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Fiber Optic Based Thermal Sensing of Lithium-Ion Cells at the Module Level


 Battery modules are made up of many individual cells connected in series/parallel to meet an application’s voltage, power, and energy requirements. Regardless of how big the battery is, its users assume it will always work safely. Wide scale deployment and the high cell count in modules bring about demand for new techniques to monitor individual cells and reduce the probability of an undetected catastrophic failure. A primary indication of a problem within a module is a significant rise in temperature and/or strain of one or more cells. Battery management systems monitor individual cell voltages and typically no more than a few temperatures. This introduces the possibility that cells may heat up without detection. This study demonstrates how a high-definition fiber optic sensor can be easily applied on each cell within a module consisting of multiple 18650 cells used to measure temperature deviations while it is being cycled. Controlled over-charge and short-circuit testing of cells within the module have been performed and compared to results from thermocouples and an infrared camera to show how the sensing system can detect anomalies and report them back to a host controller.