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

The importance of exploring new solid electrolytes for all-solid-state batteries has led to significant interest in NASICON-type materials. Here, the Sc3+-substituted NASICON compositions Na3ScxZr2-x(SiO4)2-x(PO4)1+x (termed N3) and Na2ScyZr2-y(SiO4)1-y(PO4)2+y (termed N2) (x, y = 0 – 1) are studied as model Na+-ion conducting electrolytes for solid-state batteries. The influence of Sc3+ substitution on the crystal structures and local atomic environments has been characterized by powder X-ray diffraction (XRD) and neutron powder diffraction (NPD), as well as solid-state 23Na, 31P, and 29Si nuclear magnetic resonance (NMR) spectroscopy. A phase transition between 295 and 473 K from monoclinic C2/c to rhombohedral R c is observed for the N3 compositions, while N2 compositions crystallize in a rhombohedral R c unit cell in this temperature range. Alternating current (AC) impedance spectroscopy, molecular dynamics (MD) and high temperature 23Na NMR are in good agreement, showing that with a higher Sc3+ concentration, the ionic conductivity (about 10-4 S/cm at 473 K) decreases and the activation energy for ion diffusion increases. 23Na NMR experiments indicate that the nature of the Na+-ion motion is two-dimensional on the local atomic scale of NMR though the long-range diffusion pathways are three-dimensional. In addition, a combination of MD, bond valence, maximum entropy/Rietveld and van Hove correlation methods has been used, to reveal that the Na+-ion diffusion in these NASICON materials is three-dimensional and that there is a continuous exchange of sodium between Na(1) and Na(2) sites

Determination of Electrolyte Transport Properties with a Multi-Reference-Electrode Cell

International audienceFast charging is one of the main challenges of electric vehicles, partly due to electrolyte transport limitations across porous electrodes in Li-ion cells. The determination of electrolyte transport properties is crucial for modeling fast charging and adjust cell design accordingly. In this work, diffusion coefficient and cation transference number for a 1 M LiPF6 in ethylene carbonate/diethyl carbonate mixture (1:1 in weight) are determined using a multireference electrode electrochemical cell (four herein). It is an extension of the work by Farkhondeh et al. [J. Phys. Chem. C 2017, 121, 8, 4112–4129] that was based on two reference electrodes. Long galvanostatic pulses allow for building up concentration gradients across the cell (restricted diffusion), which are subsequently let to relax under open circuit. The multiple voltages (three herein) measured between the four reference electrodes are simultaneously analyzed with four different procedures that involve a combination of analytic methods and nonlinear regression of the data with a numerical model. The parameter mean values and 95%-confidence intervals are evaluated using Student t-distribution and the bootstrap method. Values reported by combining all methods together are: $D=2.62\,\times {10}^{-10}\,\left[\pm \,2.29\, \% \right]\,{{\rm{m}}}^{2}\,{{\rm{s}}}^{-1},$ ${t}_{+}^{0}=\,0.204\,\left[\pm 12.25\, \% \right]$ at 25 °C

Thermal behaviors and grafting process of LDH/benzene derivative hybrid.

International audienceThermal behaviors of four hybrid layered double hydroxide (LDH) phases have been studied by thermogravimetric analyses coupled with mass spectroscopy, temperature dependence of X-ray powder diffraction measurements, and temperature dependence of infrared spectroscopy measurements. Inorganic zinc-aluminium LDH main layers (with a Zn2+/Al3+ cationic ratio of 2) inserted the following four organic anions: benzene carboxylate, 4-hydroxy-benzene carboxylate, benzene sulfonate and 4-hydroxybenzene sulfonate. The four LDH hybrids have been synthesized by the coprecipitation method. The as-prepared samples have been characterized and their compositions were determined. Thermal evolution of the crystalline phases during the dehydration (occurring before 200 ◦C) and the dehydroxylation (occurring between 200 and 300 ◦C) gave evidence for organic anion grafting onto the inorganic main layer. The thermal stability of the LDH hybrid system depends on the nature of the intercalated aromatic anion. The thermal grafting process can be monitored, as well as its thermal reversibility, by choosing the functionalizations of the benzenic anion and the temperature of the applied heat treatment

Size dependent dipolar interactions in iron oxide nanoparticle monolayer and multilayer Langmuir-Blodgett films

The dipolar interactions in monolayer and multilayer assemblies of iron oxide nanoparticles have been investigated as a function of the nanoparticle size. The magnetic properties of iron oxide nanocrystals of various sizes have been measured for particles as powders and assembled in mono-and multilayers by the Langmuir-Blodgett technique, and compared to the behavior of non-interacting nanoparticles. It is shown that increasing dipolar interactions lead to higher blocking temperatures and to deviation from the Neel-Brown law. Dipolar interactions are found to be stronger for particles assembled in thin films compared to powdered samples. The effect of interactions increases strongly with the nanoparticle size in agreement with simulations, leading to an unusual behaviour for the larger particles assembled in monolayer, which could be a signature of a superferromagnetic state.Financial support was provided by the Agence Nationale pour la Recherche (ANR MAGARRAYS) and the Direction Générale de l’Armement (DGA). The authors thank Cedric Leuvrey for SEM pictures, Dris Ihiawakrim and Corinne Ulhaq for TEM pictures, Christophe Lefevre for XRD refinement, and Alain Derory for technical support with SQUID measurements

Phosphate structure and lithium environments in lithium phosphorus oxynitride amorphous thin films

Lithium ion-conducting glasses attract wide interest for electrochemical applications like efficient energy storage devices. This work presents a structural study on involved bonding units, based on X-ray photoelectron spectroscopy and infrared spectroscopy, of lithium phosphorus oxide and oxynitride amorphous thin films prepared by RF magnetron sputtering. A thorough consideration of the mid- and far-infrared spectral regions demonstrated structural changes at the phosphate units and the lithium ion environments triggered by nitrogen incorporation and post-deposition thermal treatment. It was found that films prepared by sputtering in pure nitrogen atmosphere have about 75 % of their nitrogen atoms in sites doubly coordinated with phosphorus (P–N=P), and the rest in triply coordinated sites. It was shown also that nitrogen incorporation favors the stability of lithium ions, while annealing enhances ionic conductivity of the oxynitride films

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

International audienceThe importance of exploring new solid electro-lytes for all-solid-state batteries has led to significant interest in NASICON-type materials. Here, the Sc3+-substituted NASICON compositions (NaScZr2-x)-Sc-3-Zr-x(SiO4)(2-x)(PO4)(1+x) (termed N3) and Na2ScyZr2-y(SiO4)(1-y)(PO4)(2+y) (termed N2) (x, y = 0-1) are studied as model Na+-ion conducting electrolytes for solid-state batteries. The influence of Sc3+ substitution on the crystal structures and local atomic environments has been characterized by powder X-ray diffraction (XRD) and neutron powder diffraction (NPD), as well as solid-state Na-23, P-31, and Si-29 nuclear magnetic resonance (NMR) spectroscopy. A phase transition between 295 and 473 K from monoclinic C2/c to rhombohedral R (3) over barc is observed for the N3 compositions, while N2 compositions crystallize in a rhombohedral R (3) over barc unit cell in this temperature range. Alternating current (AC) impedance spectroscopy, molecular dynamics (MD), and high temperature Na-23 NMR studies are in good agreement, showing that, with a higher Sc3+ concentration, the ionic conductivity (of about 10(-4) S/cm at 473 K) decreases and the activation energy for ion diffusion increases. Na-23 NMR experiments indicate that the nature of the Na+-ion motion is two-dimensional on the local atomic scale of NMR although the long-range diffusion pathways are three-dimensional. In addition, a combination of MD, bond valence, maximum entropy/Rietveld, and van Hove correlation methods has been used to reveal that the Na+-ion diffusion in these NASICON materials is three-dimensional and that there is a continuous exchange of sodium ions between Na(1) and Na(2) sites