Promoting sulfur redox kinetics of atomically dispersed Fe–NC electrocatalysts by carbon vacancies toward robust lithium–sulfur batteries

Abstract

Single-atom catalysts (SACs) have become the key to overcoming the inherent limitations of lithium–sulfur (Li–S) batteries due to their exceptional catalytic activity, high selectivity, and strong affinity towards lithium polysulfides (LiPSs). The effectiveness of SACs is influenced by complex electronic structures. Accordingly, precise tuning of these surroundings is crucial to fully utilize SACs. In this work, we demonstrated that the performances of SACs in LiPS redox reactions can be optimized by vacancy engineering. This strategy can retain the benefits of SACs as anchoring and electrocatalytic centers for LiPSs, while optimizing their electronic structures to promote rapid charge transfer and enhance the conversion efficiency of LiPSs. Specifically, iron-based SACs supported on nitrogen-doped carbon containing abundant carbon vacancies (Fe-SAs/N–C_v) were tested as a sulfur host in Li–S batteries. Density functional theory calculations indicate that Fe-SAs/N–C_v effectively anchors LiPSs and reduces the decomposition energy barrier of Li₂S. Thermodynamic analyses further elucidate that Fe-SAs/N–C_v can accelerate LiPS redox reactions. As a result, Fe-SAs/N–C_v hosts exhibit excellent rate performance and superior cycling stability. Furthermore, we demonstrated that Fe-SAs/N–C_v can be applied in Li–S pouch cells to achieve stable cyclability. This work showcases that the vacancy engineering strategy is effective to fine-tune the performance of SACs in Li–S batteries.