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

众所周知，在许多材料中，位错都是高扩散率的途径，包括用于锂离子电池电极的电化学活性材料。然而，位错扩散的潜在机制尚不完全清楚，特别是一些材料显示出位错对扩散的不利影响。增加扩散率的一个可能来源是位错周围产生的机械应力，它影响扩散的能量垒。因此，连续模型和多尺度模拟为阐明位错丰富的微观结构与整个电池的电化学力学行为之间的关系提供了有效的工具。目前关于扩散和位错相互作用的建模工作集中在金属中的溶质偏析，即位错周围杂质的积累和/或捕获。如果考虑到应力对扩散的影响，也只是用一种简化的形式来描述。在锂离子电池电极模型中，位错迄今为止只作为额外的应力来源引起注意，对扩散动力学没有任何影响。微观结构缺陷对电池性能的影响是未知的。为了阐明位错在锂离子电池行为中的作用，本项目将在三个尺度上采用连续统模型和有限元模拟。在微观尺度上，位错结构将通过结合应力辅助扩散效应的相场模型来建模。对位错网络中输运的模拟将得到有关所考虑的微尺度样品的有效扩散率及其与所观察到的位错密度的关系的数据。在中尺度上，有效扩散特性将用于模拟单电极粒子的充放电行为。中尺度粒子模型将在宏观尺度上整合为单粒子模型。几个充放电循环的模拟将阐明有缺陷的微观结构对电池性能的影响。

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.