High loading atomically distributed Fe asymmetrically coordinated with pyridinic and pyrrolic N on porous N-rich carbon matrix driving high performance of Li-S battery

The practical application of Li-S battery is severely hampered by the sluggish sulfur-related redox reaction (SROR) kinetics along with lithium polysulfides (LiPSs) shuttle effect, advanced single-atom catalyst (SAC) is pursued to improve the SROR conversion capability. Herein, a novel SAC possessing of high loading (3.02 wt%) atomically dispersed Fe five-coordinated with pyridinic and pyrrolic N anchored on porous N-rich (16.4 at.%) carbon matrix is obtained. The resultant Fe-N₅/NC SAC has a high Brunauer-Emmett-Teller surface area of 523 m² g⁻¹. The unique asymmetrical Fe-N₅ sites in Fe-N₅/NC are identified by spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscope, X-ray photoelectron spectroscope, synchrotron X-ray absorption spectroscopy, density functional theory calculation, etc. The experimental and theoretical results demonstrate that the Fe-N₅/NC SAC not only exhibits strong adsorption for LiPSs, but also provides a significant electrocatalytic effect on the SROR in Li-S battery. A high initial capacity of 1519 mAh g⁻¹ was obtained at a current density of 0.1 C for the Li-S battery based on the Fe-N₅/NC modified separator. An ultralong life of 2000 cycles was achieved for the Li-S battery, which has good initial capacities of 1030 mAh g⁻¹ and 883 mAh g⁻¹ with low decay rates of 0.032% and 0.031% per cycles at 1 C and 2 C, respectively.