THERMODYNAMIC CONSIDERATIONS OF THE REVERSIBLE POTENTIAL FOR THE NICKEL ELECTRODE

The thermodynamics of ideal and non-ideal solutions is applied to nick el hydroxide, the electrochemically active material in the positive el ectrode of a nickel battery, to provide theoretical insight into the r eversible potential as a function of the state-of-discharge. The model s were fit to experimental discharge curves to obtain the activity-coe fficient parameters and the standard potential over a temperature rang e from 5 to 55 degrees C. The two-parameter activity coefficient model s perform significantly better than the Nernst equation and one-parame ter Margules at all temperatures, thus suggesting that the insertion o f the protons into the lattice occurs in an ordered, non-random fashio n. The standard potential decreases linearly with temperature by 0.84 mV/K. The thermodynamic expressions and parameters given here enable o ne to predict the reversible potential of nickel hydroxide as a functi on of temperature and state-of-discharge. (C) 1998 Elsevier Science Lt d. All rights reserved.