O2 Electrode Material Research Articles

Redox processes in LixNi1−yCoyO2 cobalt-rich phases

Samples of LixNi0.1Co0.9O2 (0.5≤x≤1.0), prepared by electrochemical deintercalation from LiNi0.1Co0.9O2 , have been characterized by X-ray diffraction, electrical measurements and 7Li NMR spectroscopy. A good correlation is found between the electrochemical behaviour of the LixNi0.1Co0.9O2 electrode materials and their physical properties. During lithium deintercalation from LiNi0.1Co0.9O2 , the trivalent nickel ions are oxidized preferentially to trivalent cobalt ions. This leads to a reversible break in the potential–composition curve around the composition Li0.9Ni0.1Co0.9O2 . This change in the redox regime, which occurs without any structural transformation, has been confirmed by the evolution of the electrical conduction process and that of the 7Li NMR signal.