Effect of Thermal Treatment on the Electronic Conductivity Properties of Cobalt Spinel Phases Synthesized by Electro-Oxidation in Ternary Alkaline Electrolyte (KOH, LiOH, NaOH)

A thermal treatment of Co3O4 type spinel phases, synthesized by electrooxidation of CoO powder in a mixed alkaline electrolyte (KOH, LiOH, NaOH), is shown to have an important influence on the electronic conductivity properties of the materials. The initial spinel phase contains hydrogen, lithium, cobalt vacancies, and especially Co4+ ions within the structure, leading to an electronic conductivity significantly larger than that of stoichiometric Co3O4. The thermal treatment, followed by in situ X-ray diffraction, TGA-MS and electronic conductivity measurements, induces a water release, coupled with an increase of the Co/O atomic ratio and a structural reorganization. The resulting cationic redistribution within the spinel framework entails an increase of the Co4+ amount in the [Co2O4] network and therefore of the electronic conductivity (by 3 orders of magnitude).