An accessible method of embedding fibre optic sensors on lithium-ion battery surface for in-situ thermal monitoring

Presented is a proof of concept to evaluate the suitability of a mounting technique for fibre optic sensors (FOSs) to measure Lithium-ion Battery (LIB) temperature. Two mounting techniques for the optical fibre, i.e. containing multiple Fibre Bragg Gratings (FBGs), placed on the LIB are considered. The FOS results are compared with K-type thermocouples, which are also mounted on the LIB. The first mounting technique attaches the FBGs on to the battery surface using a binding agent, while for the second technique, a “guide-tube” is used for alleviating longitudinal strain in the FOS induced by LIB expansion without the complexity of metal or glass tubes typically used for signal decoupling. The first mounting technique is calibrated over a 40 °C temperature variation to derive the sensitivity factor for each FBG; the other technique uses the free fibre sensitivity obtained by the manufacturer. The LIB is subject to 10 Watts constant power (CW) discharge, inducing 14 °C surface temperature increase. The guide-tube technique proposed in this study improves measurement accuracy from± 4.25 °C to + 2.06 °C when both mounting techniques are directly compared to the thermocouples. The proposed mounting technique is found to be a feasible method for cell-level temperature monitoring applications.