A second life for batteries

May 8, 2024

Discarded lithium-ion cells from electric vehicles can be reused as stationary energy storage devices. Researchers at Graz University of Technology have identified the first indicators to reliably assess the condition.

In 2030, approximately 1.2 million batteries in electric cars, buses and construction machinery will be retired worldwide because they have reached the end of their planned service life, expired their warranty period, or have been scrapped. There will be about 14 million old batteries by 2040.

Recycling materials makes sense, but it is also expensive and technically demanding. Therefore, the continuous use of batteries, for example to store stationary electricity, would be better and more sustainable. This requires a good evaluation of the remaining performance and security. At Graz University of Technology, researchers from the Institute for Vehicle Safety have now identified the first criteria that can be used to reliably assess the condition of discarded batteries.

13 indicators that characterize the aging process

Until now, a decrease in charging capacity and an increase in internal resistance served as an indicator of the condition of the battery in use. However, this is not enough to decide on the possible use of Second Life. So the researchers carefully examined lithium-ion cells that were used in vehicles under real conditions and matched new examples in the laboratory.

They collected 31 different measured values ​​during repeatable charging and discharging cycles, then checked how well they represented the aging state of the batteries. 13 of these indicators turned out to be meaningful – they include, for example, the charging and discharging capacity, the temperature difference between the electrodes during the charging process or the relaxation behavior of the battery cell after charging.

“Using these indicators, we can draw conclusions about the aging state of lithium-ion batteries and draw preliminary conclusions about different usage profiles without having to rely on important data protection information about the usage history of the batteries,” says Jörg Moser, Chairman of the Board of Management. From the Battery Safety Center in Graz of the Institute for Vehicle Safety at the Graz University of Technology. “On this basis, we can decide whether the battery is suitable in principle for continuous use in a particular field of application.”
Security assessment as the next step

However, the safety status of the batteries is still missing to ensure continued low-risk use. During its first life, chemical changes occur in the materials, which may affect their safe use. “It is important to understand battery cells and the processes, interactions and changes that occur in them in detail so that we can qualify them regarding their safety behaviour,” says Christian Ellersdorfer. He leads the COMET SafeLIB project at the Vehicle Safety Institute, where a consortium of research institutions and automotive and technology companies is working on the safety evaluation of new and used lithium-ion batteries. The first results are expected by the end of the year.

It will likely take a few years before used batteries are widely used in subsequent applications and electric mobility becomes more sustainable over the entire life cycle. New storage materials, the safety of different battery technologies, the economic feasibility of second life applications and legal issues around data protection, warranty or liability must also be taken into account. “This results in an interdisciplinary research area, which we at Graz University of Technology would like to work on together with national and international partners in other research projects,” says Christian Ellersdorfer.

source: Graz University of Technology