Dipl.-Ing. Hartmut Popp, MSc, BSc State Estimation of Lithium-Ion Secondary Batteries by Means of Non-Destructive Mechanical Methods PhD Thesis to achieve the university degree of Doktor der technischen Wissenschaften Doctoral Programme: Information and Communications Engineering submitted to Graz University of Technology Supervisor Univ.-Prof. Mag.rer.nat. Dr.rer.nat. Alexander Bergmann Institute of Electrical Measurement and Sensor Systems Reviewer Assoc.-Prof. Dr. Erik M. Kelder Delft University of Technology, Faculty of Applied Sciences Mekelweg 15, 2629 JB Delft, The Netherlands Institute of Electrical Measurement and Sensor Systems Head: Univ.-Prof. Mag.rer.nat. Dr.rer.nat. Alexander Bergmann Vienna, December 2020 question (your) assumptions . Affidavit I declare that I have authored this thesis independently, that I have not used other than the declared sources/resources, and that I have explicitly indicated all material which has been quoted either literally or by content from the sources used. The text document uploaded to TUG-online is identical to the present PhD thesis. 16.12.2020 Date Signature Acknowledgements First of all I want to thank my supervisor Alexander Bergmann. From the beginning he was very excited by this emerging topic and of great help and support throughout all the phases of the doctorate. Thanks to my reviewer, Erik Kelder for the helpful inputs regarding chemistry and the prompt processing of all the tasks that come with such a review. A special thanks goes to Irina Gocheva for the (initial) discussions on the topic, the scientific review of all the papers and this thesis. Thanks to my colleagues at AIT Austrian Institute of Technology GmbH where the main work of this thesis was performed. Helmut Oberguggenberger and Marcus Jahn for giving enough freedom to open this field of research in our company. Gregor Glanz and Kristijan Rajinovic for being myright hand each. Wernfried Berghold for support with test benches and applied measurement techniques in general. Hansjörg Kapeller, Marcus Jahn, Markus Koller and Martin Kriegisch for the scientific discussions and review of some of the chapters. A thousand thanks to Boschidar Ganev for linguistic corrections. Cheers to Harald Brandstätter, who recommended signing up at the Institute of Electrical Mea- surement and Sensor Systems to conduct my studies under the supervision of Alexander Bergmann. Thanks to all my co-authors of the manuscripts. Thanks to the staff and colleagues from Graz University of Technology. Thanks to Muhammad Luthfi for the exceptionally good work he did during his master thesis under my co-supervision. Thanks to all the others who supported this work in any kind of way. Of course a special thanks to my family for being supportive over all those uncounted years of my education. This work received financial support by the Austrian Research Promotion Agency (FFG) under the funding scheme ’Mobilität der Zukunft’ within the collaborative research projects ’VALERIE’ (Grant 865148) and ’MOGLI’ (Grant 879610). The author wants to express his sincerest gratitude for the financial support. Abstract Lithium-ion secondary batteries are the ubiquitous source of electrical power for many applications nowadays, ranging from consumer electronics, over power tools to electric vehicles. Great progress has been achieved over the last years to bring down cost and to increase lifetime, performance and safety of lithium-ion secondary batteries by improving its (active) materials and its production process. Optimized operational strategies can further increase the use of the battery and bring down the total cost of ownership by facilitating it fully. For this, precise knowledge of, among others, the state-of-charge and the state-of-health during the operational life of the battery is required. Knowledge of the cells internal state is also paramount for further research and development on lithium-ion secondary batteries. Hence, reliable methods for state estimation of lithium-ion secondary batteries are required. State-of-the-art battery management systems derive the parameters indirectly from the electrical two pole behaviour of the battery, which can lead to inaccurate values. Laboratory equipment on the other hand is mostly based on imaging methods which are bulky, expensive and most of the time cannot be used in-operando. To overcome these issues, an alternative route is followed in this thesis by investigating non- destructive testing methods for their potential and their boundaries for monitoring lithium-ion sec- ondary batteries as an inexpensive method which can be used in-operando. Acoustic methods in the audible and the ultrasonic region are deployed to lithium-ion secondary battery pouch cells and checked for their capability for state estimation under laboratory conditions and under realistic scenarios like dynamic load profiles and changing ambient temperature. While the methods inthe audible region were found to be more suited for deriving mechanical parameters in laboratory which are useful for battery pack design than for state estimation, the ultrasonic methods were found to be suited for state estimation also under realistic conditions and for laboratory use to gain insights in the cell. In a detailed review of the recent state of non-destructive testing of lithium-ion secondary batteries expansion-based, force-based, strain-based, and acoustic emission methods were also in- vestigated for their capabilities. Especially force- and strain-based methods show promising results for implementation in applications while expansion-based and acoustic emission methods are more suited to reflect internal processes in the laboratory. Kurzfassung Lithium-Ionen-Sekundärbatterien sind heute die allgegenwärtige Quelle elektrischer Energie für viele Anwendungen, die von der Unterhaltungselektronik über Elektrowerkzeuge bis hin zu Elektrofahrzeu- gen reichen. In den letzten Jahren wurden große Fortschritte erzielt, um die Kosten zu senken und die Lebensdauer, Leistung und Sicherheit von Lithium-Ionen-Sekundärbatterien zu erhöhen, indem die (aktiven) Materialien und die Produktionsverfahren verbessert wurden. Optimierte Betriebsstrategien können den Nutzungsgrad der Batterie steigern und so die Gesamtkosten über die Produktlebensdauer senken. Dazu ist eine genaue Kenntnis unter anderem des Lade- und des Gesundheitszustands während des Betriebs der Batterie erforderlich. Die Kenntnis der Zell-internen Zustände ist auch für die weitere Forschung und Entwicklung von Lithium-Ionen-Sekundärbatterien von größter Bedeutung. Daher sind zuverlässige Methoden zur Zustandsabschätzung von Lithium-Ionen-Sekundärbatterien erforderlich. Moderne Batteriemanagementsysteme leiten die Parameter indirekt aus dem elektrischen Zweipolverhalten der Batterie ab, was zu ungenauen Werten führen kann. Laborgeräte hingegen basieren oftmals auf bildgebenden Verfahren. Diese Geräte sind sperrig, teuer und können meist nicht im laufenden Betrieb eingesetzt werden können. Um diese Probleme zu überwinden, wird in dieser Arbeit ein alternativer Weg beschritten, in- dem zerstörungsfreie Prüfverfahren auf ihr Potenzial und ihre Grenzen für die Überwachung von Lithium-Ionen-Sekundärbatterien als kostengünstige Methode untersucht werden, welche auch in- operando eingesetzt werden können. Akustische Methoden im Hör- und Ultraschallbereich werden an Lithium-Ionen Pouch-Zellen erprobt und auf ihre Fähigkeit zur Zustandsabschätzung sowohl unter Laborbedingungen als auch unter realistischen Szenarien wie dynamischen Lastprofilen und wechseln- den Umgebungstemperaturen geprüft. Während sich die Methoden im hörbaren Bereich eher für die Ableitung mechanischer Parameter im Labor, die für das Batteriepack-Design nützlich sind, als für die Zustandsabschätzung eigneten, erwiesen sich die Ultraschallmethoden für die Zustandsabschätzung auch unter realistischen Bedingungen und für den Laboreinsatz zur Gewinnung von Erkenntnissen in der Zelle als geeignet. In einer detaillierten Übersicht über den aktuellen Stand der zerstörungsfreien Prüfung von Lithium-Ionen-Sekundärbatterien wurden auch Expansions-, Kraft-, Dehnungs- und Eigenschallemissions-basierte Methoden auf ihre Eignung zur Abschätzung von Batterieparametern untersucht. Insbesondere Kraft- und Expansionsbasierte Methoden zeigen vielversprechende Ergeb- nisse für die Umsetzung in Anwendungen, während Dehnungs- und Eigenschallemissions-basierte Methoden besser geeignet sind, interne Prozesse im Labor abzubilden. Contents List of Figures xiii List of Tables xv Nomenclature xvii 1 Introduction1 1.1 Motivation . .1 1.2 Objective . .3 1.3 Outline . .4 1.4 Authors’ Contributions to the Articles . .5 2 Fundamentals of Lithium-Ion Secondary Batteries7 2.1 Working Principle . .7 2.2 LIB Materials . .9 2.2.1 Anode . 10 2.2.2 Cathode . 13 2.2.3 Electrolyte . 15 2.2.4 Other passive components . 16 2.3 Ageing of LIB . 17 2.3.1 Anode Ageing . 17 2.3.2 Cathode Ageing . 18 2.3.3 Summary Ageing . 19 2.4 Electrical Testing of LIB . 20 2.4.1 Capacity . 20 2.4.2 Impedance . 22 3 Non-Destructive Testing 25 3.1 Experimental Modal Analysis . 27 3.2 Ultrasonics . 32 3.2.1 Types of Waves . 32 xii Contents 3.2.2 Wave Propagation . 33 3.2.3 Ultrasonic Measurements on LIB . 37 4 Results and Discussion 41 4.1 Mechanical FRF of LIB . 41 4.2 SOC Estimation of LIB by US based TOF Measurement . 42 4.3 Review of NDT on LIB . 42 5 Scientific Contribution, Conclusion and Outlook 45 5.1 Scientific Contribution Achieved With this Thesis . 45 5.2 Conclusion . 46 5.3 Outlook