Visualizing Interfacial Collective Reaction Behaviour of Li-S Batteries

Benefited from high energy density (2600 Wh kg–1) and low cost, lithium-sulfur (Li-S) batteries are considered as promising candidates for advanced energy storage systems. Despite tremendous efforts in suppressing the long-standing lithium polysulfides (LiPSs) shuttle effect, the understanding of interfacial reactions of LiPSs at nanoscale remains elusive. This is mainly due to the limitation of in situ characterization tools in tracing liquid/solid conversion of unstable LiPSs at high temporal-spatial resolution. The urgent need is to understand the coupled phenomena inside Li-S batteries, specifically, the dynamic distribution, aggregation, deposition, and dissolution of LiPSs. Herein, by using in situ liquid-cell electrochemical transmission electron microscopy, we directly visualized the transformation of LiPSs over electrode surfaces at atomic scale.[1] Strikingly, an unexpected gathering-induced collective charge transfer of LiPSs was captured on nanocluster active center immobilized surface. It further induced an instantaneous deposition of nonequilibrium Li2S nanocrystals from LiPSs dense liquid phase. Without mediation of active centers, the reactions followed a classical single-molecular pathway, LiPSs transforming into Li2S2 and Li2S step by step. Molecular dynamics simulation indicated that the long-range electrostatic interaction between active centers and LiPSs promoted the formation of dense phase consisting of Li+ and Sn2– (2<n≤6), and the collective charge transfer in dense phase was further verified by ab initio molecular dynamics simulation. The collective interfacial reaction pathway unveils a new transformation mechanism and deepens the fundamental understanding for Li-S batteries.

1. S. Zhou, J. Shi, S. Liu, G. Li, F. Pei, Y. Chen, J. Deng, Q. Zheng, C. Zhao, I. Hwang, C.-J. Sun, Y. Liu, L. Huang, Y. Qiao, G.-L. Xu, J.-F. Chen, K. Amine, S.-G. Sun, H.-G. Liao, Nature, 621, 75–81 (2023).