Distributed thermal monitoring of lithium ion batteries with optical fibre sensors

Real-time temperature monitoring of li-ion batteries is widely regarded within the both the academic literature and by the industrial community as being a fundamental requirement for the reliable and safe operation of battery systems. This is particularly evident for larger format pouch cells employed in many automotive or grid storage applications. Traditional methods of temperature measurement, such as the inclusion of individual sensors mounted at discrete locations on the surface of the cell may yield incomplete information. In this study, a novel Rayleigh scattering based optical fibre sensing technology is proposed and demonstrated to deliver a distributed, real-time and accurate measure of temperature that is suitable for use with Li-ion pouch cells. The thermal behaviour of an A5-size pouch cell is experimentally investigated over a wide range of ambient temperatures and electrical load currents, during both charge and discharge. A distributed fibre optical sensor (DFOS) is used to measure both the in-plane temperature difference across the cell surface and the movement of the hottest region of the cell during operation, where temperature difference is the difference of temperature amongst different measuring points. Significantly, the DFOS results highlight that the maximum in-plane temperature difference was found to be up to 307% higher than that measured using traditional a thermocouple approach.