Asymmetrically Coordinated Cu–N_1C_2 Single-Atom Catalyst Immobilized on Ti_3C_2T_x MXene as Separator Coating for Lithium–Sulfur Batteries

摘要

Lithium–sulfur (Li–S) batteries are receiving great attention owing to theirlarge theoretical energy density, but the shuttle effect and sluggish kineticconversion of lithium polysulfides (LiPSs) seriously restrict their practicalapplications. Herein, various metal single-atom catalysts immobilized onnitrogen-doped Ti_3C_2T_x (M SA/N-Ti_3C_2T_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 redoxconversion and adsorption of LiPSs for boosting Li–S batteries. Of particularnote, among the M SA/N-Ti_3C_2T_xs, Cu SA/N-Ti_3C_2T_x/PP exhibits amazingproperties, involving excellent rate performance (925 mAh g?1 at 3 C), superbcycling stability over 1000 cycles, and ultra-high sulfur utilization even atlarge 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 calculationsreveal that the asymmetrically coordinated Cu–N_1C_2 moieties act as the activesites, which possess a higher binding energy and a larger electron cloud withLiPSs than pristine Ti_3C_2T_x, facilitating the adsorption and kinetic conversionof LiPSs effectively. This work may provide new insights into single atomdecoratedultrathin 2D materials for enhancing electrochemical performanceof advanced batteries for energy storage and conversion.