Evolution mechanism of the Na_0.6CoO₂ conductive additive during cycling in the alkaline electrolyte of Ni–MH batteries

Myriam Douin (1, 2) , Liliane Guerlou-Demourgues (1) , Lionel Goubault (2) , Patrick Bernard (2) , Claude Delmas (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 Direction de la recherche

The stability of the Na_0.6CoO₂ phase, as intended to be used as a conductive additive at the positive electrode of Ni–MH batteries, was tested in electrochemical cycling conditions, in KOH alkaline electrolyte. Simple aging of Na_0.6CoO₂ in the electrolyte entails its spontaneous transformation into a mixture of y and B(III) cobalt oxyhydroxides. This reaction, occurring within the solid state, is based on an original mechanism, which involves cationic exchange processes and passes through an intermediate interstratified phase. Electrochemical oxidation of Na_0.6CoO₂ in the alkaline electrolyte, as well as chemical oxidation, leads to a y cobalt oxyhydroxide, which can be totally reduced to B(III), depending on the reduction conditions. It is important to understand such an evolution mechanism of the Na_0.6CoO₂ additive because it will have a significant and positive influence on the electrochemical cycling of the positive electrode in specific deep discharge or low potential storage conditions.

Mots clés: Ageing; Electrochemical electrodes; Electrolytes; Ion exchange; Nickel compounds; Oxidation; Reduction (chemical); Secondary cells; Sodium compounds

Domaines: Matériaux

Myriam Douin, Liliane Guerlou-Demourgues, Lionel Goubault, Patrick Bernard, Claude Delmas. Evolution mechanism of the Na_0.6CoO₂ conductive additive during cycling in the alkaline electrolyte of Ni–MH batteries. Journal of The Electrochemical Society, 2009, 156 (6), pp.A459-A467. ⟨10.1149/1.3111842⟩. ⟨hal-00388983⟩