Marco Di Michiel

In-operando high-speed tomography of lithium-ion batteries during thermal runaway

Prevention and mitigation of thermal runaway presents one of the greatest challenges for the safe operation of lithium-ion batteries. Here, we demonstrate for the first time the application of high-speed synchrotron X-ray computed tomography and radiography, in conjunction with thermal imaging, to track the evolution of internal structural damage and thermal behaviour during initiation and propagation of thermal runaway in lithium-ion batteries. This diagnostic approach is applied to commercial lithium-ion batteries (LG 18650 NMC cells), yielding insights into key degradation modes including gas-induced delamination, electrode layer collapse and propagation of structural degradation. It is envisaged that the use of these techniques will lead to major improvements in the design of Li-ion batteries and their safety features.

Fast microtomography using high energy synchrotron radiation

At the High Energy Beamline ID15A at the European Synchrotron Radiation Facility we have developed a fast three-dimensional x-ray microtomography system, which acquires a complete dataset in typically less than 10s. This unprecedented speed is achieved by combining a high efficiency phosphor screen, a reflecting microscope objective and a fast charge coupled device detector with the very intense high-energy white beam radiation provided by a wiggler source. The achieved spatial resolution is 2μm. The available x-ray energy spectrum spans from 20to250keV and can therefore be used for low and high Z materials. The spectrum can be modified by inserting different filters into the x-ray beam in order to optimize the signal-to-noise ratio and to avoid beam-hardening artifacts. Different phosphors with different energy sensitivity can be used. The very high speed allows in situ studies of systems evolving on the time scale of a few seconds or minutes. Three examples are given on sintering of metallic powders, so...

Weanling piglet cerebellum: a surrogate for tolerance to MRT (microbeam radiation therapy) in pediatric neuro-oncology

The cerebellum of the weanling piglet (Yorkshire) was used as a surrogate for the radiosensitive human infant cerebellum in a Swiss-led program of experimental microbeam radiation therapy (MRT) at the ESRF. Five weanlings in a 47 day old litter of seven, and eight weanlings in a 40 day old litter of eleven were irradiated in November, 1999 and June, 2000, respectively. A 1.5 cm-wide x 1.5 xm-high array of equally space approximately equals 20-30 micrometers wide, upright microbeams spaced at 210 micrometers intervals was propagated horizontally, left to right, through the cerebella of the prone, anesthetized piglets. Skin-entrance intra-microbeam peak adsorbed doses were uniform, either 150, 300, 425, or 600 gray (Gy). Peak and inter-microbeam (valley) absorbed doses in the cerebellum were computed with the PSI version of the Monte Carlo code GEANT and benchmarked using Gafchromic and radiochromic film microdosimetry. For approximately equals 66 weeks [first litter; until euthanasia], or approximately equals 57 weeks [second litter; until July 30, 2001] after irradiation, the littermates were developmentally, behaviorally, neurologically and radiologically normal as observed and tested by experienced farmers and veterinary scientists unaware of which piglets were irradiated or sham-irradiated. Morever, MRT implemented at the ESRF with a similar array of microbeams and a uniform skin-entrance peak dose of 625 Gy, followed by immunoprophylaxis, was shown to be palliative or curative in young adult rats bearing intracerebral gliosarcomas. These observations give further credence to MRTs potential as an adjunct therapy for brain tumors in infancy, when seamless therapeutic irradiation of the brain is hazardous.

Microbeam radiation therapy

The central nervous system of vertebrates, even when immature, displays extraordinary resistance to damage by microscopically narrow, multiple, parallel, planar beams of x rays. Imminently lethal gliosarcomas in the brains of mature rats can be inhibited and ablated by such microbeams with little or no harm to mature brain tissues and neurological function. Potentially palliative, conventional wide-beam radiotherapy of malignant brain tumors in human infants under three years of age is so fraught with the danger of disrupting the functional maturation of immature brain tissues around the targeted tumor that it is implemented infrequently. Other kinds of therapy for such tumors are often inadequate. We suggest that microbeam radiation therapy (MRT) might help to alleviate the situation. Wiggler-generated synchrotron x-rays were first used for experimental microplanar beam (microbeam) radiation therapy (MRT) at Brookhaven National Laboratorys National Synchrotron Light Source in the early 1990s. We now describe the progress achieved in MRT research to date using immature and adult rats irradiated at the European Synchrotron Radiation Facility in Grenoble, France, and investigated thereafter at the Institute of Pathology of the University of Bern.

Combining Time-Resolved Hard X-ray Diffraction and Diffuse Reflectance Infrared Spectroscopy To Illuminate CO Dissociation and Transient Carbon Storage by Supported Pd Nanoparticles during CO/NO Cycling

A novel combination of time-resolved hard X-ray diffraction, diffuse reflectance infrared spectroscopy, and mass spectrometry reveals how Pd nanoparticles dissociate CO and store atomic carbon and how this carbon storage dynamically changes the population of linear and bridging CO species at the surface of the Pd nanoparticles.

Active phase evolution in single Ni/Al2O3 methanation catalyst bodies studied in real time using combined μ-XRD-CT and μ-absorption-CT

A combination of synchrotron μ-XRD-CT and μ-absorption-CT (CT = computed tomography) is demonstrated, providing a unique insight into the solid state changes occurring from within crystalline materials. Specifically, we examine here the solid state changes that occur in a millimetre-sized Ni/γ-Al2O3 catalyst body in both 2D and 3D during calcination and CO methanation for the first time. The combination provides a unique insight into the spatial phase distribution of these materials and how these evolve via a series of solid state transformation processes. For example, initially, two Ni-ethylenediamine (en) complexes were observed on the impregnated and dried body; a hydrated and non-hydrated form, which 2D scans reveal possess an egg-shell and egg-yolk distribution, respectively. Furthermore, the μ-XRD data were of sufficient quality so as to be able to reveal that the particles within the ‘egg-shell’ were larger (∼35 nm) than those of the ‘egg-yolk’ (∼19 nm) and that there were more of them. On calcination, both precursors collapsed, yielding metallic fcc Ni particles with a surprisingly uniform average size distribution over the catalyst (∼4 nm). However, a comparison of the scattering at different stages of the experiment suggested that the crystalline structure of some of the Ni remained diffraction ‘silent’. Calcination in oxygen lead to both Ni oxidation and particle sintering, mainly at the exterior, which on pre-reaction reduction (in H2) yielded again fcc Ni particles (∼4 nm interior, ∼6 nm exterior) with a significant reduction in the amorphous Ni component. The catalyst proved active for CO methanation and, during 2 h time on-stream, no change in the structure composition or shape was observed, leading us to conclude that nano-sized fcc Ni particles on γ-Al2O3 are the active component in CO methanation. This work therefore demonstrates both the power of spatially resolved μ-XRD-CT/μ-absorption-CT measurement of catalytic systems and its advantage over more ‘traditional’ single point studies on small sieve fractions.

Pair distribution function computed tomography

An emerging theme of modern composites and devices is the coupling of nanostructural properties of materials with their targeted arrangement at the microscale. Of the imaging techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering. Here we describe a method that uses a combination of X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and mapped. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous catalyst system. The method may have potential impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health.

In situ microtomography investigation of metal powder compacts during sintering

Abstract The mechanisms involved in shape changes arising during sintering of complex materials like iron-based systems are still poorly understood. New information can be obtained by use of advanced techniques such as microtomography. In this study, the microstructural evolution of a Distaloy AE powder compact and of loose copper powder is investigated during a thermal cycle at the European Synchrotron in Grenoble (France). Both materials are sintered in a furnace set in front of a high-energy X-ray source in 30–45 keV range. At various steps of sintering, hundreds of radiographs are taken with different orientations of the specimen. From these images the 3D microstructure is reconstructed. This non-destructive method provides the 3D microstructural evolution of the material during sintering. Local and statistical information can be obtained and will be used in the future for modelling the sintering process. Special attention is given to the anisotropy induced by prior compaction and to its evolution through sintering.

Nanoparticulate Pd Supported Catalysts: Size-Dependent Formation of Pd(I)/Pd(0) and Their Role in CO Elimination

A combination of time-resolved X-ray absorption spectroscopy (XAS), hard X-ray diffraction (HXRD), diffuse reflectance infrared spectroscopy (DRIFTS), and mass spectrometry (MS) reveals a series of size-dependent phenomena at Pd nanoparticles upon CO/(NO+O(2)) cycling conditions. The multitechnique approach and analysis show that such size-dependent phenomena are critical for understanding Pd CO elimination behavior and, particularly, that different Pd(I) and Pd(0) centers act as active species for a size estimated by XAS to be, respectively, below and above ca. 3 nm. The relative catalytic performance of these two noble metal species indicates the intrinsic higher activity of the Pd(I) species.

Investigating lithium-ion battery materials during overcharge-induced thermal runaway: an operando and multi-scale X-ray CT study

Catastrophic failure of lithium-ion batteries occurs across multiple length scales and over very short time periods. A combination of high-speed operando tomography, thermal imaging and electrochemical measurements is used to probe the degradation mechanisms leading up to overcharge-induced thermal runaway of a LiCoO2 pouch cell, through its interrelated dynamic structural, thermal and electrical responses. Failure mechanisms across multiple length scales are explored using a post-mortem multi-scale tomography approach, revealing significant morphological and phase changes in the LiCoO2 electrode microstructure and location dependent degradation. This combined operando and multi-scale X-ray computed tomography (CT) technique is demonstrated as a comprehensive approach to understanding battery degradation and failure.