MULTIPHASE MATHEMATICAL-MODEL OF A NICKEL HYDROGEN CELL/

A mathematical model for a nickel/hydrogen cell is developed to invest igate the dynamic performance of the cell's charge and discharge proce sses. Concentrated solution theory and the volume averaging technique are used to characterize the transport phenomena of the electrolyte an d other species in the porous electrode and separator. Other physical fundamentals, such as Ohm's law, are employed to describe the electric al and other physical processes in the cell. The model is designed to predict the distribution of electrolyte, hydrogen, and oxygen concentr ations within the cell, hydrogen and oxygen pressure, potential, curre nt density, electrochemical reaction rates, and state of charge. The m odel can be used to evaluate the influences of all the physical, desig n, and operation parameters on the behavior of a nickel hydrogen cell. The model simulations show excellent agreement with experimental data for charge and discharge operations. The model simulations show the f ormation of a secondary discharge plateau by the end of discharge. Thi s plateau is caused by oxygen reduction at the nickel electrode. It is the first model that predicts this feature, which is a characteristic of the nickel electrode. The model simulations also show the existenc e of an optimum charge rate that maximizes the charge efficiency, whic h can be used for the implementation of optimal operating conditions.