Transmission microscope analysis of battery materials at the nanoscale

Quebec's electrical power production is mostly composed of Hydro-electric dams. This renewable resource is used the people and industries of the province for lighting, heating and cooling. However, transportation of people and goods still relies on fossil fuels as energy source. In order to achieve one, the provincial's government's goal of electrification of transports, better electrical power storage solutions must be made available. The current generation of lithium batteries is allowing care to autonomously travel similar distance as would their gasoline-powered counterparts. The charging time of such vehicles, however, is still much longer then the time required to fill a gas tank. Furthermore, many batteries technologies release hydrogen under high load, and can fall into thermal runaways. Such thermal runaways, or when batteries become to hot, leak charge internally and heat further, can lead to catastrophic explosions. Therefore, batteries able to carry more charge, with safer chemistries are required. Two candidate materials are of particular interest to be used in the next generation of batteries. Lithium-metal orthosilicates, Li2MSiO4, where the metal, M, is iron, manganese, or a mixture of both materials, could be used in the current battery geometry, coupled to a carbon anode. These orthosilicates have twice the lithium carrying capabilities of materials such a lithium-cobalt oxide or lithium iron phosphates. Furthermore, the de-litihiation chemistry of orthosilicates does not release hydrogen, therefore eliminating the risk of explosion. The second material of interest is lithium metal, for use in the lithium-air battery. This system has one of the highest theoretical power density of any battery system. In order to implement these chemical systems in real batteries, their micro- and nanoscale properties need to be well understood. The transmission electron microscope (TEM), is one of the only tools that can study the morphology and chemistry of materials at scales ranging from sub-nanometers to microns. TEMs rely on a high energy electron beam to probe samples. Both Li2FeSiO­4 and metallic lithium are sensitive to such high energy beam, and are readily damaged. This work is centered around minimising the beam-induced specimen damage when possible, or minimising the effect on damage on experimental results when some damage in unavoidable. Golden ratio acquisition is a tomographic acquisition scheme which reduces the effect changes in a sample, such as carbon contamination or beam damage. SR-EELS is used as a low-dose method of gathering localised chemical information.La production d'énergie électrique du Québec provient principalement d'hydro-électricité. Cette ressource renouvelable est utilisée dans la province pour subvenir aux besoins de la population et de l'industrie en matière d'éclairage, de chauffage et de climatisation. Par contre, le transport des gens et des marchandises se fait toujours à l'aide d'énergies fossiles. Il est alors nécessaire, de manière à atteindre les cibles gouvernementales en matière d'électrification des transports, que de meilleures solutions de stockage d'énergie électrique deviennent disponibles. La génération actuelle de batteries au lithium permet aux voitures électriques de parcourir, de façon autonome, des distances similaires à celles atteintes par des voitures carburant à la gazoline, sur un plein d'essence. Le temps de charge des batteries de ces voitures, quant à lui, est bien plus long que le temps que requis pour faire un plein d'essence. De plus, plusieurs types de batteries actuelles, lorsque soumises à de trop importantes charges, peuvent relâcher de l'hydrogène et initier un emballement thermique. Ces emballements thermiques sont caractérisés par des réactions internes irréversibles et inarrêtables prenant place dans les batteries. Dans des cas extrêmes, des explosions peuvent survenir. Il est donc important que des batteries ayant de plus hautes capacités, basées sur des réactions chimiques sécuritaires, soient développées. Deux systèmes chimiques sont d'un attrait particulier. L'orthosilicate de métal lithié Li2MSiO4, où le métal, M, est du fer ou du manganèse, ou encore un mélange des deux, couplé à une anode en graphite. De par la formule chimique des orthosilicates lithiés, ces matériaux ont une capacité de charge théorique faisant le double de celles de matériaux actuellement en service, tel que l'oxyde de cobalt et le phosphate de fer. De plus, la décomposition des orthosilicates ne rejette pas d'hydrogène, éliminant ainsi les risques d'explosions. Le deuxième système d'intérêt est la batterie lithium-air, où du lithium métallique est oxydé par l'atmosphère. Ce dernier système a la plus haute densité énergétique théorique de tous les systèmes connus à base de lithium. Avant que de mettre ces systèmes chimiques en service dans des batteries, leurs propriétés physiques doivent être caractérisées, à des échelles micro- et nanoscopiques. Le microscope à électron en transmission (MET) est un des seuls outils de caractérisation qui peut étudier la morphologie et la chimie de matériaux à des échelles sub-nanométriques. Les MET fonctionnent grâce à un faisceau d'électrons à haute énergie qui bombardent un échantillon. L'orthosilicate de métal lithié et le lithium métallique sont deux matériaux sensibles au faisceau d'électrons et s'endommagent facilement lors d'observations dans un MET. Ce travail est centré autour du but de minimiser l'endommagement des matériaux lors d'observation MET. L'acquisition tomographique suivant le ratio d'or est un stratagème d'acquisition qui réduit les artéfacts de reconstruction dûs à des modifications de l'échantillon au cours de l'acquisition de données. Le SR-EELS, quant à lui, est une méthode d'acquisition d'information chimique qui a la capacité de réduire la dose d'électrons à laquelle un échantillon est soumis. Ces deux méthodes permettent l'analyse MET de matériaux fragiles, qui, autrement, ne pourrait pas être étudier avec le même niveau de profondeur

Enhancing Singlet Oxygen Photocatalysis with Plasmonic Nanoparticles

International audiencePhotocatalysts able to trigger the production of singlet oxygen species are the topic of intense research efforts in organic synthesis. Yet, challenges still exist in improving their activity and optimizing their use. Herein, we exploited the benefits of plasmonic nanoparticles to boost the activity of such photocatalysts via an antenna effect in the visible range. We synthesized silica-coated silver nanoparticles (Ag@SiO2 NPs), with silica shells which thicknesses ranged from 7 to 45 nm. We showed that they served as plasmonically active supports for tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+, and demonstrated an enhanced catalytic activity under white light-emitting diode (LED) irradiation for citronellol oxidation, a key step in the commercial production of rose oxide fragrance. A maximum enhancement of the plasmon-mediated reactivity of approximately 3-fold was observed with a 28 nm silica layer along with a 4-fold enhancement in the emission intensity of the photocatalyst. Using electron energy loss spectroscopy (EELS) and boundary element method simulations, we mapped the decay of the plasmonic signal around the Ag core and provided a rationale for the observed catalytic enhancement. This work provides a systematic analysis of the promising properties of plasmonic NPs used as catalysis-enhancing supports for common homogeneous photocatalysts and a framework for the successful design of such systems in the context of organic transformations

Micro-Scale Restraint Methodology for Humidity Induced Swelling Investigated by Phase Contrast X-Ray Tomography

A new methodology for restraining the swelling of spruce wood samples in the micrometre range is developed and presented. We show that the restraining device successfully prevents the free swelling of wood during moisture adsorption, thus modifying significantly the anisotropy of swelling and provoking the intended collapse and large deformations of the wood cells at the edges of the sample in contact with the restraining device. The device consists in a slotted cube designed to restrain swelling and is made of PMMA manufactured by laser ablation. The sample undergoing the restraining experiment is imaged with high-resolution synchrotron radiation phase contrast X-Ray Tomographic Microscopy. The deformation of the restraining device itself is only approximately 2 μm with respect to a 500 μm width in cubes containing latewood samples and half of that in the case of cubes containing earlywood.ISSN:0014-4851ISSN:1741-276

A Randomized, Controlled Trial of Oral Propranolol in Infantile Hemangioma

International audienceBACKGROUND: Oral propranolol has been used to treat complicated infantile hemangiomas, although data from randomized, controlled trials to inform its use are limited. METHODS: We performed a multicenter, randomized, double-blind, adaptive, phase 2-3 trial assessing the efficacy and safety of a pediatric-specific oral propranolol solution in infants 1 to 5 months of age with proliferating infantile hemangioma requiring systemic therapy. Infants were randomly assigned to receive placebo or one of four propranolol regimens (1 or 3 mg of propranolol base per kilogram of body weight per day for 3 or 6 months). A preplanned interim analysis was conducted to identify the regimen to study for the final efficacy analysis. The primary end point was success (complete or nearly complete resolution of the target hemangioma) or failure of trial treatment at week 24, as assessed by independent, centralized, blinded evaluations of standardized photographs. RESULTS: Of 460 infants who underwent randomization, 456 received treatment. On the basis of an interim analysis of the first 188 patients who completed 24 weeks of trial treatment, the regimen of 3 mg of propranolol per kilogram per day for 6 months was selected for the final efficacy analysis. The frequency of successful treatment was higher with this regimen than with placebo (60% vs. 4%, P<0.001). A total of 88% of patients who received the selected propranolol regimen showed improvement by week 5, versus 5% of patients who received placebo. A total of 10% of patients in whom treatment with propranolol was successful required systemic retreatment during follow-up. Known adverse events associated with propranolol (hypoglycemia, hypotension, bradycardia, and bronchospasm) occurred infrequently, with no significant difference in frequency between the placebo group and the groups receiving propranolol. CONCLUSIONS: This trial showed that propranolol was effective at a dose of 3 mg per kilogram per day for 6 months in the treatment of infantile hemangioma. (Funded by Pierre Fabre Dermatologie; ClinicalTrials.gov number, NCT01056341.)