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4. Exploring Composite Indexes for Domain Adaptation in Neural Machine Translation.

Author

Minh, Nhan Vo, Minh, Khue Nguyen Tran, Nguyen, Long H. B., and Dinh, Dien

Subjects
K-nearest neighbor classification, INFORMATION technology, MACHINE learning, INDEXING, DATA analysis
Abstract

Domain adaptation in neural machine translation (NMT) tasks often involves working with datasets that have a different distribution from the training data. In such scenarios, k-nearest-neighbor machine translation (kNN-MT) has been shown to be effective in retrieving relevant information from large datastores. However, the high-dimensional context vectors of large neural machine translation model result in high computational costs for distance computation and storage. To address this issue, index optimization techniques have been proposed, including the use of inverted file index (IVF) and product vector quantization (PQ), called IVFPQ. In this paper, we explore the recent index techniques for efficient machine translation domain adaptation and combine multiple index structures to improve the efficiency of nearest-neighbor search in domain adaptation datasets for machine translation task. Specifically, we evaluate the effectiveness when combining optimized product quantization (OPQ) and hierarchical navigable small-world (HNSW) indexing with IVFPQ. Our study aims to provide insights into the most suitable composite index methods for efficient nearest-neighbor search in domain adaptation datasets, with a focus on improving both accuracy and speed. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Fe(III)-carboxythiolate layered metal–organic frameworks with interest as active materials for rechargeable alkali-ion batteries.

Author

Gedikoglu, Nusik, Salcedo-Abraira, Pablo, Nguyen, Long H. B., Guillou, Nathalie, Dupré, Nicolas, Payen, Christophe, Louvain, Nicolas, Stievano, Lorenzo, Poizot, Philippe, and Devic, Thomas

Abstract

Metal organic frameworks (MOFs) built up from metal–sulfur (M–S) bonds have shown great promise in the last decade thanks to their impressive electronic properties arising from the more covalent nature of the M–S bond when compared to M–O. In this study, we aim to expand the scope of available S-based MOFs to high oxidation state cations Mn+ (n ≥ 3). Through the systematic exploration of the reactivity of the mixed thiolate-carboxylate ligand 2,5-disulfhydrylbenzene-1,4-dicarboxylic acid (H4DSBDC) with Fe(III) salts, three new compounds were isolated. The structure of these materials consists of the same hybrid layers made of chains of edge-sharing FeS4O2 octahedra connected by fully deprotonated DSBDC4−, alternating with either organic (dimethyammonium, H2N(CH3)2+) or inorganic (Na+ or K+) cations. The Fe–S connection leads to a strong absorption in the visible range, while the +III oxidation state of Fe, evidenced by Mössbauer spectroscopy, ensures a fairly good stability towards oxygen and water, higher than that typically observed with +II cations. Furthermore, Na{Fe(DSBDC)} exhibits an interesting reversible electrochemical activity when cycled both versus Li, Na and K in half-cells with good capacity retention, confirming the potential of this family of materials for applications involving electron transfer. [ABSTRACT FROM AUTHOR]

Published
2023
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11. First 18650-format Na-ion cells aging investigation: A degradation mechanism study

Author

European Commission, LabEx STORE-EX, Région Nouvelle-Aquitaine, Agence Nationale de la Recherche (France), Ministerio de Economía y Competitividad (España), Nguyen, Long H. B., Sanz Camacho, Paula, Fondard, Jérémie, Carlier, Dany, Croguennec, Laurence, Palacín, M. Rosa, Ponrouch, Alexandre, Courrèges, Cécile, Dedryvère, Rémi, Trad, Khiem, Jordy, Christian, Genies, Sylvie, Reynier, Yvan, Simonin, Loic, European Commission, LabEx STORE-EX, Région Nouvelle-Aquitaine, Agence Nationale de la Recherche (France), Ministerio de Economía y Competitividad (España), Nguyen, Long H. B., Sanz Camacho, Paula, Fondard, Jérémie, Carlier, Dany, Croguennec, Laurence, Palacín, M. Rosa, Ponrouch, Alexandre, Courrèges, Cécile, Dedryvère, Rémi, Trad, Khiem, Jordy, Christian, Genies, Sylvie, Reynier, Yvan, and Simonin, Loic

Abstract

Several Hard carbon||Na3V2(PO4)2F3 full-cells in 18650-format are assembled to demonstrate the possible use of SIBs in stationary applications. The cell aging process is investigated in two different conditions: (i) continuous cycling at different current rates, and (ii) storage at different states-of-charge at various temperatures. The obtained results reveal that the cell degradation depends strongly on the temperature, current rates applied in cycling conditions, or state-of-charge of the storage test. Under cycling conditions, the continuous sodiation/desodiation may induce significant mechanical deformation, leading to the detachment of active materials from the current collector. Furthermore, the post-mortem analysis shows that reaction rate and aging process are not homogeneous along the electrode roll. The XRD analysis shows that Na3V2(PO4)2F3 structure is robust; nevertheless, the material cannot recover the initial Na+ content as the cycling progresses, which is the main cause for capacity loss in the positive electrode. The solid-electrolyte interphase present on the hard carbon surface was characterised using XPS. The hard carbon electrode cannot be detected during this study, evidencing the formation of a relatively thick (>5 nm) passivating layer composed of carbonate salts and NaF, which are the main products of electrolyte decomposition.

Published
2022

13. Controlling the Cathodic Potential of KVPO4F through Oxygen Substitution

Author

Wernert, Romain, primary, Nguyen, Long H. B., additional, Petit, Emmanuel, additional, Camacho, Paula Sanz, additional, Iadecola, Antonella, additional, Longo, Alessandro, additional, Fauth, François, additional, Stievano, Lorenzo, additional, Monconduit, Laure, additional, Carlier, Dany, additional, and Croguennec, Laurence, additional

Published
2022
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14. First 18650-format Na-ion cells aging investigation: A degradation mechanism study

Author

Nguyen, Long H. B., Sanz Camacho, Paula, Fondard, Jérémie, Carlier, Dany, Croguennec, Laurence, Palacín, Maria Rosa, Ponrouch, Alexandre, Courreges, Cecile, Dedryvère, Rémi, Trad, Khiem, Jordy, Christian, Genies, Sylvie, Reynier, Yvan, Simonin, Loic, European Commission, LabEx STORE-EX, Région Nouvelle-Aquitaine, Agence Nationale de la Recherche (France), Ministerio de Economía y Competitividad (España), Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire réactivité et chimie des solides - UMR CNRS 7314 (LRCS), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Réseau sur le stockage électrochimique de l'énergie (RS2E), Aix Marseille Université (AMU)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Université de Picardie Jules Verne (UPJV)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA)-Nantes Université (Nantes Univ)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), Université de Montpellier (UM), SAFT [Bordeaux], Société des accumulateurs fixes et de traction (SAFT), Advanced Lithium Energy Storage Systems - ALISTORE-ERI (ALISTORE-ERI), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut de Ciència de Materials de Barcelona (ICMAB), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux (IPREM), Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), VITO/EnergyVille, Laboratoire d'Innovation pour les Technologies des Energies Nouvelles et les nanomatériaux (LITEN), Institut National de L'Energie Solaire (INES), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), The RS2E Network for the funding of LHBN's PhD thesis as well as the financial support of Région Nouvelle Aquitaine., MRP and AP acknowledge Ministerio de Economía y Competititivad (Spain) for Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496)., ANR-10-LABX-0076,STORE-EX,Laboratory of excellency for electrochemical energy storage(2010), and European Project: 646433,H2020,H2020-LCE-2014-3,NAIADES(2015)

Subjects
[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, Batteries, [CHIM.POLY]Chemical Sciences/Polymers, Renewable Energy, Sustainability and the Environment, [CHIM.ANAL]Chemical Sciences/Analytical chemistry, Cycle-life, Cathode materials, Energy Engineering and Power Technology, [CHIM.MATE]Chemical Sciences/Material chemistry, Electrical and Electronic Engineering, Physical and Theoretical Chemistry, Solid-electrolyte interphase
Abstract

Several Hard carbon||Na3V2(PO4)2F3 full-cells in 18650-format are assembled to demonstrate the possible use of SIBs in stationary applications. The cell aging process is investigated in two different conditions: (i) continuous cycling at different current rates, and (ii) storage at different states-of-charge at various temperatures. The obtained results reveal that the cell degradation depends strongly on the temperature, current rates applied in cycling conditions, or state-of-charge of the storage test. Under cycling conditions, the continuous sodiation/desodiation may induce significant mechanical deformation, leading to the detachment of active materials from the current collector. Furthermore, the post-mortem analysis shows that reaction rate and aging process are not homogeneous along the electrode roll. The XRD analysis shows that Na3V2(PO4)2F3 structure is robust; nevertheless, the material cannot recover the initial Na+ content as the cycling progresses, which is the main cause for capacity loss in the positive electrode. The solid-electrolyte interphase present on the hard carbon surface was characterised using XPS. The hard carbon electrode cannot be detected during this study, evidencing the formation of a relatively thick (>5 nm) passivating layer composed of carbonate salts and NaF, which are the main products of electrolyte decomposition., The authors acknowledge the European Commission for funding this work through the H2020 NAIADES project (LCE10-2014, Contract number 646433). LC, DC, PSC and LHBN thank the RS2E Network for the funding of LHBN's PhD thesis as well as the financial support of Région Nouvelle Aquitaine. LC, DC, PSC, LHBN, CC, and RD acknowledge the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) for financial support. MRP and AP acknowledge Ministerio de Economía y Competititivad (Spain) for Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). The authors thank E. Garitte (SAFT, France) for her helps to coordinate this project.

Published
2022
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15. Chapter 2, Polyanionic-Type Compounds as Positive Electrodes for Na-ion batteries

Author

Nguyen, Long H. B., Chen, Fan, Masquelier, Christian, Croguennec, Laurence, Universiteit Gent = Ghent University (UGENT), Laboratoire réactivité et chimie des solides - UMR CNRS 7314 (LRCS), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Réseau sur le stockage électrochimique de l'énergie (RS2E), Aix Marseille Université (AMU)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Université de Picardie Jules Verne (UPJV)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA)-Nantes Université (Nantes Univ)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), Université de Montpellier (UM), Advanced Lithium Energy Storage Systems - ALISTORE-ERI (ALISTORE-ERI), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), and Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[CHIM]Chemical Sciences
Abstract

International audience; Polyanionic compounds form an important class of materials for positive electrodes for Na-ion batteries (NIBs). This chapter gives the structural frameworks of some typical polyanionic materials. It highlights the recent achievements in the development of new electrode materials for NIBs. Solid state reaction and wet method are two traditional synthesis routes for Na Super Ionic CONductor (NASICON) compounds. NASICON-type materials constitute an important family of polyanionic compounds. They also hold an essential role as solid electrolytes and electrode materials for both lithium-ion batteries and NIBs. Na3V2(PO4)3 and Na3V2(PO4)2F3 are two of the most promising polyanionic materials that can be used at the positive electrode in NIBs and they indeed belong to two different families of materials.

Published
2021
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18. A combined operando synchrotron X-ray absorption spectroscopy and first-principles density functional theory study to unravel the vanadium reedox paradox in the Na3V2(PO4)2F3–Na3V2(PO4)2FO2 compositions

Author

Nguyen, Long H. B., Iadecola, Antonella, Belin, Stéphanie, Olchowka, Jacob, Masquelier, Christian, Carlier, Dany, Croguennec, Laurence, Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire réactivité et chimie des solides - UMR CNRS 7314 (LRCS), Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC), Réseau sur le stockage électrochimique de l'énergie (RS2E), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Aix Marseille Université (AMU)-Université de Pau et des Pays de l'Adour (UPPA)-Université de Nantes (UN)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Advanced Lithium Energy Storage Systems - ALISTORE-ERI (ALISTORE-ERI), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), The authors thank the RS2E Network for the funding of LHBN’s Ph.D. thesis as well as the financial support of Région Nouvelle Aquitaine, the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01), and the European Union’s Horizon 2020 research and innovation program under grant agreement no. 646433-NAIADES. XAS experiments were performed on the ROCK beamline at SOLEIL synchrotron, which is benefiting from a public grant overseen by the French National Research Agency as part of the 'Investissements d’Avenir' program (reference: ANR-10-EQPX-45). The Mésocentre de Calcul Intensif Aquitain (MCIA) and the modeling center of ISM are acknowledged for computing facilities., 2020-152, ANR-10-EQPX-0045,ROCK,Spectromètre EXAFS Rapide pour Cinétiques Chimiques(2010), ANR-10-LABX-0076,STORE-EX,Laboratory of excellency for electrochemical energy storage(2010), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Université de Nantes (UN)-Aix Marseille Université (AMU)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Université de Picardie Jules Verne (UPJV)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA), and Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)

Subjects
[CHIM.MATE]Chemical Sciences/Material chemistry
Abstract

International audience; The redox processes involved in the Na+ deintercalation from Na3V2(PO4)2F3, Na3V2(PO4)2F2O, and Na3V2(PO4)2F1.5O1.5 are investigated operando by synchrotron X-ray absorption spectroscopy at the vanadium K-edge. A continuous evolution in the pre-edge and edge regions is observed for the three compositions, which is in good agreement with a progressive oxidation of vanadium. In the oxygen-substituted compositions, Na3V2(PO4)2F2O and Na3V2(PO4)2F1.5O1.5, the F–V3+O4–F and F–V4+O4═O redox centers coexist and can be simultaneously activated owing to the reverse inductive effect promoted by the presence of highly covalent vanadyl bonds on V4+ sites. Principal component analysis of the dataset collected operando for the three compositions is performed. It reveals that three independent spectra, corresponding to different charge orderings on vanadium sites at different states of charge, are required to describe these three systems. Furthermore, the extended X-ray absorption fine structure analysis of the principal components is performed in order to gain insightful information on the evolution of the vanadium local environment upon cycling. By the use of first-principles density functional theory calculations, we demonstrate that the potential step observed in all Na2V2(PO4)2F3–yOy compositions is related to a charge ordering on vanadium sites with a preferential oxidation of vanadium ions in the same bioctahedra.

Published
2020
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25. Density functional theory-assisted 31P and 23Na magic-angle spinning nuclear magnetic resonance study of the Na3V2(PO4)2F3–Na3V2(PO4)2FO2 solid solution: unraveling Its local and electronic structures

Author

NGUYEN, Long H. B., SANZ-CAMACHO, Paula, BROUX, Thibault, OLCHOWKA, Jacob, MASQUELIER, Christian, CROGUENNEC, Laurence, CARLIER-LARREGARAY, Dany, Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire réactivité et chimie des solides - UMR CNRS 7314 (LRCS), Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC), Réseau sur le stockage électrochimique de l'énergie (RS2E), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Aix Marseille Université (AMU)-Université de Pau et des Pays de l'Adour (UPPA)-Université de Nantes (UN)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), Advanced Lithium Energy Storage Systems - ALISTORE-ERI (ALISTORE-ERI), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), The authors acknowledge the French RS2E Network for the funding of L.H.B.N.’s Ph.D. thesis, the RS2E and Alistore-ERI networks for the funding of T.B.’s postdoctoral fellowship, and the financial support of Région Nouvelle Aquitaine of the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01 and SODIUM Descartes project ANR-13-DESC-0001-02) and of the European Union’s Horizon 2020 research and innovation program under the grant agreement no. 646433-NAIADES. The Mésocentre de Calcul Intensif Aquitain (MCIA) and the modeling center of ISM are acknowledged for computing facilities. The authors want to thank Yohan Biecher (ICMCB-CNRS) for his help with DMfit., ANR-13-DESC-0001,SODIUM,Batteries à ions sodium pour des robots télécommandés(2013), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Université de Nantes (UN)-Aix Marseille Université (AMU)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Université de Picardie Jules Verne (UPJV)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), and Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA)

Subjects
first- principles DFT calculations, Na3V2(PO4)2F3, Fermi contact, structural distortion * Corresponding author: D Carlier (DanyCarlier@icmcbcnrsfr), electron spin transfer, solid-state NMR, [CHIM.MATE]Chemical Sciences/Material chemistry, Na3V2(PO4)2FO2
Abstract

International audience; The local and electronic structures of Na3V2(PO4)2F3–Na3V2(PO4)2FO2 electrode materials have been investigated by a combination of 23Na and 31P magic-angle spinning NMR spectroscopy and density functional theory calculations. The spin distributions and the 31P NMR Fermi contact shifts in these materials are calculated based on the projector augmented wave approach implemented in the VASP code. Upon oxygen substitution, V4+ ions are formed and involved in highly covalent vanadyl bonds. We show that they exhibit a very specific electronic structure with a single electron on the 3dxy orbital perpendicular to the bi-octahedra axis. The V3+ ions, on the other hand, exhibit a partial occupation of the t2g orbitals by two electrons. The peculiar electronic structure of the V ions is at the origin of the complex spin transfer mechanisms observed in the Na3V2(PO4)2F3–Na3V2(PO4)2FO2 materials and results in the existence of several 23Na and 31P MAS NMR resonances. Owing to the proper signal assignment achieved using DFT calculations, we could estimate the degree of oxygen substitution for fluorine in the materials and discuss the local distribution of V3+/V4+ ions. Furthermore, through the 31P NMR study on the Na3V2(PO4)2FO2 composition, we here demonstrate that a 31P NMR resonance close to 0 ppm can also be observed in paramagnetic materials if there is no proper orbital overlap for the electron spin transfer to occur. Thanks to the proper signal assignment achieved using DFT calculations, we couldestimate the degree of substitution of oxygen for fluorine in the materialsand discuss the local distribution of V3+/V4+ions

Published
2019
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29. Crystal Structures, Local Atomic Environments, and Ion Diffusion Mechanisms of Scandium-Substituted Sodium Superionic Conductor (NASICON) Solid Electrolytes

Author

Deng, Yue, primary, Eames, Christopher, additional, Nguyen, Long H. B., additional, Pecher, Oliver, additional, Griffith, Kent J., additional, Courty, Matthieu, additional, Fleutot, Benoit, additional, Chotard, Jean-Noël, additional, Grey, Clare P., additional, Islam, M. Saiful, additional, and Masquelier, Christian, additional

Published
2018
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31. Ionothermal Synthesis of Polyanionic Electrode Material Na3V2(PO4)2FO2through a Topotactic Reaction

Author

Olchowka, Jacob, Nguyen, Long H. B., Petit, Emmanuel, Camacho, Paula Sanz, Masquelier, Christian, Carlier, Dany, and Croguennec, Laurence

Abstract

Polyanionic Na3V2(PO4)2FO2has been successfully prepared for the first time by ionothermal reaction in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) ionic liquid. Its structure and elemental stoichiometry are confirmed by X-ray diffraction, NMR spectroscopy, and ICP-OES, respectively. Furthermore, the scanning electron microscopy reveals that the as-obtained material possesses an original platelet-like morphology. A topochemical reaction mechanism is proposed to explain the formation of the 3D framework of Na3V2(PO4)2FO2from layered compound α-VOPO4·2H2O. Galvanostatic electrochemical tests indicate a modification of the desodiation and sodiation mechanism of the as-prepared Na3V2(PO4)2FO2compared to those synthesized by conventional solid-state approaches. Furthermore, the electrochemical performance of Na3V2(PO4)2FO2obtained at different cycling rates is also discussed.

Published
2020
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34. Aluminum substitution for vanadium in the Na3V2(PO4)2F3 and Na3V2(PO4)2FO2 type materials.

Author

Olchowka, Jacob, Nguyen, Long H. B., Broux, Thibault, Sanz Camacho, Paula, Petit, Emmanuel, Fauth, François, Carlier, Dany, Masquelier, Christian, and Croguennec, Laurence

Subjects
*VANADIUM, *SOLID solutions, *ALUMINUM, *OXIDATION states, *MATERIALS, *ACIDITY
Abstract

Among the positive electrode materials for Na-ion batteries, Na3V2(PO4)2F3 is considered as one of the most promising and generates high interest. Here, we study the influence of the sol–gel synthesis parameters on the structure and on the electrochemical signature of the partially substituted Na3V2−zAlz(PO4)2(F,O)3 materials. We demonstrate that the acidity of the starting solution influences the vanadium oxidation state of the final product. For the first time we report on the possibility of controlling the double Al/V and O/F substitution that leads to the preparation of the Na3V2−zAlz(PO4)2F1+zO2−z solid solution. [ABSTRACT FROM AUTHOR]

Published
2019
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38. Density Functional Theory-Assisted 31P and 23Na Magic-Angle Spinning Nuclear Magnetic Resonance Study of the Na3V2(PO4)2F3–Na3V2(PO4)2FO2Solid Solution: Unraveling Its Local and Electronic Structures

Author

Nguyen, Long H. B., Sanz Camacho, Paula, Broux, Thibault, Olchowka, Jacob, Masquelier, Christian, Croguennec, Laurence, and Carlier, Dany

Abstract

The local and electronic structures of Na3V2(PO4)2F3–Na3V2(PO4)2FO2electrode materials have been investigated by a combination of 23Na and 31P magic-angle spinning NMR spectroscopy and density functional theory calculations. The spin distributions and the 31P NMR Fermi contact shifts in these materials are calculated based on the projector augmented wave approach implemented in the VASP code. Upon oxygen substitution, V4+ions are formed and involved in highly covalent vanadyl bonds. We show that they exhibit a very specific electronic structure with a single electron on the 3dxyorbital perpendicular to the bi-octahedra axis. The V3+ions, on the other hand, exhibit a partial occupation of the t2gorbitals by two electrons. The peculiar electronic structure of the V ions is at the origin of the complex spin transfer mechanisms observed in the Na3V2(PO4)2F3–Na3V2(PO4)2FO2materials and results in the existence of several 23Na and 31P MAS NMR resonances. Owing to the proper signal assignment achieved using DFT calculations, we could estimate the degree of oxygen substitution for fluorine in the materials and discuss the local distribution of V3+/V4+ions. Furthermore, through the 31P NMR study on the Na3V2(PO4)2FO2composition, we here demonstrate that a 31P NMR resonance close to 0 ppm can also be observed in paramagnetic materials if there is no proper orbital overlap for the electron spin transfer to occur.

Published
2019
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39. Ionothermal Synthesis of Polyanionic Electrode Material Na 3 V 2 (PO 4 ) 2 FO 2 through a Topotactic Reaction.

Author

Olchowka J, Nguyen LHB, Petit E, Camacho PS, Masquelier C, Carlier D, and Croguennec L

Abstract

Polyanionic Na 3 V 2 (PO 4 ) 2 FO 2 has been successfully prepared for the first time by ionothermal reaction in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) ionic liquid. Its structure and elemental stoichiometry are confirmed by X-ray diffraction, NMR spectroscopy, and ICP-OES, respectively. Furthermore, the scanning electron microscopy reveals that the as-obtained material possesses an original platelet-like morphology. A topochemical reaction mechanism is proposed to explain the formation of the 3D framework of Na 3 V 2 (PO 4 ) 2 FO 2 from layered compound α-VOPO 4 ·2H 2 O. Galvanostatic electrochemical tests indicate a modification of the desodiation and sodiation mechanism of the as-prepared Na 3 V 2 (PO 4 ) 2 FO 2 compared to those synthesized by conventional solid-state approaches. Furthermore, the electrochemical performance of Na 3 V 2 (PO 4 ) 2 FO 2 obtained at different cycling rates is also discussed.

Published
2020
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40. Monitoring the Crystal Structure and the Electrochemical Properties of Na 3 (VO) 2 (PO 4 ) 2 F through Fe 3+ Substitution.

Author

Nguyen LHB, Olchowka J, Belin S, Sanz Camacho P, Duttine M, Iadecola A, Fauth F, Carlier D, Masquelier C, and Croguennec L

Abstract

We here present the synthesis of a new material, Na 3 (VO)Fe(PO 4 ) 2 F 2 , by the sol-gel method. Its atomic and electronic structural descriptions are determined by a combination of several diffraction and spectroscopy techniques such as synchrotron X-ray powder diffraction and synchrotron X-ray absorption spectroscopy at V and Fe K edges, 57 Fe Mössbauer, and 31 P solid-state nuclear magnetic resonance spectroscopy. The crystal structure of this newly obtained phase is similar to that of Na 3 (VO) 2 (PO 4 ) 2 F, with a random distribution of Fe 3+ ions over vanadium sites. Even though Fe 3+ and V 4+ ions situate on the same crystallographic position, their local environment can be studied separately using 57 Fe Mössbauer and X-ray absorption spectroscopy at Fe and V K edges, respectively. The Fe 3+ ion resides in a symmetric octahedral environment, while the octahedral site of V 4+ is greatly distorted due to the presence of the vanadyl bond. No electrochemical activity of the Fe 4+ /Fe 3+ redox couple is detected, at least up to 5 V, whereas the reduction of Fe 3+ to Fe 2+ has been observed at ∼1.5 V versus Na + /Na through the insertion of 0.5 Na + into Na 3 (VO)Fe(PO 4 ) 2 F 2 . Comparing to Na 3 (VO) 2 (PO 4 ) 2 F, the electrochemical profile of Na 3 (VO)Fe(PO 4 ) 2 F 2 in the same cycling condition shows a smaller polarization which could be due to a slight improvement in Na + diffusion process thanks to the presence of Fe 3+ in the framework. Furthermore, the desodiation mechanism occurring upon charging is investigated by operando synchrotron X-ray diffraction and operando synchrotron X-ray absorption at V K edge.

Published
2019
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41. Aluminum substitution for vanadium in the Na 3 V 2 (PO 4 ) 2 F 3 and Na 3 V 2 (PO 4 ) 2 FO 2 type materials.

Author

Olchowka J, Nguyen LHB, Broux T, Sanz Camacho P, Petit E, Fauth F, Carlier D, Masquelier C, and Croguennec L

Abstract

Among the positive electrode materials for Na-ion batteries, Na3V2(PO4)2F3 is considered as one of the most promising and generates high interest. Here, we study the influence of the sol-gel synthesis parameters on the structure and on the electrochemical signature of the partially substituted Na3V2-zAlz(PO4)2(F,O)3 materials. We demonstrate that the acidity of the starting solution influences the vanadium oxidation state of the final product. For the first time we report on the possibility of controlling the double Al/V and O/F substitution that leads to the preparation of the Na3V2-zAlz(PO4)2F1+zO2-z solid solution.

Published
2019
Full Text
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