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

已知位错是宽范围材料中的高扩散率的路径，包括用于锂离子电池的电极的电化学活性材料。然而，位错中扩散的基本机制尚未完全理解，特别是当一些材料显示出位错对扩散的不利影响时。增加扩散率的一个可能来源是位错周围产生的机械应力，其影响扩散的能量势垒。因此，连续介质模拟和多尺度模拟提供了一个有效的工具，以阐明一个位错丰富的微观结构和整个battery.Current的模拟工作之间的关系扩散和位错的相互作用集中在金属中的溶质偏析，也就是说，积累和/或捕获周围的位错杂质。应力对扩散的影响，如果考虑的话，只以简化的形式描述。在锂离子电池电极的模型中，位错到目前为止只被视为额外的应力源，对扩散动力学没有任何影响。有缺陷的微观结构对电池性能的作用是未知的。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建模和有限元模拟。在微观尺度上，位错结构将通过相场模型结合应力辅助扩散的影响进行建模。位错网络中的传输模拟将产生有关微尺度样品的有效扩散率及其与观测到的位错密度的相关性的数据。在介观尺度下，有效扩散性质将被用于模拟单个电极颗粒的充放电行为。在宏观尺度上，中尺度粒子模型将被整合到单粒子模型中。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.