Stoichiometry matters: correlation between antisite defects, microstructure and magnetic behavior in the cathode material Li1-zNi1+zO2

As contemporary battery applications such as electric vehicles demand higher energy densities, layered LiNiO2 (LNO) could contribute as the end-member of the LiNi1-x-yCoxMnyO2 (NCM) family with the highest extractable specific capacity in a practical voltage window. Achieving high capacities requires among other things a defect free crystal structure, which is not easily achieved due to the natural occurrence of Ni excess on the Li site (Ni-Li) and/or antisite defects where Ni and Li switch crystallographic sites. Here, we present a study of the evolution of point defects in a series of LNO samples varying from underlithiated to fully lithiated stoichiometry in layered Li1-zNi1+zO2 with -0.05 <= z <= 0.35. Using the high angular resolution of synchrotron X-ray diffraction complemented with the different elements contrast provided by neutron diffraction, we are able to identify two defect regimes. In the first regime, at the underlithiated end, both Ni-Li as well as Li on the Ni site (Li-Ni) defects are present. Inhibited crystal growth during synthesis is found to coincide with the presence of these Li-Ni defects for z >= 0.15. Upon decreasing z values and the vanishing of Li-Ni, the primary particle size distribution as well as average refined crystallite size increases. Investigation of the local structure by nuclear magnetic resonance reveals the presence of a Li environment not detected by diffraction methods at low z, the Li-rich end of the sample series. Finally, magnetometry data suggest the onset of the ferrimagnetic-to-antiferromagnetic transition in LNO correlates with the elimination of Li-Ni defects in the structure. The present study thus not only highlights the correlation between defect chemistry and physical properties, but also shows the relationship to crystal growth, a field highly relevant for industrial battery cathode materials engineering.