Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 69: Electronic structure I

O 69.2: Talk

Thursday, March 17, 2011, 11:30–11:45, WIL C107

Localized gap states in cobalt/nickel mixed oxides — •Stephan Schmidt and Dieter Schmeißer — Brandenburg University of Technology Cottbus, Konrad-Wachsmann-Allee 17, 03046 Cottbus

Replacing Co by large amounts of Ni is considered to reduce costs in Li-Ion-Batteries while maintaining their performance. We investigate the electronic structure of Co/Ni compounds because of their direct impact on battery operation. Thin Co/Ni oxide films on metal substrates were prepared by dropping/spin-coating from nitrate solutions followed by subsequent annealing in air and UHV. The following Co to Ni ratios have been investigated: 50/50, 40/60, 30/70, and 20/80. The results are compared with the pure Co-oxide and magnetron sputtered LiCoO₂ reference samples. Spectroscopic measurements on these samples were carried out at the U49/2 beamline at BESSYII, Berlin. XPS of the transition metal (TM) 2p states reveals the existence of charge transfer ground states and different oxidation states. NEXAFS at the Co L₃, Ni L₃ and O K edges reflects the density of unoccupied states while resonant PES at these edges provides the related partial density of states (pDOS). Therefore, these techniques can be used in order to distinguish between the different contributions of TM3d and O2p states in the valence band region. We find sharp localized features at the valence band edge and at the O K and Co L₃ absorption edges that are discussed to originate from the strong hybridization between metal and oxygen states in that region.