Nanostructured silicon-based alloys and composites have received great attention as a possible replacement of the conventional carbon-based anodes due to their higher lithium storage capacity. In many cases, however very little is known about their electrochemical properties and microstructure evolution during lithiation, despite their importance for overcoming many technical hurdles faced in practical use. Using first principles-based atomistic modeling, we have explored the lithiation behavior in various Si-based nanostructures and nanocomposites including nanowires and Si-C composites. This talk will present our recent progress, particularly focusing on addressing (1) the lithiation mechanisms of Si near the surface and interface, with comparisons to those in bulk Si, and (2) how the surface and interface affects the performance of Si-based nanomaterials as Li-ion battery anodes, such as charging rate and capacity retention. Our study highlights that the presence of surfaces and interfaces alters the lithiation behavior considerably; for instance, the Li mobility along the surface or interface tends to be significantly enhanced by several factors. We will also present the surface and interface effects on the structural evolution, bonding mechanism, mechanical property, and voltage profile of lithiated Si nanowires and Si-C nanocomposites. The improved understanding may offer important guidance for the rational design of nanostructured Si-based alloys and composites in order to maximize their capacity retention and rate capability.
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