1,721,021 research outputs found
“Alloy based anodes for sustainable post Lithium-ion batteries”
No full textIn questa tesi di dottorato sono stati investigati nuovi materiali ibridi nanostrutturati a base di GeFe2O4 da utilizzare come anodi in batterie a ioni di sodio (SIBs). Le caratteristiche strutturali e morfologiche dei materiali sono state analizzate e correlate con le prestazioni elettrochimiche. Inoltre, è stato studiato l’effetto dell’introduzione nella struttura cristallina di elementi dopanti come Sn, Mg e Mn, ottenendo prestazioni elettrochimiche promettenti particolarmente a bassi C-rate. Elettrodi self-standing contenti particelle di GeFe2O4 disperse in matrice di nanofibre di carbonio sono inoltre stati realizzati, migliorando la robustezza e le prestazioni degli elettrodi nelle SIBs. Parallelamente, l'attività di ricerca è stata focalizzata anche sullo studio di compositi Sn/carbonio ottenuti attraverso vari metodi di sintesi, con l'obiettivo di ridurre l'espansione delle particelle di Sn durante la sodiazione, che è il principale problema che porta al corto circuito della cella. A tal proposito, sono stati progettati nuovi elettrodi autoportanti utilizzando differenti substrati carboniosi.In this PhD thesis, new hybrid nanostructured materials based on GeFe2O4 were investigated to be used as anodes in sodium-ion batteries (SIBs). The structural and morphological characteristics of the materials were analyzed and correlated with their electrochemical performance. Furthermore, the effect of introducing dopant elements such as Sn, Mg, and Mn into the crystalline structure was studied, achieving promising electrochemical performance at low C-rates. Self-standing electrodes containing GeFe2O4 particles dispersed in a carbon nanofiber matrix were also fabricated improving the robustness and performance of the electrodes in SIBs. In parallel, the research activity focused on the study of Sn/carbon composites obtained through various synthesis methods, aiming to reduce the expansion of Sn particles during sodiation. In this regard, new self-standing electrodes were designed using different carbonaceous substrates
The Renewed Interest on Brunogeierite, GeFe2O4, a Rare Mineral of Germanium: A Review
No full textGeFe2O4, also known as brunogeierite, is a rare mineral of germanium. It has a normal spinel structure and, as with many other spinels, amazing functional properties thanks to its peculiar structural features. In the past, its spectroscopic, optical, magnetic and electronic properties were determined; then, for many years, this compound was left behind. Only recently, a renewed interest in this oxide has arisen, particularly for its application in the electrochemical field. In this review paper, the crystal structure of GeFe2O4 will be described, as well as the synthesis methods required to obtain single crystals or polycrystalline powders. Its spectroscopic, magnetic, optical and electrical properties will be reported in detail. Then, successful applications known so far will be described: its use as anode in Lithium Ion and Sodium Ion Batteries and as electrocatalyst for urea oxidation reaction
ZnFe<sub>2</sub>O<sub>4</sub>, a Green and High-Capacity Anode Material for Lithium-Ion Batteries: A Review
No full textFerrites, a broad class of ceramic oxides, possess intriguing physico-chemical properties, mainly due to their unique structural features, that, during these last 50–60 years, made them the materials of choice for many different applications. They are, indeed, applied as inductors, high-frequency materials, for electric field suppression, as catalysts and sensors, in nanomedicine for magneto-fluid hyperthermia and magnetic resonance imaging, and, more recently, in electrochemistry. In particular, ZnFe2O4 and its solid solutions are drawing scientists’ attention for the application as anode materials for lithium-ion batteries (LIBs). The main reasons are found in the low cost, abundance, and environmental friendliness of both Zn and Fe precursors, high surface-to-volume ratio, relatively short path for Li-ion diffusion, low working voltage of about 1.5 V for lithium extraction, and the high theoretical specific capacity (1072 mAh g−1). However, some drawbacks are represented by fast capacity fading and poor rate capability, resulting from a low electronic conductivity, severe agglomeration, and large volume change during lithiation/delithiation processes. In this review, the main synthesis methods of spinels will be briefly discussed before presenting the most recent and promising electrochemical results on ZnFe2O4 obtained with peculiar morphologies/architectures or as composites, which represent the focus of this review
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
Synergistic Effect of Polymorphs in Doped NaNi0.5Mn0.5O2 Cathode Material for Improving Electrochemical Performances in Na-Batteries
No full textLayered NaNi0.5Mn0.5O2, employed as cathode materials in sodium ion batteries, is
attracting interest due to its high working potential and high-capacity values, thanks to the big
sodium amount hosted in the lattice. Many issues are, however, related to their use, particularly, the
complex phase transitions occurring during sodium intercalation/deintercalation, detrimental for
the structure stability, and the possible Mn dissolution into the electrolyte. In this paper, the doping
with Ti, V, and Cu ions (10% atoms with respect to Ni/Mn amount) was used to stabilize different
polymorphs or mixtures of them with the aim to improve the capacity values and cells cyclability. The
phases were identified and quantified by means of X-ray powder diffraction with Rietveld structural
refinements. Complex voltammograms with broad peaks, due to multiple structural transitions,
were disclosed for most of the samples. Ti-doped sample has, in general, the best performances with
the highest capacity values (120 mAh/g at C/10), however, at higher currents (1C), Cu-substituted
sample also has stable and comparable capacity values
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