Masaharu Watada

Effect of Lanthanide Oxide Additives on the High-Temperature Charge Acceptance Characteristics of Pasted Nickel Electrodes

For the purpose of increasing high-temperature charge acceptance of nickel-metal hydride (NiMH) secondary batteries, we studied effect on the charge acceptance of pasted nickel electrodes by adding the oxides of a series of lanthanides (Pr to Lu) with the nickel hydroxide active material in the temperature range 20-60°C. The oxides of heavy lanthanides Er, Tm, Yb, and Lu or their mischmetal oxides, were found to shift the oxygen evolution overpotential of nickel electrodes to more noble potentials than other lanthanides and to he particularly effective in raising the high-temperature charge acceptance of nickel electrodes. The higher oxygen overpotential was correlated with the uniform distribution of the heavier lanthanides having amphoteric character. Application to sealed NiMH batteries yielded a charge acceptance of about 80% at 70°C.

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.

Electrochemical Hydrogen Storage in Ti1.6V0.4Ni1−xCox Icosahedral Quasicrystalline Alloys

The discovery of the icosahedral phase (i-phase) in rapidly quenched Ti(1.6)V(0.4)Ni(1-x)Co(x) (x=0.02-0.1) alloys is described herein. The i-phase occurs in a similar amount relative to the coexisting beta-Ti phase. The electron diffraction patterns show the distinct spot anisotropy, indicating that the i-phase is metastable. The electrochemical hydrogen storage performances of these five alloy electrodes are also reported herein. The hydrogen desorption of nonelectrochemical recombination in the cyclic voltammetric (CV) response exhibits the demand for electrocatalytic activity improvement. A discharge capacity of 261.5 mA h g(-1) was measured in a Ti(1.6)V(0.4)Ni(0.96)Co(0.04) alloy electrode at 30 mA g(-1) and 303 K and it is shown that an appropriate amount of Co element addition would enhance the cycling stability at the expense of high-rate discharging ability.

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.

Electrochemical Hydrogen Storage in Ti1.6V0.4Ni1âxCoxIcosahedral Quasicrystalline Alloys

The discovery of the icosahedral phase (i-phase) in rapidly quenched Ti(1.6)V(0.4)Ni(1-x)Co(x) (x=0.02-0.1) alloys is described herein. The i-phase occurs in a similar amount relative to the coexisting beta-Ti phase. The electron diffraction patterns show the distinct spot anisotropy, indicating that the i-phase is metastable. The electrochemical hydrogen storage performances of these five alloy electrodes are also reported herein. The hydrogen desorption of nonelectrochemical recombination in the cyclic voltammetric (CV) response exhibits the demand for electrocatalytic activity improvement. A discharge capacity of 261.5 mA h g(-1) was measured in a Ti(1.6)V(0.4)Ni(0.96)Co(0.04) alloy electrode at 30 mA g(-1) and 303 K and it is shown that an appropriate amount of Co element addition would enhance the cycling stability at the expense of high-rate discharging ability.

Electrochemical hydrogen storage in Ti(1.6)V(0.4)Ni(1-x)Co(x) icosahedral quasicrystalline alloys.

The discovery of the icosahedral phase (i-phase) in rapidly quenched Ti(1.6)V(0.4)Ni(1-x)Co(x) (x=0.02-0.1) alloys is described herein. The i-phase occurs in a similar amount relative to the coexisting beta-Ti phase. The electron diffraction patterns show the distinct spot anisotropy, indicating that the i-phase is metastable. The electrochemical hydrogen storage performances of these five alloy electrodes are also reported herein. The hydrogen desorption of nonelectrochemical recombination in the cyclic voltammetric (CV) response exhibits the demand for electrocatalytic activity improvement. A discharge capacity of 261.5 mA h g(-1) was measured in a Ti(1.6)V(0.4)Ni(0.96)Co(0.04) alloy electrode at 30 mA g(-1) and 303 K and it is shown that an appropriate amount of Co element addition would enhance the cycling stability at the expense of high-rate discharging ability.