Five compositions of Li[Co1-2x(Li1/3Mn2/3)(x)(Ni1/2Mn1/2)(x)]O-2 solid solutions (x=0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized using a solgel method with three end members of LiCoO2, Li,MnO3(Li[Li1/3Mn1/3]O-2), and Li[Ni0.5Mn0.5]O-2. The compositions of metals in transition metal sites were changed to see the effect of them on electrochemical behavior of the solid solutions. All the samples were nano-sized semispherical shaped particles with a layered structure. The reduction of cobalt content (the increase of other metals) in the sites increases the lattice parameters, a and c, resulting in the shift of Raman and XRD peak positions. The discharge capacity fading turned serious at higher Co contents, but it was significantly diminished with the decrease of Co content. At lower Co contents, the capacity increased with cycle numbers. The most stable voltage profile was obtained ftom the composition of Li[Li1/15Co3/5Ni1/10Mn7/30]O-2 (x=0.2). (c) 2005 Elsevier B.V. All rights reserved.