Samples were weighed using a Mettler Toledo XP6U balance with a readability of 0.1 μg and a repeatability of 0.4 μg. The weight of a 100 nm planar Si film was typically around 40 μg. For the co-deposited films, the weight of Si was calculated assuming the composition of the as-deposited film was nominal. Using these weights and assuming complete removal of the Al during immersion in the aqueous KOH, the specific delithiation capacity in the first cycle was typically 3000-3200 mAh/gSi for the porous films.