Interface phenomena in ionic systems: a surface science approach

• Applicants: Professor Dr. Karsten Albe; Dr. René Hausbrand
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 258032533

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).

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Wolfram Jaegermann