Li1-y,Ni-0.45 Mn0.45Al0.1O2 was synthesized and characterized using both XRD and XANES measurements. The Li/Li1-y,Ni0.45Mn0.45Al0.1O2 cell showed a discharge capacity of 125 mAh/g in the voltage range 4.5-2.5 V. The Ni K and L-II.III-edge XANES results indicated that the Li deintercalation from LiNi0.45Mn0.45Al0.1O2, proceeded mainly by the valence state change of Ni ions over the whole composition range. Structural analysis clarified that most of the Li ions and a small fraction of the Nj ions migrated from the octahedral 3a site to the tetrahedral 6c site with Li de-intercalation. This observed structural change was similar to that of Li I 1-yNi0.5Mn0.5O2,, indicating that this structural change is characteristic in the Li(NiMn)O-2 system. (c) 2007 Elsevier B.V. All rights reserved.