Anisotropic Structural Changes Research Articles

Quantifying Electrochemical Degradation in Single-Crystalline LiNi0.8Mn0.1Co0.1O2 –Graphite Pouch Cells through Operando X-Ray and Postmortem Investigations

Layered nickel-rich lithium transition-metal oxides (LiNixMnyCo1−x−yO2; where ≥ 0.8), with single-crystalline morphology, are promising future high-energy-density Li-ion battery cathodes due to their ability to mitigate particle-cracking-induced degradation. This is due to the absence of grain boundaries in these materials, which prevents the build-up of bulk crystallographic strain during electrochemical cycling. Compared to their polycrystalline counterparts, there is a need to study single-crystalline Ni-rich cathodes using x-ray methods in uncompromised machine-manufactured industrylike full cells to understand their bulk degradation mechanisms as a function of different electrochemical cycling protocols. This can help us identify factors to improve their long-term performance. Here, through in-house x-ray studies of pilot-line-built LiNi0.8Mn0.1Co0.1O2–graphite A7 pouch cells, it is shown that their electrochemical-capacity fade under harsh conditions (2.5–4.4 V and 40 °C for 100 cycles at a C/3 rate) primarily stems from the high-voltage reconstruction of the cathode surface from a layered to a cubic (rock-salt) phase that impedes the Li+ kinetics and increases cell impedance. Postmortem electron and x-ray microscopy show that these cathodes can withstand severe anisotropic structural changes and show no cracking when cycled under such conditions. Comparing these results to those from commercial Li-ion cells with surface-modified single-crystalline Ni-rich cathodes, it is identified that cathode surface passivation can mitigate this type of degradation and prolong cycle life. In addition to furthering our understanding of degradation in single-crystalline Ni-rich cathodes, this work also accentuates the need for practically relevant and reproducible fundamental investigations of Li-ion cells and presents a methodology for achieving this. Published by the American Physical Society 2024

Self-Assembly and -Cross-Linking Lamellar Films by Nanophase Separation with Solvent-Induced Anisotropic Structural Changes.

In this study, we have prepared thermally and chemically stable lamellar polymer films via humid annealing. The amphiphilic polymer poly(N-dodecyl acrylamide-stat-3-(trimethoxysilyl)propyl acrylate) [p(DDA/TMSPA)] forms a self-assembled lamellar structure via annealing at 60 °C under 98% relative humidity (humid annealing) due to nanophase separation between the hydrophobic dodecyl side and main chains with the amide groups that contain adsorbed water. Moreover, a self-cross-linking reaction of TMSPA proceeds during the humid annealing. As a result, the lamellar films maintain their structure even when annealed above their glass-transition temperature. On the other hand, the films swell when immersed in toluene. The highly ordered lamellar structure collapses due to the swelling but can be re-established by subsequent humid annealing. A multilayer freestanding film can be exfoliated via sonication in toluene. The exfoliated multilayer films initially form a dome-shaped structure, which is converted to a plate-shaped structure upon humid annealing. In their entirety, these results reveal that the molecular-scale movement associated with the formation of the lamellar structure induces a macroscopic structural change. Consequently, p(DDA/TMSPA) can be considered as a new stimulus-responsive polymer.

Layered-Rocksalt Intergrown Cathode for High-Capacity Zero-Strain Battery Operation

The continuous dependence on high-performance lithium-ion batteries leads to a pressing demand for advanced cathode materials of high energy density along with excellent cycling stability. Here we demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each individual phase, including the high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt phase. Based on this concept, lithium nickel ruthenium oxide of a main layered structure (R-3 m) with intergrown rocksalt (Fm-3 m) is developed, which delivers a high capacity with good rate performance. More importantly, the interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for the layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a general design principle is successfully extrapolated and experimentally verified in a series of compositions. The success of such layered-rocksalt intergrown structure exemplifies a new concept of battery electrode design and opens up a vast space of compositions to develop high-performance intergrown cathodes for advanced energy storage devices.

Layered-rocksalt intergrown cathode for high-capacity zero-strain battery operation

The dependence on lithium-ion batteries leads to a pressing demand for advanced cathode materials. We demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each phase, including high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt. Based on this concept, lithium nickel ruthenium oxide of a main layered structure (Rbar{3}m) with intergrown rocksalt (Fmbar{3}m) is developed, which delivers a high capacity with good rate performance. The interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a design principle is successfully extrapolated and experimentally verified in a series of compositions. Here, we show the success of such layered-rocksalt intergrown structure exemplifies a new battery electrode design concept and opens up a vast space of compositions to develop high-performance intergrown cathode materials.

(Invited) Si Anodes for Li-Ion Batteries: Experimental Studies on Li-Inventory and Pre-Lithiation Approaches

Li inventory and pre-lithiation methods for Si-anode containing Li-ion batteries are evaluated via a number of avenues, and are summarized briefly in this abstract. The capacity fade of the Si-graphite electrode was tracked using a capacity over-sized LiFePO4 cathode in a diagnostic cell. With essentially limitless Li inventory the intrinsic capacity fade was monitored over hundreds of cycles, without limitations/complications from Li metal in a half cell. The introduction of lithium inventory to the cell was accomplished in three ways. To date we have (1) investigated in detail the synthesis and electrochemistry of Li5FeO4 as a prelithiation source. Approach #1. We are currently working towards a blended LFO-NMC cathode to understand the cross-reactivity, impedance changes, and capacity changes in the resultant electrode. (2) Introducing lithium inventory to the cell #2. Overlithiated NCM, i.e., Li1+xNCM523O2, was found to be a viable way to introduce lithium to the cathode with minimal weight increase and no residual byproduct. However, we observed that the electrochemical cycling stability of overlithiated NCM is compromised, likely a result of the irreversible anisotropic structural changes. Work is ongoing to assess the nature of the irreversibility and we are developing strategies to minimize its impact. (3) Introducing lithium inventory to the cell #3. We will report that the 5 V spinel cathode, or Li1+xNi0.5Mn1.5O4, could be further lithiated (x>0) via an ammonia-based chemical lithiation reaction. This material was paired with a Si-graphite anode in a full cell. The excess lithium is released during the first charge and accounts for the first cycle irreversible capacity loss. Subsequent cycling only at 3 to 4.7 V shows a higher capacity and similar fade rate compared to the baseline, un-lithiated cathode.

High-Performance Li-Ion Batteries Using Nickel-Rich Lithium Nickel Cobalt Aluminium Oxide-Nanocarbon Core-Shell Cathode: In Operando X-ray Diffraction.

Nickel-rich layered, mixed lithium transition-metal oxides have been pursued as a propitious cathode material for the future-generation lithium-ion batteries due to their high energy density and low cost. Nevertheless, acute side reactions between Ni4+ and carbonate electrolyte lead to poor cycling as well as rate performance, which limits their large-scale applications. Here, core-shell like LiNi0.8Co0.15Al0.05O2 (NCA)-carbon composite synthesized by a solvent-free mechanofusion method is reported to solve this issue. Such a core-shell structure exhibits a splendid rate as well as stable cycling when compared to the physically blended NCA. In operando X-ray diffraction studies show that both materials experience anisotropic structural change, i.e., stacking c-axis undergoes a gradual expansion followed by an abrupt shrinkage; meanwhile, the a-axis contracts during the charging process and vice versa. Interestingly, the core-shell material displays a significantly high reversible capacity of 91% in the formation cycle at 0.1C and a retention of 84% at 0.5C after 250 cycles, whereas pristine NCA retains 71%. The robust mechanical force assisted dry coating obtained by the mechanofusion method shows improved electrochemical performance and demonstrates its practical feasibility.

Origin of focused laser irradiation-induced enhancement of perpendicular magnetic anisotropy in Pt/Co/Pt thin films investigated by spatially resolved x-ray absorption spectroscopy

The origin of the focused single-pulse laser irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt film is investigated by the x-ray absorption near-edge structure and extended x-ray absorption fine structure techniques combined with the photoelectron emission microscope. A significant increase of the Co–Co bond length in both in-plane and out-of-plane directions is observed on the periphery of the laser spot, at which perpendicular magnetization appears. With increasing laser power density towards the center of the laser spot, anisotropic structural changes are observed accompanied by the reappearance of in-plane magnetization. The enhancement of perpendicular magnetization is attributed to the lattice expansion-induced magnetoelastic effect, while the in-plane compressive strain in the Co film is suggested to be the origin of the reappearance of in-plane magnetization at higher laser power densities.

Insights on the Proton Insertion Mechanism in the Electrode of Hexagonal Tungsten Oxide Hydrate

This study reveals the transport behavior of lattice water during proton (de)insertion in the structure of the hexagonal WO3·0.6H2O electrode. By monitoring the mass evolution of this electrode material via electrochemical quartz crystal microbalance, we discovered (1) WO3·0.6H2O incorporates additional lattice water when immersing in the electrolyte at open circuit voltageand during initial cycling; (2) The reductive proton insertion in theWO3 hydrate is a three-tier process, where in the first stage 0.25 H+ is inserted per formula unit of WO3while simultaneously 0.25 lattice water is expelled; then in the second stage 0.30 naked H+ is inserted, followed by the third stage with 0.17 H3O+ insertedper formula unit. Ex situ XRD reveals that protonation of the WO3 hydrate causes consecutive anisotropic structural changes: it first contracts along the c-axis but later expands along the ab planes. Furthermore, WO3·0.6H2O exhibits impressive cycle life over 20 000 cycles, together with appreciable capacity and promising rate performance.

Unprecedented Bistability in Spin-Crossover Solids Based on the Retroaction of the High Spin Low-Spin Interface with the Crystal Bending.

There has been in recent years a continuous increase in spatiotemporal investigations of the dynamics of the first-order transitions in spin-crossover (SCO) solids. In single crystals, this phenomenon proceeds via a single domain nucleation and propagation, characterized in some systems with the presence of two equivalent and symmetric interface orientations, between the high-spin (HS) and low-spin (LS) phases, due to the anisotropic structural change of the unit cell at the transition. The present investigations bring an experimental evidence of the reversible driving of the translational and rotational degrees of freedom of the HS-LS interface. In addition to its rectilinear displacement, the interface rotates between two stable angles, 60o and 120o. It is demonstrated that while the translation motion is accompanied by a crystal's length change, the interface rotation is controlled by the crystal's bending. These results are well-explained in the frame of an elastic theoretical description in which the effect of the crystal bending, on the stability of the interface's orientation, is simulated by applying a moment of forces on the crystal. It is found that the interface orientation becomes unstable beyond a threshold load value, announcing the emergence of a bistability in SCO solids, taking place at constant HS fraction and volume. This work underlines the sensitive character of the interface orientation to any macroscopic crystal bending, an idea that can be used to develop a new generation of robust stress sensors, working at constant volume, thus avoiding deterioration problems due to crystal fatigue.

Destabilization of pseudo-Jahn–Teller distortion in cesium-doped hexagonal tungsten bronzes

In Cs-doped hexagonal tungsten bronzes (Cs-HTBs), X-ray diffraction–Rietveld analysis has revealed that an increase in the alkali dopant and oxygen vacancies (VO) elongate the c-axis, contract the a-axis, and decrease the deviations of the W–O distance and W coordinates from those of a regular WO6 octahedron. These structural changes are interpreted as a destabilization of pseudo-Jahn–Teller (PJT) distortion by electron donation from Cs+ and VO. A dramatic difference is observed in the destabilization efficiency between the donated electrons from Cs+ and VO, suggesting that the former and latter electrons should be delocalized and localized, respectively. First-principles density functional theory calculations using optB86b-vdW functionals reproduced the behavior of c-axis elongation and a-axis contraction by Cs doping. The projected orbital density of states indicates that the Cs-derived electrons are donated to W-5dyz and W-5dzx orbitals to extend along the c-axis, whereas the VO-derived electrons are donated to W-5dxy and W-5dx2−y2 orbitals to strongly localize in the a–b plane. In HTBs, an anisotropic increase and decrease in the t2g* antibonding electrons from the doped alkali are concluded to induce the anisotropic structural change in PJT distortions.

Anisotropy enhanced X-ray scattering from solvated transition metal complexes.

Time-resolved X-ray scattering patterns from photoexcited molecules in solution are in many cases anisotropic at the ultrafast time scales accessible at X-ray free-electron lasers (XFELs). This anisotropy arises from the interaction of a linearly polarized UV-Vis pump laser pulse with the sample, which induces anisotropic structural changes that can be captured by femtosecond X-ray pulses. In this work, a method for quantitative analysis of the anisotropic scattering signal arising from an ensemble of molecules is described, and it is demonstrated how its use can enhance the structural sensitivity of the time-resolved X-ray scattering experiment. This method is applied on time-resolved X-ray scattering patterns measured upon photoexcitation of a solvated di-platinum complex at an XFEL, and the key parameters involved are explored. It is shown that a combined analysis of the anisotropic and isotropic difference scattering signals in this experiment allows a more precise determination of the main photoinduced structural change in the solute, i.e. the change in Pt-Pt bond length, and yields more information on the excitation channels than the analysis of the isotropic scattering only. Finally, it is discussed how the anisotropic transient response of the solvent can enable the determination of key experimental parameters such as the instrument response function.

Electrodynamic response of the type-II Weyl semimetalYbMnBi2

Weyl fermions play a major role in quantum field theory but have been quite elusive as fundamental particles. Materials based on quasi two-dimensional bismuth layers were recently designed and provide an arena for the study of the interplay between anisotropic Dirac fermions, magnetism and structural changes, allowing the formation of Weyl fermions in condensed matter. Here, we perform an optical investigation of YbMnBi$_2$, a representative type II Weyl semimetal, and contrast its excitation spectrum with the optical response of the more conventional semimetal EuMnBi$_2$. Our comparative study allows us disentangling the optical fingerprints of type II Weyl fermions, but also challenge the present theoretical understanding of their electrodynamic response.

Magnetically driven anisotropic structural changes in the atomic laminateMn2GaC

Inherently layered magnetic materials, such as magnetic ${M}_{n+1}A{X}_{n}$ (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition ${{M}_{n}}_{+1}A{X}_{n}$ consists of ${M}_{n+1}{X}_{n}$ blocks separated by atomically thin $A$-layers where $M$ is a transition metal, $A$ an A-group element, $X$ refers to carbon and/or nitrogen, and $n$ is typically 1, 2, or 3. Here, we show that the recently discovered magnetic $\mathrm{M}{\mathrm{n}}_{2}\mathrm{GaC}$ MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of $\mathrm{M}{\mathrm{n}}_{2}\mathrm{GaC}$ MAX phases in future magnetoelectric and magnetocaloric applications.

Crystal architectures of a layered silicate on monodisperse spherical silica particles cause the topochemical expansion of the core-shell particles

Anisotropic structural changes in an expandable layered silicate (directed towards the c–axis) occurring on isotropic and monodisperse microspheres were detected by measurable increases in the grain size. The hierarchical changes were observed through pursing the sophisticated growth of expandable layered silicate crystals on monodisperse spherical silica particles with diameters of 1.0 μm; the core–shell hybrids with a quite uniform grain size were successfully produced using a rotating Teflon-lined autoclave by reacting spherical silica particles in a colloidal suspension with lithium and magnesium ions under alkaline conditions at 373 K. The size distribution of the core-shell particles tended to be uniform when the amount of lithium ions in the initial mixture decreased. The intercalation of dioctadecyldimethylammonium ions into the small crystals through cation-exchange reactions expanded the interlayer space, topochemically increasing the grain size without any change occurring in the shapes of the core–shell particles.

Synthesis and characterisation of a new six-coordinated thermochromic Ni complex

The Ni(II) complex [Ni(diethylenetriamine)(2,6-bis(hydroxymethyl)pyridine)]·PF6·CF3COO·H2O is described here. A single crystal X-ray crystallographic study revealed that the Ni(II) in the complex has a six-coordinated octahedral structure. The complex shows thermochromic behaviour in the solid state. X-ray crystallographic studies at various temperatures suggested that the thermochromism is caused by anisotropic structural change. The relationship between the structural change and the colour change was confirmed by absorption spectrum and TD-DFT calculation.

A Better Characterization of Spinal Cord Damage in Multiple Sclerosis: A Diffusional Kurtosis Imaging Study

The spinal cord is a site of predilection for MS lesions. While diffusion tensor imaging is useful for the study of anisotropic systems such as WM tracts, it is of more limited utility in tissues with more isotropic microstructures (on the length scales studied with diffusion MR imaging) such as gray matter. In contrast, diffusional kurtosis imaging, which measures both Gaussian and non-Gaussian properties of water diffusion, provides more biomarkers of both anisotropic and isotropic structural changes. The aim of this study was to investigate the cervical spinal cord of patients with MS and to characterize lesional and normal-appearing gray matter and WM damage by using diffusional kurtosis imaging. Nineteen patients (13 women, mean age = 41.1 ± 10.7 years) and 16 controls (7 women, mean age = 35.6 ± 11.2-years) underwent MR imaging of the cervical spinal cord on a 3T scanner (T2 TSE, T1 magnetization-prepared rapid acquisition of gradient echo, diffusional kurtosis imaging, T2 fast low-angle shot). Fractional anisotropy, mean diffusivity, and mean kurtosis were measured on the whole cord and in normal-appearing gray matter and WM. Spinal cord T2-hyperintense lesions were identified in 18 patients. Whole spinal cord fractional anisotropy and mean kurtosis (P = .0009, P = .003), WM fractional anisotropy (P = .01), and gray matter mean kurtosis (P = .006) were significantly decreased, and whole spinal cord mean diffusivity (P = .009) was increased in patients compared with controls. Mean spinal cord area was significantly lower in patients (P = .04). Diffusional kurtosis imaging of the spinal cord can provide a more comprehensive characterization of lesions and normal-appearing WM and gray matter damage in patients with MS. Diffusional kurtosis imaging can provide additional and complementary information to DTI on spinal cord pathology.

Transient Stress Imaging after Irradiation with a Focused Femtosecond Laser Pulse inside a Single Crystal

A focused femtosecond laser pulse inside a single crystal induces anisotropic structural changes, which depend on the atomic arrangement of the crystal. The transient stress after the photoexcitation should be responsible for the structural changes. In this study, we developed a novel transient stress observation system by time-resolved birefringence analysis and observed the relative amplitude and azimuth of the transient stresses after the photoexcitation inside MgO and LiF crystals. The principle and advantage of the observation system are described in this paper by comparing the system with a conventional stress observation method, a crossed-Nicols imaging method.

Transient Stress Imaging after Irradiation with a Focused Femtosecond Laser Pulse inside a Single Crystal

A focused femtosecond laser pulse inside a single crystal induces anisotropic structural changes, which depend on the atomic arrangement of the crystal. The transient stress after the photoexcitation should be responsible for the structural changes. In this study, we developed a novel transient stress observation system by time-resolved birefringence analysis and observed the relative amplitude and azimuth of the transient stresses after the photoexcitation inside MgO and LiF crystals. The principle and advantage of the observation system are described in this paper by comparing the system with a conventional stress observation method, a crossed-Nicols imaging method.

Theory of the orbital-selective Mott transition in ferromagneticYTiO3under high pressure

We explore the effect of pressure on the electronic properties of the ferromagnetic Mott-Hubbard insulator $\mathrm{Y}\mathrm{Ti}{\mathrm{O}}_{3}$. We show that the pressure-induced insulator-metal transition is accompanied by anisotropic structural changes driven by the competition between strongly orbital dependent one-electron hopping and strong, multiorbital electronic correlations in the real crystal structure of $\mathrm{Y}\mathrm{Ti}{\mathrm{O}}_{3}$. Our results are relevant for the general understanding of the intricate and interdependent changes in the orbital and magnetic structure of correlated ferromagnetic insulators showing Mott transitions.

Anisotropic Structural Relaxation and Its Correlation with the Excess Energy Diffusion in the Incipient Process of Photodissociated MbCO: High-Resolution Analysis via Ensemble Perturbation Method

The effectiveness of the ensemble perturbation method, in which many pairs of perturbed and unperturbed molecular dynamics simulations are executed for the ensemble average, has been demonstrated by calculating the subtle anisotropic structural change of carbonmonoxy myoglobin (MbCO) triggered by ligand photolysis. The results show that Mb largely expands in the direction perpendicular to the heme plane and slightly contracts in the horizontal one. This agrees well with the report in the transient grating experiment. In addition, it is suggested that the expansion contributes strongly to the fast energy-transfer process to the water solvent because it is undergone almost within several picoseconds. The mechanical work done on the solvent by the expansion within 1 ps was thermodynamically estimated to be 4.8 kcal/mol.