Synchrotron-based X-ray Techniques Research Articles

X-ray Spectroscopy at the SuperXAS and Debye Beamlines: from in situ to Operando.

Understanding structure-performance relationships are essential for the rational design of new functional materials or in the further optimization of (catalytic) processes. Due to the high penetration depth of the radiation used, synchrotron-based hard X-ray techniques (with energy > 4.5 keV) allow the study of materials under realistic conditions (in situ and operando) and thus play an important role in uncovering structure-performance relationships. X-ray absorption and emission spectroscopies (XAS and XES) give insight into the electronic structure (oxidation state, spin state) and local geometric structure (type and number of nearest neighbor atoms, bond distances, disorder) up to ~5 Å around the element of interest. In this mini review, we will give an overview of the in situ and operando capabilities of the SuperXAS beamline, a facility for hard X-ray spectroscopy, through recent examples from studies of heterogeneous catalysts, electrochemical systems, and photoinduced processes. The possibilities for time-resolved experiments in the time range from ns to seconds and longer are illustrated. The extension of X-ray spectroscopy at the new Debye beamline combined with operando X-ray scattering and diffraction and further developments of time-resolved XES at SuperXAS will open new possibilities after the Swiss Light Source upgrade mid 2025.

Nanotubes from Lanthanide-Based Misfit-Layered Compounds: Understanding the Growth, Thermodynamic, and Kinetic Stability Limits.

Gaining insights into the kinetics and the thermodynamic limits of nanostructures in high-temperature reactions is crucial for controlling their unique morphology, phase, and structure. Nanotubes from lanthanide-based misfit-layered compounds (MLCs) have been known for more than a decade and were successfully produced mostly via a chemical vapor transport protocol. The MLC nanotubes show diverse structural arrangements and lattice disorders, which could have a salient impact on their properties. Though their structure and charge transfer properties are reasonably well understood, a lack of information on their thermodynamic and kinetic stability limits their scalable synthesis and their applicability in modern technologies. In this study, the growth, thermodynamic stability, and decomposition kinetics of lanthanide-based misfit nanotubes of two model compounds, i.e., (LaS)1.14TaS2 and (SmS)1.19TaS2 are elucidated in detail. The nanotubes were carefully analyzed via atomic resolution electron microscopy imaging and synchrotron-based X-ray and electron diffraction techniques, and the information on their morphology, phase, and structures was deduced. The key insights gained would help to establish the parameters to explore their physio-chemical properties further. Furthermore, this study sheds light on the complex issue of the high-temperature stability of nanotubes and nanostructures in general.

In Situ X-Ray Techniques Unraveling Charge Distribution Induced by Halogen Bonds in Solvates of an Iodo-Substituted Squaraine Dye.

The importance of halogen bonds (XBs) in the regulation of material properties through a variation in the electrostatic potential of the halogen atom is not attracted much attention. Herein, this study utilizes in situ single crystal X-ray diffraction and synchrotron-based X-ray techniques to investigate the cooling-triggered irreversible single-crystal-to-single-crystal transformation of the DMF solvated iodo-substituted squaraine dye (SQD-I). Transformation is observed to be mediated by solvent-involved XB formation and strengthening of electrostatic interaction between adjacent SQD-I molecules. By immersing a DMF solvate in acetonitrile a solvent exchange without loss of long-range ordering is observed. This is attributed to conservation of the molecular charge distribution of SQD-I molecules during the process. The different solvates can be used in combination for temperature-dependent image encryption. This work emphasizes the changes caused by XB formation to the electrostatic potentials of halogen containing molecules and their influence on material properties and presents the potential utility of XBs in the design of soft-porous crystals and luminescent materials.

Development and understanding of the lithiation/de-lithiation mechanism of a low cobalt and nickel-rich cathode material for lithium‐ion batteries

Nickel-rich LiNixMnyCo1−x−yO2 (NMC, with x ≥ 0.6) layered oxides are regarded as cathode candidates for high-energy density lithium-ion batteries (LIBs). However, this technology faces several challenges due to the scarcity of crucial raw materials such as cobalt precursors and the negative environmental impact of their extraction process. It is therefore, it becomes imperative to develop low cobalt content cathode compositions that offer alternative options with comparable electrochemical performance. Herein, we have used a systematic approach to modify the composition while keeping all other properties (particle size and morphology) constant to synthesise low-Co-cathode materials, namely LiNi0·8Mn0·1Co0·1O2 (NMC-10 %) and LiNi0·8Mn0·15Co0·05O2 (NMC-5%). A co-precipitation route using a continuous stirred thank reactor was used for synthesis. The physico-chemical properties, electrochemical performances, cycling stability, and rate capabilities of NMC-5% materials are comparable to those of NCM-10 % materials. NMC-10 % and NMC-5% half cells show initial specific discharge capacities of 191 mAh.g−1, and 185 mAh.g−1, respectively, in a voltage range of 2.8–4.3 V (vs. Li+/Li). The NMC-5% exhibits excellent thermal stability, characterized by a predominant exothermic peak at 432 °C and significantly lower total heat energy when compared to NMC-10 % counterpart, which displayed its main exothermic peak at 339 °C. The structural and electronic changes of both materials were evaluated through in operando synchrotron-based X-ray techniques. Regardless of the cobalt content, both materials show comparable structural and electronic evolution upon the de-intercalation/intercalation of Li+ ions. An irreversible phase transition at the first delithiation was observed as emphasized by diffraction of synchrotron radiations.

Effects of carbonate on ferrihydrite transformation in alkaline media.

Alkaline media widely exist in natural and engineered systems such as semiarid/arid areas, radioactive waste sites, and mine tailings. In these settings, the commonly occurring iron (oxyhydr)oxides differed in their ability to influence the fate of nutrients and contaminants. Due to the substantially increased atmospheric carbon dioxide (CO2) concentration, carbonate stands to increase in these media. However, how increasing carbonate affects the transformation of poorly crystalline iron (oxyhydr)oxides (e.g., two-line ferrihydrite) under alkaline conditions still remains unclear. Here, kinetics of ferrihydrite transformation were evaluated at pH ∼10 as a function of [carbonate] = 0-286 mM using synchrotron-based X-ray and vibrational spectroscopic techniques. The results showed that carbonate slowed down ferrihydrite transformation slightly and suppressed goethite formation, but promoted hematite formation regardless of its concentration. At low carbonate concentration (11.42 mM), the effect of carbonate on product formation was obvious due to the weak inner-sphere complex; however, at high carbonate concentration (80-286 mM), the effect was retarded because of the adsorption equilibrium of carbonate as well as the initial carbonate adsorption followed by desorption. Moreover, carbonate modified the morphology of hematite from rhombic to ellipsoidal to honeycomb and goethite from rod-like to needle-like to spindle-like due to the inner-sphere adsorption-desorption of carbonate and adsorption of hydroxyl ions on reactive sites of iron (oxyhydr)oxides in alkaline media. The results suggest that the concurrently increasing carbonate with enhanced atmospheric CO2 could control the transformation and occurrence of iron (oxyhydr)oxides in natural and engineered environments and have important implications for the biogeochemical cycles of iron and carbon.

Heavy metal removal potential of olivine

Industrial wastewater containing heavy metals, such as Cd and Pb, must be treated prior to discharge to meet increasingly stringent discharge guidelines and to limit the impact of toxic metals on ecosystems and human health. The application of olivine particles is a natural mineral-based solution to treat heavy metal-laden wastewaters, but little is known about the efficiency and mechanism of metal removal by this solid phase. In this work, we investigate the potential of olivine for heavy metal treatment by combining batch metal removal experiments with solid-phase characterization by synchrotron-based X-ray techniques and electron microscopy. We probed the removal behaviour of a variety of metal contaminants (Co, Ni, Cd, Zn, Cu, Pb; initial concentration = 1500 µg/L) and used Zn specifically to identify the metal removal pathway of olivine. We found that olivine in powdered (0.3 g/L) and granulated (0.5 g/L) forms was able to remove up to >90% of the initial metal, depending on the metal identity, with the efficiency increasing in order of Co ≤ Cd ≤ Ni <Zn<Cu<Pb. This order matches the well documented selectivity sequence of other common mineral sorbents (e.g., Fe(III) and Mn(IV) (oxyhydr)oxides). In addition, metal removal was intimately linked to increases in pH during reaction (e.g., from pH 7 to 10), due presumably to H+ consumption by SiO44− ions released during olivine dissolution. Molecular-scale characterization of the solid reaction products revealed that metal removal occurred via secondary precipitation of distinct metal carbonates and silicates, which was promoted by the increase in pH, although metal adsorption to olivine surfaces might also occur at lower pH. Overall, our study provides strong evidence for the potential of olivine minerals for treatment of heavy metal-laden industrial wastewaters.

Photocatalytic activity of B-doped nano graphene oxide over hydrogenated NiO-loaded TiO2 nanotubes

A hydrogenated NiO-loaded anatase TiO2 with unique heterostructure nanotube arrays (denoted as H:(NiO/TiO2)) NTs were synthesized, followed by the attachment of boron-doped reduced nanographene oxide nanoparticles (B-nGO NPs) to form a vigorous composite photoelectrode B-nGO/H:(NiO/TiO2) NTs. The p-n junction created between p-type NiO and n-type TiO2 produces sufficient built-in electric field to facilitate the electron–hole pair separation and boost the interfacial electron transfer, subsequently a hydrogenation treatment to adjust the donor density and maximize the electron–hole separation. The microstructure characterization with synchrotron-based X-ray techniques straightened out that the created NiO oxygen vacancies can provide emptier d-orbitals to accept more photoexcited electrons. With the incorporation of B-nGO NPs, the partially replacement of C atoms of nGO by B atoms can form an electron–hole-rich configuration in the heterostructure to decrease the Fermi level, with a more rapid electron transfer toward TiO2 substrate during photocatalysis, which also confirmed by quantum-chemical calculations. The as-synthesized B-nGO/H:(NiO/TiO2) NTs exhibited a high photocurrent density (2.0 mA/cm2) and an effective photoconversion efficiency (2.07%) under simulated sunlight irradiation (AM1.5G, 100 mW/cm2). The eventuated photoconversion efficiency is 6 times enhanced with respect to the pristine TiO2, along with an impressive hydrogen evolution rate of 31 μmol/h/cm2. Moreover, the photocurrent durability test has confirmed the stability of B-nGO/H:(NiO/TiO2) electrode, with only a slight decay of <1% after continuous illumination for more than 4 h. Incident photon conversion efficiency spectra have revealed a boosted photo-response under visible light region (extended to ∼520 nm) with the synergistic attachment of NiO and B-nGO.

Surface chemical heterogeneous distribution in over-lithiated Li1+xCoO2 electrodes

In commercial Li-ion batteries, the internal short circuits or over-lithiation often cause structural transformation in electrodes and may lead to safety risks. Herein, we investigate the over-discharged mechanism of LiCoO2/graphite pouch cells, especially spatially resolving the morphological, surface phase, and local electronic structure of LiCoO2 electrode. With synchrotron-based X-ray techniques and Raman mapping, together with spectroscopy simulations, we demonstrate that over-lithiation reaction is a surface effect, accompanied by Co reduction and surface structure transformation to Li2CoO2/Co3O4/CoO/Li2O-like phases. This surface chemical distribution variation is relevant to the depth and exposed crystalline planes of LiCoO2 particles, and the distribution of binder/conductive additives. Theoretical calculations confirm that Li2CoO2-phase has lower electronic/ionic conductivity than LiCoO2-phase, further revealing the critical effect of distribution of conductive additives on the surface chemical heterogeneity evolution. Our findings on such surface phenomena are non-trivial and highlight the capability of synchrotron-based X-ray techniques for studying the spatial chemical phase heterogeneity.

Electrochemical and Structural Study on PVDF-Based Polymer Electrolytes for Solid-State Batteries

Lithium-ion batteries are widely used today in powering devices from portable electronics to electric vehicles. Despite their great success, this battery chemistry relies on organic solvent-based liquid electrolytes which are highly flammable, leading to major safety concerns. In contrast, solid-state batteries, which are based on solid-state electrolytes, are regarded to have much better safety characteristics and potentially higher energy density than the conventional lithium-ion batteries. Solid-state electrolytes usually include ceramics, polymers, gels, and composites. Among them, polymer materials have attracted considerable attention due to their great interfacial contact, flexibility, and easy fabrication. In particular, polyvinylidene fluoride (PVDF) polymer electrolyte is a promising candidate as it can potentially provide a high voltage window and enable high energy density solid-state batteries. However, the current PVDF-based polymer electrolyte is still not compatible with high voltage cathodes, such as layered lithium transition metal oxides and the interaction between the salt and PVDF polymer has not been fully elucidated.We have systematically studied the PVDF-based electrolytes with different salts and salt combinations, including lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide (LiBETI). The optimized electrolyte delivers excellent performance for solid-state Li||LiFePO4 cells, achieving a specific capacity of over 150 mAh/g and lasting more than 50 cycles with over 99% capacity retention. Similar tests have also been applied to lithium nickel manganese cobalt oxides (NMC), and the preliminary results show promising cycling stability and capacity retention. In addition to electrochemical study, we employed a range of synchrotron-based X-ray techniques, including diffraction, pair distribution function analysis, and absorption spectroscopy, to investigate the interactions between the polymer and lithium salt in the polymer electrolytes. This knowledge will provide valuable information for designing new polymer electrolyte systems.Acknowledgments: The work at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704. This research used beamline 23-ID-2 and 28-ID-2 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

X-Ray Induced Chemical Reaction Revealed by In Situ X-Ray Diffraction and Scanning X-Ray Microscopy in 15 nm Resolution

Abstract The detection sensitivity of synchrotron-based X-ray techniques has been largely improved due to the ever-increasing source brightness, which has significantly advanced ex situ and in situ research for energy materials such as lithium-ion batteries. However, the strong beam–material interaction arising from the high beam flux can substantially modify the material structure. The beam-induced parasitic effect inevitably interferes with the intrinsic material property, making the interpretation of the experimental results difficult and requiring comprehensive assessments. Here, we present a quantitative study of the beam effect on an electrode material Ag2VO2PO4 using four different X-ray characterization methods with different radiation dose rates. The material system exhibits interesting and reversible radiation-induced thermal and chemical reactions, further evaluated under electron microscopy to illustrate the underlying mechanism. The work will provide a guideline for using synchrotron X-rays to distinguish the intrinsic behavior from extrinsic structure change of materials induced by X-rays.

Self-Assembly of Nanowires: From Dynamic Monitoring to Precision Control.

Natural biomaterials often show ordered nanowire structures (ONWS) which display unique structural color or superior mechanical performance. Meanwhile, plenty of modern nanodevices with ONWS have flourished with activities focused on both basic and applied research. Manipulating synthetic nanowire (NW) from a disordered state to a hierarchically ordered structure via various assembly strategies brings about intriguing and exotic chemical/physical properties. In the past decades, many methods have been developed to assemble NWs and fabricate organized architectures, such as Langmuir-Blodgett interfacial assembly, spin-coating assembly, fluid-flow-induced assembly, and ice-template assembly. Nevertheless, for practical applications, large-scale and high-efficiency assembly strategies toward precise controlled architectures are largely limited by the lack understanding of assembly mechanisms. Especially, the manipulation principles and driving forces behind the state-of-art assembly strategies are still unclear. Besides, the lesser research attention on dynamic kinetics also impedes the revelation of the NW self-assembly mechanism. With the emergence of advanced in situ techniques, such as synchrotron-based X-ray techniques and in situ transmission electron microscopy (TEM), the dynamic monitoring of NW behavior in many practical environments becomes possible. In addition, the alignment direction and the stacking manner of NW film are of significance to the final performance. There is a lack of connection between the properties of one-dimensional nanoscale building blocks and the functionalities of the macro-assembly structures. To this end, dynamic monitoring is highly desired, which enables the precision modulation of NW assembly structure, leading to the discovery or prediction of new structures, novel properties, and performance optimization.In this Account, we aim to uncover the underlying kinetics of NW assembly or local reaction and mass transportation processes, as well as to build a solid connection from individual NWs to NW assembly structures with enhanced properties and eventually to macroscopic materials application. We first review the recent progress in state-of-art NW assembly strategies for diverse aligned structures according to the manipulation principle and the driving forces. To systematically review the NW self-assembly strategies, we categorize these strategies into three states: NWs on the liquid interface via surface tension, NW assembly in liquid via solution-shearing flow field, and NW assembly at the solid interval via physical repulsive force. Then, we introduce the existing advanced characterization techniques, including synchrotron-based X-ray scattering and in situ TEM, to dynamically monitor the intermediate states of the NW assembly and transport processes. The comprehensive understanding of this thermodynamic and kinetic mechanism facilitates the rational design, large scale, and high-efficiency fabrication of NW assemblies, thus promoting their applications in tailored optical-electrical electronics, smart electrochromic devices, electrocatalysis, structural materials, and chiral photonic crystals.

Revealing the unconventional lithium storage mechanism of ordered mesoporous NiO for lithium-ion batteries

Transition metal oxides have been intensively developed for use as anode materials to overcome the capacity limitations of commercial graphite. In this study, a highly ordered mesoporous NiO electrode material is fabricated using a hard templating method, and exhibits a reversible capacity of approximately 940 mAh g−1 that is much higher than the theoretical value based on the conversion reaction (717 mAh g−1). Combined analyses that include synchrotron-based X-ray techniques and controlled X-ray photoelectron spectroscopies attribute the lithium storage behaviors to both the conversion reaction of NiO framework and the reversible electrolyte-derived surface layer. Interestingly, the contribution of the reversible electrolyte-derived surface layer (∼440 mAh g−1) to the capacity is comparable to that of the conversion reaction with NiO (∼500 mAh g−1). The results also demonstrate that incomplete conversion occurs due to the high bonding energy of Ni–O in the framework during the electrochemical reaction, and prove that the distinctive nano-structural characteristics of the mesoporous NiO surface cause the reversible behavior of the electrolyte-derived surface layer.

The effect of high-temperature storage on the reaction heterogeneity of Ni-rich layered cathode materials

Ni-rich cathode materials with high energy and power densities have been used in Li-ion batteries for next-generation electric vehicles. However, Ni-rich cathode materials undergo severe structural degradation during operation in high-temperature environments, leading to critical performance degradation. Herein, we investigate the effect of high-temperature conditions on the crystal and electronic structure of Ni-rich cathode materials during the electrochemical reaction using synchrotron-based X-ray techniques. The bulk crystal structure of the Ni-rich layered material is maintained during high-temperature storage, but changes in the surface structure and particle integrity are observed. The conspicuous growth of an insulating NiO-like rock-salt phase on the particle surface results in an asymmetrical capacity loss in the form of charge fading, that is, capacity loss during charging. In addition to this surface degradation, particle fracture impedes the transport of Li-ions and electrons, producing several particle regions with reduced electrochemical activity. As a result, the reaction heterogeneity within the cathode is significantly intensified during the electrochemical reaction, aggravating the electrochemical performance. This study elucidates the origin of the performance degradation of Ni-rich cathode materials in high-temperature environments, which can offer valuable guidance for developing advanced Li-ion batteries with thermal durability.

Probing the atomic-scale ferromagnetism in van der Waals magnet CrSiTe3

As an emerging class of two-dimensional (2D) materials, van der Waals (vdW) magnets have attracted a lot of research attention since they can give access to fundamental physics and potential spintronic device applications. Among these 2D vdW magnets, CrSiTe3, as an intrinsic ferromagnetic semiconductor, exhibits great potentials in low-dimensional spintronics. Of particular interest in this 2D vdW magnet is the electronic and magnetic properties at the atomic-scale, which has yet been fully explored so far. Here, combing angle-resolved photoemission spectroscopy, bulk magnetic measurements, and synchrotron-based x-ray techniques, an unambiguous picture of the electronic and magnetic states of CrSiTe3 is presented. Hybridization of Cr-3d and Te-5p orbitals and the semiconducting behavior are confirmed by the band structure detection. Intrinsic ferromagnetism with a magnetic anisotropy constant of 1.56 × 105 erg/cm3 is attributed to the superexchange interaction of the Cr3+ ions. In addition, temperature-dependent spin and orbital moments are determined, and a fitted critical exponent of 0.169 implies that CrSiTe3 is in good agreement with the 2D Ising model. More remarkably, unquenched orbital moments are experimentally evidenced, bringing CrSiTe3 with orbital-dependent intriguing effects and great potentials toward the spintronic devices.

Assessment and Imaging of Intracellular Magnesium in SaOS-2 Osteosarcoma Cells and Its Role in Proliferation.

Magnesium is an essential nutrient involved in many important processes in living organisms, including protein synthesis, cellular energy production and storage, cell growth and nucleic acid synthesis. In this study, we analysed the effect of magnesium deficiency on the proliferation of SaOS-2 osteosarcoma cells. When quiescent magnesium-starved cells were induced to proliferate by serum addition, the magnesium content was 2–3 times lower in cells maintained in a medium without magnesium compared with cells growing in the presence of the ion. Magnesium depletion inhibited cell cycle progression and caused the inhibition of cell proliferation, which was associated with mTOR hypophosphorylation at Serine 2448. In order to map the intracellular magnesium distribution, an analytical approach using synchrotron-based X-ray techniques was applied. When cell growth was stimulated, magnesium was mainly localized near the plasma membrane in cells maintained in a medium without magnesium. In non-proliferating cells growing in the presence of the ion, high concentration areas inside the cell were observed. These results support the role of magnesium in the control of cell proliferation, suggesting that mTOR may represent an important target for the antiproliferative effect of magnesium. Selective control of magnesium availability could be a useful strategy for inhibiting osteosarcoma cell growth.

Boosting Reversibility of Mn-Based Tunnel-Structured Cathode Materials for Sodium-Ion Batteries by Magnesium Substitution.

Electrochemical irreversibility and sluggish mobility of Na+ in the cathode materials result in poor cycle stability and rate capability for sodium‐ion batteries. Herein, a new strategy of introducing Mg ions into the hinging sites of Mn‐based tunnel‐structured cathode material is designed. Highly reversible electrochemical reaction and phase transition in this cathode are realized. The resulted Na0.44Mn0.95Mg0.05O2 with Mg2+ in the hinging Mn‐O5 square pyramidal exhibits promising cycle stability and rate capability. At a current density of 2 C, 67% of the initial discharge capacity is retained after 800 cycles (70% at 20 C), much improved than the undoped Na0.44MnO2. The improvement is attribute to the enhanced Na+ diffusion kinetics and the lowered desodiation energy after Mg doping. Highly reversible charge compensation and structure evolution are proved by synchrotron‐based X‐ray techniques. Differential charge density and atom population analysis of the average electron number of Mn indicate that Na0.44Mn0.95Mg0.05O2 is more electron‐abundant in Mn 3d orbits near the Fermi level than that in Na0.44MnO2, leading to higher redox participation of Mn ions.

Synchrotron X-ray metrology of dopant distribution and oxidation state in high pressure CVD grown TM2+:ZnSe optical fibers

High pressure chemical vapor deposition (HPCVD) has shown to be a promising method for producing Cr2+:ZnSe and Fe2+:ZnSe mid-IR optical fiber lasers. The oxidation state of the dopants and their spatial homogeneity are critical for the characterization of effective fiber laser performance; however, this is challenging for small fiber cores and small doping concentrations. We demonstrate using synchrotron micro X-ray fluorescence (XRF) mapping to study the distribution of the dopants throughout the fiber cross-sections. Furthermore, we study the local chemical environment of these unique fiber structures using micro X-ray near edge absorption spectroscopy (XANES). Our study reveals that transition metal doped ZnSe deposited using HPCVD has nanoscale dopant aggregation although the material is chemically identical to the commercially produced diffusion doped laser crystals, as indicated by the presence +2 oxidation state of the dopants. This work demonstrates the power of synchrotron-based X-ray techniques for use as metrology tools for improving the performance of laser materials in fiber geometry.

Peering into Batteries: Electrochemical Insight Through In Situ and Operando Methods over Multiple Length Scales

Summary In order to overcome the limitations of static and destructive characterizations of Li-ion battery materials and components, comprehensive investigation peering into batteries over various length and time scales is essential. In this regard, emerging in situ and operando characterization methodologies focusing on multiple size domains become a powerful approach to resolve current challenges and navigate future directions. This perspective provides a series of illustrative examples of in situ and operando characterizations over atomic, crystallite/particle, electrode, and battery system length scales with a focus on two electrode material classes: insertion and conversion materials. The operating principles, features, analysis methods, and information gained from each characterization method are discussed. Herein, we present the necessity and opportunity for in situ and operando characterization of electrochemical energy storage materials and systems. Further, we suggest future directions to gain the insight needed to tackle currently intractable issues on Li-ion battery application, failure, and emerging design concepts.

Stabilizing Effects on Structural and Thermal Properties of Al-Doped Ni-Rich Layered Oxides for Li Rechargeable Batteries

One of the key strategies to achieve high energy density for Li rechargeable batteries is through improved layered oxides cathode materials. Ni-rich layered oxides with Ni content above 80% have been under extensive attention as promising cathodes for next-generation Li-ion batteries due to the merits of high capacity, low cost, and low toxicity [1–3]. However, these materials still require further improvement to overcome inferior capacity retention and poor thermal stability originated from Ni-rich environments [1,4].We investigated Al-doped LiNi0.80Co0.15Mn0.05O2 and undoped LiNi0.80Co0.15Mn0.05O2 layered cathodes in view of the structural, electrochemical, and thermal properties. Synchrotron-based X-ray techniques were used to analyze their structural behavior systematically during electrochemical reactions and thermal decomposition. High resolution powder diffraction (HRPD) results show that Al-doping in Ni-rich NCM cathode alleviates anisotropic lattice distortion and structural collapse as well as preserves a wider LiO6 interslab thickness, even at highly deintercalated states comparing to the undoped cathode. Al-doped Ni-rich cathode exhibits lower polarization potential, better rate capability, and cyclability compared to undoped one. This can be attributed to the alleviation of anisotropic lattice changes and volume changes during cycling. More importantly, Al-doped Ni-rich cathode maintains a wider LiO6 interslab thickness without collapse at highly charged states, allowing Li-ions to be deintercalated/intercalated reversibly. This indicates that rigid structural integrity contributes to enhanced electrochemical performance. Moreover, in situ X-ray diffraction (XRD) during the heating process and differential scanning calorimetry (DSC) analysis demonstrate that Al-doped NCM cathode outperforms bare NCM cathode significantly in terms of thermal aspects. Specially, Al-doping improves thermal stability by delaying the onset temperatures of phase transformations during the heating process. These results demonstrate that Al-doping plays a major role in stabilizing the structure by suppressing abrupt lattice changes during cycling and the formation of a rock-salt phase during thermal decomposition reaction.Based on these experimental results, we will provide the structural evidence for the Al-doping effects on Ni-rich layered materials, thereby guiding for the strategical design factor in the development of layered cathodes with high performance. More detailed results and discussion will be presented in the PRiME 2020.

Comparative Study of Lithium Storage Behavior in Mesoporous and Bulk Mn2o3 Anodes for Li Batteries

Over the last two decades, lithium-ion batteries (LIBs) have been recognized as the most satisfactory energy storage technology for numerous electric devices. In recent years, as the application of LIBs extends to electric vehicles (EVs) and energy storage systems, the demand for LIBs with increased specifications continues to increase. To meet high-power and high-energy storage systems in the rapidly growing energy storage markets, in the anode, there have been many attempts to develop high capacity anode materials to replace the graphite [1,2]. In particular, transition metal oxides have attracted attention due to their high theoretical capacity based on the conversion reaction mechanism [3,4]. However, the conversion reaction has poor kinetics leading to large polarization and causes large volume changes during discharging and charging, resulting in poor capacity retention upon cycling [5,6]. To solve these problems, nanotechnology has been applied in this field [7,8]. Nanostructured materials can act as a buffer against volume expansion, and provide high surface area and short path lengths for Li+ transport, which results in high specific capacity, excellent rate capability and cycle life [9,10]. To effectively use the advantages of nanostructured materials in next-generation batteries, it is necessary to understand the advantage of nanostructure that positively affects the electrochemical performance.In this work, using synchrotron-based X-ray techniques, we compare lithium storage of mesoporous and bulk Mn2O3 in terms of Mn central charge storage and non-Mn central charge to investigate why the mesoporous material outperforms the bulk material. As a consequence, the mesoporous structure with short path lengths for Li+ and electron transport and high surface area in contact with the electrolyte can enable larger lithium storage. X-ray absorption spectroscopy result indicates that both samples show a phase transition from Mn2O3 to Mn via MnO during the first discharge, followed by a reversible reaction between MnOx to Mn metal. However, since the mesoporous structure lowers the resistance for the conversion reaction, and accelerates the Li+ and electron transport, the mesoporous Mn2O3 has a larger capacity than bulk Mn2O3 through the further oxidation reaction from Mn2+ to a higher oxidation state during charging, and the additional reversible reaction during cycling. Furthermore, the combined results from X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy indicate that additional lithium storage reaction by reversible formation-decomposition of the electrolyte-derived surface layer occurs more in mesoporous Mn2O3 than bulk Mn2O3. Consequently, the improved oxidation reaction during charge and enhanced contribution of reversible formation and decomposition of the electrolyte-derived surface layer due to the increased specific surface area and reduced particle size as the cycle progresses also affect cycle performance of mesoporous Mn2O3. This report provides an understanding of the synergistic relationship between nanostructures and electrochemical performance and practical strategies for developing high energy density anode materials for next-generation lithium-ion batteries. More details will be discussed in the meeting. Reference s : [1] N. Nitta, F. Wu, J.T. Lee, G. Yushin, Mater. Today. 18 (2015) 252–264.[2] M. Armand, J.-M. Tarascon, Nature. 451 (2008) 652–657.[3] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.-M. Tarascon, Nature. 407 (2000) 496–499[4] F. Wang, R. Robert, N.A. Chernova, N. Pereira, F. Omenya, F. Badway, X. Hua, M. Ruotolo, R. Zhang, L. Wu, V. Volkov, D. Su, B. Key, M. Stanley Whittingham, C.P. Grey, J. Am. Chem. Soc. 133 (2011) 18828–18836.[5] R. Malini, U. Uma, T. Sheela, M. Ganesan, N.G. Renganathan, Ionics 15 (2009) 301–307.[6] S.H. Yu, S.H. Lee, D.J. Lee, Y.E. Sung, T. Hyeon, Small. 12 (2016) 2146–2172.[7] S.K. Jung, H. Kim, M.G. Cho, S.P. Cho, B. Lee, H. Kim, Y.U. Park, J. Hong, K.Y. Park, G. Yoon, W.M. Seong, Y. Cho, M.H. Oh, H. Kim, H. Gwon, I. Hwang, T. Hyeon, W.-S. Yoon, K. Kang, Nat. Energy. 2 (2017) 4–12.[8] W.D. Richards, S.T. Dacek, D.A. Kitchaev, G. Ceder, Adv. Energy Mater. 8 (2018) 1–7.[9] H. Kim, N. Venugopal, J. Yoon, W.-S. Yoon, J. Alloys Compd. 778 (2019) 37–46.[10] Y.-G. Guo, J.-S. Hu, L.-J. Wan, Adv. Mater. 20 (2008) 2878–2887.