High-energy-density materials that undergo conversion and/or alloying reactions hold promise for next-generation lithium (Li) ion batteries. However, these materials experience substantial volume change during electrochemical operation, which causes mechanical fracture of the material and structural disintegration of the electrode, leading to capacity loss. In this work, we use x-ray tomography during battery operation to visualize and quantify the origins and evolution of electrochemical and mechanical degradation. Tomography provides the time-resolved, three-dimensional chemical composition and morphology within individual particles and throughout the electrode. In the model material tin(II) oxide, we witness distributions in onset and rate of core-shell lithiation, crack initiation and growth along preexisting defects, and irreversible distortion of the electrode, highlighting tomography as a tool to guide the development of durable materials and strain-tolerant electrodes.

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We report the use of synchrotron radiation X-ray tomographic microscopy (SRXTM) to obtain statistically signifi cant volume ( ∼ 700 × 700 × 70 μ m 3 ) 3D reconstructions of porous electrode microstructures of transition metal oxide based electrodes. [ 1 ] 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 available microstructural data on porous electrodes to date, there exists a disconnect between the experimental and simulation communities. The simulation community, despite significant advances in computation over the past decades, must rely on simplifi ed pictures of porous electrode microstructure or computer generated microstructures that bear an as-of-yet unquantifi ed relationship to real battery microstructures.While one-dimensional (1D) simulations are appealing for their simplicity and computational effi ciency, there are significant limitations. Newman-type models rely on the representation of the electrode's complexity by effective medium approximations. [ 5 ] For systems featuring a broad PSD, as often found in real LIB electrodes, the validity of the Bruggeman relation, which is widely used to estimate the electrode's tortuosity from porosity, ha...

Sub-second temporal-resolution tomographic microscopy is becoming a reality at third-generation synchrotron sources. Efficient data handling and postprocessing is, however, difficult when the data rates are close to 10 GB s À1. This bottleneck still hinders exploitation of the full potential inherent in the ultrafast acquisition speed. In this paper the fast reconstruction algorithm gridrec, highly optimized for conventional CPU technology, is presented. It is shown that gridrec is a valuable alternative to standard filtered back-projection routines, despite being based on the Fourier transform method. In fact, the regridding procedure used for resampling the Fourier space from polar to Cartesian coordinates couples excellent performance with negligible accuracy degradation. The stronger dependence of the observed signal-to-noise ratio for gridrec reconstructions on the number of angular views makes the presented algorithm even superior to filtered back-projection when the tomographic problem is well sampled. Gridrec not only guarantees high-quality results but it provides up to 20-fold performance increase, making real-time monitoring of the sub-second acquisition process a reality.

Water management is an important factor for optimizing polymer electrolyte fuel cells (PEFC) under high current density conditions as required for the automotive application. The characteristics of the local liquid saturation of the gas diffusion layer (GDL) is of particular interest. Here we report on the development of in-situ X-ray tomographic microscopy (XTM) with a pixel sizes in the order of 2 μm and sensitivity for carbon and liquid water for the quantitative analysis of liquid water in GDLs. In-situ XTM of PEFC is a major experimental challenge. A complete cell needs to be operated under realistic conditions in the constraint space of the small field of view on the beamline sample stage. Further phase segmentation of the images is required to successfully analyze the quantitative properties of the different phases. For this a workflow, applying differential images between dry and wet structures has been developed. Cells with Toray TGP-H-060 GDLs were analyzed in-situ. Droplets that appear on the GDL surface are connected to a significant water structure inside the GDL. Further the water cluster size distribution in the GDL shows that while small droplets (<100 pl) are numerous, most of the water is contained in few larger clusters.

renewable power, from wind or solar by medium-to-long-term storage using hydrogen as the energy vector, [1,2] enabling effective decarbonisation of the energy sector. [3] PEWE converts electric power by electrochemical water splitting into storable chemical energy. [4][5][6][7] Hydrogen can be reconverted to power or used in other sectors, [8,9] such as fuel cell based mobility [10] and chemical industries. [11] To make hydrogen production with polymer electrolyte water electrolysis a technoeconomically relevant contender, capital and operational cost need to be reduced substantially. [12][13][14][15] Operational cost, which becomes the main cost driver for operation schemes with high duty ratio (≥6000 h p.a.), is governed by power prices and the hydrogen production efficiency of the PEWE plant, which in turn strongly depends on the electrochemical performance and efficiency of the PEWE cell technology employed. [16] The electrochemical efficiency is governed by the underlying electrochemical loss mechanisms of kinetic, ohmic, and mass transport losses, whereas capital cost is driven by limited power density and high noble metal catalyst loadings.Recent studies revealed that the structure of the interface between the anodic porous transport layer (PTL) and the catalyst layer (CL) is a crucial factor limiting cell efficiency. [17][18][19][20][21] Today's PEWE technology relies on porous, Ti based, transport layer materials in the form of sintered materials [17,18,[22][23][24][25] with original applications in filtration [26] or medical tissue growing. [27][28][29] The lack of PTL materials with suitable surface characteristics tailored for this application inhibits the further improvement of cell efficiency and development of PEWE technology.Kinetic losses are governed by the sluggish kinetics of the oxygen evolution reaction (OER). The related overpotential depends on intrinsic catalyst parameters, such as specific exchange current density, activation energy, and number of active catalyst sites. [30] It has been established with model experiments such as optical imaging of the PTL/CL interface [19,20,31] and correlation of in-depth electrochemical analysis with PTL surface structure [17,18] that the catalyst is only partially utilized and CL domains not directly contacted by the porous Timaterials showed no gas evolution hence no electrochemical activity. Schuler et al. [17,18] have quantified the effect, showing

Phase sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging and therefore new and otherwise inaccessible information. The use of gratings as optical elements in hard X-ray phase imaging overcomes some of the problems that have impaired the wider use of phase contrast in X-ray radiography and tomography. So far, to separate the phase information from other contributions detected with a grating interferometer, a phase-stepping approach has been considered, which implies the acquisition of multiple radiographic projections. Here we present an innovative, highly sensitive X-ray tomographic phase-contrast imaging approach based on grating interferometry, which extracts the phase-contrast signal without the need of phase stepping. Compared to the existing phase-stepping approach, the main advantages of this new method dubbed "reverse projection" are not only the significantly reduced delivered dose, without the degradation of the image quality, but also the much higher efficiency. The new technique sets the prerequisites for future fast and low-dose phase-contrast imaging methods, fundamental for imaging biological specimens and in vivo studies.X-ray imaging | differential phase contrast | grating interferometer | tomography O ver the last few decades X-ray imaging has experienced a true revolution. The most striking advancement has been the production of coherent X-ray beams with their intrinsic capability of generating interference signals and, as a consequence, providing access to phase information within the investigated sample. This fact has been very stimulating for the X-ray-imaging community, which had been continually challenged by the frustrating question of how to increase the contrast in X-ray images without increasing the dose imparted to a specimen. It is well known that, different from conventional visible light, the refractive index in X-ray optics is very close to and smaller than unity. In first approximation, for a small and negligible anisotropy in the medium, the index of refraction characterizing the optical properties of a tissue can be expressed-including X-ray absorptionwith its complex form: n ¼ 1-δ-iβ where δ is the decrement of the real part of the refractive index, responsible for the phase shift, while the imaginary part β describes the absorption property of the tissue. In conventional absorption-based radiography, the X-ray phase shift information is usually not used for image reconstruction. However, at photon energies greater than 10 keV and for soft tissues (made up of low-Z elements), the phase shift term plays a more prominent role than the attenuation term because δ is typically three orders of magnitude larger than β (1). As a consequence, phase-contrast modalities can generate significantly greater image contrast compared to conventional, absorptionbased radiography. In fact, far from absorption edges, δ is inversely proportional to the square of the X-ray energy while β decreases as the fourth power of it. Conseq...

Understanding the transport properties of porous materials plays an important role in the development and optimization of polymer electrolyte fuel cells (PEFCs). In this study numerical simulations of different transport properties are compared and validated with data obtained using recently developed experimental techniques. The study is based on a Toray TGP-H-060 carbon paper, a common gas diffusion layer (GDL) material in PEFC. Diffusivity, permeability, and electric conductivity of the anisotropic, porous material are measured experimentally under various levels of compression. A sample of the GDL is imaged with synchrotron-based X-ray tomography under three different compression levels. Based on these three-dimensional images, diffusivity, permeability, and conductivity are calculated numerically. Experimental and numerical results agree in general. Deviations are observed for the through-plane conductivity. An explanation for the discrepancy is presented and affirmed by numerical simulations on a virtually created structure model. This proves that numerical simulation based on tomography data is a versatile tool for the investigation and development of porous structures used in PEFCs.