金属单原子催化剂增强硫正极动力学的研究进展

单质硫具有理论能量密度高(2600 Wh·kg-1)、放电比容量高(1672mAh·g-1)、成本低等优势，是锂硫电池的理想正极材料。然而，在充放电过程中硫正极迟缓的反应动力学显著地限制了锂硫电池的性能。金属单原子催化剂(SMACs)具有独特的电子结构、金属含量低、理论上100%的原子利用率、催化活性高等优势，其不仅有效地促进了不同中间相的转化反应，而且可为含硫物质提供丰富的锚定位点，从而显著优化硫正极氧化还原反应动力学、多硫化物的穿梭行为和锂硫电池电化学性能。本文以剖析金属单原子催化剂与硫正极间的相互作用为出发点，结合其催化效应表征技术，重点解析了不同类型单原子催化剂的构筑策略、活性调控及其优化硫正极氧化还原行为的机制，展望了金属单原子催化剂在锂硫电池领域面临的挑战和未来发展方向。

Advances in Single Metal Atom Catalysts Enhancing Kinetics of Sulfur Cathode

Sulfur has been considered as an ideal cathode of lithium sulfur batteries (LSBs) owing to its high theoretical energy density (2600 Wh?Kg^-1), excellent discharge capacity (1672 mAh?g^-1), and low cost. During sulfur reduction and oxidation processes, nevertheless, the sluggish redox reaction kinetics of the sulfur cathode and severe shuttle effect of soluble lithium polysulfides intermediates significantly result in poor battery performance. It has been demonstrated that a sulfur host with high adsorption energy and excellent catalytic activity/selectivity can effectively enhance the cycle stability and rate capability of LSBs. As a result, a variety of hosts, such as metal compounds, heterojunctions, defect matrices, and single metal atom catalysts, have been widely developed. Interestingly, single metal atom catalysts with a unique electronic structure, low metal content, theoretical 100% atom utilization efficiency, and high catalytic performance can effectively promote the conversion of different lithium polysulfides intermediates and provide abundant absorption sites for sulfur-contained species, thereby optimizing the redox reaction kinetics of the sulfur cathode and shuttle behavior of the soluble lithium polysulfides. Various single metal atom catalysts, mainly including iron, cobalt, nickel, zinc, tungsten, vanadium, molybdenum, and manganese, have been developed via atomic bonding, spatial confinement, and defect engineering strategies to solve the key challenges of sulfur cathode since single metal atom catalysts were for the first time to be utilized as catalytic agents for LSBs. In this review, the interaction among support materials in single metal atom catalysts, atomically dispersed metal catalytic sites, and the sulfur cathode were addressed in detail, providing a basis for the development of high-performance single metal atom catalysts. Furthermore, advanced characterization techniques such as in situ Raman spectroscopy, X-ray absorption spectroscopy, cyclic voltammograms, and electrochemical impedance spectroscopy, were employed to investigate the catalytic effect of single metal atom catalysts. Notably, the effects of the coordination environment on the catalytic activity and selectivity of single metal atom catalysts were systematically discussed. Simultaneously, the catalytic mechanism of single metal atom catalysts with different metal/nonmetallic atoms and coordination configurations was elucidated using theoretical calculations. In addition, some significant challenges of single metal atom catalyst in LSBs were proposed. It is believed that this review will provide a novel insight into the optimization of atomic catalysts with high activity and catalytic selectivity toward long-lifespan LSBs.