THE KINETICS OF THE AGGLOMERATE-OF-SPHERES MODEL FOR THE PBO2 ELECTRODE

The structure of a particulate electrode may be modelled by an agglome rate-of-spheres, called the AOS model. For the particulate PbO2 electr ode this model assumes that the electronic connections between the par ticles are established through vase-like necks. The size of these neck s determines the electronic conductivity of the electrode. It has been demonstrated that thermodynamically there is a tendency for a spontan eous 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 d ischarge of the sphere and charge of the neck. Under this assumption t he growth rate of the neck is calculated. Using suitable estimates of the constants involved it is found that in a few hours the neck diamet er increases to similar to 0.2 times the particle diameter, however, t he development to the final structure may take many days. (C) 1998 Els evier Science S.A.