Lithium−sulfur (Li−S) batteries have become an ideal candidate for the next generation of rechargeable batteries for the high theoretical energy density. However, the sluggish redox kinetics hampered the development of Li−S batteries. It is reported that the conversion kinetics of lithium polysulfides (LiPSs) can be accelerated by introducing catalytic materials. The macrocyclic metal porphyrins have attracted extensive attention due to their excellent chemical stability and structural tunability. Herein, we designed a series of iron porphyrins substituted by the electron-donating and electron-withdrawing groups. According to electrochemical characterization and theoretical calculation, the functional group can switch the spin state of central Fe and modulate their catalytic performance. The methoxy-substituted iron porphyrin (FeTPP-4OMe) shows smaller band gap and facilitates the electron transfer. As a result, Li−S batteries with FeTPP-4OMe delivered a specific capacity of 1,062.0 mA h g and retained a high specific capacity of 771.4 mA h g at 0.5 C after 500 cycles with a capacity fading of 0.055 %. This work provides a guidance for the functional group modification of metal macrocyclic compounds in Li−S batteries.

中文翻译：

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金属大环分子外围基团诱导的自旋态开关增强锂硫电池的氧化还原动力学


锂硫（Li−S）电池因其高理论能量密度而成为下一代可充电电池的理想候选者。然而，缓慢的氧化还原动力学阻碍了锂硫电池的发展。据报道，通过引入催化材料可以加速多硫化锂（LiPS）的转化动力学。大环金属卟啉由于其优异的化学稳定性和结构可调性而受到广泛关注。在此，我们设计了一系列被给电子基团和吸电子基团取代的铁卟啉。根据电化学表征和理论计算，该官能团可以改变中心Fe的自旋状态并调节其催化性能。甲氧基取代的铁卟啉（FeTPP-4OMe）显示出更小的带隙并有利于电子转移。结果，采用 FeTPP-4OMe 的 Li−S 电池的比容量为 1,062.0 mA h g，在 0.5 C 下循环 500 次后仍保持 771.4 mA h g 的高比容量，容量衰减为 0.055%。这项工作为Li−S电池中金属大环化合物的官能团修饰提供了指导。