Silicon nanostructures have been employed as the anodes of lithium-ion batteries to mitigate mechanical and chemical degradation. Conditions for averting fracture have been identified in terms of the Si critical size and its state of charge. Strong size dependencies were observed, and the critical sizes of fracture for different shapes of Si have been found to be: ∼90 nm for nanoparticles, ∼70 nm for nanowires, and ∼33 nm for nanofilms, below which the silicon nanostructures remain undamaged upon lithiation.