Physics-Based Thermal Degradation Modelling of Lithium-Ion Batteries

自早期以来，锂离子电池（LiB）建模已经取得了长足的进步，但还有更多的工作要做。新鲜LiB的常规工作原理已经很好理解了，然而，对衰老细胞的建模却不能这么说。近年来已经开发了一些模型来预测锂离子电池的降解，其中许多模型是经验的，因此适用范围非常有限。目前还不清楚锂离子电池在第二次使用中会如何表现，因为电池在其使用寿命中会经历许多复杂的过程，这将从根本上改变其操作原理。例如，如果电池在新的时候以1C的速率充电，其表面的温差可能只有几度，后来，一旦电池使用了一段时间，由于电池中某些材料的形成和分解，这种温度梯度会发生变化。这种预期工作温度的变化可能会导致在正常温度范围内可能不会形成的新化合物的形成或不均匀降解，从而导致各种其他问题。我的研究将集中在建模上，不仅是锂电池的标准操作行为，还有电池如何退化。对于那些想要与第二人生的LiB合作的人来说，另一个紧迫的问题是知道它处于什么状态。为了了解锂电池的状态，必须进行许多测试来测量诸如充电状态（SoC）、内部阻抗、可用容量等集总参数。这里的问题是参数是集中的，这些测量不能产生对于理解上述退化至关重要的分布参数。热成像是一种很有前途的替代方法。通过给电池通电并测量相应的温度曲线，可以将电池的状态联系起来。这项研究可以帮助我们更好地理解锂离子电池是如何退化的，提供更简单的方法来确定电池是否可以在第二次使用中使用，以及使用多长时间，以及帮助开发电动汽车（EV）的快速充电方法，因为目前，快速充电会导致电动汽车电池的显著加速退化。考虑到上述所有因素，我的项目的主要目标是：*研究锂离子电池并了解基本原理*开发基于物理的锂离子电池热降解模型*研究锂离子电池的第二次使用寿命行为*研究快速充电和热降解影响*研究不同几何形状的电池如何降解，例如袋形/圆柱形电池

Lithium ion Battery (LiB) modelling has come a long way since its early days yet more work needs to be done. The regular operating principles of a fresh LiB are quite well understood, however, the same cannot be said about the modelling of aged cells. Some models have been developed in recent years to predict the degradation of LiB's, many of which empirical and hence have a very limited applicability range.It is not well understood how the LiB will behave in a 2nd life application as the battery goes through many complex processes over its lifetime which will fundamentally change its operating principles. For example, if the battery is charged with a 1C rate when it is new, the temperature difference over its surface might only be a few degrees, later, once the battery was used for some time, this temperature gradient will change due to the formation and break down of certain materials in the battery. This change in expected operating temperature might lead to formation of new compounds which may not have formed in the normal temperature range or uneven degradation which can cause a variety of other problems.My research will focus on modelling not just the standard operating behaviour of a LiB but also how the battery degrades. Another pressing issue for people who want to work with 2nd life LiB's is knowing what state it is at. In order to understand the state of a LiB many tests must be carried out to measure such lumped parameters as state of charge (SoC), internal impedance, available capacity and so on. The problem here is that the parameters are lumped and these measurements cannot yield distributed parameters which are crucial to the understanding of degradation as mentioned above. A promising alternative to this is thermal imaging. It may be possible to correlate the state of the battery by running a current through the battery and measuring the corresponding temperature profiles.This research can aid in better understanding of how lithium-ion batteries degrade, yield simpler ways to determine if a battery is usable in 2nd life applications and for how long as well as assist in developing more rapid charging methods for Electric vehicles (EV's) since currently, fast charging can causes significantly accelerated degradation of EV batteries.Considering all of the above, the main objectives for my project are:* Study lithium-ion batteries and understand the fundamentals* Develop Physics based thermal degradation model of a lithium-ion battery cell* Investigate 2nd life behaviour of a lithium-ion battery* Investigate fast charging and thermal degradation impact* Investigate how different geometry batteries degrade, e.g. pouch/cylindrical cells