Operando Neutron Powder Diffraction Using Cylindrical Cell Design: The Case of LiNi_0.5Mn_1.5O₄ vs Graphite

In order to follow the structural changes correlated to the evolution of the lithium content in high voltage battery systems (based on a disordered LiNi_0.5Mn_1.5O₄ (d-LNMO) and a graphite electrode), we developed a new cylindrical cell suitable for operando neutron diffraction measurements. The cell, containing two grams of electroactive materials, is able to cycle at a fast rate (1C) with reliable electrochemical performance. The operando neutron diffraction measurements revealed the evolution of the lattice parameters of both the d-LNMO and graphite phases, notably showing the transitions between graphite lithiation stages. Furthermore, as a result of Rietveld refinements, the lithium consumption could be attributed mainly to the formation of a solid electrolyte interphase (SEI) layer on the graphite surface. This approach provides important insights helping to optimize the loading of the electroactive materials in batteries, especially for high voltage systems in which side reactions and lithium consumption can occur during cycling

Mechanistic and Kinetic Study of the Electrochemical Charge and Discharge of La₂MgNi₉ by in Situ Powder Neutron Diffraction

The intermetallic La₂MgNi₉ has been investigated as negative electrode material for NiMH battery by means of in situ neutron powder diffraction. This hydride-forming compound exhibits suitable plateau pressures ranging within the practical electrochemical window and leads to significant reversible electrochemical capacities. Charge and discharge of the composite electrode have been performed in beam following various current rates and galvanostatic intermittent titration. From the diffraction data analysis, phase amounts and cell volumes have been extracted, allowing the interpretation of the hydride formation and decomposition. From the evolution of the diffraction line widths, differences are observed between charge and discharge with the possible formation of an intermediate γ phase on charge. The electrode readily responds to current rate variations and does not show any kinetic limitation in the range C/10 and C/5 (C/<i>n</i>: full capacity C in <i>n</i> hours). This material shows excellent properties regarding electrochemical storage of energy

Localization and Impact of Pb-Non-Bonded Electronic Pair on the Crystal and Electronic Structure of Pb₂YSbO₆

The synthesis and crystal structure evolution of the double perovskite Pb₂YSbO₆ is reported for the first time. The structure has been analyzed in the temperature range between 100 and 500 K by using a combination of synchrotron and neutron powder diffraction. This compound shows two consecutive first order phase transformations as previously observed for a subgroup of Pb₂RSbO₆ perovkites (R = rare earths). The thermodynamic parameters associated with the phase transitions were calculated using differential scanning calorimetry (DSC), and the role of the diverse cations of the structure was studied from DFT calculations for the room temperature polymorph. The crystal structure evolves from a <i>C</i>2/<i>c</i> monoclinic structure (a^–b^–b^– tilting system in Glazer’s notation) to another monoclinic <i>P</i>2₁<i>/n</i> (a^–a^–b⁺) phase with an incommensurate modulation and finally to a cubic <i>Fm</i>3̅<i>m</i> perovskite (a⁰a⁰a⁰). The highly distorted nature of the room temperature crystal structure seems to be driven by the polarization of the Pb lone pair which shows a marked local effect in the atomic spatial arrangements. Moreover, the lone pairs have been localized from DFT calculations and show an antiferroelectric ordering along the <i>b</i> monoclinic axis

Structural Evolution of Air-Exposed Layered Oxide Cathodes for Sodium-Ion Batteries: An Example of Ni-doped Na_<i>x</i>MnO₂

Sodium-ion batteries have recently aroused the interest of industries as possible replacements for lithium-ion batteries in some areas. With their high theoretical capacities and competitive prices, P2-type layered oxides (NaxTMO2) are among the obvious choices in terms of cathode materials. On the other hand, many of these materials are unstable in air due to their reactivity toward water and carbon dioxide. Here, Na0.67Mn0.9Ni0.1O2 (NMNO), one of such materials, has been synthesized by a classic sol–gel method and then exposed to air for several weeks as a way to allow a simple and reproducible transition toward a Na-rich birnessite phase. The transition between the anhydrous P2 to the hydrated birnessite structure has been followed via periodic XRD analyses, as well as neutron diffraction ones. Extensive electrochemical characterizations of both pristine NMNO and the air-exposed one vs sodium in organic medium showed comparable performances, with capacities fading from 140 to 60 mAh g–1 in around 100 cycles. Structural evolution of the air-exposed NMNO has been investigated both with ex situ synchrotron XRD and Raman. Finally, DFT analyses showed similar charge compensation mechanisms between P2 and birnessite phases, providing a reason for the similarities between the electrochemical properties of both materials

Anion−π and Halide–Halide Nonbonding Interactions in a New Ionic Liquid Based on Imidazolium Cation with Three-Dimensional Magnetic Ordering in the Solid State

We present the first magnetic phase of an ionic liquid with anion−π interactions, which displays a three-dimensional (3D) magnetic ordering below the Néel temperature, <i>T</i>_N = 7.7 K. In this material, called Dimim­[FeBr₄], an exhaustive and systematic study involving structural and physical characterization (synchrotron X-ray, neutron powder diffraction, direct current and alternating current magnetic susceptibility, magnetization, heat capacity, Raman and Mössbauer measurements) as well as first-principles analysis (density functional theory (DFT) simulation) was performed. The crystal structure, solved by Patterson-function direct methods, reveals a monoclinic phase (<i>P</i>2₁ symmetry) at room temperature with <i>a</i> = 6.745(3) Å, <i>b</i> = 14.364(3) Å, <i>c</i> = 6.759(3) Å, and β = 90.80(2)°. Its framework, projected along the <i>b</i> direction, is characterized by layers of cations [Dimim]⁺ and anions [FeBr₄]⁻ that change the orientation from layer to layer, with Fe···Fe distances larger than 6.7 Å. Magnetization measurements show the presence of 3D antiferromagnetic ordering below <i>T</i>_N with the existence of a noticeable magneto–crystalline anisotropy. From low-temperature neutron diffraction data, it can be observed that the existence of antiferromagnetic order is originated by the antiparallel ordering of ferromagnetic layers of [FeBr₄]⁻ metal complex along the <i>b</i> direction. The magnetic unit cell is the same as the chemical one, and the magnetic moments are aligned along the <i>c</i> direction. The DFT calculations reflect the fact that the spin density of the iron ions spreads over the bromine atoms. In addition, the projected density of states (PDOS) of the imidazolium with the bromines of a [FeBr₄]⁻ metal complex confirms the existence of the anion−π interaction. Magneto–structural correlations give no evidence for direct iron–iron interactions, corroborating that the 3D magnetic ordering takes place via superexchange coupling, the Fe–Br···Br–Fe interplane interaction being defined as the main exchange pathway