Battery thermal runaway chemistry simulation
- Alvaro Filho
- Mar 18
- 4 min read
Don’t try this at home – unless you’re simulating it!
Thermal Runaway: a recap
Thermal runaway of batteries is a dangerous phenomenon where the battery cell overheats uncontrollably. A self-sustaining feedback loop occurs where the battery receives a certain amount of heating, and if left unaddressed, this in turn triggers a series of chemical reactions inside the battery cell.
These reactions release even more heat and gases, which can result in huge pressure build up inside the battery. Extremely hot (over 1000oC!) and combustible venting gases are then emitted from the battery cell. When these gases ignite, fire spreads to other battery cells and catastrophic damage can occur to an electric vehicle, property and of course presents a high risk to life.
Look at this short video which shows the violent nature of a thermal runaway event:
It should be clear that these scenarios should be avoided, and battery systems designed to ensure safe operation if a thermal runaway event occurs. Indeed there are now various national and international regulations that cell makers and electric vehicle manufacturers must adhere to.
Time to test? – Accelerated rate calorimetry (ARC)
The most intuitive way to understand the behavior of batteries as they undergo a thermal runaway event is to replicate the causes of thermal runaway and see how the battery behaves. In the case of overheating, a common methodology to understand the heat release of the battery is an accelerated rate calorimetry (“ARC”) test. These tests provide clear insights but come with some issues: primarily that the tests themselves are expensive, require access to test facilities and require a physical prototype of the battery cell! Of course, this is where simulation can fit in and allow for rapid design iterations early in the design cycle, with safety in mind.
Simcenter STAR-CCM+ already has a wide range of models and functionalities for battery modelling and battery safety, from the 3D cell design right through to the full battery pack and thermal propagation during a runaway event:
In version 2502, another layer of functionality will be added – most notably the ability to model detailed thermal runaway at the cellular level with the Homogeneous Multiphase Complex Chemistry (HMMC) model.
Thermal runaway chemistry
When we consider the inside of a battery cell then there are multiple solids (anode, cathode and separators), as well as liquid electrolyte. When thermal runaway reactions occur, these components can react and decompose to release flammable gases such as hydrogen and methane. This results in multiple phases all reacting with each other e.g multiphase.
To capture this complexity, a framework has been developed in which the early stages of a thermal runaway event can be modeled with detailed chemical modeling. This allows designers to explicitly model the fundamental reactions that are triggered during a thermal runaway event. The reactions are considered as a homogeneous mixture, allowing for simple and easy setup in conjunction with our multiphase mixing model. Furthermore, this is all built on top of a proven complex chemistry solver, allowing reactions to be easily defined using standard chemkin file import and accounting for intra- and interphase reactions. This provides unique modeling functionality to deeply understand battery behavior.
For example, one can directly configure reactions for SEI decomposition/production, conductive salt decomposition, hydrogen fluoride production, and cathode decomposition; see the example of imported reactions for thermal runaway testing above.
Let’s get cookin’ – Heat-Wait-Seek
Armed with a new modelling tool, let’s apply it to the simulation of an ARC test and see how it performs. The ARC test involves an initial period of heating the battery called Heat-Wait-Seek (HWS) where the battery is gradually heated before waiting to see if exothermic reactions begin. When those reactions begin, no more heat is applied to the battery, and it is left to continue reacting / self-heating until the onset of thermal runaway.
Unveiling the interaction of reactions and phase transition during thermal abuse of Li-ion batteries https://doi.org/10.1016/j.jpowsour.2021.230881
One great thing about having this physics functionality inside Simcenter STAR-CCM+ is that it can leverage the automation capabilities. The ARC testing process can be easily implemented using Simulation Operations and Stages without any scripting. And the results are excellent:
As can be seen, the new HMMC model can accurately capture the onset of both the exothermic reaction and thermal runaway.
Being able to accurately capture this behavior allows for effective countermeasures or mitigation strategies such as heat shields to be implemented by engineers much earlier in the design process in a safe and cost-effective manner. For example, the predicted heat generation from this simulation can be used as an accurately calculated heat source directly in a larger pack level model, or the predicted vent gas compositions used for a further combustion analysis. An excellent example of how simulation is vital in the battery design cycle.
Schedule a meeting with CAEXPERTS and find out how we can help your team design safer, more efficient battery systems using advanced simulation to predict and mitigate thermal runaway events. Contact us now and take your innovation to the next level!
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