As society becomes more mobile, rechargeable batteries have become essential for a wide range of applications in strategic industries such as automotive, power grid, aerospace, robotics and consumer electronics. Such increasing societal dependence makes battery safety, reliability and performance essential. The Hong Kong Polytechnic University (PolyU) has joined an international research team led by Collège de France, together with The French National Centre for Scientific Research, Massachusetts Institute of Technology and Dalhousie University, to enable the next generation of portable energy storage systems by injecting smart sensing and monitoring functionalities into the dynamic electrochemical devices in a cost-effective and scalable way. Their study, titled "Operando decoding of chemical and thermal events in commercial Na(Li)-ion cells via optical sensors" (link), was published in the high-impact international journal Nature Energy this week.
The research team has achieved a breakthrough by incorporating optical fibre "Bragg" grating (FBG) sensors within 18650 format cells (a standard for commercial batteries) which enables twofold enhancement. Firstly, the use of optimised internal structures in the FBGs allow for the collection of clean, high-resolution optical signals from the sensors. Secondly, advanced signal analysis is employed to decode the thermal and chemical events taking place within the battery as never seen before.
The superb chemical stability and ease of scaling/expansion make FBGs ideal for deployment in new applications in the energy industry.
Prof. Hwa-yaw TAM
Chair Professor of Photonics and Head of Department of Electrical Engineering
"Currently, commercialised battery 'packs' are equipped with temperature sensors positioned at the module level (set of cells) and not directly at each cell. The conventional configuration leads to very conservative and ultimately inefficient battery management systems (BMS) since the actual sensors do not inform us what is really happening within the batteries, especially in terms of thermal/chemical events," explained Prof. Jean-Marie TARASCON, Professor at the Collège de France and senior author of the study. By optimising the positions of three optical sensors, it is possible not only to obtain the internal and surface temperatures, but it further enables direct calculation of battery heat generation and transfers with unprecedented accuracy. Consequently, new BMS systems optimised with optical fibre sensors might be capable of bringing the world one step closer towards the common goal of reaching the theoretical limits of energy storage systems.
The FBG sensors, one of the key components of the battery management system in this study, were developed in the Photonics Research Centre at PolyU by researchers of the Department of Electrical Engineering, namely Chair Professor of Photonics and Head Prof. Hwa-yaw TAM, Postdoctoral Researcher Dr Julien BONEFACINO and Associate Professor Dr Steven BOLES. Under the direction of Prof. Tam, the Photonics Research Centre has been investigating FBG sensors for around 30 years and has had great success in the past few years with deploying them in regional infrastructure projects (for example, Tsing Ma Bridge) and with international railway transportation companies (such as MTR, SMRT). For this cross-institutional research project, the team developed and fabricated a new type of "microstructured" FBG which is paired in tandem with a traditional FBG. The novel approach of putting multiple sensors together, each with a different sensitivity to the external environment, allows for the decoupling of temperature and pressure signals in real-time inside a battery. This precision monitoring can then be used to decipher key aspects of battery operation and degradation. For example, the decomposition of battery electrolyte was investigated with unprecedented resolution during real-world operation.
"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 Prof. Hwa-Yaw TAM who is renowned for his work in the area of FBGs. "The superb chemical stability and ease of scaling/expansion make FBGs ideal for deployment in new applications in the energy industry."
There is great potential for the extension of this approach in future applications. The team has already started to look to other energy storage devices, such as alkaline batteries, fuel cells and supercapacitors, as well as other important applications, such as catalysis and water splitting for the production of hydrogen.
