Modulating electronic structure via N-doping and built-in electric field in CoO@Co₉S₈ heterostructure for enabling bidirectional sulfur redox in high-performance Li-S batteries

Heterostructures have garnered significant attention in lithium‑sulfur (Li-S) batteries owing to unique advantages, but achieving an optimal balance between adsorption and catalytic strength of lithium polysulfide (LiPSs) in heterostructure remains challenging. Hence, nitrogen doping strategy was embedded into the CoO@Co₉S₈ heterostructure (denoted as N-CoO@Co₉S₈) to construct a multifunctional interlayer, which synergistically regulates LiPSs adsorption behavior and accelerates their bidirectional conversion kinetics. Both theoretical and experimental results reveal that N-doping induces lattice distortion, promotes oxygen vacancy formation, elongates the Co–O/S bonds, and optimizes the electronic structure of active sites, thereby enhancing the built-in electric field (BIEF) at the heterointerface. This tailored electronic structure of active sites, combined with the enhanced BIEF, effectively optimizes the adsorption–desorption equilibrium of LiPSs and reduces reaction energy barriers, thereby preventing excessive adsorption and enabling efficient LiPSs conversion. Consequently, Li-S batteries equipped with the multifunctional N-CoO@Co₉S₈-modified interlayer delivers a high specific capacity of 1352.5 mAh g⁻¹ at 0.2C, and an exceptional cycling stability at 1.0C with a low decay rate of only 0.07% per cycle over 400 cycles. This work highlights a rational design strategy for high-performance Li-S batteries through the synergistic integration of doping and interface engineering.