Correlative investigations into advanced silicon and silicon hybrid anode microstructures for high capacity Li-ion batteries

There is a continuing need for global attention to focus on further development of devices to enable efficient energy storage. This must align with a new and stringent renewable energy target of 32 % for the European Union by 2030. Present materials used within Li-ion batteries currently have a limitation on the amount of energy they can store and for a specified duration. In order to advance the capacity of their most advanced cylindrical cells, Tesla, Samsung, LG and Sony at present use a small fraction of silicon in graphite-dominant anodes to overcome issues around volume expansion and to extend operational life. However, to date, no successful commercial product has been reported that contains silicon as the predominant lithium host material. The solutions offered so far in literature involve complex chemical synthesis or intricate processing routes, which are not realistic solutions to produce practical or cost-effective devices. The thesis core is based on innovative approaches to stabilising silicon-based anodes via additives, which can be conveniently synthesised or commercially available and are chemically compatible with the electrode components. This research work reports on the use of metal-organic frameworks, namely UiO-66 and UiO-67, to enhance the electrochemical performance of high-capacity silicon anodes in lithium-ion batteries. This research work also studied other hybrid anode systems, based on silicon-graphene and silicon-tin powders, using conventional formulation approaches to compare with an advanced electrode manufacturing technique. This study demonstrates that certain additives improve the flexural capability and mechanical integrity of electrode materials. These additives extend the durability of silicon anodes to enable extended reversible transfer of Li-ions, and hence enable a longer lifespan of the battery. This study reports the use of high-quality physicochemical characterisation from a variety of experimental techniques to correlate the anode’s microstructure, dynamics and atomic-scale structure with the maintained performance of the battery. Focused ion beam-scanning electron microscopy (FIB-SEM) tomography, in conjunction with impedance spectroscopy and associated physical characterisation, has been employed to capture and quantify key aspects of the evolution of internal morphology and resistance build up within anodes. FIB-SEM tomography has been employed to explore the hierarchical structure of battery electrodes and for diagnosing battery failure mechanisms with high-resolution imaging. This approach will enable us to observe and quantify failures in Li-ion batteries at the electrode level. It is anticipated that this study will influence major improvements in the design of Li-ion battery materials and their processing which in turn positively impact cell performance

3D and 4D Characterisation of Lithium-Ion Battery Electrode Microstructures using X-ray Tomography

There is a direct link between electrode microstructure and their performance in lithium-ion batteries (LIBs); however, this relationship remains poorly understood. By utilising tomographic X-ray imaging techniques, it is possible to characterise LIB electrode microstructure in three dimensions. Moreover, extending these imaging techniques to explore changes in these materials gives rise to the notion of “four-dimensional” (4D) tomography to study microstructural evolution with time. This work focused on characterising, both qualitatively and quantitatively, the three-dimensional (3D) microstructure of LIB electrode materials at multiple length and time scales with the aid of laboratory and synchrotron X-ray sources. The suitability and reliability of direct 3D microstructural analysis for quantifying LIB electrodes was demonstrated by comparing it with stereological methods, which are shown to introduce bias when applied to inhomogeneous 3D microstructures. Silicon (Si) and metallic lithium (Li) are highly energy-dense electrode materials and promising candidates for use in LIBs; however, they experience significant microstructural degradation upon electrochemical cycling. Using a custom-built, X-ray transparent in-situ electrochemical cell, 4D characterisation of the microstructural evolution and degradation within the aforementioned electrode materials was performed both in-situ and in-operando. Phase transformation, fracture formation and propagation within individual Si particles was visualized and tracked in 3D during the course of a half-cell discharge. At a higher X-ray imaging resolution, microstructural evolution in Si microparticles as a result of repeated cycling was captured and quantified in 3D. Visualisation of formation and growth of pits and mossy lithium deposits along metallic Li electrode surfaces was also presented. Finally, an X-ray contrast-enhancement approach for imaging lowly attenuating electrode materials such as graphite was also demonstrated. This work has demonstrated X-ray tomography as a diagnostic tool for providing valuable insight into electrode microstructure which can aid the efficient design of these electrode materials in future generation LIB systems

X-ray imaging of failure and degradation mechanisms of lithium-ion batteries

Lithium-ion batteries are becoming increasingly energy and power dense, and are required to operate in demanding applications and under challenging conditions. Both safety and performance of lithium-ion batteries need to be improved to meet the needs of the current demand, and are inextricably linked to their microstructure and mechanical design. However, there is little understanding of the complex, multi-length scale, structural dynamics that occur inside cells during operation and failure. From the evolving particle microstructure during operation to the rapid breakdown of active materials during failure, the plethora of dynamic phenomena is not well understood. In this thesis, both ex-situ and operando X-ray imaging, and computed tomography, in combination with image-based modelling and quantification are used to characterise battery materials and components in 3D. Degradation mechanisms are investigated across multiple length-scales, from the electrode particle to the full cell architecture, and direct comparisons between materials in their fresh and failed states are made. Rapid structural evolution that occurs during operation and failure is captured using high-speed synchrotron X-ray imaging, and quantified by correlating sequential tomograms. Consistent degradation mechanisms that occur over fractions of a second are identified and are shown to contribute significantly towards uncontrolled and catastrophic failure, and previously unexplored interplay between the mechanical design of cells and their safety and performance is described. The experiments reported here assess the thermal and mechanical responses of cells to extreme operating and environmental conditions. The interaction between the dynamic architecture of active materials and the mechanical designs of commercial cells are revealed, highlighting the importance of the engineering design of commercial lithium-ion batteries and their efficacy to mitigate failure. These insights are expected to influence the future design of safer and more reliable lithium-ion batteries

Polysulfide Mitigation at the Electrode-Electrolyte Interface: Experiments in Rechargeable Lithium Sulfur Batteries

In the field of energy storage technology, the lithium sulfur battery is intensely studied in interest of its great theoretical gravimetric capacity (1672 Ah kg–1) and gravimetric density (2600 Wh kg–1). The theoretical performance values satisfy viability thresholds for petroleum–free electric vehicles and other emerging technologies. However, this elusive technology remains in the research sector due to a wealth of challenges resulting from its complex chalcogenide electrochemistry. The most infamous challenge remains the polysulfide redox shuttle, a phenomenon in which lithium polysulfide intermediates are produced as elemental sulfur S8 is reduced to lithium sulfide Li2S during the discharge cycle. Because the higher order polysulfides are soluble in organic electrolyte, battery cycling can result in dissolution of the cathode, dendrite formation upon the lithium metal anode, and passivation of electrode surfaces. These problems can ultimately cause rapid capacity fade and unstable Coulombic efficiency. As lithium sulfur battery research enters its 3rd decade, it is becoming increasingly clear that solutions will be holistic or synergistic; that is, addressing the aforementioned issues by suppressing their source in the polysulfide redox shuttle rather than isolated symptoms of the underlying mechanism. This thesis serves as a summary of research performed to study polysulfide suppression and mitigation through electrode material synthesis, electrolyte design, and in situ characterization. Synthesis techniques include solid state pyrolysis, autogenic synthesis, and ultrasound sonochemistry. Material characterization techniques include isothermal nitrogen sorption; scanning, transmission, and scanning transmission electron microscopy; thermogravimetric analysis; energy dispersive X–ray spectroscopy; organic elemental analysis; X– ray diffraction; and Raman spectroscopy. Electrochemical characterization includes galvanostatic battery cycling, differential potentiometric analysis, and electrochemical impedance spectroscopy. Altogether, this research demonstrates the challenges of polysulfide degradation are not sufficiently addressed by symptomatic approaches. Synthesis pathways for carbon sulfur cathodes that encourage homogeneous sulfur distribution (i.e., autogenic or sonochemical synthesis) improve specific capacity across extended cycling, but show excessive polysulfide production at slow cycling rates. In combination with fluorinated electrolyte, carbon sulfur cathode morphology improves Coulombic efficiency at cycling rates between C/20 — 2 C but at the cost of gravimetric capacity. Synchrotron tomography characterization, developed for Advanced Photon Source Beamline 6–BM–A, evidences that fluorinated electrolytes may also effectively suppress dendrite formation on lithium metal anodes. This suggests more holistic and optimized techniques, or their combinations, may lead to effective polysulfide suppression and successful commercialization of the lithium sulfur battery. Supplementary research explores broader impact of synthesized carbon applications in lithium sulfur batteries. Pyrolysis synthesis processes are evaluated for health and environment impacts using optical by–product sizing and life cycle analysis, respectively. In the context of pyrolytic synthesis of carbon microsheets, micro and nano-sized carbonaceous particulate by–products released during synthesis must be collected to minimize health exposure risks. The environmental impact of this synthesis process is a function of mode of oxygen deficiency, that is, whether pyrolytic atmosphere is facilitated by vacuum or inert gas stream. Finally, submicron carbon spheres, a carbon morphology produced by pyrolysis of sonochemically-synthesized polymer spheres, demonstrate gravimetric capacity which is a strong function of microstructure (i.e., pore distribution, crystallite size, structural disorder). In turn, microstructural properties are determined by synthesis temperature, a dimension of synthesis pathway

Energy, Science and Technology 2015. The energy conference for scientists and researchers. Book of Abstracts, EST, Energy Science Technology, International Conference & Exhibition, 20-22 May 2015, Karlsruhe, Germany

We are pleased to present you this Book of Abstracts, which contains the submitted contributions to the "Energy, Science and Technology Conference & Exhibition EST 2015". The EST 2015 took place from May, 20th until May, 22nd 2015 in Karlsruhe, Germany, and brought together many different stakeholders, who do research or work in the broad field of "Energy". Renewable energies have to present a relevant share in a sustainable energy system and energy efficiency has to guarantee that conventional as well as renewable energy sources are transformed and used in a reasonable way. The adaption of existing infrastructure and the establishment of new systems, storages and grids are necessary to face the challenges of a changing energy sector. Those three main topics have been the fundament of the EST 2015, which served as a platform for national and international attendees to discuss and interconnect the various disciplines within energy research and energy business. We thank the authors, who summarised their high-quality and important results and experiences within one-paged abstracts and made the conference and this book possible. The abstracts of this book have been peer-reviewed by an international Scientific Programme Committee and are ordered by type of presentation (oral or poster) and topics. You can navigate by using either the table of contents (page 3) or the conference programme (starting page 4 for oral presentations and page 21 for posters respectively)

MC 2019 Berlin Microscopy Conference - Abstracts

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2019", die vom 01. bis 05.09.2019, in Berlin stattfand

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018