Structural and electrochemical properties of LiNi1/3Co1/3Mn1/3O2: Calcination temperature dependence

The structure of the layered LiNi_1/3Co_1/3Mn_1/3O₂ has been investigated by powder X-ray diffraction and electron diffraction, and the relationship of the calcination temperature with the crystal structure, morphology and electrochemical properties has been studied. All the unit cell parameters increase monotonically with increasing the calcination temperature. Some of the 00.1] zone electron diffraction patterns for the sample calcined at higher temperature than 1000 °C show extra spots indicating the 2 × 2 ordering in the basal triangular lattice. These results indicate that the high temperature calcination leads to the formation of vacancies in the transition metal layers with the spinel-like ordering. The calcination at higher temperature lowers the specific capacities and degrades the cycle performances, while the packing density of the powder is increased by the sintering. The optimum calcination temperature is 900 °C in order to obtain the electrochemically active and dense packed oxide particles. The decrease of Li composition leads to coprecipitation of the spinel-like second phase in the range of 0.742 ≤ x ≤ 0.884 for Li_xNi_1/3Co_1/3Mn_1/3O₂, when calcined at 900 °C. The Li-deficient samples show the worse electrochemical properties similarly to the stoichiometric samples calcined at high temperature. For the Li-excess samples, no impurity phase has been detected and their cycle performances are improved.