Real-time monitoring of internal structural deformation and thermal events in lithium-ion cell via embedded distributed optical fibre

The in-operando monitoring of the cell's kinetic thermal and electrochemical processes during operation is a key requirement to understand battery performance, improve safety and to extend battery life. This research presents in-situ measurements of strain and temperature evolution within a graphite electrode during electromechanical lithiation and delithiation. By embedding distributed fibre optics sensor, the frequency shift associated with both temperature and strain are decoupled, allowing the real-time measurement of the solid electrolyte interface formation and the structural deformation within the anode. An in-depth assessment of electrode strain as a function of State of Charge (SoC) and State of Health (SoH) from the formation cycle through to electrical loading allows the assessment of cell performance over its complete life. It is observed that irreversible and non-uniformly distributed anode structural deformation was measured during the formation. The anode reveals an extensive mechanical strain increase with a coefficient of 0.96 με/SoC(%) with respect to the SoC and undergoes a compressive mechanical strain as SoH decreases from 100% to 47%. Collectively, the findings presented provide valuable new information to understand the causes of battery performance degradation as a result of electrode strain and temperature, underpinning new opportunities for battery characterisation and optimal system design.