Novel Li‐Ion Battery Diagnostics; Detection of Redox Peaks Utilising Plasmonic Fibre Optic Sensors and Evaluation of Interference on Cell Function

In this study we demonstrate detection of redox peaks in Li‐ion pouch cells during cyclic voltammetry (CV), via the optical signal of plasmonic based fibre optic sensors placed inside Li‐ion pouch cells. The sensors are placed inside the pouch cells during manufacture, allowing diagnostic data to be obtained from directly inside the cells in real time. We further present data showing the battery cell remains agnostic to the presence of fibre optic sensors over repeated cycling through analysis of the formation cycles, electrochemical impedance spectroscopy (EIS) analysis, coulombic efficiency data, capacity data and post‐mortem materials analysis. This study provides evidence of the utility of fibre optic based diagnostic sensors, and in particular the novel use of plasmonic based fibre optic sensors, as an in situ battery diagnostic technique and potential research tool to investigate battery cell phenomena.