Direct Monitoring of Li<sub>2</sub>S<sub>2</sub> Evolution and Its Influence on the Reversible Capacities of Lithium‐Sulfur Batteries
Yufeng Luo, Zhenhan Fang, Shaorong Duan, Hengcai Wu, Haitao Liu, Yuxing Zhao, Ke Wang, Qunqing Li, Shoushan Fan, Zijian Zheng, Wenhui Duan, Yuegang Zhang, Jiaping Wang
Abstract
Abstract The polysulfide (PS) dissolution and low conductivity of lithium sulfides (Li 2 S) 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 Li 2 S, lithium disulfide (Li 2 S 2 ) evolutions are always overlooked. Herein, Li 2 S 2 evolutions are monitored from the operando measurements on the pouch cell level. Results indicate that Li 2 S 2 undergoes slow electrochemical reduction and chemical disproportionation simultaneously during the discharging process, leading to further PS dissolution and Li 2 S generation without capacity contribution. Compared with the fully oxidized Li 2 S, Li 2 S 2 still residues at the end of the charging state. Therefore, instead of the considered Li 2 S and PSs, slow electrochemical conversions and side chemical reactions of Li 2 S 2 are the determining factors in limiting the sulfur utilization, corresponding to the poor reversible capacity of Li‐S batteries.