1,721,019 research outputs found
Electrode and Electrolyte Materials for the Development of High Voltage Lithium-ion Batteries and Secondary Batteries Based on Alkali and Alkaline-earth Ions
Full text linkThe research activity described in this thesis has been focused on the development and study of novel electrolyte and electrode materials for application in Lithium and Magnesium secondary batteries. The proposed materials belong to the “beyond Li-ion” class of compounds, where systems exceeding the energy density values of classic Li-ion batteries or completely innovative chemistries are presented.
Three different classes of electrolytes have been prepared and studied. A solid polymer electrolyte has been obtained by a lithium functionalization of a poly(vinyl alcohol-co-vinyl acetate), forming lithium alkoxide functional groups. In this way, the counter anion of Li+ was the overall polymer chain, giving rise to a single lithium ion conductivity. However, the room-temperature conductivity value observed for this material was quite low (4.6·10-10 S·cm-1). By ionic liquid (IL) doping of the
solid polymer electrolyte, we have obtained a double effect: i) lithium cations have been exchanged by the cations of IL, enhancing the mobility of the active species; and ii) the flexibility of polymer chains has been increased by the plasticizing effect of the IL. Thus, a room temperature conductivity of 1.3·10-5 S·cm-1 has been reached, maintaining a high value of Li transference number (0.59). By reacting glycerol with different quantities of lithium hydride, a new family of lithium-ion conducting electrolytes has been synthetized. In these electrolytes the lithium glycerolate component acts as a large and flexible macro-anion which is able to provide a singleion conductivity to the material (2.0∙10-4 at 30 °C and 1.6∙10-2 S∙cm-1 at 150 °C). In the last class of electrolytes, ionic liquid-based materials for magnesium batteries, the cation and anion replacement effect on the structure, conductivity mechanism, and electrochemical performances has been studied. The proposed materials have exhibited a conductivity value between 10-3 and 10-4 S∙cm-1, an overpotential in the magnesium deposition lower than 50 mV vs. Mg/Mg2+, an anodic stability up to +2.35 V vs. Mg/Mg2+, and a coulombic efficiency up to 99.94 %.
In the second part of this Ph.D. project, the improvement of the electrochemical features of various cathode materials has been studied. In the first case, it has been found that, by adding CuCO3 to the precursors, segregated CuO particles have been formed. The presence of these particles has improved the charge-transfer kinetics during the charge/discharge processes of the cathode material. On the other hand, graphite addition to the precursors has been found to improve the
elasticity of the 3D structure of the cathode backbone. Thus, an increased structural flexibility that facilitates the percolation of lithium ions along the 1D channels of the cathode material has been observed. In the second approach, the improvement of the electron conductivity of a high-voltage cathode has been gauged by V, Nb, or Ta insertion within its olivine structure. This approach has allowed for an improved kinetic and reversibility of Li+ insertion reaction. The specific capacity reached by these cathodes was equal to 149 mAh∙g-1. The last cathode material has been implemented in a magnesium secondary battery device. A graphene oxide surface functionalization of vanadium-based nanoparticles has been obtained thanks to electrostatic interactions through ammonium bridges. This functionalization has allowed for the obtaining of a material able to: a) sustain extremely high current rates (1000 mA∙g-1, 1700 mW∙g-1 of specific power); and b) give reasonable specific capacity values (72 mAh∙g-1)
Into the wild? Preferences of frequent mountain and forest recreationists for accessibility and mobility
Full text linkOutdoor recreation in forests and mountains is growing in popularity globally and especially in industrialised countries. Outdoor recreation has benefits both for practitioners’ body and mental health, and local communities for rev-enue opportunities. This study focuses on frequent outdoor recreationists, who are members of the Italian Alpine Club (CAI), by exploring: (i) the infra-structure preferences for accessing and moving in mountain and forest areas; (ii) possible associations between socio-demographic characteristics and frequency of mountain and forest visits; and (iii) possible relationships between sociodemographic characteristics and the frequency of use of mountain bike and e-bike. Ordinal logistic regression models were used to achieve the second and third objectives. Results show that CAI recreationists tend to prefer lim-ited or no services for accessing mountains. They rarely use e-bikes and mountain bikes and their frequency of visits to mountains are influenced by educa-tional attainment and occupation. Results can provide valuable information for land management decision processes regarding accessibility infrastructures. Future research should address more occasional mountain and forest recre-ationists and local communities
Ionic Liquid-Based Electrolytes for Secondary Mg batteries
No full text(Invited Presentation) The development of innovative electrolytes is one of the most crucial targets in order to devise secondary batteries running on alkaline- and alkaline-earth elements characterized by a high specific energy and power and an extensive cyclability, able to provide power for a wide range of applications ranging from portable electronic devices to light-duty electric vehicles. The electrolytes must satisfy very demanding requirements, including: (a) easy migration of the alkaline- and alkaline-earth cations between the electrodes of the battery; (b) high compatibility with all the other functional materials used in the assembly of the device; (c) wide potential window and excellent stability.1
This report summarizes the preparation and characterization of innovative families of ionic-liquid (IL) -based electrolytes meant to address these issues, thus opening new and promising avenues for the research in this field. The electrolytes are based on δ-MgX2 magnesium salts, AlX3 and 1-Ethyl-3-methylimidazoliumX ILs (with X=Cl-, I- or BF4-). 2,3,4
The resulting electrolytes are suitable for application in secondary Mg batteries, and demonstrates: (1) a conductivity at room temperature higher than 10-3 S/cm; and (2) good electrochemical performance. The chemical composition of the electrolytes is analyzed by ICP-AES and microanalysis. The thermal properties are investigated by HR-TG and DSC measurements. The structure and the interactions in materials is studied by vibrational spectroscopies (FT-MIR and –FIR). The electric response is elucidated by Broadband Electrical Spectroscopy (BES). Results allow to propose a conduction mechanism and to define the interplay existing between structural, thermal transitions and electric properties of proposed innovative electrolytes.
(1) Di Noto, V.; Lavina, S.; Giffin, G. A.; Negro, E.; Scrosati, B. Electrochim. Acta 2011, 57, 4–13.
(2) Bertasi, F.; Hettige, C.; Sepehr, F.; Bogle, X.; Pagot, G.; Vezzù, K.; Negro, E.; Paddison, S. J.; Greenbaum, S. G.; Vittadello, M.; Di Noto, V. ChemSusChem 2015, 8, 3069–3076.
(3) Bertasi, F.; Sepher, F.; Pagot, G.; Paddison, S. J.; Noto, V. Di. Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201601448.
(4) Bertasi, F.; Hettige, C.; Greenbaum, S. G.; Vittadello, M.; Di Noto, V. Ionic Liquid Comprising Alkaline Earth Metal. PCT Patent App. No. WO2015/069871, 2014
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
Critical Analysis of MXene Production with In-Situ HF Forming Agents for Sustainable Manufacturing
Full text linkMXenes are an emerging class of materials considered for many applications, such as sensors, catalysis, energy storage devices. The main obstacle towards their massive implementation is the synthesis requiring the direct use of HF as etching agent. The development of alternative synthetic routes exploiting in-situ forming HF agents is the main strategies to overcome this limitation. In this study four different etching methods based on the use of NH4HF2, NaF−HCl, HBF4, and NaBF4−HCl are compared to produce Ti3C2Tx from Ti3AlC2 towards the application of MXenes in sodium ion batteries. Three of such etching methods have already been reported while one is here presented for the first time. The structural analysis of the obtained products is based on X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. All the materials have been tested in half-cell configuration vs. Na; the charge/discharge profiles and the C-rate tests are discussed and related to specific structural features. Overall, the results reveal that the MXene obtained using the HBF4 etching agent under mild conditions is comparable both in structure and functional properties to the benchmark material, i. e., the MXene produced using HF at 5 % concentration. Indeed, the MXene synthetized with the HBF4 presents the lowest mean voltage and potential hysteresis and shows the highest first cycle efficiency (69.7 %), overcoming the performance of the MXene produced with 5 % HF (67 %). This study proves the possibility to produce MXene with a more sustainable route
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