Constant-current discharge curves for the nickel hydroxide electrode are simulated assuming resistances due to diffusion of protons and conduction of electrons through the nickel hydroxide film, and charge-transfer resistance at the film/electrolyte interface contribute to the polarization losses of the electrode. Good qualitative agreement is observed between the model predictions and experimental discharge curves. The results suggest that polarization losses due to diffusional limitations of protons is a critical factor in determining the characteristics of the discharge curve. Ohmic resistance has a significant effect on the discharge curves at the end of discharge, and charge-transfer resistance is a minor contributor to the polarization losses. These findings indicate that accurately measuring the diffusion coefficient of protons, the thickness of the hydroxide film, the initial state-of-charge, and the electronic conductivity as a function of state-of-charge towards the end of discharge are critical in accurately predicting the discharge characteristics of nickel hydroxide. Physical constants which were shown to have minor influence on the discharge curves are the film conductivity at the beginning of discharge, and the exchange current density and cathodic transfer coefficient for the reaction. The time-dependent, one-dimensional diffusion equation has been solved analytically which should provide a computationally efficient means of accounting for proton diffusion and variable electronic conductivity in a macrohomogeneous battery model without sacrificing accuracy.

The mathematical porous-electrode model developed at Texas A&M University has been combined with a planar model for the surface active layer to formulate a pseudo two-dimensional model for a sealed nickel-cadmium cell. The porous electrode model is based on a macrohomogeneous description of the electrodes and takes into account various processes such as mass transport in the liquid phase and porosity and conductivity changes in the solid phase. The planar electrode model describes the processes occurring across the surface layer of active material, i.e., solid-state diffusion of protons and conductivity changes in the nickel oxide, and the charge-transfer across the film-electrolyte interface. Also, various routines have been added to the pseudo two-dimensional model thus integrated, to allow predictions for any nickel-cadmium battery under any desired charge-discharge schedule. From a comparison with the experimental data of an aerospace cell, the model parameters describing charge-discharge behavior of a Ni-Cd cell have been optimized to obtain a closer prediction with the experimental data. Upon optimizing the model parameters, the performance of the aerospace nickel-cadmium cell has been simulated under various experimental conditions, i.e., at different rates and temperatures. Also, generic Ragone plots for the cell and typical Tafel plots for cadmium and nickel electrodes at different states of charge have been constructed from the simulations. Finally, this model has been made available for any interested user through COSMIC NASA's Computer Management and Information Center, along with documentation in six volumes describing the code, principles, and operating instructions.

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