24/04/2019

Electric vehicles are an important component of energy transition.

Electric vehicles are an important component of energy transition.

Source: BAM

Electric vehicles are an important component of energy transition and the number of electric vehicles driven on Germany's roads will increase in the future. Above all, lithium batteries used as electrochemical storage systems are a cutting-edge technology and represent the current standard for electric cars.

"When dealing with large amounts of energy and its storage, there is of course an associated risk," says Dr. Anita Schmidt, chemist in the Dangerous Goods Packagings division. Lithium batteries are a key area of her work. This is due to the fact that the transport of damaged lithium batteries must be approved by the authorities when they are damaged to such an extent that they can react dangerously. In Germany, BAM is the competent authority for this task and specifies criteria for transporting such defective and damaged batteries. Transport is only permitted if these criteria are fulfilled. In addition, BAM authorises the transport of unpacked, untested prototypes.

Not fundamentally dangerous, but ...

The use of lithium batteries is normally non-hazardous – provided they are used properly. However, if an electric car catches fire, the battery is immediately under suspicion. "Most of the time, a fire would be preceded by mechanical damage to the lithium battery, for example due to an accident. However, the fire may not break out immediately but can occur some time later," explains Schmidt.

Such ’thermal runaway’ of the battery after mechanical damage or heating may have different causes. In addition to mechanical influences, fire and heat or a short circuit, a deep discharge or overcharge may start the fire. "If the temperature has reached about 150 degrees Celsius, depending on the battery type, a 'point of no return' is reached," says Anita Schmidt. “The process of thermal runaway will then start and the battery can catch fire." However, according to Schmidt, in the event of a fire, electric cars with lithium-ion traction batteries are comparable to vehicles with petrol or diesel combustion engines in terms of safety. However, in extreme cases vehicles with internal petrol or diesel combustion engines can go up in flames in an accident.

A thermal runaway may be the main danger posed by lithium batteries but this battery type can also be dangerous in other ways. For example, high voltage also poses a risk as electric traction batteries for cars may produce at least 300 to 400 volts – and even more in the future.

Focus on safety

It becomes obvious that damaged lithium batteries that are liable to rapidly disassemble, dangerously react, produce a flame or a dangerous amount of heat or emit toxic gases may only be transported under very specific safety requirements.

These conditions need to be determined on the basis of scientific findings. Currently, an interdisciplinary BAM research team is investigating which substances and in what quantities are emitted in the event of a thermal runaway. BAM has set up a test stand for fire tests at its Test Site for Technical Safety (TTS) for this purpose.

"Our main concern is the safety of lithium-ion batteries, rather than the development of new battery types," explains Anita Schmidt. "This distinguishes us from other research institutions working on lithium batteries."

Container for fire test: What happens to batteries used for electromobility when set on fire?

Container for fire test: What happens to batteries used for electromobility when set on fire?

Source: BAM

The next step: international specifications for transport and packaging

However, findings from the experiments will also be used on a different route to more safety: namely through further development of regulations and laws. "A classification according to the degree of hazard would be reasonable because some batteries can thermally runaway and explode, others just burn and some only emit smoke," says Schmidt. A new working group of the responsible committee at the United Nations (UN) in Geneva is currently working on this classification scheme and BAM scientists are involved. It is the international UN recommendations that describe how lithium batteries have to be transported in principle. These recommendations are then implemented into regional law, for example in Europe - into the "European Agreement concerning the International Carriage of Dangerous Goods by Road", in short: ADR.

Incidentally, there will be new specifications in ADR in 2019, as Schmidt explains: "There are new packaging instructions for defective lithium batteries that can be dangerous during transport. They specify requirements for the packaging during transport and packaging tests. " Here, too, BAM is the competent authority for the approval of these package testing methods.