Modélisation et mise en œuvre d'environnements informatiques pour la régulation de l'apprentissage, le cas de l'algèbre avec le projet LINGOT

200 pagesCe projet a pour objectif de mettre à la disposition des enseignants des outils performants pour un travail plus individualisé avec des élèves dans le domaine de l'algèbre élémentaire. Le travail s'appuie sur des recherches théoriques en Didactique des Mathématiques et en Environnements Informatiques d'Apprentissage Humain. Le projet a produit un logiciel, appelé Pépite, qui construit automatiquement le profil cognitif en algèbre d'un élève du secondaire à partir de ses réponses à un test spécialement élaboré à cet effet

Le calcul littéral au collège. Quelle articulation entre sens et technique ?

L'enseignement de l'algèbre au collège a subi plusieurs modifications depuis la réforme des mathématiques modernes. La part des techniques de calcul a diminué, ce qui peut expliquer que les professeurs de lycées se plaignent des difficultés des élèves tant en calcul algébrique que littéral. Peut-on alors penser que les élèves sont plus outillés pour mettre un problème en équation ? Il semble que cela ne soit pas encore le cas puisque les élèves de seconde ont du mal à résoudre des problèmes où on ne leur donne pas l'inconnue. Le calcul sur les nombres relatifs est maintenant totalement introduit en classe de 5ème alors que cela était fait sur les deux niveaux de 6ème et 5ème. Dans cette communication, nous souhaitons aborder la question de l'articulation entre sens et technique en analysant notamment comment les programmes et les manuels la prennent en compte

Étude multidimensionnelle de l’impact des travaux de recherche en didactique dans l’enseignement de l’algèbre élémentaire : Quelles évolutions ? Quelles contraintes ? Quelles perspectives ?

International audienc

3D printing of solid polymer electrolytes by Fused Filament Fabrication: challenges towards in-space manufacturing

Abstract A new chapter of space exploration is opening with future long-duration space missions toward the Moon and Mars. In this context, the European Space Agency (ESA) is developing out-of-the-earth manufacturing abilities, to overcome the absence of regular supplies for astronauts’ vital needs (food, health, housing, energy). Additive manufacturing is at the heart of this evolution because it allows the fabrication of tailorable and complex shapes, with a considerable ease of process. Fused Filament Fabrication (FFF), the most generalized 3D printing technique, has been integrated into the International Space Station (ISS) to produce polymer parts in microgravity. Filament deposition printing has also a key role to play in Li-ion battery (LIB) manufacturing. Indeed, it could reduce manufacturing cost & time, through one-shot printing of LIB, and improve battery performances with suitable 3D architectures. Thus, additive manufacturing via FFF of LIB in microgravity would open the way to In-Space Manufacturing (ISM) of energy storage devices. However, as liquid and volatile species are not compatible with a space station-confined environment, solvent-free 3D printing of polymer electrolytes is a necessary step to make battery printing in microgravity feasible. This is a challenging stage because of a strong opposition between the mechanical requirements of the feeding filament and electrochemical properties. Nowadays, polymer electrolyte manufacturing remains a hot topic and lots of strategies are currently being studied to overcome their poor ionic conductivity at room temperature. This work firstly gives a state of the art on the 3D printing of Li-ion batteries by FFF. Then, a summary of ionic conduction mechanisms in polymer electrolytes permits to understand the several strategies studied to enhance polymer electrolytes performances. Thanks to the confrontation with the specifications of FFF printing and the microgravity environment, polymer blends and composite electrolytes turn out to be the most suitable strategies to 3D print a lithium-ion polymer battery in microgravity

Hindered Glymes for Graphite-Compatible Electrolytes

International audienceOrganic carbonate mixtures are used almost exclusively as lithium battery electrolyte solvents. The linear compounds (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate) act mainly as thinner for the more viscous and high-melting ethylene carbonate but are the least stable component and have low flash points; these are serious handicaps for lifetime and safety. Polyethers (glymes) are useful co-solvents, but all formerly known representatives solvate Li+ strongly enough to co-intercalate in the graphite negative electrode and exfoliate it. We have put forward a new electrolyte composition comprising a polyether to which a bulky tert-butyl group is attached (“hindered glyme”), thus completely preventing co-intercalation while maintaining good conductivity. This alkyl-carbonate-free electrolyte shows remarkable cycle efficiency of the graphite electrode, not only at room temperature, but also at 50 and 70 °C in the presence of lithium bis(fluorosulfonimide). The two-ethylene-bridge hindered glyme has a high boiling point and a flash point of 80 °C, a considerable advantage for safety

MnO Conversion Reaction: TEM and EELS Investigation of the Instability under Electron Irradiation

International audienceActive materials in batteries suffer from deleterious chemical and structural evolutions during cycling. To follow these modifications, transmission electron microscopy and associated techniques (EELS, EDX) are of great use. However, these materials can undergo drastic changes under the electron beam. In this study the various microstructural and chemical evolutions induced by electron irradiation were thoroughly investigated at different charging states on a MnO material reacting through the conversion process leading to nanoparticles. During the electron irradiation, compounds pulverization, nanograins growth as well as the formation of manganese carbide were observed. Consequently, knowing the modifications the sample can undergo under electron irradiation and managing to the best the TEM parameters (spot size, aperture size…) to limit its effect can be of help to avoid misinterpretation and to fully understand the mechanisms, which occur during cycling

Plantago lanceolata L.

https://thekeep.eiu.edu/herbarium_specimens_byname/9872/thumbnail.jp

Review—Gassing Mechanisms in Lithium-ion Battery

International audienceThis paper provides a holistic view of the different studies related to gassing in NMC/graphite lithium-ion batteries over the past couple of decades of scientific development. It underlines the difficulty of predicting the concentration and the proportion of gas released upon cycling and storage and to get a clear mechanistic insight into the reduction and oxidation pathways of electrolyte solvents, the thermal electrolyte degradation, as well as the reactions that involve secondary sources such as water, NMC surface species and cross-talk reactions. Though many relevant experiments such as operando gas analysis using isotope-labeled solvents or two-compartment cells have been conducted, they failed, for instance, to determine the exact mechanism leading to the generation of CO and CO 2 gas. Last but not least, this paper discusses different strategies that are currently proposed to reduce or eliminate gassing such as the use of electrolyte additives that enable singlet oxygen quenching or scavenging, NMC coatings that limit the contact with electrolyte and different lithium salts to prevent thermal electrolyte degradation

Environmentally Friendly Lithium-Terephthalate/Polylactic Acid Composite Filament Formulation for Lithium-Ion Battery 3D-Printing via Fused Deposition Modeling

International audienceIn this paper, the development of an environmentally-friendly lithium-terephtalate/polylactic acid (Li2TP/PLA) composite filament, for its use, once 3D-printed via Fused Deposition Modeling (FDM), as negative electrode of a lithium-ion battery is reported. Solvent-free formulation of the 3D-printable filament is achieved through the direct introduction of synthesized Li2TP particles and PLA polymer powder within an extruder. Printability is improved through the incorporation of poly(ethylene glycol) dimethyl ether average M-n similar to 500 (PEGDME500) as plasticizer, while electrical performances are enhanced through the introduction of carbon black (CB). Thermal, electrical, morphological, electrochemical and printability characteristics are discussed thoroughly. By taking advantage of the 3D-printing slicer software capabilities, an innovative route is proposed to improve the liquid electrolyte impregnation within the 3D-printed electrodes

Electrode contributions to the impedance of a high-energy density Li-ion cell designed for EV applications

International audienceElectrochemical Impedance Spectroscopy (EIS) measurements are performed on a high energy density Li-ion cell, which consists of a graphite-based composite negative electrode, a LiMn2O4-layered oxide blended composite positive electrode, and a carbonate solvents-based electrolyte. Signal analysis is applied to get information regarding cell internal components. The impedance behavior at different states of charge (SOC) is reproduced in an optimized laboratory scaled 3-electrode cell, which enables to: separate each electrode impedance contribution and understand the impedance variations when changing SOC. In the negative electrode, the impedance decreases when increasing SOC because the charge transfer process on the surface of graphite particles becomes less resistive with the lithium content. In the positive electrode, the impedance decreases rapidly at the beginning of charge because at low SOC the EIS response is governed by the layered oxide particles, whose electronic properties strongly depend on the lithium content. Finally, the negative electrode contribution to the total cell impedance varies between 60 and 74%; whereas the positive electrode contribution, being the complement, varies between 40 and 26%