A new class of divalent cation incorporated materials, Li1+xNi0.75Co0.25MgxO2(1+x), corresponding to Li(Ni0.75Co0.25)(1-y)MgyO2 (y = x/(1 + x)), have been successfully synthesized and electrochemically characterized. Good cyclability, high voltage durability (up to 4.4 V during charging) and high capacity (> 150 mA h/g) are the main characteristics of this class of materials. The successful introduction of the divalent cations alone on the transition metal sites helps to attain these characteristics while also maintaining a large nominal capacity of the material without the interference of the aliovalent cations on the Li sites. Good cycling behavior at high voltages is probably due to the prevention of overcharging of the material caused by the overoxidation of the transition metal as well as the presence of divalent cations on the transition metal site. The presence of the overoxidized transition metal as well as divalent cations on the transition metal site not only increases the cycling voltage but also enhances the phase stability of the materials during cycling.