Physics-Based Thermal Degradation Modelling of Lithium-Ion Batteries

锂离子电池(LIB)的建模自早期以来已经取得了长足的进步，但还需要做更多的工作。新鲜LIB的常规操作原理是很好理解的，然而，对于老化细胞的建模就不能说同样的话了。近年来已经开发了一些模型来预测锂离子电池的退化，其中许多模型是经验的，因此适用范围非常有限。由于电池在其寿命内经历了许多复杂的过程，这将从根本上改变其工作原理，因此还不能很好地理解锂离子电池在第二寿命应用中的表现。例如，如果电池在新的时候以1摄氏度的速度充电，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，这个温度梯度就会因为电池中某些物质的形成和分解而改变。这种预期工作温度的变化可能会导致新化合物的形成，而这些化合物可能不是在正常温度范围内形成的，或者是不均匀的降解，这可能会导致各种其他问题。我的研究重点不仅是对锂离子电池的标准工作行为进行建模，还将对电池如何退化进行建模。对于想要使用Second Life Lib的人来说，另一个紧迫的问题是知道它处于什么状态。为了了解锂离子电池的状态，必须进行许多测试，以测量电荷状态(SoC)、内阻抗、可用容量等集总参数。这里的问题是，这些参数是集中的，这些测量不能得出对如上所述的退化理解至关重要的分布参数。一个很有前途的替代方案是热成像。通过在电池中运行电流并测量相应的温度分布来关联电池的状态是可能的。这项研究可以帮助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在第二生命应用中是否可用以及持续多长时间，以及帮助开发电动汽车(EV)的更快速充电方法，因为目前，快速充电会导致EV电池显著加速退化。考虑到所有上述情况，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的热降解模型*调查锂离子电池的第二寿命行为*调查快速充电和热降解的影响*调查不同几何形状的电池如何降解，例如袋状/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