1,720,992 research outputs found
Anti-Site Reordering in LiFePO4: Defect Annihilation on Charge Carrier Injection
No full textDefects critically affect the properties of
materials. Thus, controlling the defect concentration often
plays a pivotal role in determining performance. In lithium
rechargeable batteries, the operating mechanism is based on
ion transport, so large numbers of defects in the electrode
crystal can significantly impede Li ion diffusion, leading to
decreased electrochemical properties. Here, we introduce a
new way to heal defects in crystals by a room-temperature
electrochemical annealing process. We show that defects in
olivine LiFePO4, an important cathode material, are
significantly reduced by the electrochemical recombination of Li/Fe anti-sites. The healed LiFePO4 recovers its high-power
capabilities. The types of defects in LiFePO4 and recombination mechanisms are discussed with the aid of first-principles
calculations.119201sciescopu
Highly Stable Iron- and Manganese-Based Cathodes for Long-Lasting Sodium Rechargeable Batteries
No full textThe development of long-lasting and low-cost rechargeable batteries lies at the heart of the success of large-scale energy storage systems for various applications. Here, we introduce Fe- and Mn-based Na rechargeable battery cathodes that can stably cycle more than 3000 times. The new cathode is based on the solid-solution phases of Na4MnxFe3-x(PO4)(2)-(P2O7) (x = 1 or 2) that we successfully synthesized for the first time. Electrochemical analysis and ex situ structural investigation reveal that the electrodes operate via a one phase reaction upon charging and discharging with a remarkably low volume change of 2.1% for Na4MnFe2(PO4)(P2O7), which is one of the lowest values among Na battery cathodes reported thus far. With merits including an open framework structure and a small volume change, a stable cycle performance up to 3000 cycles can be achieved at 1C and room temperature, and almost 70% of the capacity at C/20 can be obtained at 20C. We believe that these materials are strong competitors for large-scale Na-ion battery cathodes based on their low costs, long-term cycle stability, and high energy density. © 2016 American Chemical Society115141sciescopu
Lithium-excess olivine electrode for lithium rechargeable batteries
No full textLithium iron phosphate (LFP) has attracted tremendous attention as an electrode material for next-generation lithium-rechargeable battery systems due to the use of low-cost iron and its electrochemical stability. While the lithium diffusion in LFP, the essential property in battery operation, is relatively fast due to the one-dimensional tunnel present in the olivine crystal, the tunnel is inherently vulnerable to the presence of FeLi anti-site defects (Fe ions in Li ion sites), if any, that block the lithium diffusion and lead to inferior performance. Herein, we demonstrate that the kinetic issue arising from the FeLi defects in LFP can be completely eliminated in lithium-excess olivine LFP. The presence of an excess amount of lithium in the Fe ion sites (LiFe) energetically destabilizes the FeLi-related defects, resulting in reducing the amount of Fe defects in the tunnel. Moreover, we observe that the spinodal decomposition barrier is notably reduced in lithium-excess olivine LFP. The presence of LiFe and the absence of FeLi in lithium-excess olivine LFP additionally induce faster kinetics, resulting in an enhanced rate capability and a significantly reduced memory effect. The lithium-excess concept in the electrode crystal brings up unexpected properties for the pristine crystal and offers a novel and interesting approach to enhance the diffusivity and open up additional diffusion paths in solid-state ionic conductors. © 2016 The Royal Society of Chemistry112121sciescopu
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
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