A research team led by TU Graz is providing new design guidelines for batteries in electric vehicles. The concepts increase safety, make repairs easier and improve sustainability throughout the entire life cycle.

The development of traction batteries for electric vehicles is becoming increasingly complex. Electrical performance, thermal behaviour and mechanical safety interact closely and require integrated solutions. At the same time, there has been a lack of uniform design standards to date. This has disadvantages. In the event of an accident, this makes it more difficult for the emergency services to handle damaged or burning batteries safely, and recycling is also much more complicated due to inconsistent designs. In the E-Track research project, the Vehicle Safety Institute at Graz University of Technology (TU Graz), together with the Institute of Environmental Systems Science at the University of Graz and industry partners, has developed well-founded design guidelines that make battery systems safer, more sustainable and more economical.

Disadvantages due to lack of design standards

“Without uniform design standards, emergency services often face major challenges in an emergency because the structure and behaviour of battery systems are difficult to assess. At the same time, we lose valuable resources if batteries cannot be repaired or fully recycled,” explains project manager Markus Fasching from the Vehicle Safety Institute at TU Graz. “Our work shows that safety, efficiency and recyclability can be improved together through well thought-out design.”

A key shortcoming of today’s battery systems is their limited repairability and recyclability. Many manufacturers rely on bonded housings with thermally conductive pastes for temperature regulation, which offer advantages in production but often force the replacement of the entire battery pack in the event of damage. The team used this construction method as the basic design for their investigations. The researchers also investigated two alternative designs, including a concept with replaceable housing covers, in which heat dissipation pads dissipate the heat, and a liquid-cooled design. Here, an electrically insulating oil takes over the heat dissipation and the housing is screwed together with a seal. This facilitates disassembly and enables the targeted replacement of individual cells.

It pays to make repairs easier

The analyses show that battery cells are both the biggest cost factor and the decisive safety and sustainability factor. They make up around 75 per cent of the total mass, which is why their reuse after an accident is crucial for the ecological and economic balance. Life cycle analyses prove this. Repair-friendly designs are worthwhile as soon as eight per cent of the cells can be reused. Easy dismantling also promotes the recycling of materials. The research team also developed new diagnostic methods based on electrochemical impedance spectroscopy. These diagnostic methods paired with virtual multi-physical models make it possible to reliably detect internal damage such as micro-shorts, which could otherwise lead to time-delayed critical events such as battery fires.

Although the guidelines were primarily developed for electric two-wheelers, the methods and simulation approaches can be directly transferred to larger vehicle classes such as cars and lorries. The results of E-Track thus create a sound basis for future industrial standards and could also serve as a starting point for regulatory frameworks. There are already some interested parties from industry who have shown interest in follow-up projects to conduct further research on diagnostic methods for assessing the safety status and the multiphysical simulation models in follow-up projects. The completed project was funded by the Austrian Research Promotion Agency FFG.