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Lithium car batteries are discarded and recycled with a residual capacity of 80 percent. This is basically not a bad solution considering that about 95 percent of the material is recyclable. However, it would be more sustainable to give the batteries a second life. But since it is usually not known what influences the battery has been exposed to during its life in the vehicle, this is not done for safety reasons. In the best case, however, the battery could continue to be used unchanged for many years. Possible applications include electric cars with a short range, industrial trucks, machine tools and stationary storage systems. Only when the capacity has decreased to the point where operation would no longer be economical is the time right for recycling.

Thermal runaway

One argument against the reuse of lithium batteries for cars is the possibility of thermal runaway. This is a heating process that takes on a life of its own. It is triggered by an overload, which can be electrical, mechanical or thermal. In the worst case, it can lead to fire and the escape of harmful gases.

Mechanical impact in the form of a crash is particularly feared. We have all seen in the media lithium car batteries that catch fire after an accident.

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At the Institute for Vehicle Safety at Graz University of Technology in Austria, a battery testing center is operated in which crash scenarios can be simulated and tested. Even crashes with high acceleration loads are possible here. It is the world’s first and in some aspects the only battery testing center of its kind. “Vehicle safety has developed rapidly over the past twenty years. Many vehicle components can be simulated on the computer,” says Professor Christian Ellersdorfer from the Institute for Vehicle Safety at the Graz University of Technology. “But lithium car batteries are still so new that it’s not even known yet what methods are necessary – and that’s a big part of our work.”

Safety status of lithium car batteries

The team develops simulation models of battery cells, battery modules and entire battery packs to virtually map the evolution of the safety status of batteries over their life cycle. The current SafeLIB project aims to identify the influencing variables that make it possible to describe the safety of a battery. Here is Ellersdorfer in an interview with IO:

How long do lithium car batteries last?

Research and tests have shown that lithium batteries last at least as long as a normal electric car life, which is about 200,000 kilometers. However, the lifespan always depends on the general conditions. Up to a state of health of 80 percent residual capacity, reasonable use in an electric vehicle is possible. This limit results only from the short range of electric cars – not because the battery is broken. With a method for describing its safety status, it could also be used even longer.

In the previous SafeBattery project, you already established that the service life depends on how the lithium battery is handled, correct?

Definitely. For example, temperature has an influence on aging behavior. If you charge and discharge lithium car batteries in extreme heat or cold, this has a negative effect on the service life. Likewise, driving style can have a negative effect, for instance, if you constantly drive at full throttle.

After a crash, the battery is replaced, not because it is definitely broken, but because you cannot assess its condition. If there is damage, the effects are still difficult to determine and describe. There are still hardly any characteristic values and that is exactly why our research project was initiated.

What currently happens to discarded lithium car batteries?

If, for example, there is a crash after a year, then you dismantle the battery, take it apart and try to recover the raw materials as best as possible for recycling.

If there is no crash and the electric car has reached the end of its life, then the battery is either recycled or used for other applications. Automakers often use them in stationary storage systems to give them a second life, but with a slight uncertainty because you usually don’t know exactly what the battery has experienced in the vehicle. This is exactly the question we want to answer so that we can reuse these lithium car batteries on the basis of solid knowledge and with a good conscience.

What is the safety status of a lithium battery after a vehicle’s life if there has been no crash, jostling, etc.?

In the best case, you can assume a safety level of 99 to 100 percent after a normal vehicle life. But you also have to take into account the possibilities for subsequent use. Automakers are not power grid or solar park operators, and as things stand, they don’t want to be. But even if they hand the battery over to a third party, there needs to be a guarantee that the battery is safe. That’s a huge issue.

Because you’re in a legal gray area?

Exactly. That’s why our project also has a Law Lab, where we work on legal issues. The lithium battery was originally intended for a vehicle and has a completely different purpose in its second life. Is this legally permissible at all, and if so, what legal framework conditions must be observed? Also, the question of whether there can be a warranty under these circumstances is open.

In terms of warranty, it is initially unclear who owns the battery. After all, cars can also be rented. Does it then belong to the manufacturer or to the private individual – and how can it be transferred to a third party at all? If I pass it on as a private individual, do I have to guarantee that it works?

Even before the warranty, however, there is the Waste Management Act. After a battery has had its first life, it is actually waste. It is still unclear how to deal with this.

Regarding the type of use, it is questionable whether it is legally permissible to use a lithium battery developed for a vehicle in its second life in an energy storage system. And if so, what legislation applies in this case?

These are the unresolved issues that we are at least capturing once in the project.

Thank you for the interview.

Image: Christian Ellersdorfer (left) at the battery crash facility of the Battery Safety Center Graz (c) © Lunghammer – Graz University of Technology, Austria.

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