Effect of Al addition on formation of layer-structured LiNiO₂

Kinetics and formation mechanism of undoped and Al-doped LiNiO₂ from Li₂CO₃ and NiO were investigated in this study. Without the addition of Al ions, sluggish kinetics for the formation of undoped LiNiO₂ was observed. The fraction of undoped LiNiO₂ reached 50% after Li₂CO₃ and NiO reacted at 700°C for 150 min. With the addition of 25% of Al ion, the fraction of Al-doped LiNiO₂ reached 50% within 60min at 700°C. The analysis of kinetics study indicates that the formation of undoped and Al-doped LiNiO₂ is a diffusion-controlled process. Furthermore, the rate constant determined from Jander model {[1 - (1 - α)^1/3]² = Kt} was significantly enhanced by the addition of Al. The activation energy for the formation of LiNiO₂ drastically decreased from 190k J/mole (undoped reaction) to 83 kJ/mole when 25% Al was added. The enhancement of LiNiO₂ formation by Al doping is attributed to the structure resemblance between α-LiAlO₂ and LiNiO₂. α-LiAlO₂ acts as the seeding material which provides nucleation sites for the growth of LiNiO₂.