A new generation of highly efficient batteries may be closer than you think, according to a study by an international research team joined by PolyU and led by Collège de France, together with The French National Centre for Scientific Research, Massachusetts Institute of Technology and Canada’s Dalhousie University.

The team’s study, “Operando decoding of chemical and thermal events in commercial Na(Li)-ion cells via optical sensors”, was published in the high-impact international journal Nature Energy on 24 August 2020.

Although existing commercial battery packs are equipped with temperature sensors, these sensors are not placed directly at each cell. According to Professor Jean-Marie Tarascon, Professor at the Collège de France and senior author of the study, this “leads to very conservative and ultimately inefficient battery management systems (BMS) since the actual sensors do not inform us what is really happening.”

The research team achieved their breakthrough by incorporating optical fibre “Bragg” grating (FBG) sensors directly into 18650 format cells (a standard for commercial batteries). This had two benefits. Firstly, it allowed for the collection of clean, high-resolution optical signals from the sensors. And, secondly, by employing advanced signal analysis, the thermal and chemical events taking place within the battery could be decoded.

By optimising the positions of the optical sensors, the team was able not only to obtain internal and surface temperatures in real time, but also to calculate battery heat generation and transfers with unprecedented accuracy. Consequently, new BMS optimised with optical fibre sensors could bring the world one step closer towards peak performance in energy storage systems.

Towards more efficient batteries … and beyond

One of the key components of the batteries explored in this study— the FBG sensors—were developed by researchers in PolyU’s Photonics Research Centre of the Department of Electrical Engineering. They included Chair Professor of Photonics and Head Professor Tam Hwa-yaw, Postdoctoral Researcher Dr Julien Bonefacino, and Associate Professor Dr Steven Boles.

“The technical and scientific advances highlighted in this project have been made possible by the convergence of battery science and optical fibre sensor engineering,” said Professor Tam. “The superb chemical stability and ease of expansion make FBGs ideal for new applications in the energy industry.”

Indeed, the team has already started to look at other energy storage devices using FBGs, such as alkaline batteries, fuel cells and supercapacitors, as well as other important applications, including catalysis and water splitting for the production of hydrogen.