Quantifying electrochemical reactions and properties of amorphous sili-conin a realistic lithium-ion battery configuration

Despite many existing studies on silicon (Si) anodes for lithium ion batteries (LIBs), many essential questions still exist on compound formation, composition, and properties. Here we show that some previously accepted findings do not truthfully reflect the actual lithiation mechanisms in realistic battery configurations. Furthermore the correlation between structure and mechanical properties in these materials has not been properly established. Here we report a rigorous and thorough study to comprehensively understand the electrochemical reaction mechanisms of amorphous-Si (a-Si) in a realistic LIB configuration. In-depth micro-structural characterization was performed and correlations were established between Li-Si composition, volumetric expansion, and modulus/hardness. We have found that the lithiation process of a-Si in a real battery setup is a single-phase reaction rather than the accepted two-phase reaction obtained from in-situ TEM experiments. The findings in this paper establish a reference to quantitatively explain many key metrics for lithiated a-Si as anodes in real LIBs, and can be used to rationally design a-Si based high-performance LIBs guided by high-fidelity modeling and simulations.