Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 44: Elektronische Struktur (Experiment und Theorie) III

O 44.6: Talk

Friday, March 12, 2004, 12:30–12:45, H38

Characterisation of the chemical composition and electronic structure of LiCoO₂ thin films using photoelectron spectroscopy — •Andreas Thissen, David Ensling, Javier Fernandez-Madrigal, and Wolfram Jaegermann — FB Materialwissenschaften-Oberflaechenforschung, TU Darmstadt, Petersenstr. 23, D-64287 Darmstadt

LiCoO₂ is used as cathode materials for Li intercalation batteries. Polycrystalline thin films have been prepared by magnetron sputtering in an UHV chamber connected to an analysis system. Chemical analysis using (S)XPS shows that a variation of the sputtering parameters strongly influences the stoichiometry of the films, leading to different Co oxidation states (2+, 3+, 4+). Depending on the chemical composition changes in the electronic structure have been studied by UPS, ResPES and XAS. The results are in good agreement with DFT band structure calculations reported in literature. From ResPES measurements the separation of the O2p- and Co3d-like valence band contributions was possible, giving the occupation numbers as well. It has been shown by AFM, REM, XRD, Raman spectroscopy and EXAFS, that also the morphology and crystal structure of the samples depends on preparation conditions. (Dis)charging experiments have been carried out in an in-situ battery device in order to perform XPS and UPS measurements of the cathode during battery operation. Changes in the electronic structure of the Li1-xCoO₂ host can clearly be correlated to the charging state of the battery.