Synthesis and electrochemical properties of layered LiNi0.5-xMn0.5-xCo2xO2 for lithium-ion battery from nickel manganese cobalt oxide precursor

A series of LiNi0.5-xMn0.5-xCo2xO2 (0 < 2x <= 0.33) compounds were prepared by solid-state reaction from nickel manganese cobalt oxides, and their characteristics were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and charge-discharge test. LiNi0.5-xMn0.5-xCo2xO2 samples have single phase of layered structure with a space group of R (3) over barm for 2x = 0.02, 0.05, 0.10, 0.20, and 0.33. Both the lattice constants of a- and c-axis and Li/Ni mixing degree decreased with the increase in Co contents in samples. The valence states of Ni, Mn, and Co in the samples are predominantly +2, +4, and 3, respectively, with a small amount of Ni3+, Mn3+, and Co2+. LiNi0.475Mn0.475Co0.05O2 gives excellent cycling performance in the voltage range of 2.5-4.4 V at the current rate of 20 and 100 mA g(-1) over 50 cycles. High-rate capacity test of LiNi0.34Mn0.33Co0.33O2 shows that even at a current rate of 1,000 mA g(-1), stable capacity about 63 mAh g(-1) is retained.