Long term porosity of solid electrolyte interphase on model silicon anodes with liquid battery electrolytes

A stable solid electrolyte interphase (SEI) is of great importance for battery electrodes in terms of cycling as well as for its shelf life. While SEI formation on silicon anodes is generally only studied after the first charge and discharge of cells and initial reaction of electrolyte, we show the formation of a liquid/solid SEI in symmetric cells with silicon electrodes in contact with carbonate and glyme-based electrolytes under close to open circuit conditions and its behavior during long-term ageing. Activation energies of SEIs were measured via temperature-dependent electrochemical impedance spectroscopy (EIS) to study the contribution of liquid/solid phases to ion transport. The effect of different solvents, salts, their concentrations, and final water content of the glyme-electrolyte on the SEI was studied in detail. SEIs formed in cells with glyme-based electrolytes are generally more porous than the ones in cells with carbonate-based electrolytes. The addition of vinylene carbonate to glyme electrolyte is shown to be beneficial for its SEI, as it causes lower and more stable SEI resistances over time. A small amount of water in glyme electrolytes causes a denser SEI without much change in SEI resistance.