31 research outputs found
Organizational and Legal Mechanism of Public Administration of Functioning and Development of Electronic Consultations
No full textThe paper presents the results of analysis of the status of organizational and legal mechanism of public administration of electronic consultations (e-consultations) as well as scientific and theoretical substantiation of recommendations to Ukrainian authorities on their improvement. The study of national and international laws in regard to functioning of the mechanism of e-consultations has been conducted to determine positive and negative factors influencing its application. Ways to improve specified mechanism regarding the structure of units of central (regional, local) executive bodies and local governments, legal normative acts concerning e-consultations and participation of public councils in the process of e-consultations have been offered. The main shortcomings of the organizational and legal mechanism of public administration of national e-consultations have been identified, including: low 36 Yanis Yansons quality of e-consultations; unwillingness of the subjects of power to allow the civil society to have a real impact on state affairs, lack of responsibility for ignoring the law in regard to organization and conduct of e-consultations, distrust of the authorities and “digital inequality” etc. Based on the analysis of international experience in implementing the tool of e-consultations, ways to improve the procedure for its implementation in Ukraine, changes to national laws and recommendations to central (regional, local) executive bodies and local governments, public councils and the civil society to improve the organizational and legal mechanism managing tool of econsultations implementation, operation and development
E-Democracy in Ukraine: condition and development taking into account European experience
No full textThe work analyzes the mechanism of legal support of e-democracy development in Ukraine and European Union in a part of formation and implementation of its tools. A position of central executive authorities in Ukraine in the context of e-democracy development is considered. The Ukrainian legislative base of formation and realization of e-democracy tools have been studied, and ones, considered priority in the aspect of their legal support and implementation level, have been separated. These e-democracy tools in Ukraine include: e-consulting, e-petitions, e-appeals, participation budgets (public budgets). The analysis of e-democracy tools, offered and implemented in the EU countries allowed to establish a series of them, needed additional attention from both state authorities of Ukraine and Ukrainian publicity. These tools include: e-voting, e-referendum, e-plebiscites, and e-election process totally. Based on comparison analysis of using e-democracy tools in Ukraine and EU, there have been separated obstacles on the way of potential improvement of the national legal mechanism of e-democracy development as to its tools usage at the national, regional and local levels. The main ones are: imperfection of resource provision of the development legal mechanism; absence of an integral idea of the development strategy of e-democracy as an institution in the state; predominance of e-services automation development over development of tools of active involvement of citizens in participation in the public-political life of the country. Recommendations for public authorities as to improvement of the existent legal mechanism of implementation, use and development of e-democracy tools in a part of development of a series of strategic documents that must fix the priority of e-democracy development, its resource support; comprehensive support to public initiatives as to implementation and development of e-democracy and e-participation tools and so on, have been substantiated
Development of electronic petition tools in Ukraine based on international experience
No full textThe purpose of the article is to analyze the public administration mechanisms of electronic petitions (e-petitions), scientific and theoretical justification of recommendations to Ukrainian authorities on their improvement. The paper analyzes the approaches to defining the essence of the concepts of individual and collective e-petitions. The mechanisms of e-appeals (e-petitions) at the national and local levels have been studied. A comparison of the mechanisms of formation and submission of e-petitions in the Ukrainian legislation has been made. It is proposed to improve the interaction of national and local levels by redirecting petitions from local authorities to national executive bodies. The main shortcomings of the existing mechanism of public administration of e-petitions at the national level have been identified. In the process of analyzing the shortcomings of the organizational and legal mechanism, foreign experience and its possibility use in Ukraine were taken into account. Considering the identified shortcomings should further increase the level of civil society involvement in public administration of public affairs and, as a consequence, accelerate the democratization of Ukrainian society and Ukraine as a full member of the European community. In order to assess the level of availability of the electronic individual petitions tool, a study of the official web resources of central and local executive bodies was conducted and ways to improve the practical implementation of the e-petition tool in order to increase its accessibility were identified. The main identified shortcomings are: staffing issues (personnel quality); accessibility and transparency of e-democracy tools for citizens; lack of a unified approach to the implementation of e-appeals (petitions); lack of bottom-up redirection mechanisms; low civil society awareness of public authorities’ responsibilities and powers; lack of mechanisms for imperative execution of e-petitions, etc. Based on the analysis of international experience of implementation of e-appeals (e-petitions), the ways to improve national legislation have been proposed and the recommendations for central authorities, local governments and civil society organizations have been developed to improve the organizational and legal mechanism of public administration of e-democracy tools (electronic individual and collective petitions). The main ones are as follows: amendments to a number of legislative acts, including the conceptual and strategic level; taking into account the imperative implementation of e-petitions; actualization of the issue of administrative and criminal liability for non-compliance with the requirements of the legislation regarding the implementation of e-petitions
On technofeudalism: What killed capitalism? An interview with Yanis Varoufakis
No full textYanis Varoufakis is an economist and politician. After serving as Greek Finance Minister in 2015, he went on to co-found the Democracy in Europe Movement 2025, of which he is now Secretary- General. The author of many books and academic papers, his latest work, Technofeudalism: What Killed Capitalism?, was published by Bodley Head in 2023. Professor of Economics, and editor of this journal, Michel Zouboulakis interviewed Varoufakis in December 2023. What follows is a transcript of that meeting
Archaeology of a Rural Landscape (Tana Delta, Kenya)
No full textTana River County, Kenya. Taken on 12 March 2016 (Source). Author: Adam H. T. Geele (CC BY 3.0). Yanis MOKRI, “Archaeology of a Rural Landscape: The Case of the Tana Delta in Kenya.” Mambo! Vol. XVI (9), 2019. Introduction Since the 1940s, the history of coastal Kenya relies essentially on monumental trading centres studies of the last millennium and a half. On the contrary, hinterlands of those remarkable cities were not subjects of research before the late 1970s. During the 1980s two..
Tecnofeudalismo: O sucessor furtivo do capitalismo
No full textAuthor: Yanis Varoufakis
Publisher: Ariel
Place of publication: Barcelona
Year: 2024
Pages: 264Autor: Yanis Varoufakis
Editorial: Ariel
Lugar de publicación: Barcelona
Año: 2024
Páginas: 264Autor: Yanis Varoufakis
Editora: Ariel
Cidade de publicação: Barcelona
Ano: 2024
Páginas: 26
Book Review: Adults in the room
No full textBook Title: Adults in the roomBook Author: Yanis VaroufakisFarrar, Straus and Giroux: New York 2017. 550pp
Social sciences approach of medical controversy
No full textBruno Latour, dans sa Vie de Laboratoire en 1979, a rapporté son travail de recherche en anthropologie, mené en immersion dans un laboratoire de neuroendocrinologie. Dans une approche comparable, cette thèse rapporte un travail de recherche mené suite à quatre ans d’immersion en observation participante dans un centre de lutte contre les maladies infectieuses, l’IHU Méditerranée Infection. L’auteur observe, avec un regard de chercheur en sciences sociales, les intersections entre la recherche scientifique et le débat public. Cette thèse a été rédigée en quatre grandes parties. D’abord, en s’appuyant sur les travaux de Bruno Latour, l’auteur décrit son approche immersive au sein de l’IHU Méditerranée Infection. Ensuite, l’auteur présente la démarche épistémologique qui sous-tend la prévalence de certains outils et certaines méthodes dans les travaux qui émergent en temps de crise, à partir de trois références de l’épistémologie : Karl Popper, Thomas Kuhn, Paul Feyerabend, en les complétant par les travaux de John Ioannidis. Puis, en s’intéressant notamment aux travaux de Bruno Latour sur Louis Pasteur et les Pasteuriens, l’auteur s’intéresse aux interactions entre science de la santé et politique : quand la science sert de support à des décisions et à la décision politique, qu’est-ce qui est scientifique, qu’est-ce qui est politique ? Enfin, l’auteur explore un biais particulier de la recherche médicale : la question des conflits d’intérêt et l’impact qu’ont les financements de l’industrie pharmaceutique sur la médecine et la recherche, en particulier en temps de controverse.Bruno Latour, in his Laboratory Life in 1979, reported on his research work in anthropology, carried out in immersion in a neuroendocrinology laboratory. In a comparable approach, this thesis reports a research work carried out following four years of immersion in participant observation in a center for the fight against infectious diseases, the IHU Méditerranée Infection. The author observes, with the eyes of a social scientist, the intersections between scientific research and public debate. This thesis has been written in four main parts. First, drawing on the work of Bruno Latour, the author describes his immersive approach within the IHU Méditerranée Infection. Then, the author presents the epistemological approach which underlies the prevalence of certain tools and certain methods in the work that emerges in times of crisis, from three references of epistemology: Karl Popper, Thomas Kuhn, Paul Feyerabend, by supplementing them with the works of John Ioannidis. Then, by focusing in particular on the work of Bruno Latour on Louis Pasteur and the Pasteurians, the author is interested in the interactions between health science and politics: when science serves as a support for decisions and political decision-making, what is scientific, what is political? Finally, the author explores a particular bias in medical research: the issue of conflicts of interest and the impact that funding from the pharmaceutical industry has on medicine and research, especially in times of controversy
A comparison RSM and ANN surface roughness models in thin-wall machining of Ti6Al4V using vegetable oils under MQL-condition
No full textNanomechanics of Li-ion battery materials
No full textThis document deals with the research that the author, Hugues-Yanis Amanieu, carried out between 2012 and 2015 in order to obtain the academic grade of Doctor of Engineer- ing (Dr.-Ing.) delivered by the University of Duisburg-Essen, Germany. The present work was included in two larger projects: Nanomotion, funded by the European Commission through a Marie-Curie actions program, and ReLiOn, funded by the German Federal Ministry of Education and Research. The goal of the former is to design new nanoscale characterization techniques to study electrochemical systems. The latter has for objective to better understand mechanical reliability of battery materials. The work described in this manuscript consequently had for objective to develop new characterization techniques in order to obtain material parameters which are fundamental to numerical simulations allowing a better understanding of mechanical failure in active particles of lithium-ion batteries.
In part I, there is a description of the functioning of lithium-ion batteries (LiB) and of the state-of-the-art of the most important characterization techniques.
As explained in section 1.1, LiB is an electrochemical system where two electrodes exchange ions within the system and electrons in an external circuit. These electrodes contain active particles where lithium can reversibly intercalate. The ions are extracted and reintroduced repeatedly which can lead to mechanical failure of the particles (see section 1.2). In fact the speed of ions in the host material controls the gradient of ionic concentration upon cycling. This gradient provokes tensile and compressive stresses. The former can reach a critical value where fracture or disordering occurs. This process depends on some key material parameters, namely the elastic modulus E, the fracture toughness K C , and the diffusion coefficient D Li . The material of study is spinel lithium manganese(III,IV) oxide (LiMn 2 O 4 ), which is described in section 1.3.
Instrumented indentation testing (IIT), or nanoindentation, is then outlined in section 2.1. It is a tool which consists in driving a stiff diamond tip into a sample surface. Using the Oliver and Pharr (1992) method, the elastic modulus and the hardness of a homogeneous sample can be quantified. It was extended by Ulm and Vandamme (2007) for heterogeneous materials by implementing statistical deconvolution on a large data set. Section 2.2 deals with atomic force microscopy (AFM)-based techniques. The first one consists of measuring the topography of a crack in order to determine its crack- opening displacement (COD) and subsequently estimate the fracture toughness using Irwin’s near field theory. Then contactresonance atomic force microscopy (CR-AFM) is introduced. The elastic properties can be estimated through the resonance frequency of the cantilever when in contact with the sample surface. Last electrochemical strain microscopy (ESM) is presented. Here the AFM cantilever vibration amplitude is measured during application of a AC excitation between the AFM tip and the sample. The vibration is mediated via a mechanism which depends on the lithium concentration.
Time spectroscopy measurements can be carried out by monitoring the signal after applying a DC pulse: a typical relaxation process is detected and its speed depends on the ionic diffusion coefficient D Li . However the underlying mechanisms are still unknown to quantify it. A Vegard’s deformation generated by ionic diffusion was first assummed but it seems unlikely as the displacement would not be detectable.
As listed in part II, the objectives of the work were to implement Ulm’s nanoindentation statistical method and to suggest alternative methods such as CR-AFM in order to quantify E, to propose new instruments to estimate the K C of micrometric particles, and last to suggest a new model in order to make ESM a quantitative technique.
Sample preparation and experiments are described in part III. LiMn 2 O 4 cathodes obtained from fresh cells and from aged cells at different states of charge were embedded in epoxy and then prepared as polished cross-sections. Laboratory-grade reference powders of SiO 2 , MnO 2 and LiMn 2 O 4 were also similarly prepared. A LiMn 2 O 4 -based wafer oriented in the {111} direction was synthesized (see chapter 3). The different instruments used in the course of the work are mentioned in chapter 4. Among these, AFM topography measurements of the COD were numerically modeled as described in chapter 5.
It is shown in part IV that Ulm’s statistical deconvolution technique cannot be directly used on the battery samples as many spurious peaks appear in the distribution of the measurements. This part therefore relates to a method, called selective nanoindentation, that was specifically developed in order to obtain reliable measurements of the elastic moduli and the hardnesses of each phase of heterogeneous samples. It consists of filtering each experimental data by checking its consistency with the Oliver and Pharr method. First it is checked if the load-displacement curve has a quadratic shape. Second it is checked if no structural compliance induced by the epoxy matrix influences the measured stiffness. Third the filtered data are deconvoluted and compared to scanning electron microscopy (SEM) micrograms of the indented surfaces. The SiO 2 -based sample was used to verify the reliability of the method.
Part V deals with the modeling of the ESM system. A COMSOL model was developed to describe the change in the lithium concentration field in a LiMn 2 O 4 body during and after the application of a DC pulse. Its novelty is twofold. D Li is not constant but depends on the lithium concentration. More importantly, the ESM signal is not physically described like in previous work where Vegard’s deformation in the frequency domain is computed. Instead, the signal is estimated to be linearly dependent with the mean Lorentz electric force applied by the AC excitation on the lithium ions, denoted F AC .
All of the results are listed in part VI.
First, chemical analyzes of the samples are given in chapter 13. X-ray diffraction (XRD) measurements showed that every sample contains a single spinel phase. This result was nuanced by energy dispersive X-ray analysis (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES) as cobalt oxide particles (up to 2 %) were detected but also other impurities. SEM showed also that these commercial particles can be porous agglomerates of nanoparticles as well as large single grains. The wafer exhibited two phases: the main one is spinel LiMn 2 O 4 as expected but also a Mn 2 O 3 bixbyite phase was found. Only the former was characterized by the other methods.
Nanoindentation results are reported in chapter 14. The particles are quite brittle: chipping occurs around the indents and cracks grow from them. Electron backscatter diffraction (EBSD) qualitatively revealed that the mechanisms depend on the crystal orientation. IIT measurements reported an elastic modulus of around 90 GPa and a Berkovich hardness of 7 GPa. This is lower than what was previously reported on LiMn 2 O 4 thin films by Zhu and Zeng (2012), certainly because they did not take pile-up into account, hence overestimating the properties, but also because our samples are made of factory-grade particles of lower quality. These two properties increase of more than 10 % upon delithiation. We associated this behavior with Mn−O bonds which are stiffer when the valence of the transition metal increases. The average Mn valence goes from +3.5 for LiMn 2 O 4 to +4 for λ−MnO 2 . An exception was detected for the specimen obtained from a 25 % SoC cell where the hardness was much lower (6.5 GPa), which could be caused by a less hard non-stoichiometric LiMn 2 O 4 . Micro- Raman spectroscopy combined with CR-AFM revealed that neighboring particles can have different lithium concentrations, hence difference stiffnesses accordingly with the nanoindentation results. CR-AFM was also used on the reference LiMn 2 O 4 powder and it was shown that the spinel is isotropic, at least within the detection limit of the instrument. Quantitative implementation of CR-AFM was unsuccessful. Using the traditional crack-length measurement method on the wafer, a K C of 0.23 MPa·m 1/2 was found. As the unusual crack configuration around the indents of the particles do not allow this method to be used, COD measurements were carried out. A K C of about 0.9 MPa·m 1/2 was measured for the commercial particles and of about 0.8 MPa·m 1/2 for the wafer. It was also found by EBSD that cracks always propagate in the direction in the wafer. They open {101} planes just below the surface and deviate of 30 to 40 ◦ after about 100 nm. These data are given in chapter 15.
ESM measurements as well as data from the model are reported in chapter 16. It was demonstrated that the experimental signal is qualitatively similar to F AC . The concentration dependent D Li can explain the asymmetrical hysteresis loops. Using a constant D Li , it was established that time spectroscopy relaxation of F AC follows a power law of the form (at + 1) 1/p . Here p is only slightly dependent on the diffusivity 1/2 and the contact radius while a strongly depends on them and is linear with D Li /R tip . Experimentally, the relaxation process was much slower for the aged sample while no significant differences were reported for the fresh samples with different states of charge (SoCs).
Discussions of the different results are depicted in part VII.
A critique of the Ulm and Vandamme (2007) method of is discussed in chapter 17. Pavel Trtik et al. (2009) consider indeed that spurious peaks cannot be avoided when indenting heterogeneous materials. A response is given by Ulm and Vandamme (2010) which proves that their results are due to the three-dimensional configuration of their model. In our case, spurious peaks were detected nonetheless but could simply be eliminated using the selective nanoindentation method. An important drawback is that much more measurements must be performed to reach statistically significant numbers. In the same chapter, it was discussed that CR-AFM was a valuable extension to nanoindentation as qualitative stiffness maps with a nanoscale precision can be acquired within minutes. Nanoindentation still has the advantage of quantification as the AFM-based method was unreliable and much too slow. Last the COD measurements are discussed. It was shown that the user interpretation of the data is not so significant as a sample of 9 analysts found similar K IC and K IIIC on the simulated cracks as well as on two real measurements. However it is believed that the method greatly overestimates the toughness as one of the Irwin’s condition is not met: the crack walls are not traction-free due to residual tensile stresses originating from the indent plastic zone. This explains the discrepancy between the two values measured on the wafer. It was suggested to use instead the pillar splitting method developed by Sebastiani et al. (2014), as they found a likely K C of about 0.3 MPa·m 1/2 on our samples. The origin of the ESM signal is discussed in chapter 18. It is suggested that other electromechanical couplings, such as electrostriction or flexoelectricity, should be considered. Moreover, the AC electric field could hypothetically interact with the transition metals rather than with the lithium ions.
The coupling between the mechanical properties and the lithium concentration is compared with that of other similar ceramics in chapter 19. In general, a longer bond length lead to a more compliant material, whether it is induced by an increasing or decreasing lithium concentration. Then the fracture toughness is compared with that of LiCoO 2 . It was reported to be higher for the pristine material: 1 MPa·m 1/2 . But as soon as the material is electrochemically activated, the K C drops to similar values as ours, about 0.25 MPa·m 1/2 .
In the end a brief conclusion is given that first sums up the key results for people working with battery simulation. Secondly, an overview of the reliability of the different characterization methods is given.Thema dieser Dissertation ist die Forschungsarbeit, die der Verfasser Hugues-Yanis Amanieu von 2012 bis 2015 zur Erlangung des akademischen Grades eines Doktors der Ingenieurwissenschaften (Dr.-Ing.) an der Universität Duisburg-Essen durchführte. Die Arbeit fand im Rahmen zweier Projekte statt: Nanomotion, ein von der EU-Kommission durch eine Marie-Curie Maßnahme finanziertes Projekt, und das vom Bundesministerium für Bildung und Forschung geförderte Projekt ReLiOn. Das Ziel des erstgenannten ist es, neue Nano-Charakterisierungstechniken zur Untersuchung elektrochemischer Systeme zu entwerfen. Letzteres hat zum Ziel, die mechanische Zuverlässigkeit von Batteriematerial besser zu verstehen. Die hier beschriebene Arbeit bringt beide Projekte zusammen: ihr Ziel die Entwicklung neuer Charakterisierungstechniken für die Erlangung von Materialparametern, die grundlegend für numerische Simulationen sind. Diese Simulationen ermöglichen ein besseres Verstehen mechanischer Brüche in den aktiven Partikeln von Lithium-Ionen-Batterien (LiB).
Teil I enthält eine Beschreibung der Funktionsweise von LiB und der modernsten und wichtigsten Charakterisierungstechniken.
Wie in Abschnitt 1.1 erklärt wird, ist LiB ein elektrochemisches System, bei dem zwei Elektroden Ionen im Inneren der Batterie und Elektronen in einem äußeren Stromkreis austauschen. Diese Elektroden enthalten aktive Partikel, in denen Lithium in einem reversiblen Prozess interkalieren kann. Die Ionen werden wiederholt geladen und entladen, was zu mechanischen Brüchen der Partikel führen kann (siehe Abschnitt 1.2). Tatsächlich kontrolliert die Geschwindigkeit der Ionen im Interkalationsmaterial den Gradienten der Ionenkonzentration beim Zyklisieren der Zelle. Dieser Gradient verursacht Zug- und Druckspannungen. Sie können einen kritischen Wert erreichen, bei dem es zu Rissen oder Phasenumwandlungen kommt. Der Prozess ist abhängig von einigen entscheidenden Materialparametern, namentlich vom Elastizitätsmodul E, der Bruchzähigkeit K c und dem Diffusionskoeffizienten D Li . Das Untersuchungsmaterial LiMn 2 O 4 wird in Abschnitt 1.3 beschrieben.
In Abschnitt 2.1 wird die Nanoindentierung geschildert. Dabei handelt es sich um ein Werkzeug, welches eine harte Diamantspitze in eine Probenoberfläche bohrt. Durch die Oliver und Pharr (1992) Methode können das Elastizitätsmodul und die Härte eines homogenen Materials gemessen werden. Ulm und Vandamme (2007) erweiterten die Methode um heterogene Materialien. Hierbei wird eine statistische Entfaltung der Daten von großen Indentierungsmatrizen durchgeführt.
Verschiedene auf Atomkraftmikroskopie (AFM) basierende Techniken werden in Abschnitt 2.2 dargelegt. Die erste besteht in der Messung der Topographie eines Risses, um die Breite der Rissöffnung (COD) zu bestimmen und anschließend die Bruchzähigkeit K c durch die Nahfeld-Theorie von Irwin zu berechnen. Anschließend wird die Technik der Ultraschallkraftmikroskopie (CR-AFM) dargelegt. Wenn die Spitze des Cantilevers in Kontakt mit der Materialoberfläche ist, kann anhand der Resonanzfrequenz das Elastizitätsmodul berechnet werden. Zuletzt wird die Electrochemical Strain Microscopy (ESM) vorgestellt. Hierbei wird die Schwingungsamplitude des Cantilevers während einer Wechselspannungsanregung (AC-Anregung) zwischen AFM-Spitze und Probe gemessen. Die Schwingung wird durch einen Mechanismus hervorgerufen, der von der Lithiumkonzentration abhängig ist. Durch beobachten des Signals nach Anlegen eines DC-Puls können Zeitspektroskopy-Messungen durchgeführt werden: es lässt sich ein typischer Relaxations-Prozess feststellen, dessen Geschwindigkeit vom Li-Diffusionskoeffizienten D Li abhängt. Die der Methode zugrundeliegenden Mechanismen zur quantitativen Bestimmung von D Li sind aber immer noch unbekannt. Eine durch Li-Diffusion hervorgerufene Vegards Verformung wurde anfangs vermutet. Sie erscheint jedoch unwahrscheinlich, da die Verschiebung nicht messbar wäre. Wie in Teil II aufgeführt ist es das Ziel der Arbeit, die statistische Methode von Ulm zu verändern, alternative Methoden für die Quantifizierung von E, wie beispielsweise CR-AFM, zu finden und neue Geräte zur Messung der Bruchzähigkeit micrometrischer Partikel vorzuschlagen. Zudem sollen neue Modelle entworfen werden, um ESM zu einer quantitativen Technik zu machen.
In Teil III werden Probenvorbereitungen und Versuche beschrieben. Aus neuen und gealterten Zellen in verschiedenen Ladungszuständen gewonnene LiMn 2 O 4 Kathoden wurden in Epoxidharz eingebettet und als Schleifproben vorbereitet. Auf selbe Weise wurden laborreine Referenzproben von SiO 2 , M n O 2 und LiMn 2 O 4 erstellt. Ein Wafer aus LiMn 2 O 4 wurde in {111} Richtung synthetisiert. Die verschiedenen, im Laufe der Forschungsarbeit verwendeten Messgeräte werden in Kapitel 4 genannt, darunter AFM- Topologiemessungen der COD, deren numerische Modelle in Kapitel 5 beschreiben werden.
Wie in Teil IV gezeigt wird, kann die statistische Methode von Ulm und Vandamme (2007) nicht direkt auf Batterieproben angewendet werden, da mehrere unberechtigte Scheitelpunkte in der Verteilung der Messungen wirken. Deshalb verweist dieser Teil auf eine Methode, die selective Nanoindentierung, die speziell entwickelt wurde, um verlässliche Messungen des E-Moduls und der Härte zu erhalten. Sie besteht darin, jede Versuchsdatei mittels einer Überprüfung ihrer Kompatibilität durch die Oliver und Pharr Methode zu filtern. Zunächst wird überprüft, ob die Kraft-Eindringtiefe-Kurve quadratisch ist. Dann wird geprüft, ob keinerlei strukturelle Flexibilität die gemessene Steifheit beeinflusst. In einem dritten Schritt werden die gefilterten Daten entfaltet und mit Hilfe eines Rasterelektronenmikroskops (SEM) mit jeder Phase der heterogenen Probe verknüpft. Die SiO 2 -Probe wurde verwendet, um die Zuverlässigkeit der Methode zu testen.
Teil V behandelt die Modellierung des ESM-Systems. Um die Veränderung des Lithiumkonzentrationsfeldes eines LiMn 2 O 4 -Körpers während und nach Anlegen eines DC-Pulses zu beschreiben, wurde ein COMSOL-Modell entwickelt. Die Neuartigkeit im Vergleich zu anderen Modellen liegt darin, dass D Li keine Konstante darstellt, sondern von der Lithiumkonzentration abhängt. Darüberhinaus wird das ESM-Signal nicht physikalisch beschrieben wie bisher, wo Vegards Verformung im Frequenzbereich berechnet wird. Stattdessen nimmt man an, dass das Signal linear abhängig ist von der durchschnittlichen elektrischen Lorenztkraft, bezeichnet als F A C, die durch die AC-Anregung auf die Lithium-Ionen ausgeübt wird.
Sämtliche Ergebnisse werden in Teil VI aufgelistet.
In Kapitel 13 werden chemische Analysen der Proben gegeben. XRD-Messungen zeigen, dass jede Probe eine einzelne Spinellphase enthält. Das Ergebnis wurde durch EDX und ICP-OES ausdifferenziert, da Kobaltoxidpartikel (bis zu 2 %) aber auch andere Unreinheiten gefunden wurden. SEM-Abbildungen haben außerdem gezeigt, dass diese Partikel sowohl poröse Agglomerate von Nanopartikeln als auch große einzelne Körnchen sein können. Der Wafer wies zwei Phasen auf: die Hauptphase bildet wie erwartet der Spinell LiMn 2 O 4 , aber es wurde auch eine Mn 2 O 3 -Bixbyit-Phase gefunden.
Nur erstere wurde von den anderen Methoden charakterisiert.
Die Ergebnisse der Nanoindentierung sind in Kapitel 14 aufgeführt. Es wurde herausgefunden, dass die Partikel relativ brüchig sind: um die Eindrücke herum kommt es zu Absplitterungen und Risse gehen von ihnen aus. Die EBSD zeigte in qualita- tiver Hinsicht, dass die Mechanismen von der Ausrichtung der Kristalle abhängig sind. Nanoindentierungsmessungen zeigten ein E-Modul von etwa 90 GPa und eine Berkovich-Härte von 7 GPa an. Dieses Ergebnis ist niedriger als das zuvor auf LiMn 2 O 4 - Dünnschicht gemessene Ergebnis von Zhu und Zeng (2012). Das ist sicher deshalb der Fall, weil sie nicht die Aufstockung berücksichtigten und folglich die Eigenschaften überschätzten, aber auch weil unsere Proben aus weniger hochwertigen Partikeln bestehen. Das E-Modul und die Härte steigen um mehr als 10 % bei schwächeren Lithium- Konzentrationen. Wir brachten dieses Verhalten mit Mn−O-Bindungen in Zusammenhang. Diese sind steifer, wenn die Valenz des Übergangsmetalls zunimmt. Die durchschnittliche Mn-Valenz wächst um von +3,5 für LiMn 2 O 4 bis +4 für λ−MnO 2 . Eine Ausnahme bildet die aus einer 25 % SoC-Zelle gewonnene Probe, wo die Härte viel niedriger war (6,5 GPa). Dies könnte durch ein weniger hartes nicht-stöchiometrisches LiMn 2 O 4 verursacht werden. Wie die Micro-Raman-Spektroskopie in Kombination mit CR-AFM zeigte, können benachbarte Partikel unterschiedliche Lithium-Konzentrationen haben, folglich unterschiedliche Steifheit in Einklang mit den Ergebnissen der Nanoindentierung. CR-AFM wurde auch auf die Referenzprobe von LiMn 2 O 4 -Pulver angewendet. Wie sich herausgestellt hat, ist der Spinell isotrop, zumindest innerhalb der Nachweisgrenze des Messgeräts. Eine quantitative Durchführung von CR-AFM hat sich als erfolglos erwiesen.
Durch Anwendung einer traditionellen Technik, die darin besteht, die Länge der durch Indentierung ausgelösten Risse zu messen, hat sich für die Bruchzähigkeit des Wafers ein Wert von 0.23 MPa·m 1/2 ergeben. Da die ungewöhnliche Konfiguration der Risse um die Eindrücke der Partikel herum es nicht erlaubt, diese Methode anzuwenden, wurden COD-Messungen durchgeführt. Für die kommerziellen Partikel wurde eine Bruchzähigkeit von etwa 0,9 MPa·m 1/2 gemessen, für den Wafer eine Bruchzähigkeit von etwa 0,8 MPa·m 1/2 . EBSD hat außerdem gez
