Origin of Synergy in Bicomponent Metal Nitride–Metal Single Atom Catalysts for Advanced Lithium–Sulfur Batteries

To catalyze the sulfur redox kinetics of lithium-sulfur batteries (LSBs) can well enhance the capacity and longevity. However, the synergistic essence of bicomponent electrocatalysts for LSBs remains obscure. Here, this work introduces standardized descriptors to describe the underlying origin of catalysts' synergy for LSBs. Specifically, it pertains to the bi-functional electrocatalysts comprising a series of metal nitrides (MN) and partner metal single atoms (M-SA) for the conversion and migration of lithium polysulfides (LiPSs). The M-SA with higher e_g/t_2g promotes the conversion of Li₂S₄-dominated decisive steps, alleviating the shuttling. Concurrently, MN with abundant bonding facilitates the migration of lithium sulfide, which significantly reduces the accumulation of insulating sulfide. Such independent but synergistic hybridization makes the bicomponent MN/M-SA possess improved catalysis over the S electrochemistry compared to their single components, which is also experimentally verified with W-SA/WN as the representative. The batteries provide considerable sulfur utilization, superior rate capability, and the assembled 6.31 Ah pouch-pack battery even has an ultra-high incipient energy density of 506.2 Wh kg^-1 under high sulfur loading and lean-electrolyte. A thorough comprehension of the catalytic properties from both electronic and structural standpoints provides a novel viewpoint for understanding and designing LSBs' catalysts.