Sub-particle Level Research Articles

Understanding the Effect of Local Short-Range Ordering on Lithium Diffusion in Li1.3Nb0.3Mn0.4O2 Single-Crystal Cathode

Summary We report the observation of persistent chemical gradient on rock-salt Li1.3Nb0.3Mn0.4O2 single crystals transforming through a second-order reaction and reveal the dominating effect of local chemistry on Li diffusion within the percolated network. By using advanced 2D and 3D nanoscale X-ray spectro-microscopy on well-formed crystal samples, our study visualizes the mesoscale chemical distribution as a function of the state of charge at the subparticle level. We further reveal the presence of thermodynamically favorable short-range ordering of Nb-cation-only (Nb6) and Nb-cation-enriched (MnNb5) configurations, which promote non-equilibrium diffusion pathways and the expansive chemical heterogeneity observed on LixNb0.3Mn0.4O2 particles. The present study utilizes large single crystals to eliminate the influence of kinetic factors such as particle-size distribution, crystal facet, grain boundary, and strain, allowing us to clearly demonstrate the strong correlation between a material's structural defects and chemical propagation and its crucial impact on electrode performance and stability.

Mesoscale Battery Science: The Behavior of Electrode Particles Caught on a Multispectral X-ray Camera.

Functional materials and devices are usually morphologically complex and chemically heterogeneous. Their structures are often designed to be hierarchical because of the desired functionalities, which usually require many different components to work together in a coherent manner. The lithium ion battery, as an energy storage device, is a very typical example of this kind of structure. In a lithium ion battery, the cathode, anode, and separator are soaked in a liquid electrolyte, facilitating the back and forward shuttling of the lithium ions for energy storage and release. The desired performance of a lithium ion battery has many different aspects that need to be engineered and balanced depending on the targeted applications. In most cases, the cathode material has become the limiting factor for further improvements and, thus, has attracted intense attention from the research community. While the improvement in the overall performance of the lithium ion battery is the ultimate goal of the research in this field, understanding the relationship between the microscopic properties and the macroscopic behaviors of the materials/devices can inform the design of better battery chemistries for practical applications. As a result, it is of great fundamental and practical importance to investigate the electrode materials using experimental probes that can provide good chemical sensitivity and sufficient spatial resolution, ideally, under operating conditions. With this motivation, our group has been focusing on the development of the nanoscale full-field X-ray spectro-microscopy, which has now become a well-recognized tool for imaging battery electrode materials at the particle level. With nanoscale spatial resolution, this technique can effectively and efficiently tackle the intrinsically complicated mesoscale chemistry. It allows us to monitor the particles' morphological and chemical evolution upon battery operation, providing valuable insights that can be incorporated into the design of new battery chemistries. In this Account, we review a series of our recent studies of battery electrode materials using nanoscale full-field X-ray spectro-microscopy. The materials that are the subjects of our studies, including layer-structured and spinel-structured oxide cathodes, are technically very important as they not only play an important role in today's devices but also possess promising potential for future developments. We discuss how the subparticle level compositional and state-of-charge heterogeneity can be visualized and linked to the bulk performance through systematic quantification of the imaging data. Subsequently, we highlight recent ex situ and in situ observations of the cathode particles' response to different reaction conditions, including the spontaneously adjusted reaction pathways and the morphological changes for the mechanical strain release. The important role of surface chemistry in the system is also discussed. While the microscopic investigation at the particle level provides useful insights, the degree to which this represents the overall properties of the battery is always a question for further generalizing the conclusions. In order to address this concern, we finally discuss a high throughput experimental approach, in which a large number of cathode particles are scanned. We discuss a case study that demonstrates the identification and analysis of functionally important minority phases in an operating battery cell through big data mining methods. With an emphasis on the data/information mining aspect of the nanoscale X-ray spectro-microscopic study of battery cathode particles, we anticipate that this Account will attract more research to this field.

Chemical Imaging of Single-Particle Photoelectrocatalysis for Energy Conversion

Photoelectrochemical energy conversion represents a promising energy technology that converts solar energy to useful chemical fuels and electricity. The key component in a photoelectrochemical cell is a semiconductor material that upon illumination generates charge carriers (electrons and holes). Evaluation of the photoelectrocatalytic properties of these semiconductor materials are usually performed at an ensemble level. Here we use a single-molecule fluorescence microscopy technique to interrogate the photoelectrocatalytic process, at the single-particle and sub-particle level, of a semiconductor material with facet-dependent electronic structure. Using redox-selective probe molecules coupled with electrochemical modulation, we visualize the spatial distributions of the activities of both electrons and holes under different electrical potentials, providing for the first time quantitative information on the facet and potential dependences of charge carrier activities. Furthermore, using focused-laser beam illumination at a sub-facet level combined with theoretical simulation of charge carrier behaviors, we demonstrate intra-facet variation of important physical properties (photocurrent, incident-photon-to-current efficiency, flat band potential, quasi Fermi level) that are considered crucial performance metrics for photoelectrochemical energy devices. Our findings reveal the importance of edges in three-dimensional semiconductor crystals with facet-dependent electronic structure, opening up new opportunities in the rational design of energy materials with complex morphological and electronic properties.

Change the Collective Behaviors of Colloidal Motors by Tuning Electrohydrodynamic Flow at the Subparticle Level.

As demonstrated in biological systems, breaking the symmetry of surrounding hydrodynamic flow is the key to achieve autonomous locomotion of microscopic objects. In recent years, a variety of synthetic motors have been developed based on different propulsion mechanisms. Most work, however, focuses on the propulsion of individual motors. Here, we study the collective behaviors of colloidal dimers actuated by a perpendicularly applied AC electric field, which controls the electrohydrodynamic flow at subparticle levels. Although these motors experience strong dipolar repulsion from each other and are highly active, surprisingly, they assemble into a family of stable planar clusters with handedness. We show that this type of unusual structure arises from the contractile hydrodynamic flow around small lobes but extensile flow around the large lobes. We further reveal that the collective behavior, assembled structure, and assembly dynamics of these motors all depend on the specific directions of electrohydrodynamic flow surrounding each lobe of the dimers. By fine-tuning the surface charge asymmetry on particles and salt concentration in solution, we demonstrate the ability to control their collective behaviors on demand. This novel type of active assembly via hydrodynamic interactions has the potential to grow monodisperse clusters in a self-limiting fashion. The underlying concept revealed in this work should also apply to other types of active and asymmetric particles.

Phase transformation mechanism in lithium manganese nickel oxide revealed by single-crystal hard X-ray microscopy

Understanding the reaction pathway and kinetics of solid-state phase transformation is critical in designing advanced electrode materials with better performance and stability. Despite the first-order phase transition with a large lattice mismatch between the involved phases, spinel LiMn1.5Ni0.5O4 is capable of fast rate even at large particle size, presenting an enigma yet to be understood. The present study uses advanced two-dimensional and three-dimensional nano-tomography on a series of well-formed LixMn1.5Ni0.5O4 (0≤x≤1) crystals to visualize the mesoscale phase distribution, as a function of Li content at the sub-particle level. Inhomogeneity along with the coexistence of Li-rich and Li-poor phases are broadly observed on partially delithiated crystals, providing direct evidence for a concurrent nucleation and growth process instead of a shrinking-core or a particle-by-particle process. Superior kinetics of (100) facets at the vertices of truncated octahedral particles promote preferential delithiation, whereas the observation of strain-induced cracking suggests mechanical degradation in the material.

Sub-particle reaction and photocurrent mapping to optimize catalyst-modified photoanodes.

The splitting of water photoelectrochemically into hydrogen and oxygen represents a promising technology for converting solar energy to fuel. The main challenge is to ensure that photogenerated holes efficiently oxidize water, which generally requires modification of the photoanode with an oxygen evolution catalyst (OEC) to increase the photocurrent and reduce the onset potential. However, because excess OEC material can hinder light absorption and decrease photoanode performance, its deposition needs to be carefully controlled--yet it is unclear which semiconductor surface sites give optimal improvement if targeted for OEC deposition, and whether sites catalysing water oxidation also contribute to competing charge-carrier recombination with photogenerated electrons. Surface heterogeneity exacerbates these uncertainties, especially for nanostructured photoanodes benefiting from small charge-carrier transport distances. Here we use super-resolution imaging, operated in a charge-carrier-selective manner and with a spatiotemporal resolution of approximately 30 nanometres and 15 milliseconds, to map both the electron- and hole-driven photoelectrocatalytic activities on single titanium oxide nanorods. We then map, with sub-particle resolution (about 390 nanometres), the photocurrent associated with water oxidation, and find that the most active sites for water oxidation are also the most important sites for charge-carrier recombination. Site-selective deposition of an OEC, guided by the activity maps, improves the overall performance of a given nanorod--even though more improvement in photocurrent efficiency correlates with less reduction in onset potential (and vice versa) at the sub-particle level. Moreover, the optimal catalyst deposition sites for photocurrent enhancement are the lower-activity sites, and for onset potential reduction the optimal sites are the sites with more positive onset potential, contrary to what is obtainable under typical deposition conditions. These findings allow us to suggest an activity-based strategy for rationally engineering catalyst-improved photoelectrodes, which should be widely applicable because our measurements can be performed for many different semiconductor and catalyst materials.

Catalytic Kinetics of Different Types of Surface Atoms on Shaped Pd Nanocrystals.

To understand the catalytic properties or roles of different types of surface atoms on metal nanocatalysts, the catalytic kinetics and dynamics of the different types of surface atoms (plane and edge) were revealed for the first time by a statistical quantitative deconvolution of observables obtained from traditional single-molecule nanocatalysis of Pd nanocrystals.It was found that the edge and plane of Pd nanocubes show similar size-dependent product formation processes, but inverse product dissociation processes. This work helps push the traditional single-molecule nanocatalysis method towards the sub-particle level.

Single-Molecule Kinetics Reveals a Hidden Surface Reaction Intermediate in Single-Nanoparticle Catalysis

Detecting and characterizing reaction intermediates is not only important and powerful for elucidating reaction mechanisms but also challenging in general because of the low populations of intermediates in a reaction mixture. Studying surface reaction intermediates in heterogeneous catalysis presents additional challenges, especially the ubiquitous structural heterogeneity among the catalyst particles and the accompanying polydispersion in reaction kinetics. Here we use single-molecule fluorescence microscopy to study two complementary types of Au nanocatalysts—mesoporous-silica-coated Au nanorods (i.e., Au@mSiO2 nanorods) and bare 5.3 nm pseudospherical Au nanoparticles—at the single-particle, single-turnover resolution in catalyzing the oxidative deacetylation of amplex red by H2O2, a synthetically relevant and increasingly important probe reaction. For both nanocatalysts, the distributions of the microscopic reaction time from a single catalyst particle clearly reveal a kinetic intermediate, which is hidden when the data are averaged over many particles or only the time-averaged turnover rates are examined for a single particle. This intermediate is further resolvable by single-turnover kinetics at the subparticle level. Detailed single-molecule kinetic analysis leads to a quantitative reaction mechanism and supports that the intermediate is likely a surface-adsorbed one-electron-oxidized amplex red radical. The quantitation of kinetic parameters further allows for the evaluation of the large reactivity inhomogeneity among the individual nanorods and pseudospherical nanoparticles, and for Au@mSiO2 nanorods, it uncovers their size-dependent reactivity in catalyzing the first one-electron oxidation of amplex red to the radical. Such single-particle, single-molecule kinetic studies are expected to be broadly useful for dissecting reaction kinetics and mechanisms.

Local State-of-Charge Inhomogeneities in Charged and Cycled High Capacity Lithium-Manganese-Rich Composite Cathodes

Materials for electrochemical energy storage often exhibit significant chemical and structural inhomogeneity at the particle and even sub-particle level. Understanding how these mesoscale variations in the state of charge and local phase transformations impact electrochemical performance is critical to developing improved electrode materials. Raman microscopy is an excellent technique for studying inhomogeneity and interfacial phenomena in batteries, because it can measure subtle changes in chemical composition and structure at sub-micron resolution. By monitoring changes in the spectroscopic signatures, we can infer information about ion and electron transport across interfaces and through particles. In this study we use ex situ Raman mapping to study layered-layered lithium-rich manganese-rich cathode material Li1.2Mn0.525Ni0.175Co0.1O2 (LMR-NMC) as a function of the average charge. We show that variations in the microstructure and local state of charge occur at the level of individual particles within electrodes prepared from a commercial sample. Micro-Raman mapping provides both high-resolution and large field of view, but the full potential of this technique to analyze complex electrochemical systems is rarely realized, in part due to the challenge of processing the inherently large data sets. Here we take advantage of cluster analysis and other statistical methods to directly visualize interfaces and charge inhomogeneity in cathode particles. Acknowledgment This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, is sponsored by the Vehicle Technologies Program for the Office of Energy Efficiency and Renewable Energy.

ACTIVE NON-VIOLENCE AS CONFLICT RESOLUTION

Science has developed technology to the point that computers are networked, “talking” to each other and artificial intelligence is a real possibility in the future. In a parallel development, nanotechnology examines interaction on a subparticle level, too small to be seen. Yet, humankind is lagging in development of social co-operation and communication. Violence is still the “weapon of choice” on a personal level as well as a national level. Two major developments seek to address conflict resolution. On a personal level, Marshall B. Rosenburg’s study of Nonviolent Communication seeks to facilitate individual interaction. And on the macro level, Gandhi and Martin Luther King, Jr’s work in Passive Resistance has had great success in social change without loss of life. This article, in an effort to promote civil discourse asks the questions: How do these two movements relate to each other? Is there a point of connection which may offer a window through which individuals and groups might resolve conflict successfully?

Co-Processed Excipients: A Patent Review

The introduction of high speed tableting machines and the preference of direct compression as a method of tableting have increased the demands on the functionality of excipients mainly in terms of flowability and compressibility. Co-processed excipients, where in, excipients are combined by virtue of sub-particle level interaction have provided an attractive tool for developing high functionality excipients. The multifold advantages offered by co-processed excipients such as production of synergism in functionality of individual components, reduction of company's regulatory concern because of absence of chemical change during co-processing and improvement in physico-chemical properties have expanded their use in the pharmaceutical industry. In the recent years, there has been a spurt in the number of patents filed on co-processed excipients. Hence, the present review focuses on co-processed excipients and their application in pharmaceutical industry. The worldwide databases of European patent office (http://ep.espacenet.com) and United States patent office (www.uspto.gov) were employed to collect the patents and patent applications. The advantages, limitations, basis for the selection of excipients to be co-processed, methods of co-processing and regulatory perspective of co-processed excipients are also briefly discussed.

X‐Ray Tomography of Porous, Transition Metal Oxide Based Lithium Ion Battery Electrodes

We implement a segmentation algorithm that allows identifi cation of individual particles and validate it by showing that the calculated particle size distribution (PSD) is in agreement with experimentally determined PSD obtained with laser diffraction. We study the microstructure of LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC)-based cathodes, prepared with varying weight percent of carbon black and binder (2–5 wt%) and different compressions (0-2000 bar), and their electrochemical performance. Tomographic data (raw and processed with particles identifi ed and labeled) and the corresponding electrochemical data for 16 different cathodes is provided open source. [ 2 ] The microstructure datasets can be used to study electrode properties like porosity, tortuosity, electrode anisotropy, and homogeneity, or as realistic geometries for three dimensional (3D) electrochemical simulations. The electrochemical data is intended to aid in the verifi cation of simulation models. The large number of studied particles (approx. 7000-19000 per electrode) allows us to investigate spatially resolved PSD and shows that the vicinity of electrode boundaries is populated by smaller particles than the bulk electrode. In addition to insight into electrode morphology, we demonstrate that the technique is capable of resolving features on the sub-particle level such as particle fracture, which is observed here under high compression conditions. It is becoming increasingly clear that the development of next generation, higher performance lithium ion batteries (LIB) will require a concerted effort between experimentalists and simulation experts. In addition to the development of predictive tools for the selection of active materials, realization of LIBs with high C-rate capabilities and energy density will require the development of roadmaps for achieving favorable porous electrode microstructures. [ 3 , 4 ] However, due to the lack of publically

Direct Compression High Functionality Excipient Using Coprocessing Technique: A Brief Review

Tablets are still the most commonly used dosage form because of the ease of manufacturing, convenience in administration, accurate dosing and excellent stability. Direct compression is the preferred method for the preparation of tablets. However, it has been estimated that less than 20 percent of the active pharmaceutical ingredients (API) can be processed into tablets via direct compression since the majority of API lack the flow, cohesion or lubricating properties required for direct compression. Increasing trends toward direct compression suggests the need for development of high functional excipients. High functionality of excipients can be obtained by development of new excipients or by particle engineering of existing excipients. Particle engineering using coprocessing provides a way to obtain an excipient with high functionality. Coprocessed excipients are the mixture of two or more excipients interacting at sub-particle level; that can provide an excipient with improved functionality as well as masking undesirable properties. Coprocessing is very cost effective method of providing high functional excipient. The present review discusses the advantages of coprocessed excipients, role of material science in coprocessing, methods of coprocessing of excipients and properties of various coprocessed excipients available in the market.

DISCRETE ELEMENT METHOD FOR MULTISCALE MODELING

A discrete element method (DEM) has been developed to provide highly accurate and detailed predictions of the Lagrangian particle phase. Especially in this study, DEM has been used together with an Eulerian approach for the fluid phase to look at interphase exchange phenomena in a multiphase-multiscale modeling approach. The drying process inside a fluidized bed coffee bean roaster has been chosen. Herein, heat, mass, and momentum transport are solved on a fluid cell level; heat, mass, and momentum transfer coefficients are solved at a particle scale level; and 1D temperature and moisture content profiles are solved inside each coffee bean on a sub-particle scale level. Therefore, this multiscale approach provides much more information compared to existing coffee bean roaster models. In this work, a detailed description of this method is provided and results on different scale levels have been discussed. Modeling data and experimental results are compared and found to be in good agreement.

Multifunctional coprocessed excipients for improved tabletting performance

With the advancement of tablet manufacturing process, the demand of excipients with improved functionalities, mainly in terms of flow and compression properties, has increased. Coprocessed excipients are a mixture of two or more existing excipients at subparticle level, offer substantial benefits of the incorporated excipients and minimize their drawbacks. These multipurpose excipients have dramatically reduced the number of incorporating excipients in the tablet. The present review discusses the potential advantages of coprocessing and coprocessed excipients, material characteristics required for coprocessing, methods of coprocessing and various coprocessed excipients for direct compression available in the market.