Structures and Electrochemical Properties of LiNi_0.5-xCo_2x}Mn_0.5-xO₂as Cathode Materials for Lithium-ion Batteries

Abstract

LiNi0.5-xCo2xMn0.5-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. LiNi0.5-xCo2xMn0.5-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 LiNi0.5-xCo2xMn0.5-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 LiNi0.3Co0.4 Mn0.3O2 sample, and LiNi0.4Co0.2Mn0.4O2 gives excellent cycle performance in the same potential range.