Probing Al Distribution in LiCo0.96Al0.04O2 Materials Using 7Li, 27Al, and 59Co MAS NMR Combined with Synchrotron X-ray Diffraction

We prepared Al-doped LCO (LCA) powders with low Al content (4%) with a controlled Li/(Co + Al) stoichiometry by a solid-state reaction using Li 2 CO 3 and two types of Co/Al precursors: simply mixed (Co 3 O 4 and Al 2 O 3 ) or heat-treated (Co 3 O 4 and Al 2 O 3 ). These samples were thereby used to propose a reliable protocol with the aim to discuss the homogeneity of the Al doping for LiCo 1- y Al y O 2 (LCA) prepared with low Al content by evidencing the distribution of Al within the powders, which clearly affects the electrochemical profiles of associated LCA//Li cells. For all samples we initially also characterized the Li/(Co + Al) stoichiometry by 7 Li MAS NMR, to discard the possible effect of excess Li in the samples. Synchrotron XRD combined with 27 Al and 59 Co MAS NMR then provided a deep understanding of the doping homogeneity at the powder or particle scale. We showed that doping the Co 3 O 4 spinel precursor by reacting it with Al 2 O 3 may be avoided, as it most likely leads to an inhomogeneous mixture of Co 3 O 4 and Co 3- z Al z O 4 as precursor, eventually reflecting in the final LiCo 0.96 Al 0.04 O 2 powder, which shows a nonhomogeneous Al distribution. We believe that such a detailed characterization should be the first step toward a deeper understanding of the real beneficial effect(s) of Al doping on the high voltage performance of LCO.