Development and evaluation of in-situ instrumentation for cylindrical Li-ion cells using fibre optic sensors

This work demonstrates the development and evaluation of FBG optical fibre sensor technology for monitoring the distributed in-situ in-operando temperature of cylindrical 18650 lithium-ion cells. The influence of the sensing element on the electrochemical system was evaluated using EIS, CT scanning and cell cycling characterisation and was proven to be negligible. Furthermore, the FBG sensors were proven to be resistant to the strain imposed during the cell instrumentation procedure and the harsh chemical environment inside the Li-ion cells. The sensing methodologies and modification techniques developed in this work can be applied to large scale battery modules and pack systems and integrated within the cell manufacturing process. This work identified a clear and significant difference between the cells can and core temperatures of up to 6 °C at discharge and 3 °C at charge, as well as axial temperature gradient. The findings of this study are of significance to the performance and safety limits of energy storage systems. This article indicates the clear need for reliable sensing systems that enable accurate in-situ in-operando monitoring of lithium-ion energy storage systems.