Seijiro Ochiai

Structural Analysis by Synchrotron XRD and XAFS for Manganese-Substituted α - and β -Type Nickel Hydroxide Electrode

The detailed structural change in the charge-discharge process for the 10 and 20 mol % manganese-substituted nickel hydroxide was investigated by using high-energy synchrotron X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). On the charge-discharge process, the 10 and 20 mol % manganese-substituted nickel hydroxide showed the β-Ni(OH) 2 /γ-NiOOH and the α-Ni(OH) 2 /γ-NiOOH phase transformation, respectively. The manganese ions were inserted on the only nickel sites for the 10 mol % manganese-substituted nickel hydroxide, and on both nickel sites and 18h sites for the 20 mol % manganese-substituted nickel hydroxide. The α-Ni(OH) 2 structure could be stabilized by the presence of the manganese ions on the 18h sites. The structural refinement for the manganese-substituted nickel hydroxides has been done successfully on the basis of two phase models of the ideal phases and the fault ones. As compared to ideal phases, the fault phases were characterized by the shift of the nickel atoms, and showed a larger amount of the intercalated potassium ions and H 2 O (OH - ) molecules in the interlayer. The occupancy sites for the potassium ions and H 2 O molecules were contained for the refinements, bringing about a better agreement between the observed and calculated patterns.

Structural Analysis Using Synchrotron XRD and XAFS for Cobalt Oxyhydroxides Heat-Treated under Sodium Hydroxide Solution for Nickel Hydroxide Electrode

The structural analysis for the cobalt oxyhydroxide has been done by using high-energy synchrotron X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analysis. The relationship between the structure and the electrical conductivity for cobalt oxyhydroxide was investigated. The structural refinement for cobalt oxyhydroxide heat-treated in the temperature range of 80-160°C has been done successfully on the basis of two phase models (L and S phase) with large and small c lattice constants. With increasing treatment temperature, the phase abundance for the L phases was increased, whereas the one for the S phases was decreased. By heat-treatment above 100°C, the cobalt ions for the cobalt oxyhydroxide were oxidized to the higher oxidation state over 3. The electrical resistivity was extremely decreased by treatment temperatures above 100°C. The increase in the electrical conductivity for the cobalt oxyhydroxide could be explained by the increase in cobalt oxidation state.