Understanding Solid Electrolyte Interphase (SEI) Species at the Electrode-Electrolyte Interface in Liquid Lithium Metal Batteries Via in-Situ Fourier Transform Infrared (FTIR) Spectroscopy

Lithium metal is the ideal candidate to replace conventional carbonaceous anodes due to its high theoretical specific capacity of 3860 mAh/g and low negative thermodynamic potential of -3.040 V vs. SHE [1]. Fine tuning the solid-electrolyte interphase (SEI) is critical for the practical implementation of liquid lithium metal batteries [2]. The presence of particular SEI species are hypothesized to improve the coulombic efficiency and mitigate dendrite formation for enhanced lifetime and safety, respectively [2]. Recently, Zhang et al. developed a novel in-situ Fourier transform infrared (FTIR) spectroscopy method to reveal electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries [3]. We leverage this technique and apply it to the Cu side in a Li || Cu battery to probe SEI growth and evolution. In this study, we systematically change the salt, solvent and additive components of the electrolyte and monitor the organic and inorganic SEI species that form under different electrochemical conditions. Furthermore, we directly correlate the chemical composition of the SEI to cell-level coulombic efficiency [4]. Complimentary characterization techniques will be used to further resolve the chemical structure of the SEI. Finally, results from this study will help generate descriptors for the rationale design of new electrolytes. References 1. Cheng, Xin-Bing, et al. "Toward safe lithium metal anode in rechargeable batteries: a review." Chemical reviews 117.15 (2017): 10403-10473. 2. Peled, E., and S. Menkin. "SEI: past, present and future." Journal of The Electrochemical Society 164.7 (2017): A1703. 3. Zhang, Yirui, et al. "Revealing electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries by in situ Fourier transform infrared spectroscopy." Energy & Environmental Science 13.1 (2020): 183-199. 4. Hobold, Gustavo M., et al. "Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes." Nature Energy 6.10 (2021): 951-960.