At 50 mV, the effects of the constant voltage step on capacity retention are harder to interpret because of a larger change in absolute capacity. However, a similar trend is observed as the rates of capacity decay trend towards the same levels over the long run (Figure ), even as the amount of c-Li15Si4 continues to decline in the CCCV cells. The differences between silicon nanoparticles and porous silicon at 50 mV deserve some note, because while silicon nanoparticles do show formation of c-Li15Si4 at 50 mV using a constant voltage step (Figure ), the x = 0.30 porous silicon film remains amorphous (Figure ). Previous studies have typically found that c-Li15Si4 does not form above 50 mV in thin films and nanoparticles smaller than ~70 nm . Therefore, our results can be viewed as further confirmation that particle size influences the tendency to form c-Li15Si4. The larger commercial silicon nanoparticles (around 140 nm on average, Figure ) still fully crystallize at 50 mV CCCV, while the porous films, in which silicon has a size below ~50 nm (Figure ), do not.