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See detailSpray-drying as a versatile synthesis method for fluorophosphate-based compounds as cathodes material for Na-ion batteries
Bodart, Jérôme ULiege; Eshraghi, Nicolas ULiege; Mahmoud, Abdelfattah ULiege et al

Conference (2019, July 22)

Fluorophosphate compounds attract much attention as cathode materials for Na-ion batteries. Indeed, thanks to the inductive effect of the fluoride and phosphate groups, such compounds exhibit a relatively ... [more ▼]

Fluorophosphate compounds attract much attention as cathode materials for Na-ion batteries. Indeed, thanks to the inductive effect of the fluoride and phosphate groups, such compounds exhibit a relatively high working potential and good theoretical capacity [1]. In this work, we focus on the iron (Na2FePO4F (NFPF)) and vanadium (Na3V2(PO4)3F3 (NVPF)) based fluorophosphate materials which are characterized by a high theoretical capacity of 124 mAh/g and 128 mAh/g, respectively. In addition, the iron-based phase is also more environmental friendly due to the low toxicity of the iron. The preparation of such complex phases using conventional solid-state route requires at least two steps with long heat treatment durations. Here, we report a facile aqueous synthesis using the spray-drying method that can be used for both NFPF and NVPF materials and that can be tuned in order to optimize the composition and the morphology of the desired materials. The major limitation of phosphate-based electrodes is their low intrinsic electronic conductivity. The synthesis of composites with carbon is an effective strategy for the enhancement of the electronic conductivity of these compounds. Spray-drying is a suitable method to incorporate carbon in composite compounds due to the high homogeneity of the obtained particle [2]. It is also a cost effective and up-scalable technique which can produce large quantities of the desired material. Here, we report the influence of the carbon addition on the structural, morphological and electrochemical properties of NFPF and NVPF compounds. The prepared composite materials were investigated by combining several characterisation techniques such as XRD, SEM and TEM. The electrochemical properties were evaluated by galvanostatic cycling and electrochemical impedance spectroscopy in Na-ion batteries. [less ▲]

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See detailSodium Iron Sulfate Alluaudite Solid Solution for Na-ion Batteries: Moving Towards Stoichiometric Na2Fe2(SO4)3
Jungers, Thomas ULiege; Mahmoud, Abdelfattah ULiege; Malherbe, Cédric ULiege et al

in Journal of Materials Chemistry A (2019), 7

Thanks to the inductive effect of the sulfate groups, sodium iron sulfate alluaudites display the highest electrode potential amongst the Fe-based compounds studied in sodium-ion batteries. Here, we ... [more ▼]

Thanks to the inductive effect of the sulfate groups, sodium iron sulfate alluaudites display the highest electrode potential amongst the Fe-based compounds studied in sodium-ion batteries. Here, we report the synthetic strategy that has allowed us to obtain the elusive Na2Fe2(SO4)3 stoichiometric compound through a reverse-strike coprecipitation method in organic medium. We experimentally confirm the hypothesis that the stoichiometric compound transforms upon further heat treatment into the previously reported sodium-rich solid solution and an iron sulfate secondary phase. X-ray diffraction and 57Fe Mössbauer spectroscopy do not reveal any striking structure difference between the stoichiometric and Na-rich compounds, in agreement with the current understanding that the instability of the stoichiometric phase is due to the repulsion between Fe2+ ions in the Fe2O10 dimers bridged by sulfate groups. Despite less-than-optimal powder microstructure, electrochemical activity of the stoichiometric phase could be demonstrated through operando X-ray diffraction. These findings are expected to shift attention towards the (near)-stoichiometric compositions, which offer the highest theoretical specific capacities thanks to their optimal Na/Fe ratio. [less ▲]

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See detailHydrothermal synthesis and electrochemical properties of Fe1.19(PO4)(OH)0.57(H2O)0.43/C cathode material for Li-ion batteries
Mahmoud, Abdelfattah ULiege; Karegeya, Claude; Sougrati, Moulay Tahar et al

Conference (2019, January 29)

Recent rapid development of the portable electronic devices, growing interest in the electric vehicles and increasing integration the renewable energies required the development of cost-effective and high ... [more ▼]

Recent rapid development of the portable electronic devices, growing interest in the electric vehicles and increasing integration the renewable energies required the development of cost-effective and high energy storage systems. Lithium-ion batteries are considered as system of the choice for variety of mobile and stationary applications. However, new electrode materials are demanded to increase the energy density of Li-ion batteries. This presentation will report on the preparation and study of Fe1.19(PO4)(OH)0.57(H2O)0.43/C ((FPHH/C) composite as positive electrode material with high capacity and long cycle-life [1, 2]. FPHH/C (C= carbon black (CB) and carbon nanotubes (CNT)) composites were obtained by one-step the hydrothermal synthesis route. These cathode materials showed an excellent reversible capacity corresponding to 1.19 Li reaction. This is attributed to the stable and open structure of FPHH and also to the effect of carbon addition (CB and CNT) that improves the electronic percolation of the composite. The study of the reaction mechanism of FPHH/CNT during cycling by combining operando XRD and 57Fe Mossbauer spectroscopy (Figure 1) shows that the insertion mechanism is a monophasic reaction with 10% volume variations associated to the Fe3+/Fe2+ redox reaction [2]. References 1. C. Karegeya, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschini. Electrochimica Acta 250 (2017) 49-58. 2. A. Mahmoud, C. Karegeya, M. T. Sougrati, J. Bodart, B. Vertruyen, R. Cloots, P-E. Lippens, F. Boschini. ACS Applied Materials and interfaces 10 (2018) 34202-34211. [less ▲]

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See detailPoly(ionic liquid)-derived N-doped carbons with hierarchical porosity for lithium- and sodium-ion batteries
Alkarmo, Walid ULiege; Ouhib, Farid ULiege; Aqil, Abdelhafid ULiege et al

in Macromolecular Rapid Communications (2019), 40(1), 1800545

The performance of lithium‐ and sodium‐ion batteries relies notably on the accessibility to carbon electrodes of controllable porous structure and chemical composition. This work reports a facile ... [more ▼]

The performance of lithium‐ and sodium‐ion batteries relies notably on the accessibility to carbon electrodes of controllable porous structure and chemical composition. This work reports a facile synthesis of well‐defined N‐doped porous carbons (NPCs) using a poly(ionic liquid) (PIL) as precursor, and graphene oxide (GO)‐stabilized poly(methyl methacrylate) (PMMA) nanoparticles as sacrificial template. The GO‐stabilized PMMA nanoparticles are first prepared and then decorated by a thin PIL coating before carbonization. The resulting NPCs reach a satisfactory specific surface area of up to 561 m2 g−1 and a hierarchically meso‐ and macroporous structure while keeping a nitrogen content of 2.6 wt%. Such NPCs deliver a high reversible charge/discharge capacity of 1013 mA h g−1 over 200 cycles at 0.4 A g−1 for lithium‐ion batteries, and show a good capacity of 204 mA h g−1 over 100 cycles at 0.1 A g−1 for sodium‐ion batteries. [less ▲]

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See detailStudy of the Structural and Magnetic Properties of Co-Substituted Ba2Mg2Fe12O22 Hexaferrites Synthesized by Sonochemical Co-Precipitation
Koutzarova, Tatyana; Kolev, Svetoslav; Krezhov, Kiril et al

in Materials (2019), 12(9 1414),

Ba2Mg0.4Co1.6Fe12O22 was prepared in powder form by sonochemical co-precipitation and examined by X-ray diffraction, Mössbauer spectroscopy and magnetization measurements. Careful XRD data analyses ... [more ▼]

Ba2Mg0.4Co1.6Fe12O22 was prepared in powder form by sonochemical co-precipitation and examined by X-ray diffraction, Mössbauer spectroscopy and magnetization measurements. Careful XRD data analyses revealed the Y-type hexaferrite structure as an almost pure phase with a very small amount of CoFe2O4 as an impurity phase (about 1.4%). No substantial changes were observed in the unit cell parameters of Ba2Mg0.4Co1.6Fe12O22 in comparison with the unsubstituted compound. The Mössbauer parameters for Ba2Mg0.4Co1.6Fe12O22 were close to those previously found (within the limits of uncertainty) for undoped Ba2Mg2Fe12O22. Isomer shifts (0.27–0.38 mm/s) typical for high-spin Fe3+ in various environments were evaluated and no ferrous Fe2+ form was observed. However, despite the indicated lack of changes in the iron oxidation state, the cationic substitution resulted in a significant increase in the magnetization and in a modification of the thermomagnetic curves. The magnetization values at 50 kOe were 34.5 emu/g at 4.2 K and 30.5 emu/g at 300 K. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves were measured in magnetic fields of 50 Oe, 100 Oe, 500 Oe and 1000 Oe, and revealed the presence of two magnetic phase transitions. Both transitions are shifted to higher temperatures compared to the undoped compound, while the ferrimagnetic arrangement at room temperature is transformed to a helical spin order at about 195 K, which is considered to be a prerequisite for the material to exhibit multiferroic properties. [less ▲]

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See detailStructural and magnetic characterization of Y-type hexaferrite powders prepared by sol-gel auto-combustion and sonochemistry
Georgieva, B.; Kolev, S.; Krezhov, K. et al

in Journal of Magnetism and Magnetic Materials (2019), 477

We present results from a study on the influence of the preparation technique on the structural and magnetic properties of Ba0.5Sr1.5Zn2Fe12O22 powders synthesized by citric-acid sol-gel auto-combustion ... [more ▼]

We present results from a study on the influence of the preparation technique on the structural and magnetic properties of Ba0.5Sr1.5Zn2Fe12O22 powders synthesized by citric-acid sol-gel auto-combustion and sonochemistry and characterized by X-ray diffraction, scanning electron microscopy and magnetic measurements. Two magnetic intermediate phases were observed at room temperature in magnetic fields of moderate strength. Metamagnetic phase transitions were observed in an ac magnetic field. Their temperature increased with the magnetic field amplitude. © 2019 Elsevier B.V. [less ▲]

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See detailSynthesis of Na2FePO4F by spray drying in order to optimise the composition and morphology for Na-ion batteries applications
Bodart, Jérôme ULiege; Violle, Denis; Mahmoud, Abdelfattah ULiege et al

Poster (2018, December 13)

Li-ion batteries are well-developed for numerous applications but the limited resources and expensive price of lithium urge the necessity to find a viable alternative to lithium. Na-ion batteries are ... [more ▼]

Li-ion batteries are well-developed for numerous applications but the limited resources and expensive price of lithium urge the necessity to find a viable alternative to lithium. Na-ion batteries are considered as a good alternative to Li-ion batteries due to the abundance and well-distributed presence of sodium on earth crust. It is then necessary to develop new electrode material for sodium batteries, with low cost, high energy density and long cycling life. This work presents the synthesis of Na2FePO4F by spray-drying method. In order to compensate the low conductivity of phosphate based materials, carbon nanotubes (CNT) are added during the preparation of the precursor solution. The solution/suspension is spray-dried to obtain a composite precursor and after calcination the desired phase. The spray-drying technique is appropriate to variate the morphology and to control it by modifying the injection parameters (Pressure, temperature, flow rate, injection nozzle). The addition of carbon nanotubes lead to an undesired reduction of the iron to the metallic state. To resolve this problem, the concentration of carbon was modified until no metallic iron remained in the composition. In the present work, two methodology of injection are compared to study their influence on the phase purity, size and morphology of the particles as well as their electrochemical properties. X-ray diffraction is used to verify the crystallinity and the purity of the phase obtained. The results show that a pure phase is obtained in optimized condition and samples with low amount of impurities like Fe2O3 are obianed when no optimization is done. The oxidation state of Fe in the samples, the nature of the impurities and the quantities are confirmed by Mossbauer spectroscopy. During calcination, we observed a phenomenon of carbothermal reduction which was evidenced by Mossbauer spectroscopy (Figure 1). SEM analysis shows the morphology of the obtained particles with a size range between 1,5𝜇m and 8𝜇m using bi-fluid and rotary nozzles, respectively. The electrochemical performances are tested by galvanostatic cycling in sodium half cells and show significant improvement with the optimization of morphology and carbon content. [less ▲]

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See detailOne Step Hydrothermal Synthesis of Fe1.19(PO4)(OH)0.57(H2O)0.43 composite cathode material and Its Electrochemical Properties in Li-Ion Batteries
Mahmoud, Abdelfattah ULiege; Karegeya, Claude; Sougrati, Moulay Tahar et al

Conference (2018, December 13)

Lithium-ion batteries (LIBs) have been widely applied as a power source for portable and stationary energy storage systems. In this work, we report the electrochemical performance of FPHH/CB and FPHH/CNT ... [more ▼]

Lithium-ion batteries (LIBs) have been widely applied as a power source for portable and stationary energy storage systems. In this work, we report the electrochemical performance of FPHH/CB and FPHH/CNT cathode materials for Li-ion batteries where FPHH represents Fe1.19(PO4)(OH)0.57(H2O)0.43 while carbon black (CB) and carbon nanotubes (CNT) were used as precursors in the one-pot hydrothermal synthesis. We show that the addition of conducting carbon black into the solution has a strong influence on reducing the particle size and tailoring their morphology. Thanks to its favorable microstructural characteristics, the FPHH-10 wt% C and FPHH-20 wt% C materials exhibited good performance [1]. The CNT also improve the performance of FPHH such as capacity retention. The study of the reaction mechanism of FPHH/CNT during cycling by combining operando XRD and 57Fe Mössbauer spectroscopy (Figure 1) shows that the insertion mechanism is a monophasic reaction with 10% volume variations associated to the Fe3+/Fe2+ redox reaction [2]. Acknowledgements A. Mahmoud is grateful to University of Liege and FRS-FNRS for the grants and thanks to the Walloon region for a Beware Fellowship Academia 2015-1, RESIBAT n° 1510399. Part of this work was supported by the Walloon Region under the “PE PlanMarshall2.vert” program (BATWAL – 1318146). References 1. C. Karegeya, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschini, Electrochimica Acta 250 (2017) 49-58. 2. A. Mahmoud, C. Karegeya, M. T. Sougrati, J. Bodart, B. Vertruyen, R. Cloots, P-E. Lippens, F. Boschini. ACS Applied Materials and interfaces 10 (2018) 34202-34211. [less ▲]

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See detailStoichiometry in the alluaudite-type Na2Fe2(SO4)3 for Na-ion cathode
Jungers, Thomas ULiege; Vertruyen, Bénédicte ULiege

Poster (2018, December 13)

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See detailCrystal chemistry and polymorphism of an iron-tungsten mixed oxide
Caubergh, Stéphane ULiege; Jungers, Thomas ULiege; Mahmoud, Abdelfattah ULiege et al

Conference (2018, December 13)

Iron tungstate Fe2WO6 attracts increasing interest in two areas of applications due to its photoelectrochemical behaviour. Fe2WO6 is studied either as a photocatalyst for degradation of environmental ... [more ▼]

Iron tungstate Fe2WO6 attracts increasing interest in two areas of applications due to its photoelectrochemical behaviour. Fe2WO6 is studied either as a photocatalyst for degradation of environmental pollutants or as a photoanode for water oxidation in tandem devices. Recently, some of its magneto-dielectric properties have been reported but its magnetic and electric properties remain nebulous. Indeed, Fe2WO6 iron tungstate exists as two or three crystal structures with different organizations of the FeO6 and WO6 octahedra. The conditions of polymorphism are still unclear: structures were reported in the literature for only two of the three polymorphs (α and γ) and very little is known about the third polymorph (β). In the present work, we could synthesize for the first time a complete set of the three polymorphs as single-phase products by spray-drying, thereby confirming the existence of the β-polymorph. We revised the structural model for the α-polymorph and solved the structure of the β-polymorph. The new procedure of synthesis also allowed us to control and tune the Fe/W ratio and investigate the possibility for a solid solution domain. The final products were characterized by means of X-Ray Diffraction (synchrotron data), Rietveld refinement, Scanning Electron Microscopy and 57Fe Mossbauer spectroscopy. [less ▲]

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See detailSpray drying synthesis of Na3V2(PO4)2F3/C cathode material for Na-ion batteries: study of the effect of the carbon source on electrochemical performance
Eshraghi, Nicolas ULiege; Bodart, Jérôme ULiege; Mahmoud, Abdelfattah ULiege et al

Poster (2018, November 25)

Lithium-ion batteries have enjoyed great success and have outperformed other rechargeable battery system since 1980. However, Li-ion batteries face many challenges and limitations: safety, the low ... [more ▼]

Lithium-ion batteries have enjoyed great success and have outperformed other rechargeable battery system since 1980. However, Li-ion batteries face many challenges and limitations: safety, the low abundance of lithium in the Earth’s crust. Recently, Sodium-ion batteries attracted a lot of interest as a potential alternative to lithium-ion batteries for large-scale energy storage applications, due to the large natural abundance and lower cost of sodium. In recent years, fluorophosphates with the NASICON (Na Super-Ionic Conductor) type structure are considered among the most interesting series of cathode materials for Li/Na-ion batteries, because they exhibit rich chemistry, attractive lithium/sodium insertion properties and thus offer promising electrochemical properties [1]. Na3V2(PO4)2F3 (NVPF) attracted high attention thanks to its promising electrochemical properties. The inductive effects of both PO43- and F- allow for a high working potential combined with a high theoretical specific capacity due to the multiple oxidation states of vanadium[1-2]. One of the key drawbacks of Na3V2(PO4)2F3 electrodes is their low intrinsic electronic conductivity. NVPF and NVPF/carbon composite materials were prepared by spray-drying method using the same conditions used in our previous work [2]. Spray drying is a cost-effective and easily up-scalable route to prepare homogeneous multi-component powders, thus making it a suitable method to incorporate carbon in the composite powder. We used different carbon sources like conductive carbons (MWCNTs, Carbon Black, etc) and organic sources (PVA, Citric Acid, Ascorbic acid, etc) to prepare NVPF/carbon composite powders. the structural, electrochemical, and morphological properties of the synthesized Na3V2(PO4)2F3/C samples were systematically investigated in order to understand the influence of carbon source on structural and morphological properties and most importantly electrochemical performance of NVPF and NVPF/carbon composite cathode materials for Na-ion batteries. The chemical diffusion of Na ions was studied using results obtained by varying scan rates in cyclic voltammetry measurements. Raman spectroscopy is used to evaluate the quality in disordered carbon materials and its electronic conductivity [3] and compared the results with the results from EIS and cycling performance of different samples. Acknowledgments The authors are grateful to University of Liege and FRS-FNRS for grants. Part of this work was supported by the Walloon Region under the “PE PlanMarshall2.vert” program (BATWAL – 1318146). A. Mahmoud thanks to the Walloon region for a Beware Fellowship Academia 2015-1, RESIBAT n° 1510399. References: [1] R. A. Shakoor, D-H. Seo, H. Kim, Y-U. Park, J. Kim, S-W. Kim, H. Gwon, S. Leec and K. Kang, Mater. Chem. 22 (2012) 20535–20541. [2] N. Eshraghi, S. Caes, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschin, Electrochimica Acta, 228, (2017), 319-324. [3] A. Mahmoud, S. Caes, M. Brisbois, R. P. Hermann, L. Berardo, A. Schrijnemakers, C. Malherbe, G. Eppe, R. Cloots, B. Vertruyen, F. Boschin J Solid State Electrochem. 22 (2018) 103-112. [less ▲]

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See detailElectrochemical mechanism and effect of carbon addition during hydrothermal synthesis to improve the electrochemical performance of Fe1.19(PO4)(OH)0.57(H2O)0.43 cathode material for Li-ion batteries
Mahmoud, Abdelfattah ULiege; karegeya, Claude; Sougrati, Moulay Tahar et al

Poster (2018, November 25)

Since the introduction of lithium-ion batteries (LIBs) to market in 1991, their performance has improved significantly, which has been achievable through development in materials technologies. However ... [more ▼]

Since the introduction of lithium-ion batteries (LIBs) to market in 1991, their performance has improved significantly, which has been achievable through development in materials technologies. However, further breakthroughs are still needed to ameliorate cycle-life, safety and energy density of LIBs. This requires new electrode materials and a detailed understanding of the electrochemical mechanisms during cycling. Transition metal phosphates are interesting candidates as cathode materials for LIBs [1]. In this work, we report the electrochemical performance of FPHH/C and FPHH/CNT composites where FPHH represents Fe1.19(PO4)(OH)0.57(H2O)0.43 while carbon black and carbon nanotubes (CNT) were used as precursors in the one-pot hydrothermal synthesis, respectively. We show that the addition of conducting carbon black into the solution has a strong influence on reducing the particle size and tailoring their morphology, but does not interfere with the formation of the FPHH phase. Thanks to its favorable microstructural characteristics, the FPHH-10 wt% C and FPHH-20 wt% C materials exhibited good performance [2]. The CNT also improve the performance of FPHH such as capacity retention (500 cycles at 1 C). The mechanisms of lithiation-delithiation were investigated by combining operando X-ray diffraction and 57Fe Mössbauer spectroscopy. FPHH undergoes a monophasic reaction based on Fe3+/Fe2+ redox process. However, the variations of the lattice parameters and 57Fe quadrupole splitting indicate a more complex mechanism than a random occupation of the vacant sites within FPHH. This can be related to the peculiar structure of FPHH formed by chains of face sharing (Fe0.6•0.4)O6 octahedra connected by PO4 tetrahedra and by channels for Li diffusion along [100] and [010] directions. The existence of Fe vacancies provide interconnections between the one-dimensional channels, improving lithium diffusion within FPHH. This mechanism, combined with the addition carbon black or nanotubes in the solution prior to hydrothermal treatment as a simple and effective way to reduce particle size and improve electronic conductivity, provides good cycle life and rate capability for FPHH. Acknowledgements A. Mahmoud is grateful to University of Liege and FRS-FNRS for the grants and thanks to the Walloon region for a Beware Fellowship Academia 2015-1, RESIBAT n° 1510399. Part of this work was supported by the Walloon Region under the “PE PlanMarshall2.vert” program (BATWAL – 1318146). References 1. C. Karegeya, A. Mahmoud, F. Hatert, B. Vertruyen, R. Cloots, P.E. Lippens, F. Boschini, Journal of Power Sources 388 (2018) 57-64. 2. C. Karegeya, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschini, Electrochim. Acta 250 (2017) 49-58. [less ▲]

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See detailCrystal chemistry and polymorphism of an iron-tungsten mixed oxide
Caubergh, Stéphane ULiege; Jungers, Thomas ULiege; Mahmoud, Abdelfattah ULiege et al

Conference (2018, October 17)

Among the complex metal oxides, the crystal chemistry of the iron-tungsten oxide Fe2WO6 is of interest because of the existence of several crystal structures with different organizations of the FeO6 and ... [more ▼]

Among the complex metal oxides, the crystal chemistry of the iron-tungsten oxide Fe2WO6 is of interest because of the existence of several crystal structures with different organizations of the FeO6 and WO6 octahedra. The conditions of polymorphism are still unclear: structures were reported in the literature for only two of the three polymorphs (α and γ) and very little is known about the third polymorph (β). For the first time, we could synthesize a complete set of the three polymorphs as single-phase products by spray-drying. We proposed a new structural model for α-polymorph. We confirmed the existence of β-polymorph and solved its structure. With this procedure of synthesis, we were also able to control and tune the Fe/W ratio and investigate the possibility for a solid solution domain. The final products were characterized by means of X-Ray Diffraction (synchrotron data), Rietveld refinement, Scanning Electron Microscopy and 57Fe Mossbauer spectroscopy. [less ▲]

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See detailCrystal chemistry and polymorphism of an iron-tungsten mixed oxide
Caubergh, Stéphane ULiege; Jungers, Thomas ULiege; Mahmoud, Abdelfattah ULiege et al

Poster (2018, October 17)

Among the complex metal oxides, the crystal chemistry of the iron-tungsten oxide Fe2WO6 is of interest because of the existence of several crystal structures with different organizations of the FeO6 and ... [more ▼]

Among the complex metal oxides, the crystal chemistry of the iron-tungsten oxide Fe2WO6 is of interest because of the existence of several crystal structures with different organizations of the FeO6 and WO6 octahedra. The conditions of polymorphism are still unclear: structures were reported in the literature for only two of the three polymorphs (α and γ) (image A) and very little is known about the third polymorph (β). In this work, our aim is to synthesize the different polymorphs of Fe2WO6 as pure products in order to be able to investigate the crystal structures and properties in more detail. We report about the synthesis procedures that we have developed starting from aqueous solutions to minimize the effects of diffusion length and maintain a homogeneous distribution of the cations during the phase formation. The stable solutions were spray-dried in order to obtain spherical particles of dried powder as small and homogeneous as possible (around 1 µm). With this technique, we were also able to control and tune the Fe/W ratio and investigate the possibility for a solid solution domain. The dried powders underwent heat treatments at various temperatures and durations before characterization by means of X-Ray Diffraction, Rietveld refinement, Scanning Electron Microscopy and 57Fe Mossbauer spectroscopy. [less ▲]

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See detailDispersion of conductive carbon allotropes inside Na2FePO4F particles by spray-drying
Berardo, Loris ULiege; Mahmoud, Abdelfattah ULiege; Caes, Sebastien et al

Poster (2018, October 02)

Among all phosphate based compounds, Na2FePO4F (NFPF) is identified as a promising low-cost material for Li and Na-ion batteries [2]. Beside a relatively high voltage (3.6 V vs. Li+/Li0), Na2FePO4F ... [more ▼]

Among all phosphate based compounds, Na2FePO4F (NFPF) is identified as a promising low-cost material for Li and Na-ion batteries [2]. Beside a relatively high voltage (3.6 V vs. Li+/Li0), Na2FePO4F exhibits a good theoretical capacity (~135 mAh/g) and an excellent stability of the structure during the intercalation process. However, despite these powerful advantages, the main drawback of Na2FePO4F cathode material is its low conductivity leading to mediocre cycling performance. The aim of this work is to enhance the electronic conductivity of Na2FePO4F particles by addition of carbon nanotubes (CNT) or carbon black (CB) during the spray-drying synthesis [3]. The structural, electrochemical and morphological properties of the synthesized Na2FePO4F-xCB and Na2FePO4F-xCNT (x = wt% of carbon) were investigated by various techniques in order to compare the effect of CB and CNT. [less ▲]

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See detailElectrochemical Mechanism and Effect of Carbon Nanotubes on the Electrochemical Performance of Fe1.19(PO4)(OH)0.57(H2O)0.43 Cathode Material for Li-Ion Batteries
Mahmoud, Abdelfattah ULiege; Karegeya, Claude; Moulay Tahar, Sougrati et al

in ACS Applied Materials and Interfaces (2018), 10(40), 3420234211

A hydrothermal synthesis route was used to synthesize iron(III) phosphate hydroxide hydrate–carbon nanotube composites. Carbon nanotubes (CNT) were mixed in solution with Fe1.19(PO4)(OH)0.57(H2O)0.43 ... [more ▼]

A hydrothermal synthesis route was used to synthesize iron(III) phosphate hydroxide hydrate–carbon nanotube composites. Carbon nanotubes (CNT) were mixed in solution with Fe1.19(PO4)(OH)0.57(H2O)0.43 (FPHH) precursors for one-pot hydrothermal reaction leading to the FPHH/CNT composite. This produces a highly electronic conductive material to be used as a cathode material for Li-ion battery. The galvanostatic cycling analysis shows that the material delivers a specific capacity of 160 mAh g–1 at 0.2 C (0.2 Li per fu in 1 h), slightly decreasing with increasing current density. A high charge–discharge cyclability is observed, showing that a capacity of 120 mAh g–1 at 1 C is maintained after 500 cycles. This may be attributed to the microspherical morphology of the particles and electronic percolation due to CNT but also to the unusual insertion mechanism resulting from the peculiar structure of FPHH formed by chains of partially occupied FeO6 octahedra connected by PO4 tetrahedra. The mechanism of the first discharge–charge cycle was investigated by combining operando X-ray diffraction and 57Fe Mössbauer spectroscopy. FPHH undergoes a monophasic reaction with up to 10% volume changes based on the Fe3+/Fe2+ redox process. However, the variations of the FPHH lattice parameters and the 57Fe quadrupole splitting distributions during the Li insertion–deinsertion process show a two-step behavior. We propose that such mechanism could be due to the existence of different types of vacant sites in FPHH, including vacant “octahedral” sites (Fe vacancies) that improve diffusion of Li by connecting the one-dimensional channels. [less ▲]

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