New early warning system for electric car batteries strikes much faster
A system is currently being developed to provide early warning of possible damage to lithium-ion batteries. For this purpose, the electrical alternating current resistance in the cell is continuously measured and analyzed. The Federal Institute for Materials Research and Testing (Bundesanstalt für Materialforschung und -prüfung – short BAM) is working on this project together with the automotive supplier Vitesco Technologies.
In the EU, it is a legal requirement that an electric car must emit a warning signal to the people inside the vehicle at least five minutes before the battery is thermally run down. This is usually done via the battery management system (BMS), which is the electronic control unit of the battery. The BMS monitors the performance and condition of individual battery cells and cell groups.
The warning systems use sensors to register defective changes in the battery, which are triggered by suspicious changes in temperature or pressure. However, the alarm is only triggered when the battery is already seriously damaged. This is a disadvantage, as thermal runaway and, very often, the complete destruction of the battery are usually unavoidable at this point.
The Federal Institute for Materials Research and Testing (BAM) is working on a solution with the Regensburg-based automotive supplier Vitesco Technologies. Together, they are developing a warning system that is intended to indicate critical changes in individual battery cells at an earlier stage. This should make it easier to avoid total loss. A process that continuously measures and analyzes the electrical alternating current resistance - the impedance - in the cell forms the basis of the system.
Tim Tichter, a researcher on the project at BAM, explains that a change in impedance can indicate various defects or undesirable conditions. Possible causes can include thermal stress, vibrations, shocks, material failure or even manufacturing defects. However, a change in impedance is to be expected regardless of the cause.
Until now, long measurement times, which were necessary for meaningful impedance analyses, have prevented the implementation of such analyses in a BMS. For this reason, the project team is pursuing the approach of modifying the measurement methodology in order to enable a high acceleration in the recording and processing of impedance data. The planned early warning system should initiate a service in an emergency or trigger the shutdown of individual cells as an immediate protective measure.
Source: pv magazine, Ralph Diermann, 25.10.2023
Image: gorodenkoff at iStock
