Showing papers by "Dany Carlier published in 2017"
TL;DR: In this article, an operando X-ray absorption spectroscopy at vanadium K edge during the electrochemical extraction of Na+ was performed in order to monitor the redox processes involved in this compound.
Abstract: Among the series of polyanionic positive electrodes for sodium-ion batteries having the general formula Na3V2(PO4)2F3–yOy (0 ≤ y ≤ 2), the composition Na3V2(PO4)2F3 (y = 0) has the highest theoretical energy that offers competitive electrochemical performances compared to sodium transition metal oxides. Recently, the structural phase diagram from Na3V2(PO4)2F3 to Na1V2(PO4)2F3 has been thoroughly investigated by operando synchrotron X-ray diffraction revealing an unexpected structural feature for the end member composition. In fact, the crystal structure of Na1V2(PO4)2F3 has two very different vanadium environments within each bioctahedron that suggests a charge disproportionation of two VIV into VIII and VV. This work shows an operando X-ray absorption spectroscopy at vanadium K edge during the electrochemical extraction of Na+ in order to monitor the redox processes involved in this compound. The large data set provided by this experiment has been processed by the principal component analysis combined w...
53 citations
TL;DR: In this article, the projector augmented-wave (PAW) method was used to model possible defects in paramagnetic material and to compute the Fermi contact shifts expected for Li nuclei located in their proximity.
Abstract: In a recent study, we showed by solid-state NMR that LiVPO4F, which is a promising material as positive electrode for Li-ion batteries, often exhibits some defects that may affect its electrochemical behavior. In this paper, we use DFT calculations based on the projector augmented-wave (PAW) method in order to model possible defects in this (paramagnetic) material and to compute the Fermi contact shifts expected for Li nuclei located in their proximity. The advantage of the PAW approach versus FP-LAPW we have been previously using is that it allows considering large supercells suitable to model a diluted defect. In the first part of this paper, we aim to validate the Fermi contact shifts calculation using the PAW approach within the VASP code. Then we apply this strategy for modeling possible defects in LiVPO4F. By analogy with the already existing homeotypic LiVOPO4 phase, we first replace one fluoride ion, along the VO2F4 chains, by an oxygen one and consider, in a second step, an association with a lit...
32 citations
TL;DR: In this article, the synthesis of the related Na-based phase crystallizing in the Tavorite-like structure was reported for the first time, and its in-depth structural and electronic characterization was conducted by a combination of several techniques, spanning electron and X-ray powder diffraction as well as infrared and Xray absorption spectroscopy.
Abstract: Tavorite-type compositions offer rich crystal chemistry for positive electrodes in rechargeable batteries, among which LiVIIIPO4F has the highest theoretical energy density (i.e. 655 Wh kg−1). In this article, we report for the first time the synthesis of the related Na-based phase crystallizing in the Tavorite-like structure. Its in-depth structural and electronic characterization was conducted by a combination of several techniques, spanning electron and X-ray powder diffraction as well as infrared and X-ray absorption spectroscopy. The magnetic susceptibility measurement reveals an average oxidation state for vanadium slightly higher than V3+. This slight oxidation is supported by infrared and X-ray absorption spectroscopies which highlight the presence of V4+[double bond, length as m-dash]O vanadyl-type defects leading to an approximated NaVIII0.85(VIVO)0.15(PO4)F0.85 composition. In this material, the profile of the diffraction lines is governed by a strong strain anisotropic broadening arising from the competitive formation between the ionic V3+–F and the covalent V4+[double bond, length as m-dash]O bonds. This material shows a limited extraction of sodium, close to 15% of the theoretical capacity. Indeed, its electrochemical properties are strongly inhibited by the intrinsic low sodium mobility in the Tavorite framework.
29 citations
DOI•
01 Jan 2017
TL;DR: Burbano et al. as mentioned in this paper used sparse cyclic excitations to explain the low Ionic conductivity of stoichiometric Li7La3Zr2O12 and generated Figure S3 (d) in the "Validation of the Interatomic Potential" section.
Abstract: This Jupyter notebook, and the accompanying data, constitute supporting data for "Sparse Cyclic Excitations Explain the Low Ionic Conductivity of Stoichiometric Li7La3Zr2O12", Burbano et al. Phys. Rev. Lett. 116 135901 (2016) (https://doi.org/10.1103/PhysRevLett.116.135901).
This dataset reproduces the steps taken in order to generate Figure S3 (d) in the "Validation of the Interatomic Potential" section of the Supplemental Information for this article.
12 citations