Synthesis and electrochemical studies of cobalt substituted nickel hydroxide for battery applications
Date
1999
Authors
Yazdi, Iman
Major Professor
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Akinc, Mufit
Committee Member
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Abstract
Homogeneous precipitation by urea decomposition has been shown to form powders of superior performance for use as the positive electrode of rechargeable batteries. Cobalt substituted [Alpha]-Ni(OH)2 powders prepared by this method have produced micron sized spherical particles with an inner structure of nanosized sheet-like crystallites, which demonstrate a very high specific surface area for the powder. Comparative electrochemical studies and phase analyses between homogeneously precipitated, commercial, and base precipitated Ni(OH)2 powders have shown that homogeneously precipitated powders, with or without cobalt, have the highest capacity and best reversibility characteristics. The effects of coprecipitation of cobalt versus mechanical mixing were studied. Results show that even though any type of cobalt addition will improve the capacity and reversible potential of the electrode, regardless of the preparation method, the most dramatic enhancement is seen with the substitution of cobalt for nickel within the structure.
A comparison of two coprecipitation methods shows the homogeneously coprecipitated sample to have a higher capacity than the sample prepared by base precipitation. These comparisons attest to the electrochemical superiority of the [Alpha]-Ni(OH)2 versus [Beta](Il)-Ni(OH)2 structure, as well as higher surface area powders. In addition, the results of this study suggest that the morphology and size of the crystalline particulates within the spherical particles are of great consequence to the electrochemical behavior of the electrode processes. These experiments demonstrate the relationship between the electrochemical behavior of the electrode and the structure, surface area, particle size and morphology of the electrode powder, and that the preparation method of the powder has a significant effect on the powder characteristics and, therefore, on the electrochemical behavior. It is the combination of these factors that makes homogeneously precipitated cobalt substituted Ni(OH)2 powders ideal candidates for use in high capacity electrodes for rechargeable Ni/MH and Ni/Cd batteries.
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thesis