NASICON materials - a long neglected class of solid electrolytes

The so-called NASICON materials AT2P3O12 (A = alkaline metal, T = tetravalent transition metal) are known since the 1970s [1] and are derived from the first “Na+ super-ionic conductor”, Na3Zr2Si2PO12, of this group of materials. The aims of current investigations are on the one hand the better understanding of the ionic conduction and on the other hand the search for new materials with very high ionic conductivity. For this purpose, new and simple synthesis methods have been developed, which deliver very homogeneous powders with reduced temperatures for the preparation of ceramics. In this way a lithium ion conductor with the composition Li1.5Al0.5Ti1.5P3O12 was manufactured. After sintering to highly dense ceramics a total conductivity of 0.7 mS/cm was achieved at room temperature [2] and therefore this material belongs to the best known solid oxidic Li+ ion conductors. NMR and impedance spectroscopy investigations [3-5] have shown that the bulk conductivity amounts to 3-5 mS/cm and that the grain boundaries determine the quality of the material. In the case of Na+ ion conductors, the prototype Na3Zr2Si2PO12 was newly synthesized and gave a previously not achieved conductivity of 1 mS/cm [6]. The modification of the composition by substitution with scandium delivered conductivities of 0.8 mS/cm (Na3.4Sc2Si0.4P2.6O12) [7] and 4 mS/cm (Na3.4Zr1.6Sc0.4Si2PO12) [8]. The latter composition possesses one of the highest known Na+ ion conductivities of oxide ceramics and reaches the conductivity of liquid electrolytes. The mentioned compositions confirm the empirical criteria which are necessary for achieving high ionic conductivities in NASICON materials [9]. References: [1] H. Y. P. Hong, Mater. Res. Bull. 11 (1976) 173-182; H. Y. P. Hong, J. B. Goodenough, J. A. Kafalas, Mater. Res. Bull. 11 (1976) 203-220 [2] Q. Ma, Q. Xu, C.-L. Tsai, F. Tietz, O. Guillon, J. Am. Ceram. Soc., (2016), in press [3] V. Epp, Q. Ma, F. Tietz, M. Wilkening, Phys. Chem. Chem. Phys., 17 (2015) 32115-32121 [4] S. Breuer, D. Prutsch, V. Epp, Q. Ma, F. Preishuber-Pflügl, F. Tietz, M. Wilkening, J. Mater. Chem. A, 3 (2015) 21343-21350 [5] D. Rettenwander, A. Welzl, S. Pristat, F. Tietz, S. Taibl, G. J. Redhammer, J. Fleig, J. Chem. Mater. A, 4 (2016) 1506-1513 [6] S. Naqash, Q. Ma, Tietz, O. Guillon, in preparation [7] M. Guin, F. Tietz, O. Guillon, in preparation [8] Q. Ma, M. Guin, S. Naqash, C.-L. Tsai, F. Tietz, O. Guillon, in preparation [9] M. Guin, F. Tietz, J. Power Sources, 273 (2015) 1056-106

Chemical and physical properties of sodiumionic conductors for solid-state batteries

The electrochemical storage of electricity in batteries is one key solution to the future extensive use of renewable energy sources. Lithium ion batteries have received intense attention since they provide the largest energy density and output voltage. They have yet to be optimized in terms of capacity, safety and cost and the search for alternatives to lithium has already gained popularity in the past years because of the shortage of resources. One popular substitute is sodium since its chemical properties are similar to those of lithium and sodium is an abundant element. Sodium technologies are not new but the commercial sodium-ion batteries operate at temperatures as high as 300 °C raising safety issues and discussion about the energy needed to heat the battery. Therefore, solid-state sodium batteries operating at room temperature present a safer alternative as they are leak proof and non-flammable. In addition, no supplementary heating equipment is needed to operate the battery. The key in designing safe and efficient solid-state Na-ion batteries is the development of highly conductive solid electrolytes that also display high thermal and chemical stability. Amongst all possibilities, one class of ceramic electrolytes is of great interest: the so-called NASICON materials with general formula AM(PO$_{4)3}$ (in this work, A = Na). They display very attractive compositional diversity and are likely to achieve high conductivity. In this thesis, an extensive study of the composition, the crystal structure and the conductivity of approximately 110 Na-conducting NASICON materials was conducted to find guidelines for designing highly conductive NASICON type materials. For NASICON with aliovalent substitution, the electroneutrality is guaranteed by adapting the amount of Na per formula unit and an optimal Na concentration of 3.2-3.5 mol was identified. Furthermore, an optimal size for the M cations in the structure was highlighted. In addition, the substitution of P with Si proved to have a positive impact on the conductivity. Using these guidelines, the solid solution Na$_{3+x}$Sc$_{2}$(SiO$_{4)x}$(PO$_{4)3-x}$ was investigated for the first time. Various compositions with 0 $\le$ x $\le$ 0.8 were prepared by solid state reaction and their crystallographic and electrical properties were investigated. As a result, the high conductivity at room temperature of 8.3 x 10$^{-4}$ S cm$^{-1}$ was obtained for x = 0.4. In addition, the criteria for high conductivity concluded from the literature study were verified and completed with data of bulk conductivity for the solid solution. This systematic study of the substitution of P with Si provided better insights in the conduction pathway of the sodium ions in the NASICON structure. Finally, thick, dense pellets of Na$_{3.4}$Sc$_{2}$Si$_{0.4}$P$_{2.6}$O$_{12}$ were used as solid electrolyte in different solid-state battery designs and for the first time, a solid-state Na battery based on inorganic materials was cycled at room temperature

From a customizable ITS to an adaptive ITS

International audienceThe personalization of learning remains a major challenge for re- search in Intelligent Tutoring Systems (ITS). We report in this article how we used the Adapte tool to make AMBRE-add adaptive. AMBRE-add is an ITS designed to teach a problem solving method. This ITS includes a module that analyzes the learner’s activity traces in order to compute a learner profile. Furthermore a problem generator enables us to specify activities proposed to the student. In order to design an automated process of personalizing activities according to the learner profile, we used the Adapte system. This is a generic system enabling the definition of a personalization strategy and its application to an external ITS. In this article we present how this tool provides real assistance to an ITS designer wishing to make his/her system adaptive

An Authoring Tool based on Semi-automatic Generators for Creating Self-assessment Exercises

International audienceThis article presents ASKER, a tool for teachers to create and disseminate self-assessment exercises for their students. Currently used in the first year of a bachelor's degree at the University of Lyon (France), it enables students to carry out exercises in order to evaluate their acquisition of concepts considered important by the teacher. ASKER enables the creation of exercises (matching, grouping, short open-ended questions, multiple choice questions) that can be used to assess learning in many different fields. To create exercises to assess a concept, the teacher defines a model of exercises that will enable the generation of various exercises, using text or image resources. Such an exercise model is based on constraints that the exercises created from this model must comply with. Automatic generators create, from the resources defined by the teacher, many exercises respecting these constraints. The possibility for the learner to request the generation of several exercises from the same model enables her to assess herself several times on the same concept, without the teacher having to repeatedly define many exercises

From a customizable ITS to an adaptive ITS

International audienceThe personalization of learning remains a major challenge for re- search in Intelligent Tutoring Systems (ITS). We report in this article how we used the Adapte tool to make AMBRE-add adaptive. AMBRE-add is an ITS designed to teach a problem solving method. This ITS includes a module that analyzes the learner’s activity traces in order to compute a learner profile. Furthermore a problem generator enables us to specify activities proposed to the student. In order to design an automated process of personalizing activities according to the learner profile, we used the Adapte system. This is a generic system enabling the definition of a personalization strategy and its application to an external ITS. In this article we present how this tool provides real assistance to an ITS designer wishing to make his/her system adaptive

Systèmes à base de connaissances pour des EIAH fondés sur le RàPC

National audienceCet article présente tout d'abord comment nous nous sommes inspirés d'un paradigme issu de l'Intelligence Artificielle, le Raisonnement à Partir de Cas, pour proposer un processus permettant l'apprentissage de méthodes de résolution de problèmes fondées sur une classification des problèmes du domaine. Ce processus d'apprentissage ayant été mis en œuvre dans un EIAH destiné à enseigner la résolution de problèmes arithmétiques à l'école primaire, nous décrivons également les bases de connaissances permettant au système de dia- gnostiquer les réponses de l'élève et de lui fournir des explications

Une approche par compétences pour la formation toute au long de la vie

National audienceNous présentons dans cet article des modèles et outils informatiques qui pourraient être utilisés dans le cadre d'une approche par compétences pour la formation ou au long de la vie

Modèle de personnalisation de l'apprentissage pour un EIAH fondé sur un référentiel de compétences

National audienceThis article introduces a PERSUA2-based model for personalization of learning. This new model allows the system to automatically submit pedagogical activities to learners. They depend on the strategies selected by the teachers as well as the context of utilization, the learner profile and their historic in the system. This model relies on an ontology of skills and it is based on different kinds of pedagogical rules which are presented here.Cet article présente un modèle de personnalisation de l'apprentissage issu du modèle PERSUA2. Ce nouveau modèle permet de proposer automatiquement des activités pédagogiques aux apprenants. Elles sont fonction de stratégies choisies par les enseignants ainsi que du contexte d'utilisation, du profil et de l'historique des apprenants dans le système. Ce modèle s'appuie sur une représentation ontologique des compétences à acquérir et repose sur différents types de règles pédagogiques qui sont présentés ici