Detection of Internal Defects in Lithium-Ion Batteries Using Lock-in Thermography

Effective thermal management is essential for maximising performance and durability of Li-ion batteries. Infrared thermal imaging is an established technique for studying temperature distribution in real-time with high spatial resolution; however, dynamic thermal imaging offers greater sensitivity, the ability to correct for emissivity variation and identify heat transfer mechanisms and internal defects. Here, for the first time, lock-in thermography using a thermal imaging camera is applied to Li-ion batteries to investigate the effect of periodic electro-thermal stimulation on the amplitude and phase response of both new and aged Li-ion pouch cells. We demonstrate the effectiveness of this technique in the detection of gas pockets formed during cell aging and propose its application in the identification of a range of internal defects in operational systems and validation of thermal models.