1,720,991 research outputs found
L'ordre des métaux de transition dans la phase spinelle LiNi0,5-xMn1,5+xO4 à haut potentiel : caractérisation multi-échelle jusqu'au nanomètre
No full textThe performance of spinel LiNi0.5-xMn1.5+xO4 (LNMO) as positive electrode material in Li-ion batteries strongly depend on its synthesis conditions, Ni/Mn stoichiometry, and the degree of ordering of Ni and Mn. LNMO crystal structure can be described in Fd-3m or P4332 space groups, depending on the extent of this ordering. Understanding the impact of these structural properties on electrochemical performance is challenging due to the interdependent nature of each parameter and the limited spatial resolution of the common characterization techniques. In this study, we demonstrate the synthesis of impurity-free disordered (Fd-3m) platelets of LNMO presenting multiple surface orientations via molten salt synthesis. Thanks to the thin platelet morphology (thickness ~180 nm) achieved, we employed a 4D-STEM electron microscopy tool, newly growing in the battery field, to investigate the transition metal ordering on individual LNMO particles with nanometric spatial resolution for the first time. The unique ability to tune the primary particle morphology, spinel composition and control secondary phase generation enabled us to demonstrate that heterogeneity in the transition metal arrangement on the globally ordered (P4332) LNMO is beneficial for electrochemical performance. Combining electron microscopy analysis with average structural properties obtained through X-ray and neutron diffraction, and with information on the local environments obtained using Raman and 7Li NMR spectroscopies, we dissect the “synthesis-composition-properties” relation for LiNi0.5-xMn1.5+xO4 samples prepared through various annealing steps. This enables the obtention of high-performing (dis)ordered spinel LNMOs with diverse compositions, highlighting how the electrochemical properties can be tailored through structural design.Les performances de la phase spinelle LiNi0,5-xMn1,5+xO4 (LNMO) dans les batteries Li-ion dépendent fortement de ses conditions de synthèse, de la stœchiométrie Ni/Mn et du degré d'ordre des métaux de transition. La structure cristalline de LNMO peut être décrite dans les groupes d'espace Fd-3m ou P4332, en fonction de l'étendue de cet ordre. Comprendre l'impact de ces propriétés structurales sur les performances électrochimiques est difficile en raison de la nature interdépendante de chaque paramètre et de la résolution spatiale limitée des techniques de caractérisation courantes. Dans cette étude, nous démontrons la possibilité de synthétiser des plaquettes de LNMO de structure désordonnée (Fd-3m) présentant plusieurs orientations de surface, exemptes d'impuretés, en milieu sel fondu. Grâce à la morphologie fine plaquettaire obtenue (épaisseur ~180 nm), nous avons pu utiliser un outil de microscopie électronique, 4D-STEM, récent dans le domaine des batteries, afin d’étudier pour la première fois l’ordre des métaux de transition dans des particules individuelles de LNMO, avec une résolution spatiale nanométrique. La possibilité unique, de contrôler à la fois la morphologie des particules primaires, la composition de la phase spinelle et l’absence de phase secondaire, nous a permis de démontrer que l’hétérogénéité dans l’arrangement des métaux de transition au sein de particules de LNMO de structure globalement ordonné (P4332) est bénéfique pour les performances électrochimiques. En combinant l’analyse par microscopie électronique avec la connaissance acquise sur la structure moyenne par diffraction des rayons X et des neutrons et sur la structure locale à l'aide des spectroscopies Raman et RMN du 7Li, nous avons pu établir la relation ”conditions de synthèse - composition - propriétés” pour des échantillons LiNi0,5-xMn1,5+xO4 obtenus suite à diverses étapes de recuit. Cela a permis de synthétiser des phases spinelles LNMO de structures (dés)ordonnées performantes avec des compositions diverses, et de démontrer que les propriétés électrochimiques peuvent être ajustées grâce à la modification structurale
Transition metal ordering in high voltage spinel LiNi0.5-xMn1.5+xO4 : A multi-scale approach down to nanometer scale
No full textLes performances de la phase spinelle LiNi0,5-xMn1,5+xO4 (LNMO) dans les batteries Li-ion dépendent fortement de ses conditions de synthèse, de la stœchiométrie Ni/Mn et du degré d'ordre des métaux de transition. La structure cristalline de LNMO peut être décrite dans les groupes d'espace Fd-3m ou P4332, en fonction de l'étendue de cet ordre. Comprendre l'impact de ces propriétés structurales sur les performances électrochimiques est difficile en raison de la nature interdépendante de chaque paramètre et de la résolution spatiale limitée des techniques de caractérisation courantes. Dans cette étude, nous démontrons la possibilité de synthétiser des plaquettes de LNMO de structure désordonnée (Fd-3m) présentant plusieurs orientations de surface, exemptes d'impuretés, en milieu sel fondu. Grâce à la morphologie fine plaquettaire obtenue (épaisseur ~180 nm), nous avons pu utiliser un outil de microscopie électronique, 4D-STEM, récent dans le domaine des batteries, afin d’étudier pour la première fois l’ordre des métaux de transition dans des particules individuelles de LNMO, avec une résolution spatiale nanométrique. La possibilité unique, de contrôler à la fois la morphologie des particules primaires, la composition de la phase spinelle et l’absence de phase secondaire, nous a permis de démontrer que l’hétérogénéité dans l’arrangement des métaux de transition au sein de particules de LNMO de structure globalement ordonné (P4332) est bénéfique pour les performances électrochimiques. En combinant l’analyse par microscopie électronique avec la connaissance acquise sur la structure moyenne par diffraction des rayons X et des neutrons et sur la structure locale à l'aide des spectroscopies Raman et RMN du 7Li, nous avons pu établir la relation ”conditions de synthèse - composition - propriétés” pour des échantillons LiNi0,5-xMn1,5+xO4 obtenus suite à diverses étapes de recuit. Cela a permis de synthétiser des phases spinelles LNMO de structures (dés)ordonnées performantes avec des compositions diverses, et de démontrer que les propriétés électrochimiques peuvent être ajustées grâce à la modification structurale.The performance of spinel LiNi0.5-xMn1.5+xO4 (LNMO) as positive electrode material in Li-ion batteries strongly depend on its synthesis conditions, Ni/Mn stoichiometry, and the degree of ordering of Ni and Mn. LNMO crystal structure can be described in Fd-3m or P4332 space groups, depending on the extent of this ordering. Understanding the impact of these structural properties on electrochemical performance is challenging due to the interdependent nature of each parameter and the limited spatial resolution of the common characterization techniques. In this study, we demonstrate the synthesis of impurity-free disordered (Fd-3m) platelets of LNMO presenting multiple surface orientations via molten salt synthesis. Thanks to the thin platelet morphology (thickness ~180 nm) achieved, we employed a 4D-STEM electron microscopy tool, newly growing in the battery field, to investigate the transition metal ordering on individual LNMO particles with nanometric spatial resolution for the first time. The unique ability to tune the primary particle morphology, spinel composition and control secondary phase generation enabled us to demonstrate that heterogeneity in the transition metal arrangement on the globally ordered (P4332) LNMO is beneficial for electrochemical performance. Combining electron microscopy analysis with average structural properties obtained through X-ray and neutron diffraction, and with information on the local environments obtained using Raman and 7Li NMR spectroscopies, we dissect the “synthesis-composition-properties” relation for LiNi0.5-xMn1.5+xO4 samples prepared through various annealing steps. This enables the obtention of high-performing (dis)ordered spinel LNMOs with diverse compositions, highlighting how the electrochemical properties can be tailored through structural design
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
