Synthesis and electrochemical properties of layered LiNi_(0.5-x) Mn_(0.5-x) Co_(2x) O_2 for lithium-ion battery from nickel manganese cobalt oxide precursor

摘要

A series of LiNi_(0.5-x) Mn_(0.5-x) Co_(2x) O _2 (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. LiNi_(0.5-x) Mn_(0.5-x) Co_(2x) O_2 samples have single phase of layered structure with a space group of R?3m 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 Ni ~(3+), Mn~(3+), and Co~(2+). LiNi0.475Mn 0.475Co0.05O2 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 LiNi _(0.34)Mn_(0.33)Co_(0.33)O_2 shows that even at a current rate of 1,000 mA g~(-1), stable capacity about 63 mAh g~(-1) is retained.