Differences in the effects of Co and CoO on the performance of Ni(0H)2 electrode in Ni/MH power battery

摘要

The effects of metallic cobalt (Co) and cobalt monoxide (CoO), as additives in positive electrodes, on the electrochemical performance of nickel/metal hydride (Ni/MH) power batteries are studied. Commercial Co and CoO are charged at 50℃ in 6 M KOH solution. The oxidation mechanism of cobalt materials is investigated by observing structural and morphological evolutions during charging. A pure Co_3O4-type phase is formed when the starting material is CoO. When Co is used, a cobalt oxyhydroxide (CoOOH) phase is present, together with a tricobalt tetroxide (CO3O4) phase. In both cases, the cobalt concen-tration in the electrolyte decreases during oxidation. The final product is dependent on the solubility of cobalt and the kinetics of the reaction that consumes cobalt tetrahydroxide [Co(OH)4]~(2-). The highly compact CoOOH phase, which works well between the nickel foam frame and nickel hydroxide [Ni(OH)_2) particles, enhances the power performance of Ni/MH power battery. The CO3O4 phase, which works well in connecting Ni(OH)_2 particles, improves the capacitive performance of Ni/MH power battery.