Quantifying Electrochemical Reactions and Properties of Amorphous Silicon in a Conventional 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 may have limitations in reflecting the lithiation mechanisms in the conventional charging rate. 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 conventional charging rate. In-depth microstructural 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 at a conventional charging rate is a single-phase reaction while it is a two-phase reaction at high rate in 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.