In the present work, mesoporous, 3-D, nanocrystalline Si has been reduced firom the silicon monoxide particles via a magnesiothermic reaction in a scalable flow-through reactor setup.The reaction temperature and time are adjusted, and their influence on the microstructure (e.g., pore size and nanocrystallite size) of porous silicon and its final electrochemical performance are investigated.The obtained 3-D porous Si delivers a large specific capacity (e.g., > 900 mA h g-1 at a specific current of 1000 mA g-1) and has good rate capability, exhibiting great potential as an anode material for lithium ion batteries.