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

固体电解质界面对锂离子电池的性能起着至关重要的作用。SEI是负极的石墨活性物质颗粒顶部的钝化层，它在电池的第一次充电循环期间形成，并防止锂化石墨进一步分解电解液。在电池生产过程中，为了获得良好的SEI性能，必须非常缓慢地形成SEI。这一耗时的过程大大增加了电池的生产成本。此外，在电池的进一步充电/放电期间老化SEI降低了循环寿命。尽管SEI具有重要的作用，但Li+离子、分子和电子在SEI中的传输机制以及与SEI相关的形成和生长机制还不是很清楚。理想的SEI将允许快速的Li+离子传输，但会完全阻止电子和分子。然而，真正的SEI允许分子和/或电子在SEI上缓慢传输，这会导致SEI老化。在这个项目中，我们将使用一些精心挑选的补充实验技术来阐明SEI的形成条件、形成和生长动力学、化学和形态特性、机械特性以及传输特性之间的关系。为此，我们将在定义良好的碳电极上生长模型型SEI，即在接触碳酸盐基电解液的玻璃碳电极、溅射碳电极和高取向热解石墨(HOPG)电极上生长。我们将使用恒流方案来形成SEI，以便通过改变形成电流密度来改变SEI的性质。我们的结果将有助于改进的SEI模型的发展。为此，我们将与电化学多物理模拟领域的一个小组合作。

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.