Planar and porous Si films Formation of c-Li15Si4 is believed to have an intrinsically detrimental effect on capacity retention in planar Si thin films, and possibly other Si morphologies. As a starting point to test this hypothesis, two cycle life testing protocols are needed in which, using otherwise identical electrodes, c-Li15Si4 forms under one set of conditions but not the other. Even when using CCCV, c-Li15Si4 does not form in the first 18 cycles in Si films on Cu. Therefore, we hypothesized that for the planar 100 nm Si film on stainless steel, c-Li15Si4 would not form during CC lithiation, and a comparison between CC and CCCV lithiation would enable us to test the intrinsic detrimental effect of c-Li15Si4, or lack thereof. c-Li15Si4 is formed at a low lithiation potential of 5 mV, but not at 25 mV, or 50 mV vs. Li, and therefore, a lithiation potential of 5 mV was chosen for the CV step. The CV step was held for a fixed time of 10 hours rather than until a minimum current is reached, to enable comparisons with porous Si films (vide infra) that have higher surface area and, as a result, a higher rate of Li consumption by electrolyte decomposition.