The LiNi1-yCoyO2 phases were obtained by direct synthesis. They are isotypes of the extreme LiNiO2 and LiCoO2 phases. These materials have been used as positive electrodes in lithium batteries. Their electrochemical performance is highly promising in terms of applications. A detailed study of the evolution of structural, physicochemical and electrochemical properties during lithium deintercalation has been carried out as a function of y. The results show that nickel is preferentially oxidized to the tetravalent state than cobalt. In addition, the use of homologous NaNi1-yCoyO2 phases in sodium batteries revealed electrolyte decomposition catalyzed by the positive electrode material. In contrast to lithium phases, several structural transformations were observed during sodium deintercalation from the NaNi0.6Co0.4O2 phase.
