SPARTACUS project to monitor and optimise battery cells

Repeated charging and discharging of batteries accelerates aging, reduces the performance of battery cells and shortens service life. Researchers at the Fraunhofer Institute for Silicate Research ISC are now working with project partners on the SPARTACUS project, part of a pan-European research initiative, to develop technology that uses sensors to monitor the internal status of battery cells. The data from these sensors can be used by the integrated battery management system to ensure that charging and discharging currents are optimally managed.

“A major advantage is that this shortens charging times by up to 20% without reducing the performance or service life of the battery,” explained Gerhard Domann, project coordinator at Fraunhofer ISC.

The concept behind SPARTACUS (spatially resolved acoustic, mechanical and ultrasonic sensing for smart batteries) takes advantage of the many complex electrochemical and physical processes that take place inside the battery cell. The acoustic, mechanical and thermal sensors used at Fraunhofer ISC monitor and measure these processes. Ultrasonic sensors, for example, emit acoustic pulses that pass through different layers in the battery cells and are then picked up again by sensors. If a cell expands during charging or there is a defect in an electrode, this affects the duration of the acoustic signal, producing a kind of sonogram of the battery cell. Just as important are the pressure-sensitive mechanical sensors, which register changes in the volume of particular components during charging or discharging. Meanwhile, thermal sensors measure changes in temperature.

“All the sensor readings are sent to the battery management system, which then evaluates them,” Domann said. “This allows it to manage electrical currents while the battery is charging and discharging in a way that provides the maximum possible performance without putting too much stress on the relevant functional layers of the battery (anodes, cathodes, etc). In this way, we can extend the service life of the battery cell.”

The sensors also monitor a number of other effects. Mechanical stress during use and natural aging processes leave traces in the sensitive internal workings of the cells. In the battery cell electrodes, this can lead to cracks and cause the graphite layer to strip away, or create tree-like metal structures called dendrites on the outside of the electrodes. These phenomena are all detrimental to performance, and in extreme cases they can create short circuits in the cells, leading to battery fires.

“The multifunctional sensor array helps us to better understand the complex electrochemical processes in the battery and adapt battery management accordingly,” Domann said.

The sensor technology can be used for the full life cycle of a battery product, helping to optimise quality right from the construction and development phase. In production, ultrasonic sensors are designed to ensure that the finished product leaves the production line in perfect condition. In the future, the technology will not only work on lithium-ion batteries, but also on solid-state batteries or lithium-sulfur batteries, for example.

“After a few years, when the battery’s performance inevitably deteriorates to less than 80% of what it was originally, the sensors from the SPARTACUS project could also be used to qualify the battery for a second life so it can be used for another, less demanding purpose,” Domann said.

Image caption: Details of the printed circuit board for the battery sensor system with mounted temperature sensor and printed ultrasonic sensors. Image ©A Latour, CEA for SPARTACUS.

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