MATHEMATICAL-MODELING OF A NICKEL-CADMIUM CELL - PROTON DIFFUSION IN THE NICKEL ELECTRODE

In this paper we present a mathematical model of a sealed nickel-cadmium cell that includes proton diffusion and ohmic drop through the active material in the nickel electrode. The model is used to calculate sensitivity coefficients for various parameters in the model. These calculations show that the discharge voltage of the cell is affected mostly by the kinetics of the nickel reaction. Toward the end of discharge, proton diffusion also becomes important, because the proton diffusion process affects the active material utilization significantly. During charge; the cell voltage is mainly affected by the kinetics of the nickel reaction until the oxygen evolution reaction begins, after which time the kinetics of the oxygen evolution has the largest effect. The oxygen evolution reaction is also the most influencing factor on the actual charge uptake of the cell by the end of a charge operation (charge efficiency). Compared to the rates of reaction and proton diffusion, the ohmic drop in the active material of the nickel electrode and the mass transport and ohmic drop in the electrolyte have negligible effect on the behavior of the cell studied here.