1,720,986 research outputs found
Single-ion-conducting nanocomposite polymer electrolytes based on PEG400 and anionic nanoparticles: Part 1. Synthesis, structure and properties
No full textThe synthesis and the properties of single-ion-conducting nanocomposite polymer electrolytes (nCPEs) are described. The nCPEs are obtained by doping polyethylene glycol 400
(PEG400) with different amounts of a fluorinated TiO2 -based nanofiller (LiFT) that is surface-functionalized with Li+ cations. Electrolytes with general formula [PEG400/(LiFT)y] and y 1⁄4 n Ti /n PEG ranging from 0 to 26.4 are obtained. The materials are characterized by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), Thermogravimetric
Analysis (TGA), Differential Scanning Calorimetry (DSC), and Fourier-Transform Infrared Spectroscopy in both the medium (FT-MIR) and far infrared (FT-FIR). In the [PEG400/(LiFT)y]
electrolytes the concentration of LiFT nanofiller strongly affects the thermal stability and transitions of PEG400. In addition, vibrational measurements allow us to reveal the interactions occurring between: (a) different PEG400 chains; (b) PEG400 and Liþ cations; and (c) PEG400 and LiFT nanoparticles (NPs). On LiFT nanofiller concentration, results show three compositional regions in [PEG400/(LiFT)y] electrolytes which are correlated to the presence of three different interaction environments between LiFT NPs and PEG400 chains
Interplay Between Structure and Conductivity in Imidazolium-based Ionic Liquids as Electrolytes for Magnesium Batteries
No full textThe search for new electrolytes is one of the most challenging aspects in the development of secondary batteries based on Li and Mg ions.
The state of the art for Mg electrolytes is mainly constituted by organo-Mg compounds; in general, they show good Mg deposition and dissolution performance, high Coulombic efficiency and in some cases a wide electrochemical stability window. The main drawback of this class of materials is associated with their dissolution in ethereal-based solvents characterized by a high vapor pressure and flammability.
Nevertheless, the use of high-boiling solvents is known to lead to: (a) a decrease in the electrolyte conductivity; and (b) a decrease in the electrode reaction rate, which limits their practical applicability [2]. Ionic liquids (ILs) are salts that are molten at room temperature. ILs are also characterized by: (a) negligible vapor pressure; (b) high thermal stability; and (c) low flammability.
Only a few examples of the applicability of ILs as electrolytes for secondary Mg batteries are reported in the literature. Several issues regarding the conductivity mechanisms, formation of the solid-electrolyte interface (SEI) and long-term performance of these systems are still open questions.
From a fundamental point of view, the interplay between the ILs nanostructure and the conductivity is a crucial point to clarify the effect of the IL matrix on the migration mechanism of Mg2+ ions. In this report, a comparison between two Mg electrolytes based on Ethyl-methylimidazolium tetrafluoroborate (EMImBF4) and Ethyl-methylimidazolium chloride/AlCl3 (EMImCl/(AlCl3)1.5) ILs is proposed. Both ionic liquids are doped with different amounts of δ-MgCl2 , to achieve a sufficient conductivity of Mg ions.
The correlation between structure, thermal properties and conduction mechanism of the resulting EMImBF4/(δ-MgCl2) and [EMImCl/(AlCl3)1.5]/(δ-MgCl2)x is investigated by a variety of techniques: (a) FT-MIR and FIR at different temperatures; (b) differential scanning calorimetry (DSC); and (c) broadband electrical spectroscopy (BES).
BES measurements were undertaken to elucidate the electrical response of the electrolytes in terms of dielectric and polarization phenomena. At T Tm , three and four interdomain polarization events are detected respectively for EMImBF4 and [EMImCl/(AlCl3)1.5]. These polarization events are associated with the presence of cation and anion nanocluster aggregates with different permittivities
A single ion-conducting polymer electrolyte based on PEO and anionic nanoparticles: electrical and NMR characterization
No full textWe report on electrical properties of fluorine-functionalized nanoscopicTiO2and its reaction with molten Li, which produces a single ion Li conductor. It is believed that the fluorines and the lithiums are concentrated in a 2-4 nm shell around the TiO2 core, based on XRD and vibrational spectroscopic evidence.Mixing this material with PEO results in a polymer electrolyte with favorable mechanical as well as electrical properties. For example, a sample containing ~10 wt% PEO demonstrates an ionic conductivity of 1.5 x 10-5 S/cm at 20oC and 1.0 x 10-4 S/cm at 80oC, with a Li+ transference number of unity. Additional characterization, including electrochemical stability window, exchange current density, and variable temperature broadband electrical spectroscopy (covering a frequency range of 10-2 to 107 Hz) Multinuclear (1H, 7Li and 19F) solid state NMR measurements, including spectra, relaxation, and transport as a function of PEO/TiO2:F,Li ratio will be presented
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
Single-ion-conducting nanocomposite polymer electrolytes based on PEG400 and anionic nanoparticles: Part 2. Electrical characterization
No full textMolecular relaxation and polarization phenomena of twelve single-ion-conducting nanocomposite polymer electrolytes (nCPEs) are studied using Broadband Electrical Spectroscopy (BES). The electrolytes are obtained by combining PEG400 oligomers with increasing amounts of anionic nanofiller comprised of fluorinated-TiO2 associated with Li+ cations (LiFT (R)), resulting in [PEG400/(LiFT)(y)] systems with 0<=y<=26.4. This new class of [PEG400/(LiFT)(y)] electrolytes allows us to achieve a significant single-ion conductivity (1.1.10(-5) S cm(-1) at 30 degrees C for n(Li)/n(O) = 0.113) without the addition of lithium salts. To the best of our knowledge, this is the highest conductivity value reported for this class of electrolytes. This study, in conjunction with the results reported in Part 1, leads us to hypothesize a conduction mechanism in terms of two types of long-range charge-transfer processes. The first charge-transfer occurs at the interface between the filler nanoparticles and filler-PEG domains, while the second occurs through the PEG400 matrix with the assistance of polymer segmental motion. The measured Li+ transference numbers confirm that the studied materials are single-ion conductors
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
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