Numerical investigations on the influence of the electrode microstructure on the performance of lithium-ion batteries.

锂离子电池是当前研究的焦点，并作为未来的能量存储设备发挥重要作用，例如在电动汽车中的应用以及可再生能源的中间存储。锂离子电池基本上由两个多孔嵌入电极组成，它们被隔膜隔开。两个电极由金属氧化物或碳颗粒（所谓的活性颗粒）组成，并且由于其颗粒性质而具有非常复杂的微观结构。这种微结构很大程度上取决于颗粒的特定形状以及粒度分布。因此，现代锂离子电池的性能不仅取决于材料性能，还取决于电极的微观结构。特别是微观结构的影响在很大程度上仍然是未知的，应在本项目中进行更仔细的检查。直接数值模拟为锂离子电池的设计和优化提供了一个有价值的工具，也可以用来研究难以通过实验测量的影响。对于数学模型，必须考虑离子在电解质溶液中的运动以及锂在活性颗粒中的扩散。因此，锂嵌入到活性颗粒中起重要作用，因为嵌入产生机械应力。这些所谓的嵌入应力可导致活性颗粒破裂，这对电池性能具有负面影响。因此，本项目的目的是研究微观结构的影响，特别是嵌入应力对锂离子电池性能的影响。在第一步中，锂嵌入到具有任意几何形状的单个粒子中进行检查。这允许曲率效应的影响的详细调查。此外，对于不同的颗粒几何形状，可以研究活性颗粒内部的相变行为，例如在LiCoO2的情况下发生的相变。基于这些单粒子计算，开发的方法可以应用于三维微结构模拟，其中锂离子电池使用周期性单元电池建模。通过这些模拟，可以检查微观结构的影响，特别是粒度分布的影响。数值计算结果还需进一步的实验验证。因此，软包电池的生产，电化学特性，并最终与模拟比较。

Lithium ion batteries are in the focus of the current research and play an important role as a future energy storage device, with application e.g. in electric vehicles as well as an intermediate storage for renewable energies. Lithium ion batteries basically consist of two porous intercalation electrodes, which are separated by a separator. The two electrodes consist of metal oxide or carbon particles, the so-called active particles, and have, due to their particulate nature, a very complex microstructure. This microstructure dependents largely on the particular shape of the particles as well as on the particle size distributions. The performance of modern lithium ion batteries is therefore not only dependent on the material properties but also on the microstructure of the electrodes. Especially the effects of the microstructure are still largely unknown and shall be closer examined in this project. Direct numerical simulations provide a valuable tool for the design and optimization of lithium ion batteries but also to investigate effects which are difficult to measure by experiments. For the mathematical model, one has to consider the movement of the ions in the electrolyte solution as well as the diffusion of lithium in the active particles. Thereby, the intercalation of lithium into the active particles plays an important role, since the intercalation generates mechanical stresses. These so-called intercalation stresses can cause the active particles to break, which has a negative influence on the cell performance. Therefore, the aim of this project is to study the influence of the microstructure, and in particular the influence of the intercalation stresses, on the performance of lithium-ion batteries. In a first step, the intercalation of lithium into a single particle with arbitrary geometry is examined. This allows a detailed investigation of the influence of curvature effects. Furthermore, the behavior of a phase transition inside the active particles, as it occurs e.g. in the case of LiCoO2, can be investigated for different particle geometries. Based on these single-particle calculations, the methods developed can be applied to three-dimensional microstructure simulations in which the lithium-ion battery is modeled using a periodic unit cell. With these simulations, it is possible to examine the influence of the microstructure and especially the influence of particle size distribution. The numerical results should be validated by additional experiments. Therefore, pouch cells are produced, electrochemically characterized and finally compared with the simulations.