The synthesis of lithiated manganese oxides, Li0.45MnO2, and lithiated mixed manganese cobalt oxides, Li0.45Mn0.85Co0.15O2, obtained via a sol-gel process combined with an ion-exchange reaction is reported. X-ray powder diffraction patterns reveal that these compounds exhibit a tetragonal symmetry. These tetragonal phases present attractive properties as rechargeable cathode materials for secondary lithium batteries. During cycling experiments performed at discharge-charge rates of C/20, a stabilization of the specific capacity around 160 mAh g(-1) (0.6 Li per mol) occurs after the 40th cycle for the best compound obtained with an optimal composition of 15% in cobalt ions, Li0.45Mn0.85Co0.15O2.