Divalent cation incorporated Li(1+x)MMgxO2(1+x) (M = Ni0.75Co0.25): viablecathode materials for rechargeable lithium-ion batteries

A new class of divalent cation incorporated materials, Li1+xNi0.75Co0.25Mgx O2(1+x), corresponding to Li(Ni0.75Co0.25)(1-y)MgyO2 (y = x/(1 + x)), have been successfully synthesized and electrochemically characterized. Good cyc lability, high voltage durability (up to 4.4 V during charging) and high ca pacity (> 150 mA h/g) are the main characteristics of this class of materia ls. The successful introduction of the divalent cations alone on the transi tion metal sites helps to attain these characteristics while also maintaini ng 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 b y the overoxidation of the transition metal as well as the presence of diva lent 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 stabilit y of the materials during cycling. (C) 2000 Elsevier Science S.A. All right s reserved.