Callum Briggs, Project Engineer at WMG, University of Warwick

Temperature is an essential factor to determine the safe and reliable operation of batteries. Temperature gradients can lead to local ageing differences and hence to global ageing of batteries. Consequently, several temperature sensing methods have been adopted in ESS (Energy Storage System) applications including thermocouples, thermistors, and resistance temperature detectors, all of which are sensitive, respond quickly and are relatively cheap. However instrumenting ESS with such sensors can be challenging without affecting both sensor and ESS performance.

Of all the battery sensing methods available, optical fibre sensing is an emerging technology that has captured the attention of ESS designers. Optical fibres are small in format and resilient to electromagnetic and chemical interference permitting both internal and external battery instrumentation. Optical fibres can provide both temperature and strain measurement in real-time with fine temporal and spatial resolution when interrogated with a light source; such information can be used with algorithms to estimate battery State of Charge (SoC) and State of Health (SoH) to high degrees of accuracy. Distributed Optical Fibre Sensors (DOFS) show the most promise in battery technologies as the only non-pointwise optical sensing method and utilise light scattering effects.

Dr Yifei Yu leads the Optical Sensing team at WMG supported by High Value Manufacturing Catapult. The team recently employed Coherent Optical Frequency Domain Reflectometry (C-OFDR) to monitor internal temperature and strain evolution within a Pouch Cell during electrochemical lithiation and delithiation. A DOFS which incorporates the Rayleigh scattering technique: C-OFDR is ideal for battery monitoring due to its significant spatial resolution and simple configuration compared to other optical sensing methods. The system uses a tuneable laser source (TLS), the output frequency of which is linearly tuned in time. Redistributed Rayleigh backscattering light along the test fibre can be mapped against a specific fibre location with any variation in scattering attributed to local information including temperature, strain, and vibration.

Figure 1: A schematic of ε-DFOS and T-DFOS instrumented the pouch cell

Applying Rayleigh Scattering techniques, Dr Yu simultaneously decoded temperature and strain evolution within a Pouch Cell anode with millimetre spatial and temporal accuracy. By discriminating between thermal and mechanical anode deformation, Dr Yu was able to accurately monitor the battery’s Solid Electrolyte Interface (SEI) formation and corresponding irreversible anode strain, both of which play a significant role in determining a battery’s electrochemical performance.

Figure 2: Strain and Temperature evolution during first cycling of instrumented pouch cell at a constant rate of C/10.

It is evident fibre optic sensing can support the real-time monitoring of key battery parameters necessary to underpin future developments in battery design and manufacture and optimise the algorithms required to manage and extend battery life. Moving forward the Optical Sensing team hope to validate DFOS in additional cell components, formats, and chemistries. The team believe enhancing both optical system configuration and fibre pattern to improve the quality of measurement data will secure a place for DFOS within future battery management systems (BMS) providing alternative methods of SoH estimation and a real-time estimation of internal temperature and mechanical stress as a function of SoC.

Gaoce Han et al. A review on various optical fibre sensing methods for batteries, Renewable and Sustainable Energy Reviews, 2021.

Yifei Yu et al. Distributed thermal monitoring of lithium-ion batteries with optical fibre sensors, Journal Energy Storage, 2021.

Zhen Guo et al. Ultimate Spatial Resolution Realisation in Optical Frequency Domain Reflectometry with Equal Frequency Resampling, Sensors, 2021.

Elena Vergori et al. Monitoring of Li-ion cells with distributed fibre optic sensors, Procedia Structural Integrity, 2019.

Zhen Guo, etc, and Yifei Yu. High Sensing Accuracy Realisation with Millimetre/sub-Millimetre Resolution in Optical Frequency Domain Reflectometer, Journal of Lightwave Technology (accepted) 2022.

Y. Yu, D. Greenwood, J. Marco et al. Real-time monitoring of internal structural deformation and thermal events in lithium-ion cell via embedded distributed optical fibre, Journal of Power Source, 521, 2022.