Redox processes in Li_xNi_1–yCo_yO₂ cobalt-rich phases

Abstract

Samples of Li_xNi_0.1Co_0.9O₂ (0.5≤x≤1.0), prepared by electrochemical deintercalation from LiNi_0.1Co_0.9O₂ , have been characterized by X-ray diffraction, electrical measurements and ⁷Li NMR spectroscopy. A good correlation is found between the electrochemical behaviour of the Li_xNi_0.1Co_0.9O₂ electrode materials and their physical properties. During lithium deintercalation from LiNi_0.1Co_0.9O₂ , 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 Li_0.9Ni_0.1Co_0.9O₂ . 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.

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