Structures and electrochemical properties of LiNi_0.5-xCo_2xMn_0.5-xO₂ as cathode materials for lithium-ion batteries

LiNi_0.5-xCo_2xO₂Mn_0.5-xO₂ (x = 0, 0.1, 1/6, 1.2, 0.3) were synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray powder diffraction and Rietveld refinement. LiNi_0.5-xCo_2xMn_0.5-xO₂ samples give single phases of hexagonal layered structures with a space group of R-3m for x = 0.1, 1/6, 0.2, and 0.3. The lattice constants of a and c-axis were decreased with the increase in Co contents in samples. The thickness of MO₂ slab was decreased and inter-slab distance was increased with the increase in Co contents in LiNi_0.5-xCo_2xMn_0.5-xO₂. According to XPS analysis, the valence states of Mn, Co, and Ni in the sample are mainly +4, +3, and +3, respectively. The discharge capacity of 202 mAh/g at 0.1C-rate in the potential range of 4.7 - 3.0 V was obtained in LiNi_0.3Co_0.4 Mn_0.3O₂ sample, and LiNi_0.4Co_0.2Mn_0.4O₂ gives excellent cycle performance in the same potential range.