Coordinatively Deficient Single-atom Fe-N-C Electrocatalyst with Optimized Electronic Structure for High-performance Lithium-sulfur Batteries

The rationally-designed single-atom catalyst that promotes efficient sulfur electrochemistry is highly desired yet still challenging for the development of high-performance lithium-sulfur (Li-S) batteries. Herein, the deficient coordination of single-atom Fe site is firstly and theoretically predicted to endorse higher sulfur affinity and catalytic activity, due to the stronger hybridization between Fe 3d(zz) and S 3p(y) orbitals compared with that in common FeN4 scenario. The following validation is conducted to prepare the monodispersed Fe single atoms with tuned coordination number on nitrogen-doped carbon (denoted as FeN2-NC and FeN4-NC) via the ligand control on the Fe precursor. As expected, the undercoordinated FeN2-NC fulfills significantly stronger sulfur immobilization and catalyzation as confirmed by a series of physicochemical and electrochemical evaluations. As a result, sulfur electrodes hosted by FeN2-NC realize excellent cyclability and rate capability, and particularly, a highly reversible areal capacity up to 4.5 mAh cm(-2) under a high areal sulfur loading of 5.0 mg cm(-2) and a low electrolyte to sulfur ratio of 5.3 mL g(-1). This work highlights the great feasibility and validity of coordinative defect engineering in single-atom catalysts for improving the Li-S battery electrochemistry, which could also enlighten advanced material designs in other related energy areas.