The kinetics of the agglomerate-of-spheres model for the PbO2 electrode

The structure of a particulate electrode may be modelled by an agglomerate-of-spheres, called the AOS model. For the particulate PbO2 electrode this model assumes that the electronic connections between the particles are established through vase-like necks. The size of these necks determines the electronic conductivity of the electrode. It has been demonstrated that thermodynamically there is a tendency for a spontaneous growth of the neck at the expense of the particles. Finally, this should result in a three-dimensional network of PbO2 strings. In the present paper it is shown that the transfer of material from sphere to neck can take place by an electrochemical path, established through discharge of the sphere and charge of the neck. Under this assumption the growth rate of the neck is calculated. Using suitable estimates of the constants involved it is found that in a few hours the neck diameter increases to similar to 0.2 times the particle diameter, however, the development to the final structure may take many days. (C) 1998 Elsevier Science S.A.