New spinel cobalt oxides, potential conductive additives for the positive electrode of Ni-MH batteries

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 Co3O4 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 Co3O4 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.