A comparison of the capacity retention with and without a CV step at 5 mV during lithiation and selected dQ/dV curves of the planar Si film is shown in Figure . For planar Si films on Cu, the ratio between c-Li15Si4 peak area and the total delithiation capacity has been found to keep increasing, even as the total capacity rapidly declined. The difference in the onset of the increase and decay of the c-Li15Si4 peak area in different research works may be due to the choice of substrate, electrode design with and without adhesion and protective layers or length of the CV step, which was fixed at 10 hours here rather than using a lower current cut-off of 20 mA/g. As shown in Figure , no trace of c-Li15Si4 was found in the delithiation dQ/dV curves for any shown in Figure . Figure shows that aside from XRD, crystallinity of Si is also easily deduced from the lithiation voltage profile. The first cycle was carried out in CC mode for all electrodes, to ensure all films had the same starting point when the CV step was initiated. Crystalline Si shows a long flat lithiation plateau at ~0.15 V vs. Li, which is observed in the first cycle for the de-alloyed films, as per Figure . Amorphous Si, on the other hand, shows a series of sloping plateaus, as observed for the planar Si film (Figure ) and for the de-alloyed films in the second cycle (Figure ). for all the porous Si films is shown in Figure . For x = 0.75, the capacity is slightly higher after 200 cycles using the CV step, but the electrode cycled in CC mode only degrades faster in the beginning, whereas the CV step causes a relatively faster degradation beyond cycle 50. For x = 0.30 on the other hand, capacity retention is consistently better for CV as compared to CC and the difference in relative capacity retention becomes ever larger as cycling progresses. When the porous films are cycled using only constant current (Figure ), no sign of the c-Li15Si4 phase is found for x = 0.30. A small peak at ~0.42 V is visible in the first cycle for x = 0.75, never from the second cycle onwards. This is the first hint that the Si morphology has a big, perhaps decisive, influence on the formation of c-Li15Si4.