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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 (BMSs) 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 (HD-FOS) 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 IR camera to show how the sensing system can detect anomalies and report them back to a host controller.

Lithium-ion batteries are widely deployed in commercial and industrial applications. Continuous monitoring is necessary to prevent destructive results that can occur due to thermal runaway. Thermocouples and thermistors are traditional sensors used for thermally monitoring cells, modules, and batteries, but they only sense changes at the physical point where they are deployed. A high density of these sensors within a module or battery is desirable but also impractical. The study documented here shows that a commercial grade fiber optic sensor can be used as a practical replacement for multiple discrete thermocouples or strain gauges for a battery or module, to monitor a battery module at millimeter resolution along the fiber length. It is shown here that multiple fiber optic sensors can be series connected to allow for monitoring of a battery consisting of more than one module. In addition, it is shown that the same type of fiber can also be used to identify the onset of fault conditions by correlating the response in a fiber optic sensor suspended close to the module with an audible signature detected by a microphone at the time of failure. Early detection and identification of abnormal cell operation is demonstrated within batteries employing many cells.