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-cadmi um cell that includes proton diffusion and ohmic drop through the acti ve material in the nickel electrode. The model is used to calculate se nsitivity coefficients for various parameters in the model. These calc ulations show that the discharge voltage of the cell is affected mostl y 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 ni ckel 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 a ctual charge uptake of the cell by the end of a charge operation (char ge efficiency). Compared to the rates of reaction and proton diffusion , the ohmic drop in the active material of the nickel electrode and th e mass transport and ohmic drop in the electrolyte have negligible eff ect on the behavior of the cell studied here.