Synthesis and characterization of nickel hydroxide powders for battery application
Date
1997
Authors
Widjaja, Agus
Major Professor
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Akinc, Mufit
Committee Member
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Abstract
Synthesis of nickel hydroxide by homogeneous precipitation has been studied with the emphasis of the characterization put on the morphology and specific surface area of the precipitate. The composition of the precursors as synthesized was a mixture of nickel hydroxide and nickel bicarbonate, 2(Ni(OH)₂, Ni(HCO₃)₁.₈₅(NO₃)₀.₁₅, as inferred from the chemical analysis and the TGA data. The XRD patterns showed peaks common to those observed for α-Ni(OH)₂. The specific surface area of the Ni(OH)₂ powders was measured to be as high as 167 m²/g and was found to be related to its morphology. Different surface characteristic was observed for low and high concentration powders. The difference was explained by the nucleation process and growth rate of the particles. The addition of dispersants reduced the crystallite size and increased the specific surface area further. However, the presence of dispersant was not very effective in preventing agglomeration at longer aging time.
Homogeneously precipitated Ni(OH)₂ which has high specific surface area, has been shown to have a higher coulombic efficiency ( -90%) and degree of reversibility compared to a commercial powder. Prior to the electrochemical measurements, the as-synthesized Ni(OH)₂ powders were aged in 6 M KOH solution to sort out the structural change due to the charge-discharge mechanism from that due to storage in KOH solution. The α-to-β transformation was completed after 2 days of aging. Observation of the XRD data at different aging times suggests that the aging mechanism proceeds through dissolution and recrystallization of the particles. The specific surface area increases to a constant value of approximately 160-170 m²/g after 8 days of aging. Comparison of this value to the 20 m²/g measured for the commercial powders suggests that the morphology of the particles plays an important role in the electrochemical behavior of the active materials.
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thesis