Elemental sulfur, an abundant and low toxicity material, is emerging as a promising cathode material due to higher theoretical specific capacity compared with traditional metal oxides used in Li-ion batteries. Lithium-Sulfur (Li-S) batteries rely on the reduction of sulfur (S₈) to lithium sulfide (Li₂S) through gradual evolution of polysulfide (Li₂S_n) during the discharge process. Many of the intermediate polysulfide species (Li₂S_n; 4 ≤ n ≤ 8) are highly soluble in electrolyte solvents, leading to cathode corrosion and capacity loss. The dissolved polysulfide species shuttle towards the reactive Li-anode, and accelerates Li anode poisoning through highly a complex solid-electrolyte interphase (SEI) layer formation. The SEI layer is generated by complex interfacial reactions involving transient species/structures; the challenge is to detect, identify and quantify these reactions, which typically span a wide spatial and temporal region and are inaccessible by any single spectroscopic and/or classical computational method. Traditional ex-situ spectroscopic capabilities^1-4 often fail to capture critical transient and metastable species which dictate the SEI layer evolution. Hence, it is critical to develop in situ multimodal approaches that can provide unprecedented chemical imaging of these complex interfaces⁵. In this presentation, we will discuss our recent in-situ X-ray photoelectron spectroscopy (XPS) analysis which yielded an unparalleled view of the chemical speciation and microscopic evolution of the SEI layer (see Figure 1). In combination with computational modeling these data provided a method to establish quantitative understanding of complex interfacial interactions in Li-S batteries.

References:

1. J. Chen, K. S. Han, W. A. Henderson, K. C. Lau, M. Vijayakumar, T. Dzwiniel, H. Pan, L. A. Curtiss, J. Xiao and K. T. Mueller, Advanced Energy Materials 6 (11) (2016).
2. H. Pan, K. S. Han, M. Vijayakumar, J. Xiao, R. Cao, J. Chen, J. Zhang, K. T. Mueller, Y. Shao and J. Liu, ACS Applied Materials & Interfaces 9 (5), 4290-4295 (2017).
3. N. N. Rajput, V. Murugesan, Y. Shin, K. S. Han, K. C. Lau, J. Chen, J. Liu, L. A. Curtiss, K. T. Mueller and K. A. Persson, Chemistry of Materials 29 (8), 3375-3379 (2017).
4. M. Vijayakumar, N. Govind, E. Walter, S. D. Burton, A. Shukla, A. Devaraj, J. Xiao, J. Liu, C. Wang, A. Karim and S. Thevuthasan, Physical Chemistry Chemical Physics 16 (22), 10923-10932 (2014).
5. M. I. Nandasiri, L. E. Camacho-Forero, A. M. Schwarz, V. Shutthanandan, S. Thevuthasan, P. B. Balbuena, K. T. Mueller and V. Murugesan, Chemistry of Materials 29 (11), 4728-4737 (2017).