The influence of nickel-hydroxide composition and microstructure on the high-temperature performance of nickel metal hydride batteries

A special precipitation process developed at Ovonic Battery Company has been utilized to produce spherical, high-density nickel-hydroxide powders with different chemical compositions. These powders were tested in sealed, cylindrical C-cell size nickel metal hydride batteries to study the effect of chemical composition on high-temperature performance. Charging measurements were made at 25, 45, and 65 C. It was found that coprecipitated cobalt in the presence of magnesium, zinc, and calcium increases the voltage gap between the oxygen-evolution potential and the midpoint voltage of the battery. The larger voltage gap dramatically increases the charge acceptance of the battery, improving its charging efficiency (normalized to the room-temperature value) from around 50% for conventional nickel hydroxide to 85% for the improved materials when measured at 65 C. (c) 2006 The Electrochemical Society.