Modeling Volume Changes in Porous Electrodes

A three-dimensional mathematical model is presented to describe volume changes in porous electrodes occurring during operation. Material conservation equations are used to derive governing relationships between electrode dimensions and porosity for deposition/precipitation, intercalation, and ionomer-based electrodes. By introducing a parameter, called the swelling coefficient, the relative magnitudes of the change in electrode dimensions and the change in porosity are determined. The swelling coefficient is design-dependent and measured experimentally for a given cell design. The model is general and forms a critical addition required to extend the existing porous electrode models to include volume change effects. For the special case of uniform reaction distribution, analytical solutions are presented and used to illustrate the effect of volume changes in porous electrodes.