Smart polymer foils for safe batteries

Duration: June 2016 – May 2019 

Lithium-ion batteries are used with different shapes, sizes and chemical configurations for an increasing number of industrial or personal applications. Especially for high energy cells, but also in the environment of critical infrastructure such as cleanrooms, a safe operation of the battery has to be ensured at any time. Therefore important state parameters like the cell temperature or state of charge have to be known, but sometimes these parameters only can be obtained insufficiently or in a difficult manner, which can lead to catastrophic accidents.

Based on the principle of periodic refractive index changes, which are processed by a femtosecond laser into a waveguide’s core (e.g. of an optical fiber) at the Fraunhofer Heinrich Hertz Institute, it is possible to measure temperature and strain changes at the particular sensor position. So called Bragg sensors feature a small, high precision and lightweight way to realize a close mesh monitoring on small areas so that for example the cell’s temperature can be measured directly on its surface. In case of flexible cell housing materials the strain provides additional information that can be used for an enhanced state of charge and state of health calculation as well as a possibility to timely predict a thermal runaway.

Hence it is aimed to transfer this established technology for optical fibers into polymer foils for the first time.