Probing Li-Ni Cation Disorder in Li1−xNi1+x−yAlyO2Cathode Materials by Neutron Diffraction

Abstract

Neutron diffraction is a unique technique to study Li-ion batteries because of its high sensitivity toward detecting lithium ions and ability to differentiate between different cations. This information is essential for understanding the subtle structure/property relationships of active electrode materials. In this study, neutron diffraction was utilized to probe the cation disorder in LiNiO₂ with and without Al³⁺ substitution by different synthesis processes. The powder neutron diffraction revealed that a strong oxidizer rather than Al³⁺-doping greatly reduces Li⁺ and Ni²⁺ mixing. The amount of Ni²⁺ at Li-site is 6% for Li_1−x(Ni_0.75Al_0.25)_1+xO₂ synthesized from excess LiOH, while it is only 0.6% for Li_1−x(Ni_0.75Al_0.25)_1+xO₂ which was synthesized from excess Li₂O₂. The reduction of Ni²⁺ at Li-sites greatly improves electrochemical performance. The substitution of Al³⁺ stabilizes the hexagonal lattice of Li_1−xNi_1+x−yAl_yO₂ even for highly lithium-deficient phases.