Chemo-Thermo-Mechanical Model for Imperfect Interfaces
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Capacity loss is a major issue in rechargeable batteries, resulting from multiple mechanisms that depend on the cell composition. It is primarily caused by degradation processes at the interface between the active material and the electrolyte, but also by irreversible bonding of mobile species in the bulk. We present a chemo-thermo-mechanical model to account for mass transport, reaction, and trapping. The model accounts for irreversible trapping phenomena in bulk and across imperfect interfaces. A generalization of the canonical interface is accomplished with full thermodynamic consistency. The setting allows for the chemical potential, the (molar) concentration, and the normal component of mass flux of the diffusing species to be discontinuous across interfaces. Guided by the dissipation inequality, we select constitutive relations for (i) the reaction that governs the rate of trapping, (ii) the normal flux of ions across the interface. Restriction is made to small strain kinematics. The model, implemented within a finite element framework, is employed to investigate the capacity loss of carbon fiber electrodes typically employed in structural batteries. On the one hand, Li-ion bulk trapping is known to constitute a substantial part of the capacity fade of carbon fibers during conditioning cycles. On the other hand, Li-ion trapping within the solid electrolyte interface (SEI) layer provides a suitable illustration of the canonical setting. The results of the numerical simulations demonstrate the model capability to predict the experimentally-observed capacity loss at repeated charge-discharge.
