Combining Fiber Optic Sensing with Galvanostatic Intermittent Titration for Improved State of Health Analysis of Lithium-Ion Batteries
Authors: Tewari Neha , Cheung Yin Nee , Madithedu Muneeswara , Ghashghaie Sasan , Tam Hwa-yaw , Boles Steven T 
Published: December 2024

Fiber Bragg grating (FBG) sensors are a compelling choice for monitoring strain, pressure, and temperature of lithium-ion batteries as this combination offers significant potential for monitoring crucial cell parameters in real-time.1 During conventional charging and discharging, the movement and reactions of lithium-ions cause cells to generate heat and experience mechanical stress, both of which are of long-term concern to the end users of the cells. Furthermore, more extreme conditions such as overcharging, excessive pressure/mechanical stress, and other external factors can lead to a range of severe problems such as overheating, distortion, gas generation, swelling, and thermal runaway.2 Challengingly, the ability to estimate and predict cell stability and performance is limited once the cell has departed from its pristine state at the factory.
To enable better understanding of the lithium-ion batteries and their evolution over time, the galvanostatic intermittent titration technique (GITT) is combined with FBG sensing. GITT is a commonly employed electroanalytical method which measures the transient voltage change and open-circuit voltage (OCV) change during the charging and discharging processes using only a constant current supply and specified cut-off intervals and retrieves both thermodynamic and kinetic parameters.3 The GITT approach allows for the determination of overpotential and internal resistance at different states of charge (SOC), yielding a comprehensive view of the battery's charging and discharging procedures through a microscopic view.
Our research employs non-invasive optical sensing with FBGs inscribed silica single-mode fiber (SMF) and polymer optical fiber (POF) to evaluate temperature and strain changes in conjunction with the GITT technique as depicted in Figure 1 to examine the overpotential of various states of charge (SOC) or discharge (SOD) of commercial lithium-ion batteries for 200 cycles. Integrating GITT and FBG sensing enhances our understanding of the battery's operation, as correlations between the overpotential values at different SoCs and temperature monitoring (overpotential heat) via FBG sensors reveal the irreversible heat generation change in these batteries, which will be discussed and elaborated upon further with implications for general strategies pertaining to lithium-ion battery sensing.

1 Julien Bonefacino, Sasan Ghashghaie, Tianye Zheng, Chun-Pang Lin, Wenwei Zheng, Laura Albero Blanquer, Jiaqiang Huang, Charlotte Gervillié, Hwa-Yaw Tam, and Jean-Marie Tarascon, J. Electrochem. Soc.
169 (10), 100508 (2022).

2 Dongying Chen, Qiang Zhao, Yi Zheng, Yuzhe Xu, Yonghua Chen, Jiasheng Ni, and Yong Zhao, Sensors
23 (12), 5609 (2023).

3 Wrah Weppner and Robert A. Huggins, J. Electrochem. Soc.
124 (10), 1569 (1977).
This work is supported by the Centre for Advances in Reliability and Safety (CAiRS) admitted under AIR@InnoHK Research Cluster.

Figure 1