René Hausbrand

Surface and Interface Analysis of LiCoO2 and LiPON Thin Films by Photoemission: Implications for Li-Ion Batteries

Abstract Thin film technology is applied in different fields of Li-ion battery research and development, such as the fabrication of thin film cells and model electrodes. Data obtained by surface and interface analysis of thin films provides important insights into fundamental processes such as charge compensation mechanism or interface formation. In this overview, we present the analysis of LiCoO2 and LiPON thin films using photoemission. It includes data obtained directly after preparation, after exposure to molecular species and/or after electrode-electrolyte interface formation. Information both on electronic structure and surface chemistry of the films is deduced from core level spectra, valence band spectra, Fermi level position and work function. Next to PES analysis of our films, we address composition, structure and functionality in more general terms in relation to literature.

In-operando photoelectron spectroscopy for batteries: Set-up using pristine thin film cathode and first results on NaxCoO2

A model all-solid-state battery cell with a thin film NaxCoO2 cathode was assembled under ultra-high vacuum conditions and cycled inside the vacuum chamber, using a dedicated sample holder. We present in-operando x-ray photoelectron spectroscopy measurements of a NaxCoO2 cathode at different charging states. During battery operation, the change in sodium content, the change in cobalt oxidation state, and the evolution of the O1s and VB emissions could be monitored. Comparison with a conventional post-mortem analysis technique showed that the new measurement technique produces comparable results regarding the oxidation state of the transition metal, but sodium and oxygen results show differences due to cathode/electrolyte interfacial reactions for conventional analysis. By using surface layer-free samples in the presented techniques, we could circumvent such reactions and obtain reliable spectra for the pure bulk-like active cathode material.