the electrolyte by a variety of materials has been well studied in Li-S batteries. Here we discover that some of those materials can play an important role as an activation catalyst to facilitate oxidation of the discharge product, Li₂S, back to the charge product, sulfur. Combining theoretical calculations and experimental design, we select a series of metal sulfides as a model system to identify the key parameters in determining the energy barrier for Li₂S oxidation and polysulfide adsorption. We demonstrate that the Li₂S decomposition energy barrier is associated with the binding between isolated Li ions and the sulfur in sulfides; this is the main reason that sulfide materials can induce lower overpotential compared with commonly used carbon materials. Fundamental understanding of this reaction process is a crucial step toward rational design and screening of materials to achieve high reversible capacity and long cycle life in Li-S batteries.