We investigate the effects of the Co and Mn ratio on the structure, morphology, electrochemical properties, and thermal stability of Li[Ni0.52Co0.16+x Mn0.32−x ]O2 cathode materials. Li[Ni0.52Co0.16+x Mn0.32−x ]O2 (x =0, 0.08, 0.16) cathode materials are prepared via high temperature calcination of LiOH and coprecipitated [Ni0.52Co0.16+x Mn0.32−x ](OH)2 hydroxides. From an X-ray diffraction investigation, the prepared materials have a well ordered O3 type α-NaFeO2 layer structure ( R 3 ¯ m ) . As the Co content (x) is increased, the initial discharge capacity increase slightly but it is accompanied by severe capacity fading during extensive cycling. Meanwhile, a small increase of Mn enhances the electrochemical stability at high temperature (55°C) as well as the thermal stability. Electrochemical impedance spectroscopy reveals that manganese substitution is effective to reduce the resistance during cycling due to stabilization of the host structure.