The structural and electronic effects of Al-substitution in LiNi0.45Mn0.45Co0.1-yAlyO2 electrode materials were explored on a local scale using X-ray absorption spectroscopy (XAS). Homogeneous substitution of Al is observed between 0 <= y <= 0.10, additionally causing relaxation within the strained edge-sharing metal octahedra composing the transition metal plane. Ex situ measurements on electrochemically charged electrodes confirm that the main charge compensation mechanism occurs via oxidation of Ni, though a contribution centered at the Co-sites was detected in the early stages of charging. Al-substitution, meanwhile, appears to have a negligible local order effect. Analysis of electrochemically cycled materials suggests that there is a beneficial structural consequence of the Al-substitution, which limits the disorder within the local structure of the substituted samples compared to the fresh layered oxides. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.048209jes] All rights reserved.