Synthesis and characterization of LiNi1−x−yCoxMnyO2 as the cathode materials of secondary lithium batteries

LiNi1−x−yCoxMnyO2 (0≤x≤0.5, 0≤y≤0.3) were prepared by heating Ni1−x−yCoxMny(OH)2 and LiNO3 in flowing oxygen for 10 h at 550°C, followed by another heating at 750°C. The XRD patterns of LiNi1−x−yCoxMnyO2 (0≤x≤0.5, 0≤y≤0.3) samples with different x and y values show a pure phase of layered hexagonal structure. The lattice parameters a, c and the unit cell volume are found to decrease with increasing x in LiNi1−xCoxO2. The partial substitution of Ni by Co and Mn as in LiNi1−xCoxO2 and LiNi1−yCo0.2MnyO2 has a positive effect on lithium stoichiometry. However, lithium deficiency is still found after a prolonged thermal treatments (24 h). Among the doped materials synthesized, LiNi0.8Co0.2O2 and LiNi0.7Co0.2Mn0.1O2 have shown the best characteristics in terms of initial capacity and cycle life.