Understanding Mechanisms of Ethylene Carbonate Gassing and Gas-Reducing Additives Using Isotopically Labeled Solvents

Gas generation during Li-ion battery operation remains a problem that can affect both safety and operational lifetime of the battery. Electrolyte solvents are a key source of gas generation1 and while gas-reducing additives have been identified, the underlying mechanisms require more study to fully understand the role between solvent structure and gas generation. Understanding of these gassing mechanisms can lead to optimized electrolyte systems with reduced gassing for the next generation of Li-ion batteries. Previous studies in the literature2 have detailed the use of 13C-labeled EC and DEC to identify the proportions of CO2 and CO that are derived from solvent sources, which in turn can help inform mechanistic understanding on gas generation in Li-Ion Batteries. As previously studied by Silatronix®, electrolytes containing organosilicon (OS) materials show significantly reduced gas generation during high temperature storage and cycling in pouch cells primarily through CO2 reduction.3 Studies utilizing simple carbonate blends indicated that EC was the primary source of CO2; therefore, it was hypothesized that OS materials reduce gassing by preventing EC decomposition during high temperature testing. In this work, 13C-labeling was used to identify the sources of gas species in ternary carbonate electrolytes after both first charge (SEI formation4) and high temperature storage (extended aging) to allow the effects of electrolyte additives gas reduction to be elucidated. Gas component analysis was performed using a calibrated GC-MS, providing identification and quantification of each gas species (labeled and unlabeled). These data give insight into how the labeled carbonate solvent may decompose into the observed gas phase products during the first charge (i.e., during SEI layer formation) and high temperature storage. Ethylene carbonate (EC) is found to be the primary source of ethylene generation, as well as a significant source of CO2 and CO. With the addition of OS, the most notable effect is that the previously seen reduction in all gas components is due to not only reduction of EC-related sources, but reduction in non-EC gas sources as well. 1 Rowden, B.; Garcia-Araez, N., A Review of Gas Evolution in Lithium-Ion Batteries. Energy Rep. 2020, 6, 10-18. 2Onuki, M.; Kinoshita, S.; Sakata, Y.; Yanagidate, M.; Otake, Y.; Ue, M.; Deguchi, M., Identification of the Source of Evolved Gas in Li-Ion Batteries using 13C-labeled Solvents. Journal of the Electrochemical Society 2008, 155, A794. 3 Guillot, S.L.; Usrey, M.; Peña-Hueso, A.; Kerber, B.; Zhou, L.; Du, P.; Johnson, T., Reduced Gassing In Lithium Ion Batteries With Organosilicon Additives. Journal of the Electrochemical Society 2021, 168, 030533. 4 Ktristiina Heiskanen, S.; Kim, J.; Lucht, B., Generation and Evolution of the Solid Electroyte Interphase of Li-Ion Batteries. Joule 2019, Volume 3 Issue 10, 2322.