In Situ X‑ray Absorption Spectroscopic Investigation of the Capacity Degradation Mechanism in Mg/S Batteries

• Published in: Nano letters Vol. 19; no. 5; pp. 2928 - 2934
• Main Authors: Xu, Yan, Ye, Yifan, Zhao, Shuyang, Feng, Jun, Li, Jia, Chen, Hao, Yang, Ankun, Shi, Feifei, Jia, Lujie, Wu, Yang, Yu, Xiaoyun, Glans-Suzuki, Per-Anders, Cui, Yi, Guo, Jinghua, Zhang, Yuegang
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08.05.2019
• Subjects: capacity degradation mechanism; Mg−S battery; catalyst; in situ XAS
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.8b05208

The Mg/S battery is attractive because of its high theoretical energy density and the abundance of Mg and S on the earth. However, its development is hindered by the lack of understanding to the underlying electrochemical reaction mechanism of its charge–discharge processes. Here, using a unique in situ X-ray absorption spectroscopic tool, we systematically study the reaction pathways of the Mg/S cells in Mg­(HMDS)2–AlCl3 electrolyte. We find that the capacity degradation is mainly due to the formation of irreversible discharge products, such as MgS and Mg3S8, through a direct electrochemical deposition or a chemical disproportionation of intermediate polysulfide. In light of the fundamental understanding, we propose to use TiS2 as a catalyst to activate the irreversible reaction of low-order MgS x and MgS, which results in an increased discharging capacity up to 900 mAh·g–1 and a longer cycling life.