(Invited) Understanding Lithiation Mechanisms in Silicon-Based Nanomaterials from First Principles

Silicon-based alloys, composites and nanostructures have received great attention as a possible replacement of conventional carbon-based anodes due to their higher lithium storage capacity.  However, still fundamental aspects of lithiation processes and properties in Si-based nanomaterials remain largely ambiguous, despite their importance in overcoming many technical hurdles faced in practical use.  Using first principles-based atomistic modeling, we have explored lithiation mechanisms in various Si-based nanosystems including nanowires, composites, oxides, and alloys.  In this talk, I will present our recent progress in understanding the impacts of surfaces, interfaces and alloying elements on the properties and performance of Si-based anode materials for Li-ion batteries.  Our first principles study shows that the lithiation behavior of Si nanostructures and composites is considerably different from the case of bulk Si because of surface and interface effects.  For instance, the mobility of Li along the surface or interface tends to be significantly enhanced by several factors.  We also find that by alloying Si with certain metal (M) elements, the theoretical capacity is compromised slightly, but in return the Si-M network may help stabilize the lithiated host matrix and therefore contributes to the improved cycling performance.  I will also briefly touch on the importance of alloy composition and local atomic environment in determining the lithiation properties and performance.  The improved understanding can contribute to the rational design of Si-based anode materials to maximize capacity retention and rate performance.