Overall, we have shown that combined experimental and theoretical model studies, using structurally well-defined electrodes as well as an equally well-defined, simplified environment, in this case ultrahigh vacuum, can provide detailed insights into the complex molecular scale processes during the initial stages of SEI formation. They allow us to separate chemical and electrochemical effects and provide information on the role of the electrode surface in the underlying electrolyte decomposition processes. These are key ingredients for a systematic, knowledge-based development of electrolytes with improved stabilities and SEI formation, and thus indispensable for the development of improved future battery systems.