1,721,195 research outputs found
New opportunities from the microstructural and electrochemical modelling of lithium-ion battery electrodes
No full textIntroduction
Automotive batteries for electric vehicles require fast discharge capability to guarantee sufficient driving range under complex driving cycles. Understanding the intricate physical and chemical processes occurring within battery electrodes across multiple length-scales is critical to assist the design of electrodes for improved performance. Although excellent modelling studies have been published in recent years, an integrated multi-scale modelling framework capable to assist the design from particle level to cell scale is still missing.
Material and Methods
Both continuum-based and particle-resolved electrochemical models, fed by microstructural information coming from X-ray nano-computed tomography, are developed, describing transport of charges and species, as well as electrochemical reactions, within active material particles, electrolyte and carbon-binder domain. The models use concentrated solution theory, Butler-Volmer kinetics and mass balance equations, implemented in Comsol Multiphysics across a range of length scales, from pseudo-2D up to 3D geometries.
Results
At the particle scale, simulations show that crystal orientation and cracks reduce the specific accessible capacity of cathode active materials up to ca. 20 % at C-rates higher than 2. A core-shell double-layer particle design, with primary particles oriented along the radial direction in the outer layer of secondary particles, along with a core of active material with higher specific energy density, is proved to be an ideal particle design for fast discharge capability.
At the electrode level, simulations show that the heterogeneous distribution of the carbon-binder domain, which is rarely resolved in 3D models, critically affects the distribution of charges in the electrode. Grading the particle size and the porosity in the through-thickness direction, with smaller particles and larger porosity at the separator interface, enables for both increased accessible capacity beyond 1C and reduces the heterogeneous lithiation of particles, arguably reducing mechanical stresses.
Discussion
The study shows that coupling microstructural and electrochemical modelling can provide useful guidelines for optimizing the design of lithium-ion batteries. In particular, simulations must coherently and simultaneously capture both particle-level and electrode-level phenomena, paying attention to the heterogeneous distribution of lithiation
Recycling streams for lithium-ion batteries and modelling to compensate performance loss of recycled cathode active materials
No full textIntroduction
The increasing demand of lithium-ion batteries (LIBs) for electric vehicles, combined with the lack of critical raw materials (e.g., cobalt, nickel, lithium) and the necessity to dispose spent batteries, is pushing proper recycling strategies to recover these materials for their re-use in new batteries. Pyrometallurgical and hydrometallurgical processes are rather established, while direct recycling processes are promising. In any case, the regenerated cathode materials might have a lower quality than those prepared from virgin precursors. In order to meet the stringent requirements of the automotive sector, changes in the electrode design may be required when recycled cathode active materials are used.
Material and Methods
An extensive survey of the main recycling processes is provided, focusing specifically on the ones which are currently at industrial level. A Doyle-Fuller-Newman electrochemical model is used to provide guidelines to the electrode design to compensate the performance loss of recycled cathode materials, focusing mainly on LiNixMnyCo1-x-yO2 (NMC) chemistry for which an extensive parametrization and validation is performed.
Results
Pyrometallurgical processes can handle a broader variety of LIB chemistries compared to hydrometallurgical processes, although with a lower recycling efficiency. Hydrometallurgical processes, instead, are limited by initial mechanical separation treatments to obtain the black mass, which affect the material recovery rate and flexibility to treat different LIB chemistries.
The electrochemical model is validated against experimental data of a commercial cell (Samsung SDI 94 Ah), showing accurate predictions of voltage and capacity. When recycled active materials with reduced solid-state diffusivity and nominal capacity are simulated, the model shows a decrease in accessible capacity of a few percentages at 0.3-1 C, which can be compensated by increasing marginally the electrode thickness, ultimately resulting in a minor decrease in specific energy density of the battery pack.
Discussion
The analysis shows that the current recycling processes have some limitations, namely the loss of lithium in the slag in pyrometallurgical processes and the sensitivity to mechanical separations for the recovery of the black mass in hydrometallurgy. Nevertheless, electrochemical modelling indicates that recycled active materials can be effectively used to re-build new batteries with minor modifications to the cell design, suggesting that a sustainable chain for LIBs is feasible
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
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
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