Full-range thermal-mechanical investigation of large capacity lithium-ion pouch battery based on distributed optical fiber dual U-shaped layout

Real-time temperature and strain monitoring is widely recognized in both academia and industry as essential for ensuring battery safe and reliable operation. Traditional contact-based measurement techniques, such as thermocouples, strain gauges, and fiber Bragg grating sensor, are often limited by the incomplete information provided by discrete surface points. Hence, a full-range thermal-mechanical measurement method is proposed, which primarily relies on the distributed optical fiber sensor (DOFS) with dual U-shaped layout. Unlike conventional FBG sensor, the DOFS enables accurate measurement with spatial resolution of 1.28mm along a single optical fiber to truly reflect variations. The dual U-shaped layout provides comprehensive temperature-strain variations monitoring across the entire surface, not just limited to specific location. Experimental investigations are conducted on the thermo-mechanical behavior of large-sized pouch cell (354mm×99mm) used in BYD actual EVs, which is charge and discharge under various load current profiles. The results demonstrate that this method can accurately and real-time measure the surface temperature distribution and strain variation. The corresponding physical fields can be obtained through simple reconstruction. As the current rate increases, the heat generation region gradually shifts from the negative tab area towards the centre and then to the positive tab area. The maximum in-plane temperature difference is 38.4% higher than the results obtained by thermocouples. The fundamental causes of the strain variations are the interaction between Li+ insertion and diffusion, as well as the non-uniform intercalation/deintercalation effects.