Interface phenomena in ionic systems: a surface science approach

具有离子电极的电化学装置对我们未来的能源经济具有重要意义。这种电化学装置中的界面对其性能起着关键作用，但在基本水平上还没有被理解。在这个项目中，我们的目标是提高对实际界面的基本理解。为此，我们对锂离子电池中的界面进行了研究，更具体地说，该方案旨在研究锂离子电池复合正极中非均相界面的结构和反应性，以及它们对锂离子和电子传输的影响。通过实验和计算相结合的研究，我们的目标是更好地了解电池的性能和故障模式，并随后阐述接口的合理设计。因此，我们的建议解决了未来先进电池器件以及一般电化学器件设计的关键问题。我们的方法是用表面科学方法表征定义良好的异质界面，并将结果与理论计算相结合。通过气相的冷凝逐步制备界面，并在每一步后进行光电子能谱分析。这一方法已被证明对界面的形成和性质产生了独特的见解，例如能级排列、偶极和空间电荷层的存在以及离子和电子转移。工作的重点是电极/电解液界面。在工作的实验部分，我们应用了我们在达姆施塔特的超高压集群系统，专门用于电池研究，以及我们的基于超高压的固液分析系统，在柏林的贝西II。我们通过沉积异质膜序列，使用物理气相沉积方法，或通过吸附挥发性电解质物种来制备特定的界面。光电分析得到了其他表面科学技术的支持，如HREELS和HRTEM，以及标准的电化学和电学测量。由于该提议的基本性质，工作是在众所周知的材料上进行的。讨论了正极材料与电解液(液体和固体)和集电体材料的界面。具体地说，我们将制备LixCoO2薄膜，并研究界面形成与锂含量的关系。固体电解质为含氮磷酸盐玻璃(Lipon)，标准液体电解质为碳酸二乙酯(DEC)。

Electrochemical devices with ionic electrodes are of central importance to our future energy economy. Interfaces in such electrochemical devices play a key role for their performance, but are not understood on a fundamental level. In this project, we aim to improve the fundamental understanding of practical interfaces. To this end, we investigate interfaces in Li-ion batteries.More specifically, this proposal aims to investigate the structure and reactivity of heterogeneous interfaces inside Li-ion battery composite cathodes and their influence on lithium ion and electron transport. By combining experimental and computational studies our goal is to better understand battery performance as well as failure modes and subsequently elaborate a rational design of the interfaces. Our proposal therefore addresses key issues for the future design of advanced battery devices, as well as electrochemical devices in general.Our approach is to characterize well defined hetero-interfaces by surface science methods and combine the results with theoretical calculations. Interfaces are prepared step-by-step by condensation from the gas phase, and analyzed by photoemission after each step. This methodology has been shown to yield unique insights about interface formation and properties, such as energy level alignment, presence of dipole- and space charge layers as well as ion- and electron transfer. The focus of the work is on electrode/electrolyte interfaces.For the experimental part of the work, we apply our UHV-cluster system at Darmstadt, dedicated to battery research, and our UHV-based solid-liquid analysis system at Bessy II in Berlin. We prepare specific interfaces by deposition of hetero film sequences, using physical vapor deposition methods, or by adsorption of volatile electrolyte species. Analysis by photoemission is supported by other surface science techniques, such as HREELS and HRTEM, as well as standard electrochemical and electrical measurements.Due to the fundamental nature of the proposal, work is conducted on well known materials. Interfaces of cathode material both with electrolyte (liquid as well as solid) and current collector materials are addressed. Specifically, we will prepare LixCoO2 thin films and investigate the interface formation as function of lithium content. The solid electrolyte is nitrogen-substituted phosphate glass (LiPON), the standard liquid electrolyte species the solvent diethyl carbonate (DEC).