(Poster Award Winner 1) Investigating the Impact of Ethylene Carbonate Reaction Pathways on the Solid Electrolyte Interphase in Li-Ion Batteries

Abstract

A high-performing Li-ion battery relies heavily on the solid electrolyte interphase (SEI), which is composed of various decomposition products, primarily from reduced additives or electrolyte species such as ethylene carbonate (EC). The composition of the SEI evolves and continues to form during the operation of a Li-ion battery, making it challenging to fully understand through post-mortem analysis alone. To gain a complete understanding of the EC reaction pathways and their respective contributions to the SEI, it is necessary to employ analytical techniques that monitor the battery during operation. Online Electrochemical Mass Spectrometry (OEMS) is one such technique that can sample the gas composition of a battery, providing an overview of voltage-dependent gas evolution processes.1 This presentation focuses on two EC reaction pathways that occur on a model carbon electrode.2 The first pathway, the "EC ring-opening" reaction pathway, is initiated by hydroxides/alkoxides at potentials above 1.5 V vs. Li+/Li and is associated with CO2 evolution.3 , 4 The second pathway, the "EC reduction" pathway, occurs at potentials below 0.9 V vs. Li+/Li and is identified by C2H4 evolution.5 Both reaction pathways contribute to the formation of the SEI, and they compete with each other. If EC ring-opening is favoured, it can suppress EC reduction. Figure 1 illustrates the competing relationship between the two different EC reaction pathways, where the addition of EC ring-opening initiators (H2O) increases CO2 and reduces C2H4. It is essential to consider all possible EC reaction pathways, not just the desired one, when forming the SEI. The presentation concludes with a discussion of the potential implications that EC ring-opening may have on a Li-ion cell. Figure 1 . Comparison between the total CO2 and C2H4 evolution during the initial cyclic voltammetry cathodic sweep in a Glassy carbon | 1 M LiPF6 EC:DEC | LiFePO4 cell. References R. Lundström and E. J. Berg, J. Power Sources, 485, 229347 (2021).R. Lundström, N. Gogoi, X. Hou, and Berg Erik J., Submitted (2023).M. Metzger, B. Strehle, S. Solchenbach, and H. A. Gasteiger, J. Electrochem. Soc., 163, 1219–1225 (2016).L. Gireaud, S. Grugeon, S. Laruelle, S. Pilard, and J.-M. Tarascon, J. Electrochem. Soc., 152, A850 (2005).R. Imhof and P. Novák, J. Electrochem. Soc., 145, 1081–1087 (1998). Figure 1