Direct Monitoring of Li2S2 Evolution and Its Influence on the Reversible Capacities of Lithium‐Sulfur Batteries

• Published in: Angewandte Chemie Vol. 135; no. 11
• Main Authors: Luo, Yufeng, Fang, Zhenhan, Duan, Shaorong, Wu, Hengcai, Liu, Haitao, Zhao, Yuxing, Wang, Ke, Li, Qunqing, Fan, Shoushan, Zheng, Zijian, Duan, Wenhui, Zhang, Yuegang, Wang, Jiaping
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 06.03.2023
• Subjects: Batteries; Chemical Reactions; Chemical reduction; Chemistry; Conductive Interlayer; Constraining; Disproportionation; Dissolution; Electrochemistry; Evolution; Lithium; Lithium Disulfides; Lithium sulfur batteries; Lithium Sulfur Battery; Low conductivity; Operando Measurement; Sulfur
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202215802

The polysulfide (PS) dissolution and low conductivity of lithium sulfides (Li2S) are generally considered the main reasons for limiting the reversible capacity of the lithium‐sulfur (Li‐S) system. However, as the inevitable intermediate between PSs and Li2S, lithium disulfide (Li2S2) evolutions are always overlooked. Herein, Li2S2 evolutions are monitored from the operando measurements on the pouch cell level. Results indicate that Li2S2 undergoes slow electrochemical reduction and chemical disproportionation simultaneously during the discharging process, leading to further PS dissolution and Li2S generation without capacity contribution. Compared with the fully oxidized Li2S, Li2S2 still residues at the end of the charging state. Therefore, instead of the considered Li2S and PSs, slow electrochemical conversions and side chemical reactions of Li2S2 are the determining factors in limiting the sulfur utilization, corresponding to the poor reversible capacity of Li‐S batteries. A series of operando spectral results reveal that Li2S2 undergoes chemical reactions accompanied by its electrochemical conversions during operation for the first time. The chemical reactions related to Li2S2 can increase polysulfide dissolution and Li2S generation without capacity contribution. Instead of the commonly considered Li2S, Li2S2 is the solid “dead” sulfur species and restricts the actual sulfur utilization and reversible capacity.