Global thermal image of cylindrical 21700 Li-ion batteries with distributed optical fibre sensor
Zhen Guo, Calum Briggs, Timothy A. Vincent, Begum Gulsoy, Jonathan E.H. Sansom, James Marco
Abstract
The ability to monitor the thermal behaviour of lithium-ion batteries (LIB) is an essential pre-requisite to optimise performance and ensure safe operation. However, traditional point measurement (thermocouples) faces challenges in accurately characterising LIB behaviour and notably in defining the hotspot and the magnitude and direction of the thermal gradient. To address these issues, an optical-frequency-domain-reflectometer (OFDR) based distributed-optical-fibre-sensor has been employed to quantify the heat generation within a cylindrical 21700 LIB. A 3 mm spatial resolution within the optical sensor is realised. The optical fibre has been wound around the cell surface for over 1300 unique measurement locations; distributed around the circumference and axially along the LIB. Distributed measurements show the maximum thermal difference can reach 8.37 °C during a 1.5C discharge, while the point-like sensors have 4.31 °C thermal difference. While a temperature gradient along the cell axial length is well understood, for the first time, this research quantifies the temperature variations along the circumference of the cell. The global thermal image highlights heat generation is accumulated around the positive current tab, implying that a fundamental knowledge of internal LIB structure is required when defining sensor placement within the traditional characterisation experiments and deployment within the battery management system (BMS).