Direct Observation of Hybridization Between Co 3d and S 2p Electronic Orbits: Moderating Sulfur Covalency to Pre‐Activate Sulfur‐Redox in Lithium–Sulfur Batteries

Abstract Lithium–sulfur batteries (LSBs) offer high energy density and environmental benefits hampered by the shuttle effect related to sluggish redox reactions of long‐chain lithium polysulfides (LiPSs). However, the fashion modification of the d ‐band center in separators is still ineffective, wherein the mechanism understanding always relies on theoretical calculations. This study visibly probed the evolution of the Co 3 d ‐band center during charge and discharge using advanced inverse photoemission spectroscopy/ultraviolet photoemission spectroscopy (IPES/UPS), which offers reliable evidence and are consistent well with theoretical calculations. This, coupled with in situ Raman and X‐ray diffraction (XRD) and electrochemical data, co‐evidences a novel pre‐activating S redox mechanism in LSBs: LiPSs desert/insert in C‐N matrixes within a series of Co@NCNT‐based separators. The insight of the S redox pre‐activation is discovered that the Co 3 d ‐band center downshifts to hybridized with S 2 p orbitals in LiPSs, giving rise to a more pronounced S covalency and thus accelerating the conversion of LiPSs to S₈. Benefiting from these advantages, the optimized LSB possesses a minimal decay rate of 0.0058% after 200 cycles at a high discharge rate of 10 C. This study provides new insights into LSB mechanisms and supports conventional theoretical models of the d ‐band center's impact on LSB performance.