Status monitoring of battery cells

Dielectric Elastomer Sensor
© Fraunhofer ISC
Monitoring the expansion of battery cells by using dielectric elastomer sensors that are clamped in the battery module.
Dielectric Elastomer Sensor Diagram
© Simon Feiler et. al., Fraunhofer ISC, Battery 2030 Annual Conference
The graph shows the change in thickness of a cell during a C/10 cycle, measured at four sensors. The curve of the thickness change indicates the expected phase transitions of the active material within the cell.

Battery cell separating layer with integrated dilation sensors

In a battery pack, the cells are usually clamped separately from each other by a functional material, e.g. to ensure uniform pressure distribution between the cells or to dissipate thermal energy during charging and discharging. As part of the SPARTACUS project, soft, silicone elastomer-based dielectric elastomer sensors are developed that act as such a functional separating layer and can simultaneously measure the expansion of the battery cell for condition monitoring. This information can be used in the battery management system (BMS) to increase the safety of the system.


Detection of cell expansion

Capacitive dilation sensors precisely measure the volume changes of the cells during charging and discharging. They also recognise irreversible and permanent volume changes caused by cell ageing. For this purpose, the sensor properties, such as their mechanical stiffness and measurement range, are adapted to the specific requirements of the battery cell. 


Mechanical decoupling

Elastomers, whose compression modulus can be adjusted over a wide range, provide a uniform damping layer that separates the individual cells in a battery module and thus ensures a more even pressure distribution. In this way, pressure peaks that accelerate cell ageing can be avoided. In addition, these elastomers provide thermal shielding, which can be further optimised depending on the application.


More about project "SPARTACUS"

Specifications deformation sensor

Type of data
Value / range Note
Measurement of cell volume changes in z-direction 10 … 300 µm Adaptable range, depending on expected cell expansion (dynamic/static)
Sensor sensitivity: dilation 0,16 pF/µm  
Absolute sensor sensitivity: dilation 3 µm Depending on preload
Sensor sensitivity: compression load 0.78 pF/kPa  
Absolute sensor sensitivity: compression load 2 kPa Depending on preload
Size of sensor element 2 cm x 2 cm Size of one sensor element
Mechanical pre-load 25 kPa Beneficial for enhanced cell lifetime
Compression modulus 300 kPa Optimized stiffness for homogeneous pressure dispersion (adaptable)
Size of sensor array   Adaptable to battery cell dimensions
Sensor thickness ~ 2 mm Low installation space
Weight   polymer density ~ 1 g/cm³
Sensor array   multiple sensors possible on battery cell surface
Lateral resolution 2 cm x 2 cm Minimum: 0.5 cm x 0.5 cm
Sensor electronics   Microcontroller-based: low energy consumption