Thermal Runaway for batteries

Thermal runaway refers to the thermal runaway of a system, i.e. the immediate release of a system's energy in the form of heat. It occurs when more heat is generated than can be dissipated or cooled.

In the case of a reactor meltdown or the runaway of a battery pack, this mechanism of thermal runaway is at work.

You can think of it like a box of fireworks. A spark falls into it and one firecracker explodes.  The explosion of one firecracker sets others on fire. Now not only the one box burns, but also the neighboring boxes and the inferno takes its course.

What does this actually mean for batteries or rechargeable batteries for electric vehicles?

Individual cells can be defective and overheat locally, but there can also be a local short circuit due to the deformation of the battery or cells in an accident and consequently a chain reaction.

As with fireworks, the more capacity, the more energy is released. Here, chemistry and charging, i.e. the currently stored capacity, play an important role.

Extensive tests on test rigs fail or are delayed due to very long lead times, as the test capacities are currently still too low.

The test also provides information about what happens, but less about what can be done to prevent or optimize it.

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How can simulation support here?

It makes things visible that would otherwise remain hidden.

A simple consideration helps. A battery cell contains a certain amount of stored energy. If this is released, for example, by a short circuit, a thermal runaway occurs if the cooling system cannot sufficiently dissipate the heat that occurs, neighboring cells exceed a limit temperature, the current resistance increases and the cooling also fails here, or if neighboring cells are also short-circuited by exploding cells.

The physics of this can be described with simulation models of varying complexity.

The most important thing is that the cooling concept works sufficiently well on all cells. There are always nests that are not cooled quite as well and are therefore particularly vulnerable.

The simulation provides an insight into this, but the risk to neighboring cells from exploding cells can also be mapped. From a simple cell structure (cardboard box in which a gas volume is created) to a detailed replica of the cells.

The investigation of crash scenarios in case of an accident helps to avoid damage to the cells by appropriate design of the battery case. The simplest here are static pressure tests up to the consideration of the whole vehicle in a crash case.

The safety of batteries in e-vehicles can thus be significantly increased by proper design and the use of suitable materials. The simulation shows how.

We at Merkle CAE Solutions support you in developing safe cooling concepts, identifying critical areas and optimizing them.

We will be happy to advise you without obligation on how we can also help you to ensure greater safety for e-vehicles.

Please contact Maik Brehm or Chadi Serhan with the keyword "Thermal Runaway".

Your Stefan Merkle