Probing Li-Ni Cation Disorder in Li_1−xNi_1+x−yAl_yO₂Cathode Materials by Neutron Diffraction

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 LiNiO 2 with and without Al 3+ substitution by different synthesis processes. The powder neutron diffraction revealed that a strong oxidizer rather than Al 3+ -doping greatly reduces Li + and Ni 2+ mixing. The amount of Ni 2+ at Li-site is 6% for Li 1− x (Ni 0.75 Al 0.25 ) 1+ x O 2 synthesized from excess LiOH, while it is only 0.6% for Li 1− x (Ni 0.75 Al 0.25 ) 1+ x O 2 which was synthesized from excess Li 2 O 2 . The reduction of Ni 2+ at Li-sites greatly improves electrochemical performance. The substitution of Al 3+ stabilizes the hexagonal lattice of Li 1− x Ni 1+ x − y Al y O 2 even for highly lithium-deficient phases.