In this study, we report on the effect that an externally applied compressive stress has on the electrochemical performance of Si anodes. Using the compression of an all-solid-state cell as a convenient format for simulating volume confinement, the electrochemical performance of Si anodes as a function of externally applied compressive stress has been systematically investigated. We verify that the extent of Si lithiation is limited by confining the free volume expansion of nano-Si particles. Volume confinement of Si particles is manifested as an overpotential and results in a stable anode for lithium-ion batteries. These results are foundational and lead to the best understanding to date of the complex electrochemomechanics of a Si-based anode. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.064301jes] All rights reserved.