Boosting Bi-Directional Redox of Sulfur with Dual Metal Single Atom Pairs in Carbon Spheres Toward High-Rate and Long-Cycling Lithium-Sulfur Battery

The severe shuttle effect of polysulfides and sluggish redox kinetics are the main problems that hinder the practical applications of lithium-sulfur (Li-S) batteries. In this study, dual metallic single atom pairs are implanted into carbon nanospheres to address the shuttle effect and facilitate the bi-directional redox kinetics of sulfur. Fe sites are found to be favorable for the reduction reaction of polysulfides, while Co sites facilitate the dissolution of Li2S experimentally and theoretically, promoting the overall electrochemical performance of Li-S batteries due to the synergetic effect. The sulfur cathode with the dual metallic single atom pairs exhibits an ultrahigh capacity retention of 96.4% after 100 cycles at 0.5 C. More importantly, it demonstrates excellent rate performance (618 mAh g(-1) at current density of 10 C) and outstanding cycle performance at 2 C after 2800 cycles with only 0.01% decay per cycle. Impressively, the assembled pouch cell delivers a high discharge capacity of 1385 mAh g(-1) and retains 869 mAh g(-1) after 100 cycles at 0.2 C. These results demonstrate the potential of dual single atom catalysts for the favorable bi-directional redox kinetics in Li-S batteries.