Stoichiometry matters: correlation between antisite defects, microstructure and magnetic behavior in the cathode material LiNiO

As contemporary battery applications such as electric vehicles demand higher energy densities, layered LiNiO 2 (LNO) could contribute as the end-member of the LiNi 1− x − y Co x Mn y O 2 (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 Li 1− z Ni 1+ z O 2 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. Using synchrotron X-ray and neutron diffraction, NMR and magnetometry techniques, this study reveals how point defects evolve and critically affect particle growth and magnetic properties in the cathode material Li 1− z Ni 1+ z O 2 (−0.05 ≤ z ≤ 0.35).