1,721,009 research outputs found
A High-Voltage, Multi-Metal LiNi0.35Cu0.1Mn1.45Fe0.1O4Spinel Cathode for Lithium Batteries
No full textA LiNi0.35Cu0.1Mn1.45Fe0.1O4 spinel cathode exploiting the multi-metal approach and operating in a lithium battery at 4.7 V is prepared by co-precipitation of metal oxalates followed by annealing. Our investigation demonstrates that the designed electrode formulation including Ni, Cu, Mn and Fe may actually ensure suitable structural and morphological characteristics, as well as an extended stability in cells operating at 25 C and 55 C. Indeed, the LiNi0.35Cu0.1Mn1.45Fe0.1O4 cathode shows reversible capacities of 108 mAh g-1 at 0.75C and 91 mAh g-1 at 1.5C (where 1C is 147 mA g-1), with a retention between 84% and 80% after 200 cycles and coulombic efficiency values of about 99%. Notably, optimal cathode composition in terms of metals nature and content avoids material degradation upon cycling and enables stable operation in the lithium cell even at a temperature higher than 25 C, with satisfactory retention of the initial capacity of 110 mAh g-1, i.e., 77%, after 200 cycles at 0.5C. Therefore, the strategy adopted herein is considered adequate for allowing practical battery application of the high-voltage spinel cathode
Investigation of Mn and Fe Substitution Effects on the Characteristics of High-Voltage LiCo1- xMxPO4 (x = 0.1, 0.4) Cathodes Prepared by Sol-gel Route
No full textHerein, we provide a fundamental study revealing the substantial changes promoted by manganese and iron substitution for cobalt in a high-voltage LiCoPO4 olivine cathode. Therefore, LiCoPO4, LiCo0.9Fe0.1PO4, LiCo0.6Fe0.4PO4, LiCo0.9Mn0.1PO4, and LiCo0.6Mn0.4PO4 are synthesized by a sol-gel pathway and comparatively investigated in terms of structure, morphology, and electrochemical features in lithium battery. Besides the observed effects on structure, particle size, and metals distribution, the work reveals a gradually enhancing electrode reaction by increasing the Fe content in LiCo0.9Fe0.1PO4 and LiCo0.6Fe0.4PO4, with Co3+/Co2+ and Fe3+/Fe2+ signatures at 4.8 and 3.5 V vs Li+/Li, respectively. On the other hand, the introduction of Mn leads to a progressive electrode deactivation in LiCo0.9Mn0.1PO4 and LiCo0.6Mn0.4PO4 due to an intrinsic hindering of the Mn3+/Mn2+ process at 4.1 V vs Li+/Li. The reasons accounting for such an intriguing behavior are investigated in detail using electrochemical impedance spectroscopy within the potential range of the redox processes. The study reveals that manganese and iron substitutions in the high-voltage olivine have opposite effects on the charge transfer resistance, i.e., detrimental for the former while beneficial for the latter, with remarkable enhancement of the reversible capacity, the Coulombic efficiency, and the cycle life. Such results provide to the scientific community useful information on possible strategies to enhance the emerging LiCoPO4 high-voltage electrode by transition metal substitution
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
Novel Lithium-Sulfur Polymer Battery Operating at Moderate Temperature
No full textA safe lithium-sulfur (Li−S) battery employs a composite polymer electrolyte based on a poly(ethylene glycol) dimethyl ether (PEGDME) solid at room temperature. The electrolyte membrane enables a stable and reversible Li−S electrochemical process already at 50 °C, with low resistance at the electrode/electrolyte interphase and fast Li+ transport. The relatively low molecular weight of the PEGDME and the optimal membrane composition in terms of salts and ceramic allow a liquid-like Li−S conversion reaction by heating at moderately high temperature, still holding the solid-like polymer state of the cell. Therefore, the electrochemical reaction of the polymer Li−S cell is characterized by the typical dissolution of lithium polysulfides into the electrolyte medium during discharge and the subsequent deposition of sulfur at the electrode/electrolyte interphase during charge. On the other hand, the remarkable thermal stability of the composite polymer electrolyte (up to 300 °C) suggests a lithium-metal battery with safety content significantly higher than that using the common, flammable liquid solutions. Hence, the Li−S polymer battery delivers at 50 °C and 2 V a stable capacity approaching 700 mAh gS−1, with a steady-state coulombic efficiency of 98 %. These results suggest a novel, alternative approach to achieve safe, high-energy batteries with solid polymer configuration
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
- …
