Promoting Sulfur Redox Kinetics of Atomically Dispersed Fe-NC Electrocatalyst by Carbon Vacancy 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 for 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 LiPSs 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 LiPSs conversion efficiency. Specifically, iron-based SACs supported on nitrogen-doped carbon containing abundant carbon vacancies (Fe-SAs/N-Cv) were tested as a sulfur host in Li-S batteries. Density functional theory calculations indicate Fe-SAs/N-Cv effectively anchors LiPSs and reduces the decomposition energy barrier of Li2S. Thermodynamic analyses further elucidate that Fe-SAs/N-Cv can accelerate the LiPSs redox reactions. As a result, Fe-SAs/N-Cv hosts exhibit excellent rate performance and superior cycling stability. Furthermore, we demonstrated that with Fe-SAs/N-Cv can be applied in Li-S pouch cells to achievestable cyclability. This work showcases that the vacancy engineering strategy is effective to fine-tune the performance of SACs in Li-S batteries.