Average and Local Crystal Structure and Electronic Structure of 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 Using First-principles Calculations and Neutron Beam and Synchrotron X-Ray Sources

The average and local crystal structures, and the electronic structure of 0.4Li(2)MnO(3)-0.6LiMn(1/3)Ni(1/3)Co(1/3)O(2) were investigated using a combination of a pair distribution function (PDF) analysis and first-principles calculations. A Rietveld analysis showed that the sample had a Li2MnO3-type structure (space group: C2/m) and that Ni and Co existed at two sites, 49 and 2b, in the transition metal layer. Based on the maximum entropy method using synchrotron X-ray diffraction data, and first-principles calculations, it was determined that the covalencies between 2b and 8j sites in the transition metal layer, and between 2c and 8j sites in the lithium layer, were relatively low. In addition, based on the average length of bonds between transition metal and oxygen ions in the local structure determined by a PDF analysis using synchrotron X-ray and neutron total scattering data, and the ionic radius, the valence of Mn, Ni and Co in this material before charging was tetravalent, between divalent and trivalent, and trivalent, respectively. These results were consistent with the valence obtained from the density of states calculated by the WIEN2k code. (C) The Electrochemical Society of Japan, All rights reserved.