Electronegativity Matching of Asymmetrically Coordinated Single‐Atom Catalysts for High‐Performance Lithium–Sulfur Batteries

Asymmetrically coordinated single‐atom catalysts are attractive for the implementation of high‐performance lithium–sulfur (Li─S) batteries. However, the design principle of the asymmetric coordination that can efficiently promote bidirectional conversion of polysulfides has not been fully realized. Herein, a series of Co─N3X1 (X refers to F, O, Cl, S, or P) configurations are established, and theoretically unravel that the relative electronegativity value (REV) can be used as an index parameter for characterizing the catalytic activity. By virtue of enhanced chemical affinity with sulfur species and lowered Li2S decomposition, chlorine‐atom‐constructed asymmetric configurations with an optimal REV exhibit stronger catalytic effect to inhibit shuttling. Such a REV‐related catalytic effect is termed as REV effect. Following this principle, a novel single‐atom catalyst with dominated Co─N3Cl1 configuration is successfully synthesized through an inside‐out thermal reaction strategy and used as a modified layer on the cathode‐side separator. Interestingly, the assembled Li─S batteries exhibit quite high rate capacity (804.3 mAh g−1 at 5.0 C), durable cyclability (0.023% capacity decay per cycle), and competitive areal capacity (7.0 mAh cm−2 under 7.5 mg cm−2 sulfur loading and lean electrolyte). The guideline provided in this work gives impetus to the pursuit of highly efficient single‐atom catalysts for practical Li─S batteries. A new parameter, relative electronegativity value (REV), is demonstrated as a direct index parameter for evaluating the catalytic effect of asymmetric electrocatalysts. Such a REV effect can guide the rational design of asymmetric coordination to tailor the catalytic kinetics of bidirectional conversion of polysulfides. A novel electrocatalyst with Co─N3Cl1 configuration endows Li─S batteries with high rate capability and durable cyclability.