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A versatile method of preparation of carbon-rich LiFePO4: A promising cathode material for Li-ion batteries
No full textLiFePO4/C composites were prepared by using organo-phosphonates as a single source of iron, phosphorus and carbon. Fe[RPO3](H2O)-H-. (R = methyl or phenyl group) was heated in the presence of Li2CO3 at high temperature and under nitrogen flux. Elemental carbon is formed on the surface of LiFePO4 particles leaving a carbon coated material. The materials were characterized by elemental analysis, TG/DTA, XRPD and SEM. Coulometric titration showed that some impurities are present in the final products. The material prepared starting from the iron(II) phenyl phosphonate showed higher discharge capacity, specific energy, and specific power. The specific energy evaluated at C/10 rate was about 520 Wh kg(-1). The specific power calculated at 3C rate was in excess at 1400 W kg(-1) while the specific energy was about 63% of the energy delivered at C/10. No capacity fading was observed upon cycling. The performance of LiFePO4 prepared from the iron(H) methyl phosphonate was found to be slightly lower, probably due to the lower carbon content. (c) 2005 Elsevier B.V. All rights reserved
A Versatile New Synthesis of Carbon Rich LiFePO4 Enhancing Its Electrochemical Properties.
No full textIn this contribution we report a new reproducible synthetic route to prepare LiFePO4/C composites. As starting materials an intimate stoichiometric mixture of lithium carbonate and an hybrid organic-inorganic Fe(II) organophosphonate, i.e. Fe[(RPO3)(H2O)] (R = methyl or phenyl group) were used. The idea behind it was to provide a single source for phosphorus, iron and carbon. The hybrid organic-inorganic compounds of formula Fe[(CH3PO3)(H2O)] and Fe[(C6H5PO3)(H2O)] are easy to handle because they are stable to the air and moisture [1,2]. The mixture of Li2CO3 and Fe[(RPO3)(H2O)] (R=CH3-, C6H5) was heated in a tubular furnace under N2 gas at temperatures above 600°C for at least 16 h [3]. Nano-crystalline LiFePO4 samples were obtained. One of the most interesting aspects of this new synthetic method is the formation of elemental carbon during the decomposition of Fe(II) methyl- and phenylphosphonate. In the final LiFePO4 samples amounts of 2.5 wt. % C in the case of Fe[(CH3PO3)(H2O)] precursor and 12 wt. % C in the case of Fe[(C6H5PO3)(H2O)] precursor have been found. This means that part of the theoretical carbon content in the reaction mixtures (8.8 wt. % and 29.6 wt. % respectively) is lost during the heating process. TG measurements on the initial precursor mixtures showed in both cases the elimination of the water molecules coordinated to the Fe(II) ions at temperatures up to 200°C, while at higher temperatures (200-800°C) weight losses of 30 and 45 % have been observed. An exothermic effect at 400°C (Fe[(CH3PO3)(H2O)]) and 450°C (Fe[(C6H5PO3)(H2O)]) has been evidenced in the DTA curves and might be related to the initial formation of Li2O from the corresponding carbonate followed by the decomposition of the organophosphonate precursor and final formation of LiFePO4. The exact mechanism of the reaction is still under investigation. The crystalline LiFePO4 powders were further characterized by X-ray powder diffraction analysis (XRPD) and Scanning Electron Microscopy (SEM). Our LiFePO4 samples crystallize in the orthorhombic space group Pnma and the LiFePO4 phase consists of spherical aggregates of about 0.2 μm diameter. Composite cathode tapes were made by roll milling a mixture of 75 wt. % active material and 10 wt. % binder (Teflon, DuPont). Carbon (KJB Carbon) was added until 15 wt. % final carbon content was reached. Electrodes disks of typically diameter of 10 mm were punched and the electrode weight ranged from 7.4 to 10.7 mg. T-shaped battery cells with lithium metal as counter and reference electrode were used for electrochemical characterization. The cells, filled with a 1M solution of LiPF6 in ethylene carbonate / diethyl carbonate (1:1), were automatically cycled by means of a battery cycler (Maccor 4000). Composite cathode preparation, cell assembly, tests and storage were performed in the dry room (R.H. < 0.1 % at 20°C). To test the effect of different discharge rates, a cell was subjected to various discharge rates, i.e. C/10, 1C, 3C, 10C, 20C and 30C. The cell was always charged using the same procedure to insure identical initial conditions: a constant current step at 1C rate until the voltage reached 4.0 V, followed by a constant voltage step until the current fell below C/10 rate. Figure 1 shows the Ragone plot for the cell discharged at different rates. The specific energy and specific power are based on the weight of the active material. The specific energy calculated at C/10 rate was about 550 Wh kg-1. The specific power calculated at 30C rate was in excess at 14,000 W kg-1 while the specific energy was about 28 % of the energy delivered at C/10. The excellent electrochemical performance of the LiFePO4/C composites can be ascribed to the tailored synthesis addressed to enhance the electrochemical properties of the material. The main advantage of this synthetic route is the formation of elemental carbon from the organic constituent of the precursor. The carbon particles interact with the LiFePO4 grains just during their formation providing a good electronic contact between the grains and the carbon added for the composite electrode fabrication. The low particle size and the enhanced surface conductivity both result in the outstanding performance of the LiFePO4/C cathode. In conclusion, electrodes made of the cathode material reported here showed very high specific energy, specific power and capacity retention upon cycling. The new synthetic method is very simple and the Fe(II) organophosphonate precursors are air-stable. The good electrochemical performance of LiFePO4/C indicates that the reported method is very promising for developing high power lithium-ion batteries.
Figure 1. Ragone plot for the cell discharged at different rates. LiFePO4 was prepared starting from the Fe(II) phenylphosphonate. The cathode loading of LiFePO4 was 7.1 mg cm-2. Electrode area was 0.16 cm2.
ACKNOWLEDGEMENTS
We thank the Ministero Italiano per la Ricerca Scientifica e Tecnologica (MIUR) for financial support.
REFERENCES
1. C. Bellitto, F. Federici, M. Colapietro, G. Portalone, and D. Caschera, Inorg. Chem., 41, 709 (2002).
2. A. Altomare, C. Bellitto, S.A. Ibrahim, and M.R. Mahmoud, Inorg.Chem., 39, 1803 (2000).
3. Italian Patent no. RM2003A000048 (2003)
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
A Novel 1D-AF Hybrid Organic-Inorganic Chromium(II) Methyl Phosphonate Dihydrate: Synthesis, X-Ray Crystal and Molecular Structure, and Magnetic Properties
No full textLight-blue crystals of chromium(II) methyl phosphonate dihydrate, [Cr(CH(3)PO(3))(H(2)O)].H(2)O, were obtained in water by mixing filtered solutions of methylphosphonic acid and chromium(II) chloride in the presence of urea in an inert atmosphere. The compound was characterized by elemental analysis, TGA-DSC, X-ray crystallography, magnetic measurements, and UV-visible and FT-IR spectroscopies. The crystal and molecular structures (orthorhombic Pnma (no. 62): a = 4.4714(5) A, b = 6.8762(7) A, c = 19.180(2) A, Z = 4) have been solved using single-crystal X-ray diffraction. The chromium(II) ion is six-coordinated by oxygens (4 + 2) to form an elongated octahedron, with the four equatorial oxygen atoms belonging to [-PO(3)](2-) phosphonate groups. This stereochemistry of the Cr(II) ion (high-spin d(4) electronic configuration) is ascribed to the Jahn-Teller effect. The [CrO(6)] chromophore, the [CH(3)PO(3)](2-) anions, and the water molecules build a novel one-dimensional (1D) metal(II) oxide chain, anchored to each other within the ab plane by two oxygens of the phosphonate ligand. Within the chain, each Cr(2+) ion is connected through double oxygen bridges to its two neighbors, forming edge-sharing octahedra running along the b axis. The chains are further connected with the adjacent chains by phosphonate [-PO(3)](2-) groups of the ligand, forming an inorganic layer that alternates along the c axis of the unit cell with bilayers, consisting of methyl groups and water of crystallization. The thermal variation of the magnetic susceptibility follows the Curie-Weiss law, with a large negative Weiss constant, theta = -60 K, indicating the presence of antiferromagnetic AF exchange interactions between neighboring Cr(II) ions. The magnetic behavior and the magnetic dimensionality have been analyzed in terms of Fisher's classical limiting form of the Heisenberg chain theory, and a value of J = -9.3 cm(-1) was found. The negative value of the intra-chain exchange constant coupling J confirms the presence of an AF coupling. No sign of long-range magnetic ordering down to 2 K (the lowest measured temperature) is observed, in agreement with the predominant one-dimensional character of the exchange interactions
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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