Determination of Degradation Mechanisms During the Cyclic Ageing of Li-ion Batteries

Degradation mechanisms in commercial Li-ion batteries have been extensively studied over the past decades. However, there are still open questions regarding the link between the observed changes on the system level of the battery with the actual degradation on the material level happening inside the battery. Therefore, different techniques are applied and findings combined to improve the understanding of material degradation influences on the system level behavior. A tailored electrochemical strain microscopy (t-ESM) technique, which is based on atomic force microscopy, is presented. The technique is applied to laboratory made silicon composite anodes and commercial LiFePO4 cathodes. The surface displacement induced by the Vegard strain is proportional to the ionic concentration change and activity of Li-ions within the probed volume under the tip. The probed volume spans only a few nanometers in depth inside the material. The results indicate a structural dependency, with higher mobility and activity at boundaries. The technique provides time constants and hence diffusion coefficients on the nano-scale. The electrochemical activity, which is analyzed with the t-ESM technique, is found to decrease due to ageing. The ageing of commercial battery cells is monitored using system level methods such as incremental capacity analysis (ICA), differential voltage analysis (DVA) and tracking of the open-circuit voltage (OCV). Ageing at 50% depth of discharge (DOD) leads to higher capacity fading compared to cycling over 100% of the available capacity. In total, 14 different features of the cell behavior are tracked during the ageing process using various analysis techniques. The intensity of the first discharge peak of the ICA curves is found to correlate well with the capacity fading and is used to predict the remaining capacity and lifetime. The loss of lithium and the loss of active material, especially at the cathode, are the main factors leading to the observed capacity decay. The post-mortem analysis reveals the formation of lithium fluoride crystals on the anode surfaces, aged at 55°C. The iron dissolution (from the electrode into the electrolyte) is shown to be temperature dependent and in addition dependent on the depth of discharge. Next to iron dissolution, vanadium dissolution (from the electrode into the electrolyte) from the cathode is observed. Micrometer sized agglomerates (consisting out of nano particles from cathode active material) are observed on the cathode surface, which decrease the surface conductivity, but does not directly correlate with the capacity fading. Ageing at -20°C leads to the formation of stable Li plating, which is subsequently observed at room temperature cycling

Visualization of local ionic concentration and diffusion constants using a tailored electrochemical strain microscopy method

A tailored electrochemical strain microscopy technique is presented and used to analyze the ionic mobility and diffusion coefficients in composite Si/C anodes. The resulting surface displacement after a voltage pulse is proportional to the ionic concentration change and is measured by the deflection of an atomic force microscopy tip. The results show a higher ionic mobility at the steps of silicon composite anode microcrystals compared to the crystal centers. Diffusion coefficients are extracted from the time dependence of the surface displacement. Mappings with nanoscale resolution of local diffusion coefficients are displayed. The results demonstrate higher diffusion coefficients at the steps.Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research

Influence of cycling profile, depth of discharge and temperature on commercial LFP/C cell ageing : post-mortem material analysis of structure, morphology and chemical composition

The paper presents post-mortem analysis of commercial LiFePO4 battery cells, which are aged at 55 °C and - 20 °C using dynamic current profiles and different depth of discharges (DOD). Post-mortem analysis focuses on the structure of the electrodes using atomic force microscopy (AFM) and scanning electron microscopy (SEM) and the chemical composition changes using energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results show that ageing at lower DOD results in higher capacity fading compared to higher DOD cycling. The anode surface aged at 55 °C forms a dense cover on the graphite flakes, while at the anode surface aged at - 20 °C lithium plating and LiF crystals are observed. As expected, Fe dissolution from the cathode and deposition on the anode are observed for the ageing performed at 55 °C, while Fe dissolution and deposition are not observed at - 20 °C. Using atomic force microscopy (AFM), the surface conductivity is examined, which shows only minor degradation for the cathodes aged at - 20 °C. The cathodes aged at 55 °C exhibit micrometer size agglomerates of nanometer particles on the cathode surface. The results indicate that cycling at higher SOC ranges is more detrimental and low temperature cycling mainly affects the anode by the formation of plated Li.Bundesministerium für Bildung und ForschungProjekt DEA

Upgrades of a small electrostatic dust accelerator at the University of Stuttgart

In this paper, we describe the upgrade of a small electrostatic dust accelerator located at the University of Stuttgart. The newly developed dust source, focusing lens, differential detector and linac stage were successfully installed and tested in the beam line. The input voltage range of the dust source was extended from 0-20 kV to 0-30 kV. A newly developed dust detector with two differential charge sensitive amplifiers is employed to monitor particles with speeds from several m/s to several km/s and with surface charges above 0.028 fC. The post-stage linac provides an additional acceleration ability with a total voltage of up to 120 kV. The entire system of this dust accelerator works without protection gas and without a complex high voltage terminal. The volumes to be pumped down are small and can be quickly evacuated. The new system was used to accelerate micron- and submicron-sized metal particles or coated mineral materials. Improvements in the acceleration system allow for a wider variety of dust materials and new applications.Deutsche Forschungsgemeinschaft (DFG

SUDA: A SUrface Dust Analyser for Compositional Mapping of the Galilean Moon Europa

The Surface Dust Analyser (SUDA) is a mass spectrometer onboard the Europa Clipper mission for investigating the surface composition of the Galilean moon Europa. Atmosphereless planetary moons such as the Galilean satellites are wrapped into a ballistic dust exosphere populated by tiny samples from the moon’s surface produced by impacts of fast micrometeoroids. SUDA will measure the composition of such surface ejecta during close flybys of Europa to obtain key chemical signatures for revealing the satellite’s composition such as organic molecules and salts, history, and geological evolution. Because of their ballistic orbits, detected ejecta can be traced back to the surface with a spatial resolution roughly equal to the instantaneous altitude of the spacecraft. SUDA is a Time-Of-Flight (TOF), reflectron-type impact mass spectrometer, optimized for a high mass resolution which only weakly depends on the impact location. The instrument will measure the mass, speed, charge, elemental, molecular, and isotopic composition of impacting grains. The instrument’s small size of 268mm×250mm×171mm, radiation-hard design, and rather large sensitive area of 220 cm 2 matches well the challenging demands of the Clipper mission

Close Cassini flybys of Saturn's ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus

Saturn’s main ring system is associated with a set of small moons that are either embedded within it, or interact with the rings to alter their shape and composition. Five close flybys of the moons Pan, Daphnis, Atlas, Pandora, and Epimetheus were performed between December 2016 and April 2017 during the Ring-grazing Orbits of the Cassini mission. Data on the moons’ morphology, structure, particle environment, and composition were returned, along with images in the ultraviolet and thermal infrared. The optical properties of the moons’ surfaces are determined by two competing processes: contamination by a red material formed in Saturn’s main ring system, and by accretion of bright icy particles or water vapor from volcanic plumes originating on the planet’s moon Enceladus

Membranes, Electrodes, and Membrane-Electrodes Assemblies Analyzed before and after Operation by Atomic Force Microscopy

Material-sensitive and conductive atomic force microscopy was applied to the investigation of cross sections of membraneelectrode-assemblies (MEA) at operating conditions, 80% relative humidity and 75°C, before and after operation. The ionomer content inside the electrodes could be measured due to their characteristic mechanical, chemical and physical properties. By surface potential measurements across MEAs after degrading fuel cell operation, a severe influence of the re-deposited platinum on the potential distribution was found

Li2S Kathoden der nächsten Generation

Um die steigende Nachfrage nach sicheren, kostengünstigen und leistungsfähigen Energiespeichern für z. B. die Elektromobilität und tragbaren Consumer Geräten zu decken, müssen neue Lösungen gefunden werden, um die Bedürfnisse der einzelnen Bereiche zu erfüllen. Dabei sind Lithium-Schwefel Batterien wegen der hohen theoretischen Energiedichte von bis zu 500 Wh kg-1, was ca. dem doppelten von aktuellen Lithium-Ionen Zellen entspricht, eine vielversprechende Alternative. Weltweit gibt es hohe Vorkommen von Schwefel was ihn zu einem kostengünsitgen Werkstoff macht. Die atoxische Eigenschaft von Schwefel ist ein weitere Vorteile des Lithium-Schwefel Systems. Bei der Verwendung von Li2S als Kathodenmaterial kann theoretisch gänzlich auf metallisches Lithium verzichtet werden, wodurch die Sicherheit des Systems gesteigert wird. Aktuelle Lithium-Schwefel Systeme besitzen bereits höhere Energiedichten als Lithium-Ionen Batterien. Dennoch sind Verbesserungen nötig, um die noch geringe Zyklenstabilität zu erhöhen und damit ein breiteres Einsatzgebiet für Li-S Batterien zu ermöglichen. In dieser Arbeit wurden Li2S Kathoden hergestellt und dabei die Einflussparameter auf die Entladekapazität untersucht. Es wurden unterschiedliche Herstellungsverfahren mit verschiedenen Geräten zur Pastenelektrodenherstellung eingesetzt und die Auswirkungen auf die Kapazität untersucht. Zusätzlich wurden lösungsmittelfreie Elektroden mit einer Presse hergestellt und charakterisiert. Bei den Materialien wurden verschiedenen Elektrodenbinder, Kohlenstoffe und Kohlenstoffadditive, sowie Elektrolytaddivite eingesetzt und deren Auswirkung auf die Aktivmassenausnutzung analysiert. Die Elektroden wurden in Messzellen gegen eine Lithium Anode verbaut und elektrochemisch analysiert. Das Ziel der Arbeit war es, die verschiedene Einflussparamter auf die Kapazität von Li2S Zellen zu definieren. Es sollten dabei nicht nur hohe theoretische Kapazitäten erreicht werden, sondern auch möglichst hohe Kapazitäten mit praxisrelevanten Elektrodeneigenschaften erzielt werden. Die Elektroden sollten eine hohe Li2S Beladung und einen hohen Li2SMassenanteil besitzen

SUBJECTIVE PERSPECTIVES OF DIABETES MELLITUS AMONG IMMIGRANTS ON THE FORMER SOVIET UNION

Aim: The purpose of this study was to explore data concerning subjective theories, personal resources, and recommendations for counseling changes in people with diabetes mellitus from different Russian-speaking nationalities. Russian-speaking immigrants and Russian Germans may require a different type of diabetes education to native inhabitants. Design: A literature review of subjective theories of illness, personal resources, and recommendations for counseling was conducted. Methods: Literature published since 2009 was searched, including qualitative and quantitative studies. Data were found for Jewish and Russian-speaking immigrants with diabetes mellitus, but not for Russian Germans. The scope of the search was, therefore, widened. Literature on general loci of control, health beliefs, and diabetes education was included. Results: Seventeen articles were identified. These studies discussed health beliefs and behaviors, including externalized attribution of causes, and internalized locus of control. Homeopathic and natural therapies were generally preferred over other medications. However, socioeconomic status, level of education, and external circumstances in the country of origin were more important than differentiation by nationality. Conclusion: Therapists require knowledge of the living conditions in immigrants’ country of origin to inform their provision of medical advice. Immigrants’ general level of education, socioeconomic status, and previous living conditions are also important. Keywords: Russian-speaking immigrants, Russian Germans, diabetes mellitus, health belief, health behavior, personal resources, counseling