Experimental and theoretical characterization of electrode materials that undergo large volume changes and application to the lithium-silicon system

The life and performance of lithium-ion batteries are related to the mechanical expansion and contraction of the active materials, particularly for silicon-enhanced negative electrodes. In this work, we develop a theory and commensurate equations to describe how lithium diffuses within lithiated silicon, and we include the influence of active material expansion (upon lithiation) and contraction (upon delithiation). The treatment of diffusion is based on irreversible thermodynamics, and a charge-transfer relationship is employed at the electrode-electrolyte interface. The experimental approach allows us to isolate our analysis to the active material and avoids the necessity of treating binders, conductive diluents, and complicated geometries associated with conventional porous electrodes used in most practical lithium-ion batteries and in the construction and modeling of a Li-Si porous electrode. The model is shown to compare favorably with experimental results. The final section of this paper addresses significant open questions.