Mechanical behavior of electrochemically lithiated silicon

The time-independent and time-dependent mechanical behavior of electrochemically lithiated silicon was studied with nanoindentation. As indentation was performed with continuous stiffness measurements during loading and load-hold, new insight into the deformation behavior of lithiated silicon is furnished. Supporting other research, Young's modulus and the hardness of lithiated silicon are found to decline with increasing lithium content. However, the results of this study indicate that Young's modulus of the fully lithiated phase, at 41 GPa, is in fact somewhat larger than reported in some other studies. Nanoindentation creep experiments demonstrate that lithiated silicon creeps readily, with the observed viscoplastic flow governed by power law creep with large stress exponents (>20). Flow is thought to occur via local, shear-driven rearrangement at the scale of the Li15Si4 molecular unit volume. This research emphasizes the importance of incorporating viscoplasticity into lithiation/delithiation models. Additionally, more broadly, the work offers insight into nanoindentation creep methodology.