Defect‐Rich Single Atom Catalyst Enhanced Polysulfide Conversion Kinetics to Upgrade Performance of Li–S Batteries

Lithium–sulfur (Li–S) batteries have attracted considerable attention owing to their extremely high energy densities. However, the application of Li–S batteries has been limited by low sulfur utilization, poor cycle stability, and low rate capability. Accelerating the rapid transformation of polysulfides is an effective approach for addressing these obstacles. In this study, a defect‐rich single‐atom catalytic material (Fe‐N4/DCS) is designed. The abundantly defective environment is favorable for the uniform dispersion and stable existence of single‐atom Fe, which not only improves the utilization of single‐atom Fe but also efficiently adsorbs polysulfides and catalyzes the rapid transformation of polysulfides. To fully exploit the catalytic activity, catalytic materials are used to modify the routine separator (Fe‐N4/DCS/PP). Density functional theory and in situ Raman spectroscopy are used to demonstrate that Fe‐N4/DCS can effectively inhibit the shuttling of polysulfides and accelerate the redox reaction. Consequently, the Li–S battery with the modified separator achieves an ultralong cycle life (a capacity decay rate of only 0.03% per cycle at a current of 2 C after 800 cycles), and an excellent rate capability (894 mAh g−1 at 3 C). Even at a high sulfur loading of 5.51 mg cm−2 at 0.2 C, the reversible areal capacity still reaches 5.4 mAh cm−2. The abundant local defects of Fe‐N4/DCS catalytic material are not only beneficial to the uniform dispersion, but also contribute to provide stable sites for single Fe atom. And, the Fe‐N4/DCS‐based functional separator can accelerate the transmission of electrons, effectively inhibit the shuttle of polysulfides, and improve the sulfur electrochemistry. Therefore, the battery with Fe‐N4/DCS‐based separator achieves ultralong cycle life and excellent rate capability.