Temperature limitations of alkaline battery electrodes

The study described here is concerned with possible temperature limitations in Ni-Fe and Ni-Zn aqueous alkaline battery systems in the temperature range -20°C to 120°C. Thermodynamic studies involved the calculation of potential/concentration relationships for concentrated solutions. Kinetic studies have employed potential step and sweep, rotating ring disk and ac impedance methods. The principal temperature limitation of Ni appears to be reduced coulombic efficiency at high temperature as a result of the coevolution of oxygen at a high state of charge. The irreversible component of charging also increases immediately following prolonged discharge of Ni. The temperature limitation of the negative electrode materials, Fe and Zn, are more serious and more complex than those for Ni. In addition to the effects of increased hydrogen evolution, oxidative and reductive dissolution processes may substantially reduce the coulombic efficiency of Fe electrodes at 7>80°C. At r^O°C, charge/discharge kinetics of Fe become limited by the resistance of a residual surface oxide film. Discharge of Zn electrodes also is severely curtailed at reduced temperatures by reduced dissolution current and the premature onset of passivation. Under potentiostatic or high load conditions, zinc electrodes undergo an oscillatory activation/passivation process within a defined region of potential. This potential region increases with increasing temperature.