Delocalized Isoelectronic Heterostructured FeCoOxSy Catalysts with Tunable Electron Density for Accelerated Sulfur Redox Kinetics in Li‐S batteries

High interconversion energy barriers, depressive reaction kinetics of sulfur species, and sluggish Li+ transport inhibit the wide development of high‐energy‐density lithium sulfur (Li−S) batteries. Herein, differing from random mixture of selected catalysts, the composite catalyst with outer delocalized isoelectronic heterostructure (DIHC) is proposed and optimized, enhancing the catalytic efficiency for decreasing related energy barriers. As a proof‐of‐content, the FeCoOxSy composites with different degrees of sulfurization are fabricated by regulating atoms ratio between O and S. The relationship of catalytic efficiency and principal mechanism in DIHCs are deeply understood from electrochemical experiments to in situ/operando spectral spectroscopies i.e., Raman, XRD and UV/Vis. Consequently, the polysulfide conversion and Li2S precipitation/dissolution experiments strongly demonstrate the volcano‐like catalytic efficiency of various DIHCs. Furthermore, the FeCoOxSy‐decorated cell delivers the high performance (1413 mAh g−1 at 0.1 A g−1). Under the low electrolyte/sulfur ratio, the high loading cell stabilizes the areal capacity of 6.67 mAh cm−2 at 0.2 A g−1. Impressively, even resting for about 17 days for possible polysulfide shuttling, the high‐mass‐loading FeCoOxSy‐decorated cell stabilizes the same capacity, showing the practical application of the DIHCs in improving catalytic efficiency and reaching high electrochemical performance. The delocalized isoelectronic heterojunction catalyst (DIHC) is constructed by substituting isoelectronic S for O to further complement the heterojunction theory. With the formation of the more catalytic sites in the DIHC, the catalytic behaviors at the heterojunction interface are regulated to realize the continuous capture—adsorption—catalysis of Li2Sn, thus improving the sulfur reaction kinetics and performance of lithium‐sulfur batteries.