Influence of Cathode Origin on the Crystallization of LiNbO3 Coatings on Ni-Rich Layered Oxides.

Layered transition-metal oxides are widely used as cathode materials for lithium-ion batteries, and surface coating with lithium niobates is a common strategy to improve their electrochemical performance. In many studies, the formation of crystalline Li3NbO4 is reported as the final product of Li-Nb-O coating processes after thermal treatment. However, experimental observations obtained for different cathode morphologies and processing conditions indicate that the structural evolution of Li-Nb-O coatings is more complex. A systematic analysis of temperature-dependent diffraction data, combined with comparison to literature results for structurally related systems, shows that Li3NbO4 is not the only crystalline phase that can form during high-temperature treatment. Depending on coating optimization, cathode morphology, and thermal history, the formation of an Nb-stabilized rock-salt-type Li-Nb-M-O phase, described as xLi3NbO4-(1-x)LiMO2 (M = Ni, Co, Mn), is observed. These findings explain the absence of LiNbO3 and/or Li3NbO4 reflections in certain coated materials and demonstrate that the frequent assignment of Li-Nb-O coating products solely to Li3NbO4 is incomplete. The results were obtained from samples containing increased Li-Nb coating amounts to facilitate detection of crystalline reaction products by laboratory X-ray diffraction (XRD).