ECN: When Electric Vehicles Crash, What Happens To The Battery?

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ECN: When Electric Vehicles Crash, What Happens To The Battery?

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When Electric Vehicles Crash, What Happens To The Battery?
by TU Graz

Safety, range and costs: these are the three big premises of
electromobility. Safety definitely comes first. Lithium-based traction
batteries are usually completely enclosed in the battery case and
integrated in the vehicle to protect the battery from all conceivable
stresses and external influences. This "armour" has an effect on
construction, weight, size and overall design of the vehicle.

Deeper Insights

"For the sake of safety, vehicle producers protect traction battery
components usually more than is necessary, just to be on the safe side.
As payback, however, there are certain restrictions. One reason for this
practice is that too little research has been done into the behaviour of
battery components under crash conditions, such as battery cells,"
explains Wolfgang Sinz from the Institute of Vehicle Safety at TU Graz.
Current research restricts itself mostly to the behaviour of new vehicle
traction batteries, without for example taking into account the possible
influence of previous stress, such as ageing. And this is the point at
which the team led by Wolfgang Sinz together with well-known national
and international partners from research and industry takes up its work
in the COMET project "SafeBattery," which moved on in April 2017.

Every battery has a history

In the four-year research project funded by the Austrian Research
Promotion Agency, the focus is on the mechanical, electrochemical,
chemical and thermodynamic behaviour of single cells and single modules
on a lithium basis under crash loads. In the course of this, the
researchers will investigate components with different histories, since
"safety should be ensured not just of new batteries, but also of
traction batteries in vehicles which have a certain amount of vibration,
possible minor mechanical shortcomings due to small accidents and
calendrical ageing behind them," says Wolfgang Sinz. Other factors
influencing battery behaviour in crash cases will be examined carefully,
such as charging status and temperature.

The SafeBattery team wants to sound out the limits of battery cells to
subsequently define parameters which can be used to ensure that these
limits are never exceeded in practice. A lot of collaboration is needed,
not only from industry partners such as AVL, Steyr Motors, Audi and
Daimler, but also from within TU Graz in the form of experts from the
Institute for Chemistry and Technology of Materials and the Virtual
Vehicle competence centre. "There is a lot of interdisciplinary
crossover in this project. We have a huge range of influencing
parameters and have to examine and break down the mosaic into its
constituent parts. Only then can we make recommendations concerning
construction, integration and operation of the batteries," says Sinz.

Tailor-made crash test rig

The team has developed and built its own test rigs with tailor-made
measuring and sensor technology for a variety of crash scenarios for
batteries and their components in the Institute's own crash test hall:
"A unique experimental setup which can yield high-quality measuring data
and findings from among the entire, highly complex procedures which
usually only take milliseconds to complete," says Sinz. On top of this
come numerical calculation methods and simulations to help better
understand the multi-physical processes involved. This should result in
a comprehensive knowledge of the behaviour of traction batteries under
crash loads in order to better integrate them in relevant vehicle
concepts. This knowledge can be used to recognise early on critical
states in batteries during development and in operation and to avoid
them through specific measures. Furthermore, cell manufacturers are
interested in precise requirement specifications. "Using the results
obtained, we want to contribute to achieving more leeway in range and
vehicle design while always guaranteeing safety," summarises Sinz.

A look at future generations

Another focus of the project is that, together with the Institute of
Chemistry and Technology of Materials, not only state-of-the-art
lithium-ion batteries with liquid electrolytes will be investigated, but
also next-generation lithium batteries with all solid state
electrolytes. "What interests us here is whether the coming generation
of drive batteries simply no longer has the failings of the current
systems or whether they'll have new or different vulnerabilities," says
Wolfgang Sinz.

The partners in the K-project "SafeBattery" of the COMET programme are
AVL List GmbH, SFL technology GmbH, Kreisel Electric GmbH, Steyr Motors
GmbH, Audi AG, Daimler AG and Porsche AG. From academia, the Virtual
Vehicle competence centre and Institute for Chemistry and Technology of
Materials are assisting the Institute of Vehicle Safety, as is TU Graz.
The project period is four years and will have a total financial volume
of six million euros.

This project is anchored in the Field of Expertise "Mobility &
Production," one of five research foci of TU Graz.

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