An optic fiber sensing system developed by researchers in China and Canada can peer inside supercapacitors and batteries to observe their state of charge. Renewable energy sources are naturally inconsistent, and so require new energy storage technologies. Supercapacitors offer rapid charging and long-term storage, but it is important to be able to monitor their working state. To tackle this issue, a team including Tuan Guo and Wenjie Mai at Jinan University adapted an approach that based on an optical fiber-based plasmonic sensor. The sensor is embedded inside the capacitor and is able to measure the state of charge of the electrodes and electrolytes in real time, while it operates, and over its lifetime. The sensor demonstrated a clear and repeatable high correlation between measurements of the optical transmission of the fiber device and simultaneous supercapacitor's state of charge, offering a unique, low-cost method for real-time monitoring of energy storage devices in operation. This result has been published and selected as the front cover of the recent issue of Light: Science & Applications (July 11, 2018), with a manuscript title of In Situ Plasmonic Optical Fiber Detection of the State of Charge of Supercapacitors for Renewable Energy Storage. This work has also been highlighted in the official website of the National Natural Science Foundation of China.
Electrochemical energy storage devices (such as supercapacitors) are considered to be the new generation of energy storage devices with the highest energy storage efficiency and very promising prospects. They are widely used in clean electric power, electric vehicles, mobile medical, portable electronic devices and other fields. In situ and continuous monitoring the electrochemical activities of energy storage devices is a key way for understanding and evaluation of their mechanism and operation quality. However, the present methods cannot offer the real time charge state information when the energy storage devices are in operation. They are required to take the supercapacitors off line (thus interrupting their function) and carrying out electrical measurements and even in some cases opening up the supercapacitors to examine their components by electron microscopy.
To address this fundamental challenge, Prof. Guo and Prof. Mai and their colleague report an original and reliable optical technique to monitor the health of this important energy storage device used to regulate the power supplied by renewable energy sources. This approach is based on an optical fiber-based plasmonic sensor that is embedded inside the capacitor and that is able to measure the state of charge of the electrodes and electrolytes in real time, while it operates, and over its lifetime. Such optical fiber devices are small enough to be inserted near the surface of the capacitor electrodes, and being based on telecommunication-grade fibers, they can be left there and monitored remotely at any time and from any distance. Another important aspect of their approach is that in contrast to current techniques that rely on an indirect estimate of the state of charge from current/voltage tests, the optical fiber devices detect the amount of charge accumulated in a sub-micrometer sized layer on the electrodes and the adjacent electrolyte directly through its impact on the plasmonic properties of a nanometer-scale gold coating applied to the fiber surface. It demonstrated a clear and repeatable high correlation between measurements of the optical transmission of the fiber device and simultaneous electrical validation measurements. This new technology will have important implications for energy suppliers who rely on renewable energy sources from sun, wind and hydro-electricity for at least part of their power grid requirements. The main implication is that faulty or deteriorating capacitors will be identified before catastrophic failures can occur, and that no interruption of power systems will be required for testing them.