Innovative Devices for Enhanced Safety and Reliability in Battery Systems

Printed Temperature Sensors and Heating Elements

© Fraunhofer IISB
Printed temperature sensor for battery cells
© Fraunhofer IISB
Foil with printed electronic devices for battery cells

We are developing temperature sensors, heating elements, and balancing resistors for applications in battery systems. Our focus is on highly integrated devices satisfying simultaneously the low-cost and high robustness targets coming from the automotive and industrial businesses.

The devices have to withstand mechanical forces related to expansion and contraction of the battery cells during normal operation, including vibrations. Printed electronic technologies meet these requirements to a high extend and are also very well suited for high-volume production, for example with sheet-fed or roll-to-roll processing, at low-cost. Furthermore, thin printed layers constituting the temperature sensor yield to a low heat capacity and therefore result in a low time delay for the detection of temperature changes of the sensed device. The low thickness of the printed elements, compared to conventional discrete temperature sensors or devices, make them easy to place between the battery cells, including pouch cells. Moreover, research is done for implementing the sensors onto the cell surface, or even inside the cell packaging.

Power Antifuses

© Fraunhofer IISB
Symbols of the antifuse devices
© Fraunhofer IISB
Antifuse showing occured aluminum spiking
© Fraunhofer IISB
High-power antifuse device (activated)

A power antifuse can shorten a faulty battery cell in a battery system in order to remove the cell from the current path. The novel antifuse device has outstanding advantages over state-of-the-art devices: it provides a low leakage current before activation and very low resistance in both directions after activation. With such a bypass device, the system can still continue to operate, for example in a kind of degraded mode. Traditional semiconductor devices like silicon diodes, MOSFETs or IGBTs are too expensive to fulfill the specifications required for the power antifuse device (on-resistance lower than 1mΩ, continuous current higher than 100A, material costs lower than 0.20€).

The development and integration of power antifuses in parallel to battery cells is an easy to implement solution for dramatically improving the reliability and the lifetime of the whole battery pack in electric vehicles. Further, it not only provides a very cost efficient solution for enhancing the reliability of the battery pack, but it also reuses the available developments that have been done on monitoring and management systems.

Two versions of the power antifuse are in development. One version is a self-triggering device, reacting on a reverse voltage biasing over one battery cell. The other version is controlled by an external driver and can be activated anytime.

The proposed antifuse devices are considerably cheaper, their series resistance much lower and the processing technology less complex than conventional silicon substrate based active solutions. The activating mechanisms used in the antifuse are based on irreversible failure mechanisms, which are used in a controlled way.