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Silicon (Si) electrodes possess a theoretical specific capacity nearly ten times that of current graphite electrodes used in lithium ion batteries. However, lithiation and delithiation induce large volume changes within the Si, resulting in cracking and eventual capacity loss with cycling. Recent experimental evidence indicates that the presence of nanoporosity may mitigate capacity fade. By implementing a scalable differential effective medium approach, we elucidate the effects of nanoporosity upon the mechanical properties of fully-lithiated amorpohous Si anode films. Our analytical findings suggest that increased pore volume fraction significantly alters the mechanical properties of nanofilms and enhances anode survivability. Meanwhile, the auxetic limit imposes an upper bound on porosity specific fracture toughening. Overall, the results of this paper provide design guidelines for multilayered nanoporous Si thin films with increased capacity retention. [ABSTRACT FROM AUTHOR]