Li[Li(1/3-x)Mn(2/3-x)NixCox]O2 (x=0.1, 0.15, 0.2, 0.22, 0.25) compounds were synthesized and studied by the X-ray diffraction method and electrochemical techniques. The XRD analysis showed that these compounds could be classified as the α-NaFeO2 structure type. Both a and c parameters decreased linearly, while c/a increased with the increase of Ni and Co content. The first discharge capacity increases with increasing lithium content at the 3a sites in the Li[Li(1/3-x)Mn(2/3-x)NixCox]O2. A Li[Li0.23Mn0.57Ni0.1Co0.1]O2 electrode delivers discharge capacities of 238 mAh/g at C/10 between 4.6V and 2.5V.