The effect of cobalt on the chemical and electrochemical behaviour of the nickel hydroxide electrode

✍ Scribed by C. Delmas; C. Faure; Y. Borthomieu

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 653 KB
• Volume: 13
• Category: Article
• ISSN: 0921-5107
• DOI: 10.1016/0921-5107(92)90147-2

✦ Synopsis

New hydrated cobalt-substituted nickel hydroxides were prepared and characterized. These materials were obtained either by precipitation (a) or by the "chimie douce" technique (a* and a'). Cobalt generally stays in the trivalent state. In contrast with the aco~+ phases, the aco,* phases are stable in KOH if at least 20% cobalt is substituted for nickel. In order to compensate for the excess of positive charge resulting from the presence of trivalent ions in the brucite-type layers, anions (sulphate or carbonate) are inserted between the Ni~ _/Cox(OH)2 slabs. In the case of weil-crystallized a* phases, an interstratified packing is obtained for low cobalt contents (x < 0.20). As shown by a study of the physical properties, the electronic conductivity of the oxidized phases (Tco)'increases with the amount of cobalt.

These phases were used as the positive electrode material of Ni/Cd cells. At the beginning of cycling, 1.3e-per (Ni + Co) atom can be reversibly exchanged between the 7 and a phases. During long-range cycling tests, a slow evolution from the y/a system to the fl(lIl)/fl(II) system is observed. This point is discussed in relation to the amount of cobalt.