Probing Al Distribution in LiCo 0.96 Al 0.04 O 2 Materials Using 7 Li, 27 Al, and 59 Co MAS NMR Combined with Synchrotron X-ray Diffraction

• Published in: Inorganic chemistry 2020-03, Vol.59 (5), p.2890-2899
• Main Authors: Duffiet, Marie, Blangero, Maxime, Cabelguen, Pierre Etienne, Song, Kyeong Se, Fauth, François, Delmas, Claude, Carlier, Dany
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b03260

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 CO and two types of Co/Al precursors: simply mixed (Co O and Al O ) or heat-treated (Co O and Al O ). These samples were thereby used to propose a reliable protocol with the aim to discuss the homogeneity of the Al doping for LiCo Al O (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 Li MAS NMR, to discard the possible effect of excess Li in the samples. Synchrotron XRD combined with Al and Co MAS NMR then provided a deep understanding of the doping homogeneity at the powder or particle scale. We showed that doping the Co O spinel precursor by reacting it with Al O may be avoided, as it most likely leads to an inhomogeneous mixture of Co O and Co Al O as precursor, eventually reflecting in the final LiCo Al O 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.