Fraunhofer automates X-ray analysis of electric vehicle batteries
Fraunhofer IIS has developed software that automatically examines X-ray images of entire electric vehicle batteries for mechanical defects. The method created as part of the AIR research project is intended to complement traditional battery diagnostics, providing additional insights especially in accident vehicles and before potential second-life use.
The X-ray software detects displaced round cells and automatically identifies deformed areas.
Image: Fraunhofer IIS
The Fraunhofer IIS Röntgentechnik Development Center, in collaboration with the University of Munich, has developed a method that allows for the inspection of entire high-voltage batteries without opening the battery casing or removing individual components. The AIR system itself (where AIR stands for Antriebsbatterieinspektion mittels Röntgentechnik) is not new: Fraunhofer introduced this inspection technology in 2024 and tested it on more than 100 private electric vehicles among others. What is new now is a software library that automatically analyzes the generated 2D X-ray projections.
According to Fraunhofer IIS, the software can automatically locate round cells, prismatic cells, and pouch cells in the battery types examined so far. It can then detect geometric abnormalities that may indicate displaced or deformed cells as well as cell swelling.
The measurement setup resembles a washing machine: an X-ray source positioned above the vehicle irradiates the vehicle and the underfloor battery, while a detector below detects the radiation. Depending on the testing setup, only the battery pack may be examined. The Fraunhofer Institute previously indicated that scanning an entire vehicle took about ten minutes. According to the institute, the automated analysis of a battery pack demonstrated in this case took roughly five minutes in the testing environment used. However, the total testing time depends on factors such as the size of the pack, the measurement setup, and the number of projections required.
For evaluating used electric vehicle batteries, various methods exist alongside X-ray analysis to determine primarily the electrical and electrochemical condition, or State of Health (SoH). The relevance of individual testing was recently illustrated by a study by Aviloo: among more than 500,000 tested electric cars, the SoH varied significantly even among vehicles of the same model with similar mileage.
However, SoH does not directly indicate whether the cells and modules inside a closed battery pack are mechanically intact. Aging, vibrations, or accidents can cause shifts and deformations. This is precisely where the AIR project focuses its efforts.
X-ray analysis complements traditional battery diagnostics
X-ray inspection is not intended to replace electrical battery tests. Instead, the images are meant to provide additional information about mechanical integrity, thereby becoming part of a more comprehensive assessment of condition and safety. This could be relevant, for example, when deciding whether an accident-stricken battery should be further investigated, transported, stored, reused, or disposed of.
The project partners investigated how this could work, using a VW ID.3 as one of the test vehicles. Under laboratory conditions at DEKRA, the vehicle collided head-on at 79 km/h with the rear of a stationary VW Tiguan. Despite significant deformation in the front area, no safety-critical structural issues were detected in the X-ray projections of the underfloor battery, according to Fraunhofer.
The software automatically located the pouch cells in the nine battery modules and compared, among other things, the curvature of selected cell edges. According to the findings, no critical deviations, overlaps, or bulges were observed.
The battery was approved not solely based on these images. In addition, a hazard assessment according to DEKRA guidelines, data from the event data recorder and battery management system, as well as further electrical tests were considered. Based on this overall evaluation, the high-voltage battery was classified as having the lowest EUCAR hazard level of 0 and approved for continued use.
For another crash battery with round cells, the analysis yielded a different result. Here, the software detected a significantly deformed area and cells that were displaced relative to a reference. Although no signs of cell swelling were found, the mechanical deformation meant that further use of the battery was not recommended.
X-ray technology is also used elsewhere for battery testing. For example, Fraunhofer EMI has developed a high-speed X-ray system that enables the visualization of dynamic processes within individual large-format battery cells during stress and safety tests. Such a system is scheduled to be installed at Volkswagen’s battery subsidiary PowerCo in Salzgitter by 2028.
In the context of the AIR approach, other use cases besides accident vehicles could become interesting in the future. Fraunhofer IIS mentions second-life applications as a possible application area. The institute also considers this technology potentially relevant for future inspection concepts related to the regular safety checks of electric vehicles. However, Fraunhofer has not yet announced specific plans for integrating it into the standard safety check process. Looking ahead, the planned “Giant Eye” CT system at the Röntgentechnik development center in Fürth is set to enable three-dimensional analysis of entire electric vehicles.