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Interaction between High-Voltage Cathode Materials and Ionic Liquids for Novel Li-Ion Batteries
No full textThe fast-growing market on electronic portable devices is possibly due to the development of Li-ion batteries. Besides, such batteries are the most promising candidates as energy storage media in (hybrid) electric vehicles, in the near future. However, improvements on electrochemical performances and on safety need to be achieved. With respect to energy density, positive electrodes with a high voltage vs. Li/Li+ are favourable, provided they are stable against the rest of the battery materials, thereby reflecting safety issues. Regarding this safety, misuse of a Li-ion battery often leads to promoting side reactions between the electrodes and the electrolyte. This then results in gas formation, packaging breaking and fire evolution due to exposure to air by reaction of highly reactive materials with oxygen. Therefore, novel electrolytes, such as ionic liquids are proposed, which may significantly reduce these parasitic reactions with the electrodes, and further allows the battery to operate at higher voltages due to its high voltage stability window. In this respect, the presented work concerns the research on a high voltage positive electrode material in combination with ionic liquids as electrolyte solvents. In Chapter 1, a brief history about the Li-ions intercalation concept, which is at the basis of Li-ion batteries, is introduced. Afterwards, the most important components of a Li-ion battery are discussed. Examples of negative and positive electrodes are shown, emphasizing the reasons why nano structures are to preferred in the beginning. Besides, ionic liquids are introduced and explained, as possible candidates as electrolytes or electrolyte additives. In Chapter 2, the synthesis of magnesium-doped nickel-based high-voltage positive electrode materials (LiMg0.05Ni0.45Mn1.5O4) via four different synthesis routes is shown: a solid-state method; a sol-gel method; a xerogel route and an auto-ignition method. A preliminary structural analysis is performed with XRD and SEM, showing the crystallinity and the agglomerations of the powders, respectively. Furthermore, TEM analysis on the powders showed agglomerated nanoparticles ranging from 10 nm to 200 nm. Finally, electrodes made with the synthesized materials are tested with a charge-discharge galvanostatic technique, showing the existence of impurity - mainly LiMn2O4, increasing from sol-gel, xerogel, to auto-ignition. It also gives promising results in terms of capacity retention at high charge-discharge rates. In Chapter 3, the powders made via the auto-ignition method, which showed the most promising result in the previous chapter, were further studied with an in situ charge-discharge galvanostatic technique coupled with X-ray absorption spectroscopy (XAS), which proved the presence of manganese ions in LiMg0.05Ni0.45Mn1.5O4 being reduced and oxidized, explained by the presence of manganese-rich nanodomains within the particles. Chapter 4 concerns certain safety issues of Li-ion batteries. Here, ionic liquids as possible novel electrolyte additives are studied as possible candidates to contribute to safer batteries. In this respect, the CO2-adsorption ability of the ionic liquid N-buthyl-N-methylimidazolium tetrafluoroborate ([BMIm][BF4]) is tested with a Cailletet apparatus. The interaction between ionic liquids and CO2 has been analyzed from a thermodynamical point of view. The most common theories to study the gas and gas-liquid mixtures were introduced, together with a novel approach based on the Langmuir adsorption theory. In contrast to most models, the Langmuir isotherm has a very general approach: the solvent is seen as a storage medium, in which the number of available sites depends on the number of available solvent species which adsorb gas molecules. The Langmuir model can be used in a wide concentration range and the dissolution energies, together with the entropy values, can be calculated. In the case of the presence of a lithium salt, the Langmuir model could easily be extended to the Langmuir-Hinselwood model, so as to take the adsorption/association of lithium ions to the solvent sites into account. In the [BMIm][BF4] + CO2 system studied, both the Langmuir and Langmuir-Hinselwood models could be very well used to explain the results. The obtained solubility energy and entropy do not differ so much from the evaporation energy and entropy of pure CO2, showing small solvent-CO2 interaction. When to the mixture [BMIm][BF4] + CO2 a lithium salt, i.e., LiBF4 is added, a Langmuir-Hinselwood isotherm describes the obtained data very well. However, addition of the salt reduces the amount of CO2 that can be dissolved. Actually, the results of applying this model show that the lithium ions rather stay at the anion, preventing dissociation of the salt in this IL. Consequently, it can be argued that the lithium salt, even if undissociated provides sites which can be exploited by either the lithium ions or by the CO2 molecules, as they contribute to the equilibrium equations. In Chapter 5, the electrochemical behavior of PYR14TFSI + LiTFSI is studied in relation to electrodes made from LiMg0.05Ni0.45Mn1.5O4 (LMNMO). In this respect, cyclic voltammetry (from 3.5 to 4.9 V) and electrochemical impedance spectroscopy have been used. For further comparison, also batteries made with a commercially available electrolyte has been exploited. The cyclic voltammetry showed slower redox processes regarding the cell with the ionic liquid. Another cell with the ionic liquid has been tested at a lower cycle scan rate up to 5.2 V, proving that the current is significantly hampered by kinetics in this ionic liquid. However, it showed the stability of the system a higher voltages compared to the battery with the commercial electrolyte. The electrochemical impedance spectroscopy (EIS) measurements of the system with the ionic liquid showed a process which was not present in the cell with the commercial electrolyte, possibly introduced by the slow kinetics. However, in symmetrical cells with metallic lithium at both sides, it was possible to ascribe the EIS features of the cell with the commercial electrolyte to the lithium-electrolyte interface. On the other hand, EIS measurements of the battery with the ionic liquid reveals the presence of a layer also at the LMNMO-electrolyte side, which continuously grows upon cycling. In summary, while the positive electrode materials can be employed in novel Li-ion batteries, provided they have a higher purity, the use of ionic liquids as electrolytes is still hampered by their poor electrochemical performances. Nevertheless, they are still promising, due to their electrochemical stability at high voltages . Besides, thanks to their high gas-adsorption ability, ionic liquids can be taken into consideration as electrolyte additives, for safety purposes.DelftChemTechApplied Science
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
An Electrochemical Study of High Voltage Cathode Materials in Contact with Mixtures of Ionic Liquids and Commercial Electrolytes
No full textChemE/Chemical EngineeringApplied Science
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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