Implanting single-atom N2-Fe-B2 catalytic sites in carbon hosts to stabilize high-loading and lean-electrolyte lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries suffer from soluble lithium polysulfide (LiPS) shuttling and sluggish redox kinetics. The rational design of carbon-supported single-atom catalysts (SACs) as both LiPS immobilizers and sulfur redox promoters is of great significance for high-loading and lean-electrolyte Li-S batteries. However, the most popular nonpolar porphyrin-like transition metal-nitrogen (M-N4) SACs cannot maximize the catalytic activity of the metal center. Herein, a B, N co-coordinated N2-Fe-B2 SAC embedded in a B, N-rich carbon matrix (denoted as Fe SAs@BCN) is disclosed for the first time to construct state-of-the-art Li-S batteries. We reveal experimentally and theoretically that the asymmetric N2-Fe-B2 configuration not only rapidly captures LiPSs through strong Lewis acid-base interactions, but also greatly catalyzes the bidirectional sulfur redox chemistry by lowering the Li2S deposition/decomposition energy barriers. As such, the well-designed SACs enable Li-S batteries to promise extraordinary durability (82% retention over 1000 cycles at 5 C) and high areal capacities even under harsh sulfur mass loadings. More encouragingly, a 359 Wh kg−1 pouch cell with an ultrahigh loading of 11.6 mg·S cm−2 and a lean electrolyte to sulfur (E/S) ratio of 3 µL mg·S−1 is further demonstrated. This work shows that N2-Fe-B2 SACs hold great promise in realizing high-energy-density Li-S batteries.