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 be 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.