The dQ/dV curves for selected cycles of the x = 0.75 and x = 0.30 porous films using CCCV protocol are also shown in Figure . For x = 0.75, the amorphous peak around 0.30 V is lowest in the second cycle and therefore, the amount of c-Li15Si4 is highest. The doublet structure of the c-Li15Si4 peak has also been observed for C/Si multilayers and Si-Ti alloy films, although the spacing between the peaks is much less than the 40 mV separation we observed in Si/C multilayer structures. Although the c-Li15Si4 peak height increases up to cycle 10, it also narrows and a broad peak around 0.30 V, characteristic of delithiation of amorphous LixSi, appears immediately after cycle 2 and starts to increase in height as well. The total capacity has in fact slightly degraded by cycle 10 (2%), so it appears that the tendency of the material to form c-Li15Si4 diminishes with cycling. A similar picture emerges for x = 0.30, where the peak at 0.42 V reaches a maximum height around the 8th cycle and where the peak at 0.30 V increases in height between cycle 10 and cycle 50, despite severe degradation of the total capacity, indicating a diminished tendency towards formation of c-Li15Si4 as well. Formation of c-Li15Si4 is strongly dependent on stress exerted by a rigid substrate or inert interlayers present in the film. Here too, we demonstrated that in a planar Si film, the quantity of c-Li15Si4 reaches its maximum around cycle 40, which is believed to be correlated in large part with delamination. The porous films are much less constrained by the substrate, resulting in a reversal of the trend, with the amount of c-Li15Si4 diminishing with continued cycling. While part of the decrease is due to degradation of the total capacity, the (absolute) increase in the amorphous peak at 0.30 V indicates a reduced tendency to form c-Li15Si4. There are two possible explanations for these observations for the porous silicon films: 1) fracture of the Si particle network, as there are several studies showing an influence of particle size on the tendency to form c-Li15Si4 30,48 and 2): a new source of mechanical stress, such as that exerted by the SEI.