The passivation of the lithium-solvent interface is an example of a layer formation where both growth and corrosion mechanisms play a significant role. A simple model for the numerical simulation of such an interface is studied. This simulation corresponds to the mesoscopic scale and it is not aimed to describe a given experiment but conversely to determine, at a qualitative level, the effect of some elements which in any case are present in the actual interface. We first take into account the fact that the chemical species forming the layer and the corroded metal have not the same size for a given number of corroded metal atoms. Then we consider that the restructuring of the growing layer, following an elementary step of the metal corrosion, takes place in the localized vicinity of this corrosion step. The growing and the corrosion processes are treated on an equal footing, and therefore we consider here a problem which includes two different fronts that we analyse in terms of scaling laws. Moreover, the corrosion mechanism generates a specific porosity in the layer, the behavior of which appears to be an interesting feature of the present model.