Multiscale modeling of the impact of dislocations on the electro-chemo-mechanical behavior of lithium-ion battery electrodes

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Dislocations are known to be paths of high diffusivity in a wide range of materials, including the electrochemically active materials that are employed for the electrodes of lithium-ion batteries. However, the underlying mechanisms of diffusion in dislocations are not fully understood, in particular as some materials show an adverse effect of dislocations on diffusion. A possible source of increased diffusivity are the mechanical stresses arising around dislocations, which affect the energy barriers for diffusion. Continuum modeling and multiscale simulations hence provide an effective tool to elucidate the relation between a dislocation-rich microstructure and the electro-chemo-mechanical behavior of a whole battery.Current modeling efforts regarding the interaction of diffusion and dislocations focus on solute segregation in metals, that is, the accumulation and/or trapping of impurities around a dislocation. The impact of stresses on diffusion, if considered at all, is described only in a simplified form. In models for lithium-ion battery electrodes, dislocations have so far only found attention as an additional source of stresses, without any influence on the diffusion kinetics. The role of a defective microstructure on the performance of a battery cell is unknown.In order to elucidate the role of dislocations in the behavior of lithium-ion batteries, continuum modeling and finite element simulations will be employed at three scales in the scope of this project. At the microscale, dislocation structures will be modeled by means of a phase-field model incorporating effects from stress-assisted diffusion. Simulations of the transport in the dislocation network will yield data on the effective diffusivity of the regarded microscale samples and their correlation with the observed dislocation densities. At the mesoscale, the effective diffusion properties will be employed in simulations of the charge-discharge behavior of single electrode particles. The mesocale particle model will be integrated into a single-particle model at the macroscale. Simulations of several charge-discharge cycles will then elucidate the impact of a defective microstructure on the performance of a battery cell.