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

摘要

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 solution diffusion descriptions of sparingly soluble reactant. Calculations were made for constant current (50 mA/sq cm and 25 mA/sq cm) charging and discharging of Ag/AgCl electrodes. Results of calculations indicate that the concentration of the electrolyte, KCl, inside the porous electrode plays an important role in the performance of the electrode. During charging, the electrolyte 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 mm, for the current densities investigated. On discharging, the electrolyte concentration in the depth of the electrode increases. Consequently, the electrical conductivity of the solution as well as the solubility of AgCl increases. A high reaction rate in the depth of the electrode is possible even at high current discharge. Charge utilization over 90% is predicted if the charge is stored uniformly by employing a slow charging rate.