Large-Area Flexible Pressure Sensors for In Situ Monitoring of Cell Swelling in Vehicle Battery Packs

Li-ion batteries have emerged as a leading energy storage technology, garnering widespread attention due to their numerous advantages. However, alongside their benefits, safety concerns have arisen and become more important due to a pursuit of higher energy density. To address this, monitoring battery cell swelling has been identified as one of the most effective preventive measures as a warning for potential fire or explosion hazards. Current swelling measurement methods, such as x-ray diffraction, neutron imaging, strain gauge, and optical fibers, are bulky and not easily integrated into battery packs for in situ monitoring. Herein, we propose a flexible pressure sensor that may integrate between arrays of cells without interfering the battery assembling and normal operation. The proposed pressure sensor, fabricated by all mass-production processes, exhibits properties such as large-area, high-uniformity, and high-robustness, along with other features like high sensitivity and low hysteresis. The proposed flexible pressure sensors are effectively demonstrated in both an imitative and a real battery cell string, verified by a laser displacement sensor. This approach could open a promising pathway to provide new insights into the operational state of batteries and thus safety enhancement of electric vehicles.