Manufacturing and characterization of femtosecond laser-inscribed Bragg grating in polymer waveguide operation in an IR-A wavelength range

Optical sensors, such as fiber Bragg gratings, offer advantages compared to other sensors in many technological fields due to their outstanding characteristics. This sensor technology is currently transferred to polymer waveguides that provide the potential for cost-effective, easy, and flexible manufacturing of planar structures. While sensor production itself, in the majority of cases, is performed by means of phase mask technique, which is limited in terms of its degrees of freedom, other inscription techniques enable the manufacture of more adaptable sensor elements for a wider range of applications. In this article, we demonstrate the point-by-point femtosecond laser direct inscription method for the processing of polymer Bragg gratings into waveguides of the epoxy-based negative photoresist material EpoCore for a wavelength range around 850 nm. By characterizing the obtained grating back-reflection of the produced sensing element, we determined the sensitivity for the state variables temperature, humidity, and strain to be 45 pm/K, 19 pm/%, and 0.26 pm/με, respectively. Individual and more complex grating structures can be developed from this information, thus opening new fields of utilization

Toxic gas emissions from damaged lithium ion batteries - analysis and safety enhancement solution

Lithium ion batteries play an increasing role in everyday life, giving power to handheld devices or being used in stationary storage solutions. Especially for medium or large scale solutions, the latter application confines a huge amount of energy within a small volume; however, increasing the hazard potential far above the common level. Furthermore, as the safety hazards of lithium ion cells have been known for years, impressively shown by several burning cars or laptops, the need for a further enhancement of the safety of these systems is rising. This manuscript presents measurements of the gas emission from lithium ion batteries in case of a malfunction for different scenarios, showing a large variety of species with mostly toxic to highly toxic properties. The measurements were carried out using a combination of gas chromatography-mass spectrometry (GC-MS), quadrupole mass spectrometry (QMS), photoacoustic spectroscopy, and chemical analysis. It is shown that the inflammation of a cell can be overcome, also preventing a cascading effect to neighboring cells, but giving rise to worse toxic gas emission. Furthermore, a filtration concept is presented that decreases the concentration of the emitted components significantly and promises filtration below immediately dangerous to life or health (IDLH) equivalent levels

Photonische Sensoren zur Zustandserkennung von Lithiumionenbatteriezellen und deren Beitrag für einen sicheren und optimierten Betrieb dieses Stromspeichertyps

Das übergeordnete Ziel der in dieser Arbeit vorgestellten Forschungstätigkeiten ist die Entwicklung eines optischen Batteriemanagementsystems basierend auf den Zustandsgrößen Spannung, Strom, Temperatur und Volumenausdehnung. Diese Variablen wurden als die für eine Lithiumionenbatteriezellüberwachung der gegenwärtigen Generation kritischen Parameter identifiziert. Während vor allem die Spannungs- und Strommessung durch elektrische Sensoren vollständig etabliert sind, befinden sich photonische Messsysteme noch im Entwicklungsstadium; dies betrifft einerseits technische Faktoren wie Auflösungsvermögen, Störgrößenabhängigkeit oder Haltbarkeit und andererseits wirtschaftliche Aspekte wie Stückkosten oder Vermarktungsstrukturen. Nichtsdestotrotz sind optische Sensoren mit prinzipbedingten Vorzügen versehen, die zuvörderst die Zustandsgrößen Dehnung und Temperatur anbelangen. Beispielsweise besteht die Möglichkeit mit sehr geringem Verkabelungsaufwand eine Vielzahl an planaren Sensorstellen zu realisieren, die zudem keine Querempfindlichkeit gegenüber elektromagnetischen Feldern und ein hohes Maß an Miniaturisierung aufweisen. Unter diesem Hintergrund wurden Lithiumionenbatteriezellen im Pouch-Format extern auf dem Hüllenmaterial mit faseroptischen Dehnungs- und Temperatur-Bragg-Gittersensoren versehen, mit denen ein lade- und gesundheitszustandsabhängiges Signalverhalten festgestellt wurde. Zusätzlich wurden charakteristische Punkte im Dehnungsprofil der Zellen als Anhaltspunkte für eine Zustandsbestimmung identifiziert. Änderungen der Expansions- und Kompressionsraten der Aktivmaterialien signalisieren relevante und zumeist alterungsabhängige Vorgänge in den Kristallgittern, welche insbesondere dadurch veranschaulicht werden können, wenn die Dehnungsrate mit der Temperatur- beziehungsweise Ladungs- oder Spannungsänderung gegenübergestellt wird. Für eine praxistaugliche Zustandsmessung ist es erforderlich die Sensorik von der Zell- auf die Modulebene zu übertragen. Speziell bei einer ortsaufgelösten Feldmessung auf den Zelloberflächen innerhalb einer Reihenverschaltung mit einer Vielzahl an benötigten Dehnungs- und Temperaturmessstellen konnte das Potenzial der faseroptischen Sensorsysteme demonstriert werden, in dem eine zuverlässige und reproduzierbare Bestimmung des Zellverhaltens erfolgte. Um eine verzögerungsfreie Beurteilung und präzise Zuordnung der elektrochemischen Reaktionen zu bewerkstelligen, besteht die Notwendigkeit zellintern anoden- und kathodenseitige Messungen sowie Untersuchungen im Elektrolyten vorzunehmen. Es wurde mithilfe optischer Anodendehnungssensoren festgestellt, dass ein gegenüber der externen Signalaufnahme unverkennbareres Verlaufsprofil auftritt. Für die chemischen Untersuchungen im Elektrolyten wurden brechungsindexsensitive Bragg-Sensoren entwickelt, mit denen eine Messung der Leitsalzkonzentration durchgeführt wurde. Eine wesentliche Herausforderung beim Einsatz faseroptischer Sensorsysteme für Batterieanwendungen ist die Applizierbarkeit und Integrierbarkeit im industriellen Maßstab. Deshalb wurde ein Konzeptentwurf für eine polymeroptische Sensorstruktur entwickelt. Die Hauptkomponenten dieser Polymersensorfolie sind Ein- und Auskoppler, Polymer-Bragg-Gitter und Polymer-Zeilenwellenleitergitter, wovon die beiden letztgenannten Bestandteile im Rahmen der Arbeit realisiert wurden. Als eine wesentliche Herausforderung hat sich der Einfluss von Störgrößen beim Vermessen von Zuständen mittels polymeroptischer Sensoren herausgestellt. Durch gezielte Experimente konnte dargelegt werden, welches Potenzial anwendungsoptimiert programmierte und angelernte Neuronale Netzwerke für die Auswertung der Bragg-Sensoren im Hinblick auf eine Störgrößenbeseitigung verfügen. In diesem Zusammenhang wurden fernerhin optische Sensorsysteme an vorgealterten Zweitelebensdauerbatterien mit dem Ziel getestet, eine Schnellcharakterisierung von Alterungsvorgängen sowie einen sicheren Betrieb von Lithiumionenbatteriezellen bei einem gleichzeitig vollständigen Ausnutzen der Leistungsfähigkeit unter geringstmöglicher Degradation zu realisieren.The main objective of the research activities presented in this thesis is the development of an optical battery management system based on state variables voltage, current, temperature and volume expansion. These variables were identified as the critical parameters for monitoring of lithium ion battery cells in the current generation. While particularly voltage and current measurements by electrical sensors are fully established, photonic measurement systems are still in the development stage. On the one hand, this concerns technical factors such as resolution capability, disturbance dependency or durability and, on the other hand, economic aspects such as unit costs or marketing structures. Nevertheless, optical sensors have physical principle-related advantages, which primarily involve the state variables strain and temperature. For instance, it is possible to realize a large number of planar sensor positions with a very low wiring effort, which in addition have no cross-sensitivity to electromagnetic fields and a high degree of miniaturization. With this in mind, pouch-format lithium ion battery cells were equipped externally on the casing material with fiber-optical strain and temperature Bragg grating sensors, which were utilized to detect signal behavior depending on the state of charge and state of health. Furthermore, characteristic points in the expansion profile of the cells were identified as indicators for a status determination. Changes in the expansion and compression rates of the active materials signal relevant and mostly agedependent processes in the crystal lattices, which can be illustrated in particular by contrasting the strain rate with the temperature or charge or voltage change. For a practice-oriented status monitoring, it is essential to transfer the sensor technology from the cell to the module level. The potential of fiber optical sensor systems was demonstrated, especially in a spatially resolved field measurement on the surfaces of cells within a series connection with a large number of required strain and temperature measurement points, where a reliable and reproducible determination of the cell behavior was carried out. In order to achieve a delay-free assessment and precise assignment of the electrochemical reactions, it is required to perform cell-internal anode and cathode measurements as well as investigations in the electrolyte. By using optical anode strain sensors, it was identified that a more distinctive gradient profile occurs compared to the external signal image. For the chemical investigations in the electrolyte, refractive index-sensitive Bragg sensors were developed, with which a measurement of the conductive salt concentration was conducted. A major challenge in the utilization of fiber optic sensor systems for battery applications is the applicability and integrability on an industrial scale. Therefore, a conceptual design for a polymer optical sensor structure was created. The main elements of this polymer sensor foil are input and output couplers, polymer Bragg gratings and polymer arrayed waveguide gratings, of which the latter two were realized as part of the work. The influence of disturbance variables when measuring state conditions using polymer optical sensors has proved to be a major challenge. By means of selective experiments, it was possible to demonstrate the potential of application-optimized programmed and trained neural networks for the evaluation of Bragg sensors with respect to the elimination of disturbance variables. In this context, optical sensor systems were also tested on pre-aged second-life batteries with the aim of realizing a rapid characterization of aging processes as well as a safe operation of lithium ion battery cells, while fully exploiting their performance capability with a minimum of degradation at the same time

Blueprint and implementation of rural stand-alone power grids with second-life lithium ion vehicle traction battery systems for resilient energy supply of tropical or remote regions

Developed societies with advanced economic performance are undoubtedly coupled with the availability of electrical energy. Whilst industrialized nations already started to decrease associated carbon emissions in many business sectors, e.g., by substituting combustion engines with battery-powered vehicles, less developed countries still lack broad coverage of reliable electricity supply, particularly in rural regions. Progressive electrification leads to a need for storage capacity and thus to increasing availability of advanced battery systems. To achieve a high degree of sustainability, re-used batteries from the electromobility sector are appropriate, as they do not consume further primary resources and still have sufficient residual capacity for stationary electrical storage applications. In this article, a blueprint for the electrification of a remote region by utilizing second-life lithium ion traction batteries for an integrated energy system in a stand-alone grid is presented and the implementation by the example case of a Tanzanian island in Lake Victoria is demonstrated. First, economic potentials and expected trends in the disposability of second-life lithium ion batteries and their foreseeable costs are outlined. Subsequently, key decision variables are identified to evaluate logistic aspects and the feasibility of the implementation of an off-grid electrical system in remote areas for economically and geographically unfavorable environments. The practical realization is pictured in detail with a focus on technical performance and safety specificities associated with second-life applications. Therefore, a new type of battery management system is introduced, which meets the special requirements of climate compatibility, low maintenance, enhanced cell balancing capability and cell configuration flexibility, and combined with a fiber-optical sensor system, provides reliable status monitoring of the battery. By carrying out on-site measurements, the overall system efficiency is evaluated along with a sustainability analysis. Finally, the socioeconomic and humanitarian impact for the people on the island is debated

Development of a Polymeric Arrayed Waveguide Grating Interrogator for Fast and Precise Lithium-Ion Battery Status Monitoring

We present the manufacturing and utilization of an all-polymer arrayed waveguide grating (AWG) interacting with a fiber Bragg grating (FBG) for battery status monitoring on the example of a 40 Ah lithium-ion battery. The AWG is the main component of a novel low-cost approach for an optical interrogation unit to track the FBG peak wavelength by means of intensity changes monitored by a CMOS linear image sensor, read out by a Teensy 3.2 microcontroller. The AWG was manufactured using laser direct lithography as an all-polymer-system, whereas the FBG was produced by point-by-point femtosecond laser writing. Using this system, we continuously monitored the strain variation of a battery cell during low rate charge and discharge cycles over one month under constant climate conditions and compared the results to parallel readings of an optical spectrum analyzer with special attention to the influence of the relative air humidity. We found our low-cost interrogation unit is capable of precisely and reliably capturing the typical strain variation of a high energy pouch cell during cycling with a resolution of 1 pm and shows a humidity sensitivity of −12.8 pm per %RH

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

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

Toxic gas emissions from damaged lithium ion batteries - analysis and safety enhancement solution

Lithium ion batteries play an increasing role in everyday life, giving power to handheld devices or being used in stationary storage solutions. Especially for medium or large scale solutions, the latter application confines a huge amount of energy within a small volume; however, increasing the hazard potential far above the common level. Furthermore, as the safety hazards of lithium ion cells have been known for years, impressively shown by several burning cars or laptops, the need for a further enhancement of the safety of these systems is rising. This manuscript presents measurements of the gas emission from lithium ion batteries in case of a malfunction for different scenarios, showing a large variety of species with mostly toxic to highly toxic properties. The measurements were carried out using a combination of gas chromatography-mass spectrometry (GC-MS), quadrupole mass spectrometry (QMS), photoacoustic spectroscopy, and chemical analysis. It is shown that the inflammation of a cell can be overcome, also preventing a cascading effect to neighboring cells, but giving rise to worse toxic gas emission. Furthermore, a filtration concept is presented that decreases the concentration of the emitted components significantly and promises filtration below immediately dangerous to life or health (IDLH) equivalent levels