  Controlled formation of porous silicon has been of primary importance for
numerous landmark applications such as light emitting sources, sensors,
actuators, drug delivery systems, and energy storage applications. Frequently
explored methods to form the structures have long relied on selective etching
of silicon, which still stands as the most controllable and reliable methods to
highlight essence of the applications. Here, we demonstrate an unprecedented
approach to form silicon framework, which is spontaneously formed with
atomistic arrangement of silicon without gravimetric loss via single
electrochemical (de)alloying with lithium. Carefully controlling bare
crystallinity of Si and composite/electrode designs, we reveal that the key
prerequisite to forming the structure lies in using unique dealloying dynamics
of crystalline-amorphous phase transformations at room temperature. Using the
feature, we clearly highlight that commercially available nano-structured
silicon particles can abruptly yet uniformly transform into continuous sub-2 nm
spherical silicon frameworks with size-tunable pores.
