image: Figure 1 | A multiresonant fiber-optic grating sensor developed by researchers can peer inside sodium-ion batteries to analyze ion transport processes at the electrode-electrolyte interface, providing key parameters for the precise quantification of battery SoC.
Credit: Tuan Guo et al.
As the demand for large-scale energy storage technologies grows, SIBs have garnered immense attention. To meet the stringent requirements of commercial applications, it is crucial to deeply understand the dynamic process of sodium-ion (de)intercalation at the electrode-electrolyte interface. Currently, methods to characterize ion migration near electrodes are mostly offline or rely on bulky laboratory equipment, making operando monitoring under working conditions extremely difficult. Moreover, precise SoC estimation remains a grand challenge in the field of battery monitoring. Traditional methods are highly susceptible to temperature fluctuations, aging effects, and severe nonlinearities at high and low SoC levels, which limits their measurement accuracy.
In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Tuan Guo and Professor Wenjie Mai from Jinan University, and Professor Yongjin Fang from Wuhan University, have developed an implantable optical fiber electrochemical sensor to address these bottlenecks. By generating a sub-micron evanescent field, the sensor becomes exceptionally sensitive to minute refractive index changes caused by local ion transport at the electrode-electrolyte interface. By tracking the amplitude changes of the cut-off mode of MFG, the team achieved a remarkable refractive index resolution of 10-6 RIU and sub-micron spatial resolution. By continuously monitoring the time derivative of the resonance amplitude, the researchers decoded interfacial sodium-ion kinetics, revealing an elusive “intermediate stage” between ion adsorption and diffusion. They demonstrated that a shorter intermediate stage directly correlates with superior fast-charging performance of the electrode material.
The research results established an ion flux-based calculation model and successfully established a highly linear relationship between the time integral of the optical signal amplitude and SoC. This operando measurement tool offers exciting opportunities to build a ‘‘lab-on-fiber’’ platform. It lays a solid physical foundation for integrating real-time optical fiber monitoring into commercial battery management systems (BMS) and paving the way for robust state-monitoring and early warning platforms.
This research received funding from the National Key Research and Development Program of China, and the National Natural Science Foundation of China.
Journal
Light: Science & Applications
Article Title
Operando tracking of ion kinetics and state-of-charge via multiresonant fiber-optic grating sensors in sodium-ion batteries