Characterization of the Transport Properties and of the Formation and Growth Mechanims of the Solid Electrolyte Interphase (SEI) on Carbon Model-Type Electrodes

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The solid electrolyte interphase (SEI) plays an important role for the performance of lithium-ion batteries. The SEI is a passivation layer on top of the graphite active material particles of the negative electrode, which is formed during the first charging cycle of the battery and which prevents further decomposition of the electrolyte by the lithiated graphite. During battery production, the SEI has to be formed very slowly in order to achieve good SEI properties. This time-consuming process contributes significantly to the battery production costs. Furthermore, the ageing the SEI during the further charging/discharging of the battery reduces the cycle life. Despite the important role of the SEI, the transport mechanisms of Li+ ions, molecules, and electrons across the SEI and the related formation and growth mechanisms of the SEI are not well understood. An ideal SEI would allow for fast Li+ ion transport, but would block electrons and molecules completely. However, real SEI allow for a slow transport of molecules and/or electrons across the SEI, which leads to SEI ageing. In this project, we will use a number of carefully chosen complementary experimental techniques to elucidate the relations between formation conditions of the SEI, formation and growth kinetics, chemical and morphological properties, mechanical properties, as well as transport properties. To this end, we will grow model-type SEIs on well-defined carbon electrodes, namely on glassy carbon electrodes, sputtered carbon electrodes and high-oriented pyrolytic graphite (HOPG) electrodes in contact to carbonate-based electrolytes. We will use galvanostatic protocols for SEI formation in order to alter the SEI properties by varying the formation current density. Our results will contribute to the development of improved SEI models. To this end, we will collaborate with a group in the field of electrochemical multiphysics modeling.