Degradation Mechanisms of SiOx Composite Electrodes in Various Electrolytes: Insights from Solid-Electrolyte Interphase Growth Modeling and Characterization

The detailed mechanisms of the growth of the solid electrolyte interphase (SEI) and its impact on the degradation of battery performances are still largely unknown, in particular since they depend on the combination of active materials with electrolyte. Here, we investigate the degradation of SiO x negative electrodes of industrial grade combined in full cells with LiCoO 2 positive electrodes and two different carbonate electrolytes, one including fluoroethylene carbonate (FEC) and the other ethylene carbonate (EC). Post-mortem study at different state of health of the battery, based on combined electrochemical methods and X-ray photoelectron spectroscopy, allow to link the lithium consumption in both electrolytes to the formation of the SEI, whose chemical composition and thickness depends on the nature of the used electrolyte. We find that cycling aging is about two times slower in the electrolyte with FEC compared to the electrolyte with EC. We propose a simple numerical model of SEI growth based on experimental insights, that allows us to describe electrochemical capacity losses as a function of electrolyte composition. Our findings evidence the relation between the evolution of the SEI composition across battery life and the global amount of electrolyte consumption.