PREDICTIONS FROM THE MACROHOMOGENEOUS MODEL OF AN AEROSPACE NI-CD BATTERY

The mathematical porous-electrode model developed at Texas A&M Univers ity has been combined with a planar model for the surface active layer to formulate a pseudo two-dimensional model for a sealed nickel-cadmi um cell. The porous electrode model is based on a macrohomogeneous des cription of the electrodes and takes into account various processes su ch 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 nick el oxide, and the charge-transfer across the film-electrolyte interfac e. Also, various routines have been added to the pseudo two-dimensiona l model thus integrated, to allow predictions for any nickel-cadmium b attery 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 optimiz ed to obtain a closer prediction with the experimental data. Upon opti mizing the model parameters, the performance of the aerospace nickel-c admium 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 simulati ons. Finally, this model has been made available for any interested us er through COSMIC NASA's Computer Management and Information Center, a long with documentation in six volumes describing the code, principles , and operating instructions.