A Combination of X‐Ray Tomography and Carbon Binder Modeling: Reconstructing the Three Phases of LiCoO2 Li‐Ion Battery Cathodes

X‐ray tomography allows the active‐material domain (LiCoO₂) of Li‐ion battery cathodes to be imaged, but it is unable to resolve the carbon‐binder domain (CBD). Here, a new method for creating a complete 3D representation (virtual design) of all three phases of a cathode is provided; this includes the active‐material domain, the CBD, and the electrolyte‐filled pore space. It combines X‐ray tomographic data of active material with a statistically modeled CBD. Two different statistical CBD morphology models are compared as examples: i) a random cluster model representing a standard mixture of carbon black and polyvenylidene fluoride (PVDF) and ii) a fiber model. The transport parameters are compared in a charged and a discharged cathode. The results demonstrate that the CBD content and morphology changes the ionic and electronic transport parameters dramatically and thus cannot be neglected. Calculations yield that the fiber model shows up to three times higher electrical conductivity at the same CBD content (discharged case) and better ionic diffusion conditions for all CBD contents. In the charged case, the morphology impact on electrical conduction is small. This effective method to generate transport parameters for different CBDs can be transferred to other CBD morphologies and electrodes.     

Dynamics of the Morphological Degradation of Si‐Based Anodes for Li‐Ion Batteries Characterized by In Situ Synchrotron X‐Ray Tomography

The alloying reaction of silicon with lithium in negative electrodes for lithium‐ion batteries causes brutal morphological changes that severely degrade their cyclability. In this study, the dynamics of their expansion and contraction, of their cracking in the bulk and of their debonding at the interface with the current collector are visualized by in situ synchrotron X‐ray computed tomography and quantified from appropriate 3D imaging analyses. Two electrodes made with same silicon material having reasonable particle size distribution from an applied point of view are compared: one fabricated according to a standard process and the other one prepared with a maturation step, which consists in storing the electrode in a humid atmosphere for a few days before drying and cell assembly. All morphological degradations are significantly restrained for the matured electrode, confirming the great efficiency of this maturation step to produce a more ductile and resilient electrode architecture, which is at the origin of the major improvement in their cyclability.     

Lithiation‐Induced Dilation Mapping in a Lithium‐Ion Battery Electrode by 3D X‐Ray Microscopy and Digital Volume Correlation

Recent advances in high‐resolution 3D X‐ray computed tomography (CT) allow detailed, non‐destructive 3D structural mapping of a complete lithium‐ion battery. By repeated 3D image acquisition (time lapse CT imaging) these investigations of material microstructure are extended into the fourth dimension (time) to study structural changes of the device in operando. By digital volume correlation (DVC) of successive 3D images the dimensional changes taking place during charge cycling are quantified at the electrode level and at the Mn₂O₄ particle scale. After battery discharging, the extent of lithiation of the manganese (III/IV) oxide grains in the electrode is found to be a function of the distance from the battery terminal with grains closest to the electrode/current collector interface having the greatest expansion (≈30%) and grains furthest from the current collector and closest to the counter electrode showing negligible dilation. This implies that the discharge is limited by electrical conductivity. This new CT+DVC technique is widely applicable to the 3D exploration of the microstructural degradation processes for a range of energy materials including fuel cells, capacitors, catalysts, and ceramics.     

Mechanism of Sodium Storage in Hard Carbon: An X‐Ray Scattering Analysis

Hard carbon is a standard anode material for Na‐ion batteries. However, its low crystallinity and diverse microstructures make obtaining a full understanding of the sodium storage mechanism challenging. Here, the results of a systematic ex situ small and wide angle X‐ray scattering study of a series of nanostructured hard carbons, which reveal clear evidence of sodium storage in the graphene–graphene interlayers and nanopores, are presented. Particularly, an emergence of a broad peak around q ≈ 2.0–2.1 Å^?1 in the low voltage region is suggested to be an indicator that sodium is densely confined in the nanopores. Thus, classical X‐ray scattering techniques are demonstrated to be effective in elucidating the overall reaction scheme of Na insertion into hard carbon.     

Visualization of Light Elements using 4D STEM: The Layered‐to‐Rock Salt Phase Transition in LiNiO2 Cathode Material

The layered oxide LiNiO₂ (LNO) has been extensively investigated as a cathode active material for lithium‐ion batteries. Despite LNO's high gravimetric capacity, instability issues hinder its commercialization. It suffers from capacity loss during electrochemical cycling and is difficult to synthesize without defects. This is related to poor structural stability, leading to decomposition into the parent rock‐salt‐type oxide. In order to understand such phase transformations and to develop measures to inhibit them, the development of techniques able to image all atoms is crucial. In this study, the use of a fast, pixelated detector and 4D imaging in scanning transmission electron microscopy are explored to tackle this challenge. Selecting specific angular regions in the diffraction patterns and calculating virtual annular bright‐field images significantly enhances the contrast of the lithium atoms, such that all atoms are visible even in realistic samples. The developed technique is applied to image the layered‐to‐rock salt phase transition region. The data show that in this region, nickel atoms are in tetrahedral positions and the oxygen atoms are asymmetrically distributed. Taken together, the results shed light on the phase transformation mechanism at the atomic scale and can guide future research toward stabilizing LNO.     

Electrochemical Reaction of Lithium with Nanostructured Silicon Anodes: A Study by In‐Situ Synchrotron X‐Ray Diffraction and Electron Energy‐Loss Spectroscopy

Silicon‐based anodes are an appealing alternative to graphite for lithium‐ion batteries because of their extremely high capacity. However, poor cycling stability and slow kinetics continue to limit the widespread use of silicon in commercial batteries. Performance improvement has been often demonstrated in nanostructured silicon electrodes, but the reaction mechanisms involved in the electrochemical lithiation of nanoscale silicon are not well understood. Here, in‐situ synchrotron X‐ray diffraction is used to monitor the subtle structural changes occurring in Si nanoparticles in a Si‐C composite electrode during lithiation. Local analysis by electron energy‐loss spectroscopy and transmission electron microscopy is performed to interrogate the nanoscale morphological changes and phase evolution of Si particles at different depths of discharge. It is shown that upon lithiation, Si nanoparticles behave quite differently than their micrometer‐sized counterparts. Although both undergo an electrochemical amorphization, the micrometer‐sized silicon exhibits a linear transformation during lithiation, while a two‐step process occurs in the nanoscale Si. In the first half of the discharge, lithium reacts with surfaces, grain boundaries and planar defects. As the reaction proceeds and the cell voltage drops, lithium consumes the crystalline core transforming it into amorphous Li_xSi with a primary particle size of just a few nanometers. Unlike the bulk silicon electrode, no Li₁₅Si₄ or other crystalline Li_xSi phases were formed in nanoscale Si at the fully‐lithiated state.     

Multiscale Morphological and Electrical Characterization of Charge Transport Limitations to the Power Performance of Positive Electrode Blends for Lithium‐Ion Batteries

In this work, exhaustive characterizations of 3D geometries of LiNi_1/3Mn_1/3Co_1/3O₂ (NMC), LiFePO₄ (LFP), and NMC/LFP blended electrodes are undertaken for rational interpretation of their measured electrical properties and electrochemical performance. X‐ray tomography and focused ion beam in combination with scanning electron microscopy tomography are used for a multiscale analysis of electrodes 3D geometries. Their multiscale electrical properties are measured by using broadband dielectric spectroscopy. Finally, discharge rate performance are measured and analyzed by simple, yet efficient methods. It allows us to discriminate between electronic and ionic wirings as the performance limiting factors, depending on the discharge rate. This approach is a unique exhaustive analysis of the experimental relationships between the electrochemical behavior, the transport properties within the electrode, and its 3D geometry.     

Developments,applications, and prospects of cryo‐electron microscopy

Cryo‐electron microscopy (cryo‐EM) is a structural biological method that is used to determine the 3D structures of biomacromolecules. After years of development, cryo‐EM has made great achievements, which has led to a revolution in structural biology. In this article, the principle, characteristics, history, current situation, workflow, and common problems of cryo‐EM are systematically reviewed. In addition, the new development direction of cryo‐EM—cryo‐electron tomography (cryo‐ET), is discussed in detail. Also, cryo‐EM is prospected from the following aspects: the structural analysis of small proteins, the improvement of resolution and efficiency, and the relationship between cryo‐EM and drug development. This review is dedicated to giving readers a comprehensive understanding of the development and application of cryo‐EM, and to bringing them new insights.     

On the Localized Nature of the Structural Transformations of Li2MnO3 Following Electrochemical Cycling

Although the Li‐excess layered‐oxide Li₂MnO₃ has a high theoretical capacity, structural transformations within the oxide during electrochemical cycling lead to relatively low experimental capacities, hindering its use in practical applications. Here, aberration‐corrected scanning transmission electron microscopy/electron energy loss spectroscopy and high‐resolution X‐ray diffraction are used to characterize the oxide following electrochemical cycling. Microscopy reveals the coexistence of regions with local monoclinic, spinel, and rock‐salt symmetries, indicating localized and inhomogeneous structural evolutions. Crystal structure transformations are observed both at the particle surface and in the bulk. At the surface, these transformed regions resemble spinel Mn₃O₄ or rock‐salt MnO, consistent with oxygen loss. In the bulk, the regions resemble defect spinels, such as the layered‐spinel Li_xMn_4/3O₄, which suggest a partial phase transformation consistent with oxygen retention. Both microscopy and diffraction data of the cycled sample indicate areas of pristine Li₂MnO₃; the presence of such areas, in close proximity to Li_xMn_4/3O₄ areas, suggests that the layered to spinel structure transformation is partially reversible. Spinel, disordered rock salt, and pristine areas are also observed in Li₂MnO₃ samples intentionally damaged by electron beam irradiation. This observation indicates that the dynamic processes resulting in phase transformations can be studied for a variety of oxide systems by a judicious selection of irradiation conditions.     

Elemental composition of strawberry plants inoculated with the plant growth‐promoting bacterium Azospirillum brasilense REC3, assessed with scanning electron microscopy and energy dispersive X‐ray analysis

The elemental composition of strawberry plants (Fragaria ananassa cv. Macarena) inoculated with the plant growth‐promoting bacterium Azospirillum brasilense REC3, and non‐inoculated controls, was studied using scanning electron microscopy (SEM) and energy dispersive X‐ray (EDS) analysis. This allowed simultaneous semi‐quantification of different elements in a small, solid sample. Plants were inoculated and grown hydroponically in 50% or 100% Hoagland solution, corresponding to limited or optimum nutrient medium, respectively. Bacteria‐inoculated plants increased the growth index 45% and 80% compared to controls when grown in 100% and 50% Hoagland solution, respectively. Thus, inoculation with A. brasilense REC3 in a nutrient‐limited medium had the strongest effect in terms of increasing both shoot and root biomass and growth index, as already described for Azospirillum inoculated into nutrient‐poor soils. SEM‐EDS spectra and maps showed the elemental composition and relative distribution of nutrients in strawberry tissues. Leaves contained C, O, N, Na, P, K, Ca and Cu, while roots also had Si and Cl. The organic fraction (C, O and N) accounted for over 96.3% of the total chemical composition; of the mineral fraction, Na had higher accumulation in both leaves and roots. Azospirillum‐inoculated and control plants had similar elemental quantities; however, in bacteria‐inoculated roots, P was significantly increased (34.33%), which constitutes a major benefit for plant nutrition, while Cu content decreased (35.16%).     

Lipids status and copper in a single astrocyte of the rat model for amyotrophic lateral sclerosis: Correlative synchrotron‐based X‐ray and infrared imaging

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, causing death of motor neurons controlling voluntary muscles. The pathological mechanisms of the disease are only partially understood. The hSOD1‐G93A ALS rat model is characterized by an overexpression of human mutated SOD1, causing increased vulnerability by forming intracellular protein aggregates, inducing excitotoxicity, affecting oxidative balance and disturbing axonal transport. In this study we followed the bio‐macromolecular organic composition and compartmentalization together with trace metal distribution in situ in single astrocytes from the ALS rat model and compared them to the control astrocytes from nontransgenic littermates by simultaneous use of two synchrotron radiation‐based methods: Fourier transform infrared microspectroscopy (SR‐FTIR) and hard X‐ray fluorescence microscopy (XRF). We show that ALS cells contained more Cu, which colocalized with total lipids, increased carbonyl groups and oxidized lipids, thus implying direct involvement of Cu in oxidative stress of lipidic components without direct connection to protein aggregation in situ.     

Direct imaging electron microscopy (EM) methods in modern structural biology: Overview and comparison with X‐ray crystallography and single‐particle cryo‐EM reconstruction in the studies of large macromolecules

Determining the structure of macromolecules is important for understanding their function. The fine structure of large macromolecules is currently studied primarily by X‐ray crystallography and single‐particle cryo‐electron microscopy (EM) reconstruction. Before the development of these techniques, macromolecular structure was often examined by negative‐staining, rotary‐shadowing and freeze‐etching EM, which are categorised here as ‘direct imaging EM methods’. In this review, the results are summarised by each of the above techniques and compared with respect to four macromolecules: the ryanodine receptor, cadherin, rhodopsin and the ribosome–translocon complex (RTC). The results of structural analysis of the ryanodine receptor and cadherin are consistent between each technique. The results obtained for rhodopsin vary to some extent within each technique and between the different techniques. Finally, the results for RTC are inconsistent between direct imaging EM and other analytical techniques, especially with respect to the space within RTC, the reasons for which are discussed. Then, the role of direct imaging EM methods in modern structural biology is discussed. Direct imaging methods should support and verify the results obtained by other analytical methods capable of solving three‐dimensional molecular architecture, and they should still be used as a primary tool for studying macromolecule structure in vivo.     

Small‐angle X‐ray scattering reveals architecture and A2B2 stoichiometry of the UvrA–UvrB DNA damage sensor

The UvrA–UvrB (AB) protein complex operates in the bacterial nucleotide excision repair pathway as the main sensor of DNA damage. Crystallographic analysis of the AB complex revealed a linear UvrB–UvrA–UvrA–UvrB arrangement of subunits with an internal two‐fold axis that became incorporated into the crystal. Here, we have used small‐angle X‐ray scattering (SAXS) to show close correspondence between the crystal structure and the entity in solution. This result confirms the number and disposition of subunits in the crystallographic model and rules out other possible arrangements suggested by packing in the crystal. The current SAXS analysis failed to detect significant changes to the structure as a function of nucleotide. Proteins 2013. © 2012 Wiley Periodicals, Inc.     

Structural characterization of Er3+,Yb3+‐doped Gd2O3 phosphor,synthesized using the solid‐state reaction method,and its luminescence behavior

We report the synthesis and structural characterization of Er³⁺,Yb³⁺‐doped Gd₂O₃ phosphor. The sample was prepared using the conventional solid‐state reaction method, which is the most suitable method for large‐scale production. The prepared phosphor sample was characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermoluminescence (TL), photoluminescence (PL) and CIE techniques. For PL studies, the excitation and emission spectra of Gd₂O₃ phosphor doped with Er³⁺ and Yb³⁺ were recorded. The excitation spectrum was recorded at a wavelength of 551 nm and showed an intense peak at 276 nm. The emission spectrum was recorded at 276 nm excitation and showed peaks in all blue, green and red regions, which indicate that the prepared phosphor may act as a single host for white light‐emitting diode (WLED) applications, as verified by International de I'Eclairage (CIE) techniques. From the XRD data, the calculated average crystallite size of Er³⁺ and Yb³⁺‐doped Gd₂O₃ phosphor is ~ 38 nm. A TL study was carried out for the phosphor using UV irradiation. The TL glow curve was recorded for UV, beta and gamma irradiations, and the kinetic parameters were also calculated. In addition, the trap parameters of the prepared phosphor were also studied using computerized glow curve deconvolution (CGCD). Copyright © 2015 John Wiley & Sons, Ltd.