Asymmetrically Coordinated Cu–N₁C₂ Single-Atom Catalyst Immobilized on Ti₃C₂T_x MXene as Separator Coating for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are receiving great attention owing to their large theoretical energy density, but the shuttle effect and sluggish kinetic conversion of lithium polysulfides (LiPSs) seriously restrict their practical applications. Herein, various metal single-atom catalysts immobilized on nitrogen-doped Ti₃C₂T_x (M SA/N-Ti₃C₂T_x, M = Cu, Co, Ni, Mn, Zn, In, Sn, Pb, and Bi) are successfully prepared by a neoteric vacancy-assisted strategy, applied as polypropylene (PP) separator coatings to facilitate the fast redox conversion and adsorption of LiPSs for boosting Li–S batteries. Of particular note, among the M SA/N-Ti₃C₂T_xs, Cu SA/N-Ti₃C₂T_x/PP exhibits amazing properties, involving excellent rate performance (925 mAh g⁻¹ at 3 C), superb cycling stability over 1000 cycles, and ultra-high sulfur utilization even at large sulfur loadings (7.19 mg cm⁻²; an areal capacity of 5.28 mAh cm⁻²). X-ray absorption fine spectroscopy and density functional theory calculations reveal that the asymmetrically coordinated Cu–N₁C₂ moieties act as the active sites, which possess a higher binding energy and a larger electron cloud with LiPSs than pristine Ti₃C₂T_x, facilitating the adsorption and kinetic conversion of LiPSs effectively. This work may provide new insights into single atom-decorated ultrathin 2D materials for enhancing electrochemical performance of advanced batteries for energy storage and conversion.