Mechanical Modeling of Particles with Active Core-Shell Structures for Lithium-Ion Battery Electrodes

Active particles with a core shell structure exhibit superior physical, electrochemical, and mechanical properties over their single-component counterparts in lithium-ion battery electrodes. Modeling plays an important role in providing insights into the design and utilization of this structure. However, previous models typically assume a shell without electrochemical activity. Inaccurate interfacial conditions have been used to bridge the core and the shell in several studies. This work develops a physically rigorous model to describe the diffusion and stress inside the core shell structure based on a generalized chemical potential. Including both chemical and mechanical effects, the generalized chemical potential governs the diffusion in both the shell and the core. The stress is calculated using the lithium concentration profile. Our simulations reveal a lithium concentration jump forming at the core shell interface, which is only possible to capture by modeling the shell as electrochemically active. In sharp contrast to a single-component particle, a tensile radial stress develops at the core shell interface during delithiation, while a tensile tangential stress develops in the shell during lithiation. We find that the core shell interface is prone to debonding for particles with a thick shell, while shell fracture is more likely to occur for particles with a large core and a relatively thin shell. We show a design map of the core and shell sizes by considering both shell fracture and shell debonding.