The older an e-car battery, the lower the risk it poses. This is what researchers at Graz University of Technology discovered after they spent four years studying the behavior of lithium-based batteries in electric cars in the event of crashes in the “Safe Battery” project.
With the help of crash tests, simulation models and calculation methods according to the researchers’ own statementsthat vibrations and accelerations hardly affect the behavior of batteries. However, more significant mechanical and electrical changes were evident from the constant charging and discharging of the battery. Battery cells aged in this way have a higher rigidity when subjected to mechanical stress.
“However, the changes do not necessarily mean that batteries become more dangerous with age. The sum of the influences makes them safer over time because they also lose electrical energy,” explains project manager Christian Ellersdorfer. After an internal short circuit, cells with a greatly reduced capacity content have a weakened course of the so-called thermal runaway. Due to the reduced energy potential of aged batteries, the probability of accidental battery fires decreases.
Further battery usage
The researchers are concerned with the entire charging cycle of batteries, since the nature of new energy storage systems is largely known. Based on the research results, manufacturers could now know what they can trust a battery cell to be. This enables material-saving designs and greater efficiency.
“Up to now, the battery was installed in such a way that deformations could be ruled out in every conceivable scenario,” explains Ellersdorfer. Now manufacturers can make better use of the installation space. Safety checks on a new cell are also valid for the entire life of the battery.
The research now focuses on the further use of batteries. Used batteries with a capacity of 80 percent are no longer suitable for e-cars, but they are for stationary energy storage devices or for machine tools. “For the first time, we are determining generally applicable measurement parameters in the area of security,” says Ellersdorfer, describing the project.