Layered LiAl1/3−x Co x Ni1/3Mn1/3O2 (0≦ x ≦1/3) compounds were studied via the combination of computational and experimental approach. The calculated voltage curve of LiNi1/3Al1/3Mn1/3O2 compound is presented, indicating it is of great potential for a cathode material of lithium-ion batteries. Unfortunately, it was found that the LiNi1/3Al1/3Mn1/3O2 compound without impurity phase could not be synthesized via a sol–gel process. To obtain a layered compound without impurity phase, partial of Al is replaced by Co in LiNi1/3Al1/3Mn1/3O2 compound in this study. Layered LiAl1/3−x Co x Ni1/3Mn1/3O2 (0≦ x ≦1/3) compounds were synthesized via sol–gel reaction at 900°C under a oxygen stream. Single phase of the LiAl1/3−x Co x Ni1/3Mn1/3O2 in 1/6≦ x ≦1/3 region could be prepared successfully. The discharge capacity and conductivity increased with an increase in the Co-substitution content. The enhancement of the conductivity and phase purity by the introduction of Co content shows profound influence on the performance of the LiAl1/3−x Co x Ni1/3Mn1/3O2 compounds.