Monitoring Energy Storage with Optical Fibers

Electrochemical surface-plasmon-resonance sensing principle and experimental demonstration with a gold-coated TFBG optical fiber sensor. Sketch of the configuration of a plasmonic optical fiber sensor for in situ monitoring of supercapacitors. (Source: NNSF China)

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.

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 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, Guo, Mai and their colleagues 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. (Source: Changchun Inst.)

Reference: J. Lao et al.: In situ plasmonic optical fiber detection of the state of charge of supercapacitors for renewable energy storage, Light: Sci. & Appl. 7, 34 (2018); DOI: 10.1038/s41377-018-0040-y

Link: Guangdong Key Laboratory of Optical Fiber Sensing and Communications, Institute of Photonics Technology, Jinan University, Guangzhou, China

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