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Refractive Index Measurement of Lithium Ion Battery Electrolyte with Etched Surface Cladding Waveguide Bragg Gratings and Cell Electrode State Monitoring by Optical Strain Sensors

1
Department Fiber Optical Sensor Systems, Fraunhofer Heinrich Hertz Institute, Am Stollen 19H, 38640 Goslar, Germany
2
Institute of Energy Research and Physical Technologies, Clausthal University of Technology, Am Stollen 19B, 38640 Goslar, Germany
3
Department Electrical Energy Storage, Fraunhofer Institute for Manufacturing Technology and Advanced Materials, Marie-Curie-Straße 1-3, 26129 Oldenburg, Germany
*
Author to whom correspondence should be addressed.
Batteries 2019, 5(1), 30; https://doi.org/10.3390/batteries5010030
Received: 30 January 2019 / Revised: 5 March 2019 / Accepted: 6 March 2019 / Published: 12 March 2019
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Abstract

In this scientific publication, a new sensor approach for status monitoring, such as state of charge and state of health, of lithium ion batteries by using special Bragg gratings inscribed into standard optical glass fibers is presented. In addition to well-known core gratings, embedded into the anode of 5 Ah lithium ion pouch cells as a strain monitoring unit, the manufacturing of a surface cladding waveguide Bragg grating sensor incorporated into the cell’s separator, that is sensitive to changes of the refractive index of the surrounding medium, is demonstrated. On the basis of the experiments carried out, characteristics of the cell behavior during standard cyclization and recognizable marks in subsequent post-mortem analyses of the cell components are shown. No negative influence on the cell performance due to the integrated sensors have been observed; however, the results show a clear correlation between fading cell capacity and changes of the interior optical signals. Additionally, with the novel photonic sensor, variations in the electrolyte characteristics are determinable as the refractive index of the solution changes at different molar compositions. Furthermore, with the manufactured battery cells, abuse tests by overcharging were conducted, and it was thereby demonstrated how internal battery sensors can derive additional information beyond conventional battery management systems to feasibly prevent catastrophic cell failures. The result of the research work is an early stage photonic sensor that combines chemical, mechanical and thermal information from inside the cell for an enhanced battery status analysis. View Full-Text
Keywords: lithium ion; battery safety; status monitoring; optical sensors; fiber Bragg grating; cladding waveguide; battery electrolyte; electrode active material; battery aging lithium ion; battery safety; status monitoring; optical sensors; fiber Bragg grating; cladding waveguide; battery electrolyte; electrode active material; battery aging
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Nedjalkov, A.; Meyer, J.; Gräfenstein, A.; Schramm, B.; Angelmahr, M.; Schwenzel, J.; Schade, W. Refractive Index Measurement of Lithium Ion Battery Electrolyte with Etched Surface Cladding Waveguide Bragg Gratings and Cell Electrode State Monitoring by Optical Strain Sensors. Batteries 2019, 5, 30.

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