948 research outputs found
Investigation on Next Generation Materials for Rechargeable Lithium-ion Batteries: Alloying- and Conversion-based Materials as Viable Anode Candidates
No full textThe current lithium-ion batteries (LIBs) technology has allowed the spread of portable electronic devices such as cameras, laptops, and smartphones, and at the same time has triggered the development of the electric vehicles (EVs). In order to increase LIBs mass diffusion and meet the market demands, a reduction in costs and environmental impact are required. Graphite is the conventional anodic material, but because of its relatively low specific capacity (372 mAh g-1), and its implementation in the list of critical raw materials of European Union, it has to be replaced by more performant and environmentally-friendly materials. Since graphite has a capacity limitation due to its lithium storage mechanism (insertion process), the use of materials based on different lithium storage mechanisms, such as alloying and conversion materials, has been taken into consideration. Silicon is one of the most studied alloying materials because of its low cost, relatively low working potential, and high theoretical specific capacity of 3579 mAh g-1 (corresponding to the formation of Li15Si4 phase). Since the formation of the most lithiated phase is associated with a huge volume expansion (≈ 300%), silicon is plagued by structural instability resulting in poor performances and safety. Thus, it is mandatory to stabilize its structure in order to have it commercialized in the future. Several strategies have been proposed such as the use of nanosize active materials, the implementation of carbonaceous and inorganic matrices, the use of tailored electrolyte and additives, and the use of more elastic and eco-friendly binders. In this thesis, different approaches have been used in combination, in order to buffer the silicon volume expansion, thus enhancing its capacity, safety and long-term perfomances. The perfomances of two silicon-based composites (Si@V2O5 and Si@TiO2) have been evaluated by the means of structural, morphological and electrochemical characterizations. A whole chapter of this thesis will be focused on the scale-up of typical laboratory scale processes, where an in-depth study of silicon-based electrodes processing has been carried out. This study has been performed in a pre-industrial plant, starting from the electrode slurry preparation up to the electrochemical characterization of the assembled full cell. Different aspects have been taken into consideration, demonstrating that the scale-up of established laboratory-scale processes reserves important problems at an industrial level. At last, the use of a conversion material has been evaluated. These materials suffer from issues similar to those of alloying materials. Indeed, a big volume expansion associated with a low electronic conductivity and a large hysteresis in the first cycle hinder their commercialization. Fe2O3 nanoparticles have been synthesized using vanillin as soft template, in a cheap and very reproducible way. The electrochemical characterization showed remarkable cycling perfomances even at high currents
Buffering volume changes of Si nanocomposite anodes
No full textThe massive development of Li-ion technology has allowed for massive spreading of portable electronics, as well as for a progressive development of electrical vehicles (EV) with higher driving range. Despite this, the ever-increasing demand in energy density requests for a breakthrough in Li-storage materials. In this context, anode materials alternative to conventional graphite, with improved capacity, have been investigated for several years. Among these, Si plays a special role because of its extremely high theoretical capacity (4200 mAh g-1 corresponding to the formation of a Li22Si4 alloy). Nevertheless, the volume changes of about 300% associated with the alloying/dealloying processes represent a severe limitation to the electrode reversibility, so that actions aimed at counteracting this drawback are needed for the development of durable Si anodes.
The electrochemical behaviour of nanocomposite materials, based on commercial Si powder of about 100 nm size in which the volume changes are buffered by dispersing matrixes such as reduced graphene oxide (RGO) or transition metal oxides, is here presented. The electrodes and cells performances, in terms of specific capacity and durability, are optimized by the use of tailored binders and electrolyte formulations. A rationale of the improved behaviour is explored by applying several morphological, structural and electrochemical investigation techniques, with a special focus on electrode/electrolyte interfacial properties.
References:
1. M.N. Obrovac, L. Chistensen, Electrochem. Solid State Lett. 7 (2004) A93.
2. F. Maroni, R. Raccichini, A. Birrozzi, G. Carbonari, R. Tossici, F. Croce, R. Marassi, F. Nobili, J. Power Sources 269 (2014) 873
Sol-Gel Synthesis of Iron-Manganese Mixed Oxide as Superior and Eco-Friendly Anode for Lithium-Ion Batteries
No full textLithium-ion batteries (LIBs) are the perfect balance between portability, low cost and good performances. Considering the anodic side, graphite is the most used active material 1, which despite its wide use, and a specific capacity of 372 mAhg-1, has been included in the European Commission list of critical raw materials that have to be replaced in the future. For this reason, a great deal of effort has been devoted to investigate a relatively new class of materials emerged in this last few years, showing a different reactivity from traditional insertion materials, the so-called conversion materials. Among these, transition metal oxides (TMOs), can reach extremely high capacity values, up to five times higher than graphite 2. Despite this, they have evidenced several drawbacks: short cyclic life, a large first cycle irreversible capacity, and a relevant volume variation during cycling. In this work, an Iron-Manganese mixed oxide was synthesized by Sol-Gel method and tested as anode for Li-ion batteries. In order to address the aforementioned drawbacks, and improve the mechanical stability of the electrodes, improved binders with superior mechanical properties 3, such as Polyacrylic Acid (PAA) and Sodium-Carboxymethyl Cellulose (Na-CMC), and an environmentally friendly electrode processing using ethanol or H2O as solvents, were evaluated. The experimental data shown superior performance with respect to the standard Polyvinylidene Fluoride system, which makes use of the expensive and toxic N-Methyl-2-pyrrolidone (NMP) solvent.
References:
1 Scrosati, B.; Garche, J.; Journal of Power Sources 2010, 195, 2419-2430.
2 Cabana, J.; Monconduit, L.; Larcher, D.; Palacìn M.R.; Advanced Material 2010, 22, 170-192.
3 Magasinski, A.; Zdyrko, B.; Kovalenko, I.; Hertzberg, B.; Burtovyy, R.; Huebner, C.F.; Fuller, T.F.; Luzinov, I.; Yushin, G.; ACS Applied Materials & Interfaces 2010, 2, 3004-3010
Anatase-TiO2 as low-cost and sustainable buffering filler for nanosize Silicon anodes in Lithium-ion batteries
No full textThe design of effective supporting matrices to efficiently cycle Si nanoparticles is often difficult to be achieved and requires complex preparation strategies. In this work, we present a simple synthesis of low-cost and environmentally benign Anatase-TiO2 nanoparticles as buffering filler for Si nanoparticles (Si@TiO2). Average anatase crystallite size is estimated in 5 nm. A complete structural, morphological and electrochemical characterization is performed. Electrochemical test results show very good specific capacity values around up to 1000 mAhg-1 and cycling at several specific currents, ranging from 500 mAg-1 to 2000 mAg-1, demonstrating a very good tolerance to high cycling rates. Post-mortem morphological analysis shows very good electrode integrity after 100 cycles at 500 mAg-1 specific current
Synthesis and Characterization of TiO2@SnO2 Nanocomposite as Viable Anode for Lithium-Ion Batteries
No full textWith the market growth and increasing development of hybrid electric vehicles (HEVs) and electric vehicles (EVs), high-energy density and high-power materials are needed. SnO2 is one of the proposed materials to replace the industry standard graphite (372 mAh g-1), thanks to its high theoretical capacity of 1411 mAh g-1,1; but its use is hindered by low cycling stability due to the volume expansion/contraction during alloying/dealloying reaction respectively.
In this regard, a composite anode material based on SnO2 and anatase TiO2 have been prepared using commercial SnO2 nanopowder and Ti-isopropoxide as starting materials. A sol-gel step, consisting in controlled hydrolysis of Ti-[O-iPr]4 in SnO2 dispersion followed by thermal annealing in inert atmosphere, yielded the composite made of SnO2:TiO2 in the approximate ratio 3:1. Structural characterization was pursued by XRD, SEM, TGA and Raman spectroscopy. Electrodes have been prepared using high-molecular weight PAA as binder, which is a greener alternative than PVdF and has better mechanical stability towards tin volume changes upon lithiation.
Cyclic voltammetries at different scan rates revealed a linear relationship between the peak current and the square root of scan rates, with an estimated lithium diffusion coefficient in accordance with literature2,3. Prolonged galvanostatic cycling shows improved stability and average specific capacity of 908 mAh g-1 at 1000 mA g-1, together with remarkable rate capability. PEIS applied every 10 cycles revealed a stable SEI upon cycling. Two main factors concur in determining this behaviour, namely: (i) the efficient dispersion of SnO2 and TiO2, which act as volume buffering matrix; (ii) the formation of a stabilized SEI by VC additive in the electrolyte
El Tlacuache Núm. 442 (2010). 442 Año 10 (2010) noviembre. El Tlacuache
No full textIronías en la historia de las ideas De diestros y siniestros por Fanny Campillo. -Tesis en torno a la autonomía de los pueblos indios por Gilberto López y Rivas
El Tlacuache Núm. 388 (2009). 388 Año 9 (2009) noviembre. El Tlacuache
No full textEl impacto de la Revolución Cubana en América Latinatados por Gilberto López y Rivas. - Del Tlalocan: uno de los reinos de los muertos por Isabel Garza Gómez
Preparation and Electrochemical Characterization of High-Stability MnO Anodes for Li-Ion Batteries
No full textThe article deals with the optimization of an anode based on commercial manganese oxide. Several parameters are considered in order to enhance capacity, rate capability and long-term cycleability. Particularly, Polyacrylic Acid as a green binder with enhanced mechanical features is proposed, while Vinylen Carbonate is added to a standard carbonate-based electrolyte system in order to enhance the stability of passivation layer and of electrode/electrolyte interface. The role of a reversible “gel-like” layer toward interfacial stability is investigated as well. Several structural, morphological and electrochemical investigation techniques are applied in order to fully characterize the behavior of baseline and modified electrodes and cells. This process results in an optimized system able to deliver, in a half-cell vs. metal Li, specific capacity values up to 725 mAh g−1 at 1C-rate, stable for 100 cycles, and relevant rate capability, confirming a major influence of electrode and electrolyte formulation toward electrochemical performance
Cultura e sociedade em Gilberto Freyre
No full textRESUMO
O autor se propõe identificar as matrizes teóricas do pensamento de Gilberto Freyre. Comenta a influência de Herbert Spencer, Oliveira Lima e Franz Boas – registrada pelo próprio Gilberto Freyre – e detém-se na análise das marcas provenientes do contato daquele sociólogo com a chamada Escola de Chicago. Para o autor, a influência de Robert E. Park e William I. Thomas é decisiva na formação da abordagem pessoal de Gilberto Freyre. O autor detém-se, também, na identificação das afinidades de Gilberto Freyre com as abordagens de Max Weber, George Simmel e a chamada “Escola dos Annales”.
ABSTRACT
Culture and society in Gilberto Freyre. v. 19, n. 2, p. 311-326, jul./dez. 1991
The author proposes to identify the thoeretical origins of Gilberto Freyre’s thinking. He comments on the influence of Herbert Spencer, Oliveira Lima and Franz Boas – registred by Gilberto Freyre himself – and analyses in greater detail the influence originating in Freyre’s contact with the “Chicago School”. For the author, the influence of Robert E. Park and William I. Thomas is decisive in forming the personal approach of Gilberto Freyre. The author also considers Freyre’s rapport with the approaches of Max Weber, George Simmel and the so-called “School of the Annales”.
RESUMÉ
Culture et société vues par Gilberto Freyre. v. 19, n. 2, p. 311-326, jul./dez. 1991
L’auteur se propose tout d’abord d’identifier les matrices théoriques de la pensée de Gilberto Freyre. Dans ce but, il sougline l’influence de Herbert Spencer, de Oliveira Lima et de Franz Boas – reconnue para Gilberto Freyre lui-même – et analyse les marques laissées par ses contacts avec “L’École de Chicago”. Selon l’auteur, l’influence de Robert E. Park et de William I. Thomas a été fondalementale pour la formation de Gilberto Freyre. Le travail se ferme en montrant l’identification des idées de Gilberto Freyre avec celles de Max Weber, de Georg Simmel et de “l’Ecole des Annales”
(S)em nome do Pai: a escrita órfã de João Gilberto Noll// (No-)name of the Father: The Orphan Writing of João Gilberto Noll
No full textResumo: Este artigo pretende apresentar a relação entre o movimento errante dos narradores da obra de João Gilberto Noll e a sua impossibilidade de manterem um vínculo com a figura paterna. Para tanto, a inviabilidade do narrador em ter um pai ou de ser um pai será analisada neste artigo por meio de duas perspectivas: primeira, a partir do paralelo entre a ruptura de toda e qualquer possibilidade de ascendência e de descendência genealógica e o movimento errante constitutivo das narrativas nollianas. Em seguida, através da possível associação entre a figura de autoridade do Pai e a figura de autoridade do Autor. Como base teórica deste estudo, o pensamento de Maurice Blanchot e de Roland Barthes se farão presentes.Palavras-chave: João Gilberto Noll; errância; não nomeação; paternidade; autoria.Abstract: This study intends to present the relationship between the wandering movement of the narrators of João Gilberto Noll’s work and their impossibility of keeping connected to the father figure. Thus, the unfeasibility of the narrator having or being a father is going to be analyzed in this article through two perspectives: the first, from the parallel between the rupture of any possibility of genealogical ancestry or descent, and the constitutive wandering movement of Noll’s narratives. The second, considering the possible association between the authority figure of the Father and the authority figure of the Author. Maurice Blanchot and Roland Barthes’s thoughts constitute the theoretical background of this research.Keywords: João Gilberto Noll; wandering; non-nomination; fatherhood; authorship
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