Analysis of Porous Electrodes with Sparingly Soluble Reactants III. Short Time Transients

A mathematical model which describes the operation of porous battery electrodes has been developed. It includes short time transient behavior of electrolyte concentration, porosity, current distribution, reaction rate, and detailed solutio.n diffusion descriptions of a sparingly soluble reactant. Calcula-tions were made for constant current (50 and 25 mA/cm 2) charging and dis-charging of Ag/AgC1 electrodes. Results of calculations indicate that the con-centration of the electrolyte, KC1, inside the porous electrode plays an im-portant role in the performance of the electrode. During charging, the elec-trolyte concentration falls in the depth of the electrode, thereby decreasing the solution electrical conductivity. Reaction penetration depth on charging is very shallow, less than 0.3 ram, for the current densities investigated. On dis-charging, the electrolyte concentration i the depth of the electrode increases. Consequently, the electrical conductivity of the solution as well as the solu-bility of AgC1 increases. A high reaction rate in the depth of the electrode i