NUCLEATION OF LEAD SULFATE IN POROUS LEAD-DIOXIDE ELECTRODES

A one-dimensional mathematical model of a porous lead-dioxide electrode is described and used to investigate lead-sulfate nucleation and growth during discharge. Derivation of a nucleation rate expression that is based on classical, heterogeneous nucleation theory is outlined. An electrochemical kinetic expression is derived based on a reaction mechanism involving elementary steps, and concentrated ternary electrolyte theory is used in formulating material-transport equations. Nucleation and electrochemical kinetic parameters are estimated by comparison of model results with experimental results available in the literature. The interplay of nucleation and growth kinetics of lead sulfate is responsible for the initial minimum in the voltage-time curve that is commonly observed during constant-current discharge. The model simulates the voltage minimum, which is referred to as the coup de fouet, and calculates the degree of lead-ion supersaturation, the number density of lead-sulfate particles, and the free energy of formation as well as the size of critical nuclei. The model also predicts a disappearance of the voltage minimum with the addition of seed particles for lead-sulfate nucleation, which is experimentally observed. The satisfactory agreement between model and experimental results confirms that the voltage dip is caused by a temporary oversaturation of lead ions during discharge and supports the proposed theoretical approach. © 1990, The Electrochemical Society, Inc. All rights reserved.