Temperature plays a key role in the formation of the cobalt-based conductive network at the positive electrode of alkaline batteries during the first charge. Electrodes pasted with CoO were oxidized in various concentrated alkaline media, in order to understand the phenomena involved. In these conditions, the experiments show the formation of a Co 3 O 4 type phase with defects. The presence of lithium in the electrolyte is proven to play an important role in the conductivity of the synthesized phases. Especially in 2.5 M LiOH, a pure phase is isolated that has a spinel structure close to Co 3 O 4 but containing H and Li. This phase is shown to be a good conductor and is also observed in (KOH, NaOH, LiOH) ternary industrial electrolyte. It could hence take part to the improvement of the properties of nickel electrodes observed when the beginning of the first charge is performed at high temperature.

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).