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.
Highlights
During the last decade, electrochemical energy storage devices have advanced into entirely new fields of application [1]
The 100 optical sensor obtained optical wavelength shift predominantly result ofsensor diverse strainover influences and not signal due decrease with decreasing capacity, this behavior differs from the one behavior obtained by thesensor means of the over cycles tends tocell decrease decreasing cell capacity, this differs from signal the one to changes of the refractive index of with the surrounding electrolyte
Two different fiber-optical sensors for a cell-internal status monitoring of lithium ion batteries were developed. It was demonstrated how a core Bragg grating in a standard telecommunication glass fiber integrated into the anode active material can be utilized to measure the expansion of electrodes and temperature variations directly on the reaction site
Summary
Electrochemical energy storage devices have advanced into entirely new fields of application [1]. By utilizing the developed optical sensor in the experiments presented in this work, a foundation for future non-electrical measurements for simultaneous internal and external condition monitoring of lithium ion battery cells should be created To achieve this objective, as a first step, the manufacturing and subsequent integration of the sensor into the anode active material of a cell is conducted in order to carry out cyclization and abuse strain measurements with the core. The surface cladding waveguide grating is included on the one hand as a stand-alone sensor to measure the refractive index temperature-compensated within ionic solutions, and on the other hand, integrated in the cell’s separator layer, to investigate the charging behavior and revealing characteristics. Core Fiber Bragg Grating Sensors for Electrode Active Material-Internal Status Monitoring
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