The influences of some additives on electrochemical behaviour of nickel electrodes

Nickel hydroxide is used as an active material in positive electrodes of rechargeable alkaline batteries. Since the nickel hydroxide electrode exhibits a poor performance which results not only from the competitive reactions of the oxidation of the active material but also from the evolution of oxygen. Its reduced charge acceptance is suspected to be related to a relatively long distance between nickel hydroxide particles and the nearest portion of the substrate. The practical capacity of the positive nickel electrode depends on the efficiency of the conductive network connecting the Ni(OH)(2) particle with the current collector. In this study, a pasted-type electrode is prepared using spherical nickel hydroxide powder as the main active material on a foamed nickel grid as a current collector. The effects of additives such as metallic cobalt powder, cobalt hydroxide, calcium carbonate and cobalt powder with calcium carbonate on the electrode performance are examined. The calcium carbonate addition increases the oxygen evolution potential while the metallic cobalt powder and its compounds enhance the conductivity of the active material. This combined effect in nickel hydroxide electrode in turn increases the capacity of the NiMH battery due to the augmentation in the utilization of the active material of the positive electrode. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.