Many efforts in the area of renewable energies are focused in the development of batteries of electrochemical cells to store energy fulfilling the requirements of high energy and power density. Electrochemical cells based on Li-ions are able to satisfy the requirements of high energy and power density. In general, cell electrode materials based on intermetallic and conversion compounds possess higher capacity to store Li -ions than those based on intercalation compound. Among intermetallic materials, silicon is a very attractive material for anodes of Li -ion cells, since it has a very high gravimetric capacity ( 3572 m A h g − 1 ) compared to graphite ( 372 m A h g − 1 ), being graphite an intercalation material and the most common anode in Li -ion cells. However, the main problem associated to these intermetallic and conversion materials is capacity fading. In this work it is shown how the capacity fading of electrodes based on silicon can be theoretically described by considering a simple model for the solid electrolite interface, where the active surface of the electrode is allowed to increase during the process of lithiation and delithiation.