Silicon (Si) is a highly attractive anode material for next generation lithium-ion (Li-ion) batteries due to its exceptional specific capacity (up to 4200 mAh g^-1), natural abundance, and low environmental impact. However, practical implementation of anodes with high Si loading is hindered by the dramatic volumetric change Si undergoes during lithium insertion and extraction (~300%); such change in the electrode structure causes rapid capacity fade, poor cycle life, and electrolyte degradation from repeated solid-electrolyte interphase (SEI) formation. As such, a better understanding of the alloying behavior of Si in Li-ion systems is necessary to alleviate the problems caused by the lithiation and delithiation volume changes.

In this work, we utilize a combination of operando x-ray transmission microscopy and in-situ x-ray computed tomography at high resolutions to directly observe the lithium-silicon alloy phase nucleation and propagation. Three-dimensional reconstructions of Si electrodes at varying stages of cycling are used to resolve the spatiotemporal changes of the lithium-silicon alloy phases, and the changes in x-ray absorption are used to determine the predominant alloy phase within the electrode.

This material is based upon work supported by the National Science Foundation under Grant No. CBET-1705321. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.