Showing papers by "Dany Carlier published in 2019"
01 Apr 2019
TL;DR: In this paper, the electrochemical and structural properties of a series of three different Na3V2(PO4)2F3 samples (with or without carbon coatings of different natures), obtained via different synthesis methods, are compared through operando high-resolution synchrotron X-ray diffraction.
Abstract: The electrochemical and structural properties of a series of three different Na3V2(PO4)2F3 samples (with or without carbon coatings of different natures), obtained via different synthesis methods, are compared through operando high‐resolution synchrotron X‐ray diffraction. The pristine materials all possess negligible quantities of oxygen defects, as probed by the b/a lattice parameters ratios and solid‐state NMR. Operando X‐ray diffraction recorded during charge at C/2 reveals subtle differences between the samples (of different particle size, morphology, and carbon‐coating nature) in the crystallinity of the intermediate compositions formed within the Na3V2(PO4)2F3–NaV2(PO4)2F3 phase diagram. A new temperature‐controlled operando cell is used to determine this phase diagram at 0 °C, mostly unchanged compared to that of recorded at 25 °C. Very high charging and discharging rates are demonstrated and intermediate compositions can be spotted operando even up to 25 C rate at which the compositional phase diagram is only slightly altered compared to that recorded under equilibrium conditions. Optimized carbon‐coated Na3V2(PO4)2F3 shows exceptional rate and electrochemical cycling capabilities, as demonstrated by hard carbon//Na3V2(PO4)2F3 18650 prototypes of 75 Wh kg−1 that can be charged or discharged 4000 times at 1 C rate.
80 citations
TL;DR: For the first time, it is demonstrated that the acidity of the starting solution influences the vanadium oxidation state of the final product.
39 citations
TL;DR: In this paper, the local and electronic structures of Na3V2(PO4)2F3-nodes have been investigated by a combination of 23Na and 31P magic-angle spinning NMR spectroscopy and density fun.
Abstract: 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 fun...
33 citations
TL;DR: The electrochemical profile of Na3(VO)Fe(PO4)2F2 in the same cycling conditions shows a smaller polarization which could be due to a slight improvement in Na+ diffusion process thanks to the presence of Fe3+ in the framework.
Abstract: We here present the synthesis of a new material, Na3(VO)Fe(PO4)2F2, by the sol–gel method. Its atomic and electronic structural descriptions are determined by a combination of several diffraction a...
25 citations
TL;DR: DFT calculations are used to elucidate the solid-state nuclear magnetic resonance (NMR) spectra of Li2MnO3 which, combined with X-ray diffraction (XRD), provide a full description of disorder in this compound.
Abstract: The complete description of defective structures and their impact on materials behavior is a great challenge due to difficulties associated with their reliable characterization in the nanoscale. In this paper, density functional theory (DFT) calculations are used to elucidate the solid-state nuclear magnetic resonance (NMR) spectra of Li2MnO3 which, combined with X-ray diffraction (XRD), provide a full description of disorder in this compound. While XRD allows accurate quantification of planar defects, the use of solid-state NMR reveals limited vacancy concentrations that were undetected by XRD as NMR is highly sensitive to the atomic local environments. The combination of these methods is here proved highly effective in overcoming the challenges of describing in great detail limited concentrations of disorder in transition metal oxides, providing information about structural variables that are essential to their application.
16 citations
TL;DR: Layered oxide compositions Li3-xNaxNi2SbO6 have been prepared by solid-state synthesis and a complete solid solution is evidenced and characterized by X-ray and neutron diffraction as well as 7Li and 23Na solid- state nuclear magnetic resonance spectroscopy.
Abstract: Layered oxide compositions Li3–xNaxNi2SbO6 have been prepared by solid-state synthesis. A complete solid solution is evidenced and characterized by X-ray and neutron diffraction as well as 7Li and 23Na solid-state nuclear magnetic resonance spectroscopy. The transition-metal layer is characterized by the classic honeycomb Ni2+/Sb5+ ordering, whereas a more uncommon randomly mixed occupancy of lithium and sodium is evidenced within the alkali interslab space. In situ X-ray diffraction and density functional theory calculations show that this alkali disordered feature is entropically driven. Fast cooling then appears as a synthesis root to confine bidimensional alkali glass within crystalline layered oxides.
14 citations
TL;DR: The use of density functional theory calculations are presented to assign the experimentally observed NMR shifts to the crystallographic sites in Na2FePO4F, where it is found that the results do not agree with the previously reported assignment based upon simple geometry arguments.
12 citations