Surface properties of LiCoO₂, LiNiO₂ and LiNi_1-xCo_xO₂

Authors

Anthony W. Moses, University of Nebraska - Lincoln
Harry G. Garcia Flores,, University of Nebraska - Lincoln
Jong-Gyu Kim, University of Nebraska - LincolnFollow
Marjorie Langell, University of Nebraska - LincolnFollow

Date of this Version

March 2007

Comments

Published in Applied Surface Science 253:10 (March 15, 2007), pp. 4782–4791. doi:10.1016/j.apsusc.2006.10.044 Copyright © 2006 Elsevier B.V. Used by permission. http://www.sciencedirect.com/science/journal/01694332

Abstract

The surface composition and chemical environment of LiCoO₂, hexagonal LiNiO₂, cubic LiNiO₂, and the mixed transition metal oxide LiNi_0.5Co_0.5O₂ have been determined by Auger electron and X-ray photoelectron spectroscopies. While the LiCoO₂ surface properties can easily be extrapolated from bulk composition, the nickel-containing materials are less straightforward. Their surface concentration tends to be depleted in lithium relative to that of the bulk and shows an atypical chemical environment for the constituent elements. The Ni 2p XPS photoemission suggests a near “ NiO-like” selvedge through the XPS binding energies and satellite structure which are essentially identical to that of NiO; the spectrum appears fairly insensitive to lithium concentration. Although there is little evidence for higher binding energy Ni³⁺ species or for an electron poor Ni^2.δ+derived band structure in the XPS, the lattice oxygen is very electron-rich and yields among the lowest binding energies reported for a transition metal oxide. The nickel-containing lithium oxide selvedge is thus not simply “NiO” and the surface lithium cations have a measurable effect on the electronic structure even in their more highly depleted levels. This is explained in the context of the charge-transfer model of the oxide band structure.