Thermal Monitoring of Series and Parallel Connected Lithium-ion Battery Modules Using Fiber Optic Sensors

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.