Abstract
Newly developed LiNi 0.75-x Co 0.25 Mn x O 2 (0.1 ≤ x ≤ 0.25) cathode materials were successfully synthesized by mixing Ni 0.75-x Co 0.25 Mn x (OH) 2 and Li 2 CO 3 via the solid-state reaction followed by heating to elevated temperatures. X-ray diffraction patterns showed that the samples calcined at 900°C exhibited a typical hexagonal α-NaFeO 2 structure without any other impurities present. The ratio of peak intensities of (003) to (104) decreased with the increasing Mn content. The scanning electron microscopy micrograph revealed uniform primary particle size, and the small primary particles agglomerated to form the secondary ones with size distribution in the range of 6-9 μm. The X-ray photoelectron spectroscopy measurement indicated that the valence of Ni ions was a mixture of 2+ and 3+. The amount of Mn substituted for Ni increased proportional to the ratio of Ni 2+ /Ni 3+ in the samples was increased. Besides, for dynamic equilibrium (Ni 2+ + Mn 4+ ↔ Ni 3+ + Mn 3+ ), small amount Mn 4+ was reduced to Mn 3+ . After cycling, the cathode materials showed good electrochemical performance, with initial discharge capacity around 170 mAh/g at 0.1 C rate in the voltage range of 3-4.3 V. At a high rate of 1 C, 85% efficiency was still attainable in all samples. © 2005 The Electrochemical Society. All rights reserved.