Over the last fifteen years, there has been a rapid growth in the use of high resolution X-ray computed tomography (HRXCT) imaging in material science applications. We use it at nanoscale resolutions up to 50 nm (nano-CT) for key research problems in large scale operation of polymer electrolyte membrane fuel cells (PEMFC) and lithium-ion (Li-ion) batteries in automotive applications. PEMFC are clean energy sources that electrochemically react with hydrogen gas to produce water and electricity. To reduce their costs, capturing their electrode nanostructure has become significant in modeling and optimizing their performance. For Li-ion batteries, a key challenge in increasing their scope for the automotive industry is Li metal dendrite growth. Li dendrites are structures of lithium with 100 nm features of interest that can grow chaotically within a battery and eventually lead to a short-circuit. HRXCT imaging is an effective diagnostics tool for such applications as it is a non-destructive method of capturing the 3D internal X-ray absorption coefficient of materials from a large series of 2D X-ray projections. Despite a recent push to use HRXCT for quantitative information on material samples, there is a relative dearth of computational tools in nano-CT image processing and analysis. Hence, we focus on developing computational methods for nano-CT image analysis of fuel cell and battery materials as required by the limitations in material samples and the imaging environment. The first problem we address is the segmentation of nano-CT Zernike phase contrast images. Nano-CT instruments are equipped with Zernike phase contrast optics to distinguish materials with a low difference in X-ray absorption coefficient by phase shifting the X-ray wave that is not diffracted by the sample. However, it creates image artifacts that hinder the use of traditional image segmentation techniques. To restore such images, we setup an inverse problem by modeling the X-ray phase contrast optics. We solve for the artifact-free images through an optimization function that uses novel edge detection and fast image interpolation methods. We use this optics-based segmentation method in two main research problems - 1) the characterization of a failure mechanism in the internal structure of Li-ion battery electrodes and 2) the measurement of Li metal dendrite morphology for different current and temperature parameters of Li-ion battery cell operation. The second problem we address is the development of a space+time (4D) reconstruction method for in-operando imaging of samples undergoing temporal change, particularly for X-ray sources with low throughput and nanoscale spatial resolutions. The challenge in using such systems is achieving a sufficient temporal resolution despite exposure times of a 2D projection on the order of 1 minute. We develop a 4D dynamic X-ray computed tomography (CT) reconstruction method, capable of reconstructing a temporal 3D image every 2 to 8 projections. Its novel properties are its projection angle sequence and the probabilistic detection of experimental change. We show its accuracy on phantom and experimental datasets to show its promise in temporally resolving Li metal dendrite growth and in elucidating mitigation strategies. Keywords: X-ray computed tomography, 4D X-ray computed tomography, phase contrast optics, fuel cells, Li-ion batteries, signal processing and optimization.

Mg alloys have spurred a renewed academic and industrial interest because of their ultra-light-weight and high specific strength properties. Hexagonal close packed Mg has low deformability and a high plastic anisotropy between basal and non-basal slip systems at room temperature. Alloying with Li and other elements is believed to counter this deficiency by activating non-basal slip by reducing their nucleation stress. In this work I study how Li addition affects deformation mechanisms in Mg using atomistic simulations. In the first part, I create a reliable and transferable concentration dependent embedded atom method (CD-EAM) potential for my molecular dynamics study of deformation. This potential describes the Mg-Li phase diagram, which accurately describes the phase stability as a function of Li concentration and temperature. Also, it reproduces the heat of mixing, lattice parameters, and bulk moduli of the alloy as a function of Li concentration. Most importantly, our CD-EAM potential reproduces the variation of stacking fault energy for basal, prismatic, and pyramidal slip systems that influences the deformation mechanisms as a function of Li concentration. This success of CD-EAM Mg-Li potential in reproducing different properties, as compared to literature data, shows its reliability and transferability. Next, I use this newly created potential to study the effect of Li addition on deformation mechanisms in Mg-Li nanocrystalline (NC) alloys. Mg-Li NC alloys show basal slip, pyramidal type-I slip, tension twinning, and two-compression twinning deformation modes. Li addition reduces the plastic anisotropy between basal and non-basal slip systems by modifying the energetics of Mg-Li alloys. This causes the solid solution softening. The inverse relationship between strength and ductility therefore suggests a concomitant increase in alloy ductility. A comparison of the NC results with single crystal deformation results helps to understand the qualitative and quantitative effect of Li addition in Mg on nucleation stress and fault energies of each deformation mode. The nucleation stress and fault energies of basal dislocations and compression twins in single crystal Mg-Li alloy increase while those for pyramidal dislocations and tension twinning decrease. This variation in respective values explains the reduction in plastic anisotropy and increase in ductility for Mg-Li alloys.

Pursuant the comparison of novel Farewell, my concubine written by a Hong Kong novelist Li Bihua with its film adaptation, this master's thesis is analyzing the way of transition from literary text to audio-visual media and observes the differences, which are not only the result of this transformation, but also an example of different cultural environment of Hong Kong and the PRC.

O presente trabalho tem como objetivo investigar como se caracterizam as práticas educativas e como se constroem as representações sociais de um professor de italiano que atuava em uma escola pública, mas que, do ponto de vista trabalhista, estava vinculado a uma associação italiana. No que diz respeito aos procedimentos metodológicos, esta é uma pesquisa de cunho qualitativo, cuja coleta de dados consistiu em gravações de dez reuniões entre o pesquisador e o professor de italiano. Para fins de análise dos dados, foram identificados três eixos temáticos: (1) a relação construída entre o professor e a direção da escola, (2) as representações do professor sobre os alunos da escola pública e (3) as representações sobre o ensino de língua italiana nesse contexto. Procuramos relacionar cada um os eixos temáticos a diversos conceitos, tais como: autoridade (ADORNO, 2006), representação social (MOSCOVICI, 2011) e ensino comunicativo de línguas (WIDDOWSON, 1991; ALMEIDA FILHO, 1993). Como veremos nesta dissertação, os dados revelam uma relação conflituosa entre o professor e a direção da escola pública, indicam também, que as suas representações sobre o contexto da escola pública, bem como sua formação universitária, influenciaram sua prática didática. Ao mesmo tempo, os dados apontam que essas representações não são estáticas, mas dinâmicas, pois foram reelaboradas, à medida que o professor se deparava com situações imprevistas e vivenciava novas experiências. Visto que este trabalho se insere em um contexto de escola pública, decidimos iniciá-lo fazendo um mapeamento dos municípios brasileiros que oferecem o ensino de LI em estabelecimentos públicos, algo até então inédito nos estudos de Italianística no Brasil. Um dos resultados desse mapeamento foi ver o importante papel que as associações ítalo-brasileiras têm em difundir a LI em escolas públicas pertencentes às suas respectivas áreas de atuação. De forma específica, apoiados na Metodologia da História Oral (MEIHY e HOLANDA, 2011; ALBERTI, 2005), analisamos o percurso da Associação Cultural Ítalo-Brasileira do Rio de Janeiro (ACIB-RJ), que fornecia professores para a escola pública foco desta pesquisa, mas que encerrou suas atividades em 2012 devido a uma crise financeira. Com este trabalho, esperamos contribuir para uma melhor compreensão da sala de aula de italiano em escolas públicas e também, para uma cartografia do ensino de italiano no Brasil em contextos públicos. / This research aims to investigate how educational practices are characterized and how social representations are built by a teacher who has taught Italian at a state school, but that, from a labor standpoint, has been connected to an Italian Association. In relation to the methodological procedures, this research is a qualitative study, whose data acquisition was made through the recording of ten meetings between the researcher and the teacher of Italian. For the purpose of analyzing data, there have been identified three thematic axes: (1) the relationship between the teacher and the principal of the school, (2) the teachers representations about the state school students and (3) the representations about the teaching of the Italian language in this educational context. We have considered associating each of the thematic axes to various concepts, such as: authority (ADORNO, 2006), social representations (MOSCOVICI, 2011) and communicative language teaching (WIDDOWSON, 1991; ALMEIDA FILHO, 1993). As we will see in this study, the data reveal a conflicting relationship between the teacher and the state school principal. They also indicate that the teachers representations about the state school context as well as his university training have affected his teaching practice. At the same time, the data pointed out that these representations are not static, but dynamic, because they were reformulated as the teacher faced unexpected situations and lived new experiences. Since this study is part of a state school context, we have decided to map the Brazilian districts whose state schools teach Italian, something unique in the area of studies of the Italian language in Brazil until then. One of the results of this mapping was to see the relevant role of the Italian-Brazilian associations in disseminating the Italian language at the state schools under their responsibility. In a specific way, based on the Oral History Methodology (Meihy e Holanda, 2011: Alberti, 2005), we analyzed the journey of the Associação Cultural Ítalo-Brasileira do Rio de Janeiro (ACIB-RJ), which provided teachers of Italian to the state school that was the focus of this research, but ended its activities in 2012 due to a financial crisis. With this work, we hope to promote a better understanding of the Italian language classroom at state schools, as well as a mapping of the teaching of Italian at state schools in Brazil.

Parmi les différents systèmes de stockage d’énergie électrique étudiés depuis plus de 2 siècles, le stockage électrochimique de type batterie Li-Ion est vraisemblablement le plus pertinent et le plus efficace. Des verrous demeurent cependant pour avoir des batteries Li-Ion répondants aux besoins actuels, et une des limitations provient des matériaux d’électrodes. Le silicium est un candidat de choix pour répondre aux problématiques batteries posées, cependant sa tenue au cyclage est courte et les méthodes de synthèse sont souvent très contraignantes. Associant deux laboratoires de recherche acteurs majeurs dans le domaines des nanosciences (le LRN à l’URCA) et des matériaux et batteries (le LRCS à l’UPJV) le projet pluridisciplinaire NanoSiBL d’une durée de 36 mois se fixe pour objectif d’apporter des solutions aux deux points précédents par : 1, la réalisation d’électrodes négatives en Silicium par une voie de synthèse bas coût originale et innovante développée au LRN (l’électrodépôt en milieu liquide ionique), 2 un accroissement de la durée de vie de l’électrode grâce à deux types de structuration (soit une électrode constituée de nanofils/nanotubes de Si monolithique soit une électrode nanostructurée composite de Si/TiO2). L’expertise dans le domaine des batteries du LRCS devrait permettre sur ce deuxième point de déterminer la géométrie et configuration idéale de l’électrode en termes de performance. Basé des méthodes d’élaboration par électrochimie bas coût et originale, NanoSiBL a pour objectif, grâce au partage de compétences et de technologie entre physiciens et chimistes impliqués, d’initier une nouvelle thématique inter-établissement axée sur la valorisation de nanostructures de silicium et silicium composite nanostructuré. L’intérêt scientifique de ce projet réside dans la mise en œuvre et le contrôle des propriétés intrinsèques de ces nanostructures à base de silicium pour la réalisation d’électrodes négatives performantes de batterie Li-Ion. Dans la littérature, les électrodes négatives à base silicium ou silicium composite (type Si/TiO2) ont déjà démontré une amélioration par rapport aux électrodes de silicium massif. Néanmoins, le passage à des dispositifs opérationnels reste peu fréquent car les voies permettant de contenir l’expansion en volume du silicium restent à éprouver et car les méthodes utilisées pour élaborer ces nanofils de silicium (Chemical Vapor Deposition, évaporation réactive…) restent très contraignantes, tant au niveau des conditions de croissance (nécessité d’utiliser des précurseurs métalliques et des gaz très toxiques) que des coûts de fabrication (travail sous ultra-vide, nombreuses étapes pour la réalisation des dispositifs avec la nécessité de réaliser des contacts post-croissance…). NanoSiBL propose donc une alternative en réelle rupture technologique avec les méthodes de synthèse actuelles. Les techniques de croissance (électrodépôt en liquide ionique) et de nanostructuration (au sein de membranes polycarbonates ou nanotubes de TiO2) utilisées dans le projet permettront la mise au point d’électrodes à bas coût performantes pour l’application batterie Li-Ion visée. En outre la variété conséquente de géométries possibles proposées par les membranes nanoporeuses qui seront utilisées dans le projet (polycarbonate ou nanotubes de TiO2) permettra d’établir un comparatif essentiel de l’impact de la nanostructuration ou encore de la composition des électrodes pour contenir l’expansion en volume du silicium lors du cyclage et ainsi améliorer la durée de vie de telles électrodes (batterie). / Among the various electric energy storage systems studied for more than two centuries, the electrochemical storage battery type Li-Ion is probably the most relevant and most effective. however locks remain for Li-Ion batteries respondents to current needs, and limitations comes from the electrode materials. Silicon is a prime candidate to meet the challenges posed batteries, however its resistance to cycling is short and synthesis methods are often very restrictive. Combining two research laboratories major players in the fields of nanoscience (the LRN to URCA) and materials and batteries (the LRCS to UPJV) the multidisciplinary project NanoSiBL a period of 36 months set the objective of provide solutions to the above two points: 1, the realization of negative electrodes in silicon by a synthetic route down original and innovative cost developed LRN (electrodeposition in ionic liquid medium), 2 increased lifetime of the electrode through two types of structuring (or one electrode made of nanowires / nanotubes Si monolithic or a composite nanostructured electrode Si / TiO2). The expertise in the field of LRCS of batteries should allow this second point to determine the geometry and ideal configuration of the electrode in terms of performance. Based methods developed by electrochemistry low cost and original NanoSiBL aims, through the sharing of expertise and technology between physicists and chemists involved, to initiate an inter-establishment new theme focused on valuation and silicon nanostructures composite nanostructured silicon. The scientific interest of this project lies in the implementation and control of the intrinsic properties of these nanostructures based on silicon for making efficient negative electrodes of Li-Ion battery. In the literature, the negative electrodes based on silicon or silicon composite (type Si / TiO2) have already demonstrated improvement compared to bulk silicon electrodes. However, the transition to operational devices remains uncommon for ways to contain the expansion in volume of the silicon are experiencing and because the methods used to develop these silicon nanowires (chemical vapor deposition, reactive evaporation ...) remain very restrictive both in terms of growth conditions (the need to use metal precursors and highly toxic gases) that manufacturing costs (labor UHV, many steps for the realization of devices with the need for contacts post- growth…). NanoSiBL proposes an alternative in real technological break with the current methods of synthesis. growth techniques (electrodeposition in ionic liquid) and nanostructuring (in polycarbonates or TiO2 nanotube membranes) used in the project will enable the development of electrodes at low cost efficient for application referred Li-Ion battery. Furthermore the consequent variety of possible geometries offered by the nanoporous membranes to be used in the project (polycarbonate or TiO2 nanotubes) will establish a critical comparison of the impact of the nanostructure or composition of electrodes to contain expansion by volume of the silicon during the cycling and improve the life of such electrodes (battery).

劉傑泉. / 手稿本(cops. 2&3 複印本) / Thesis (M.A.)--香港中文大學. / Shou gao ben (cops. 2&3 fu yin ben) / Includes bibliographical references (leaves 354-367). / Liu Jiequan. / Thesis (M.A.)--Xianggang Zhong wen da xue. / 內容提要 / Chapter 第一章 --- 緒言：從晚清中越宗藩關係說起 --- p.1 / Chapter 第二章 --- 李鴻章外交識見的根源 --- p.18 / Chapter 第一節 --- 早年行生涯對李氏的啟示　　　 --- p.18 / Chapter 第二節 --- 同光新政時期李鴻章商務思想的轉變 --- p.37 / Chapter 第三節 --- 李氏早期的外交歷練 --- p.49 / Chapter 第三章 --- 李、寶協議 --- p.68 / Chapter 第一節 --- 法國早期之侵越活動與二次柴楊條約之簽訂 --- p.68 / Chapter 第二節 --- 曾紀澤與法國外交部的分歧 --- p.78 / Chapter 第三節 --- 從巴黎交涉到李鴻章之參與會談 --- p.103 / Chapter 第四節 --- 由河內失陷至李、寶協議 --- p.121 / Chapter 第四章 --- 李、脫辯難 --- p.141 / Chapter 第一節 --- 協議之破壞：法政府單方面推翻和議 --- p.141 / Chapter 第二節 --- 和戰兩難：李、脫晤談前的局勢 --- p.148 / Chapter 第三節 --- 李、脫談判及其中斷　 --- p.161 / Chapter 第四節 --- 續議之無成 --- p.182 / Chapter 第五章 --- 由李、福媾和到大戰結局 --- p.205 / Chapter 第一節 --- 北圻戰局之惡化 --- p.205 / Chapter 第二節 --- 李、福天津簡約之締結 --- p.218 / Chapter 第三節 --- 北黎衝突導因之探討 --- p.243 / Chapter 第四節 --- 大戰．結局．尾聲 --- p.274 / Chapter 第六章 --- 李氏外交初評暨結論 --- p.282 / Chapter 第一節 --- 和與戰之分歧 --- p.282 / Chapter 第二節 --- 軍力、餉力的透視 --- p.309 / Chapter 第三節 --- 結論：李氏中法交涉之得失 --- p.338 / Chapter 附錄： --- 越南廣西雲南交界地區圖 --- p.348 / 譯名對照表 --- p.349 / 參考書目　 --- p.354 / 參考論文目錄

Thesis (M.A.)--香港中文大學. / Manuscript. / Includes bibliographical references (leaves 1-34 (3d group)). / Thesis (M.A.)--Xianggang Zhong wen da xue. / 前言 --- p.1 / Chapter 第一章 --- 京漢鐵路修築的倡議與鐵路總公司的成立 --- p.7 / Chapter 第一節 --- 甲午戰爭前劉銘傳、張之洞築路建議的失敗 --- p.7 / Chapter 第二節 --- 盛宣懷與鐵路總公司 --- p.24 / Chapter 第二章 --- 盧漢鐵路借款 --- p.45 / Chapter 第一節 --- 張之洞、盛宣懷與美、英財團的活動 --- p.45 / Chapter 第二節 --- 比利時借款的一波三折 --- p.55 / Chapter 第三章 --- 盧漢鐵路的修築 --- p.83 / Chapter 第一節 --- 準備階段與築路初期所遇之困難 --- p.83 / Chapter 第二節 --- 工程的進展與完成 --- p.110 / Chapter 第四章 --- 京漢鐵路的支线 --- p.124 / Chapter 第一節 --- 正太鐵路 --- p.125 / Chapter 第二節 --- 道清鐵路 --- p.142 / Chapter 第三節 --- 汴泈鐵路 --- p.153 / Chapter 第五章 --- 京漢鐵路的贖回 --- p.160 / Chapter 第一節 --- 贖路運動的背景及盛宣懷的先見 --- p.160 / Chapter 第二節 --- 陳璧、梁士詒的籌集贖款 --- p.170 / Chapter 第三節 --- 英法匯豐、匯理贖路借款 --- p.179 / Chapter 第六章 --- 京漢鐵路業務成績的檢討 --- p.197 / Chapter 第一節 --- 京漢路業務成績之優良表現 --- p.197 / Chapter 第二節 --- 京漢路業務成績優良的原因 --- p.218 / Chapter 第七章 --- 京漢鐵路對中國鐵路事業的影响 --- p.239 / Chapter 第一節 --- 鐵路總公司之成立 --- p.239 / Chapter 第二節 --- 路權爭奪戰的導火线 --- p.254 / Chapter 第三節 --- 漢路與粤漢鐵路贖回運動 --- p.286 / Chapter 第八章 --- 京漢路與中國煤礦資源的開發 --- p.320 / Chapter 第一節 --- 京漢路沿线煤礦的開發 --- p.327 / Chapter 第二節 --- 鐵路沿線煤礦發展所受之限制 --- p.353 / Chapter 第三節 --- 山西煤礦開發的失敗 --- p.393 / Chapter 第九章 --- 華北農村經濟變化與京漢鐵路之關係 --- p.425 / Chapter 第一節 --- 定縣高陽土布業的興起 --- p.426 / Chapter 第二節 --- 許昌種菸事業的發達 --- p.467 / Chapter 第三節 --- 華北農村其他方面的轉變 --- p.479 / Chapter 第十章 --- 京漢鐵路的其他影響 --- p.506 / Chapter 第一節 --- 金融事業的發展與京漢鐵路的關係 --- p.506 / Chapter 第二節 --- 京漢鐵路與漢陽鐵廠 --- p.528 / Chapter 第三節 --- 京漢路與監運的變化 --- p.540 / 結論 --- p.558 / 清季京漢鐵路大事年表 --- p.569 / 參考書目 --- p.588

O presente trabalho tem como objetivo investigar como se caracterizam as práticas educativas e como se constroem as representações sociais de um professor de italiano que atuava em uma escola pública, mas que, do ponto de vista trabalhista, estava vinculado a uma associação italiana. No que diz respeito aos procedimentos metodológicos, esta é uma pesquisa de cunho qualitativo, cuja coleta de dados consistiu em gravações de dez reuniões entre o pesquisador e o professor de italiano. Para fins de análise dos dados, foram identificados três eixos temáticos: (1) a relação construída entre o professor e a direção da escola, (2) as representações do professor sobre os alunos da escola pública e (3) as representações sobre o ensino de língua italiana nesse contexto. Procuramos relacionar cada um os eixos temáticos a diversos conceitos, tais como: autoridade (ADORNO, 2006), representação social (MOSCOVICI, 2011) e ensino comunicativo de línguas (WIDDOWSON, 1991; ALMEIDA FILHO, 1993). Como veremos nesta dissertação, os dados revelam uma relação conflituosa entre o professor e a direção da escola pública, indicam também, que as suas representações sobre o contexto da escola pública, bem como sua formação universitária, influenciaram sua prática didática. Ao mesmo tempo, os dados apontam que essas representações não são estáticas, mas dinâmicas, pois foram reelaboradas, à medida que o professor se deparava com situações imprevistas e vivenciava novas experiências. Visto que este trabalho se insere em um contexto de escola pública, decidimos iniciá-lo fazendo um mapeamento dos municípios brasileiros que oferecem o ensino de LI em estabelecimentos públicos, algo até então inédito nos estudos de Italianística no Brasil. Um dos resultados desse mapeamento foi ver o importante papel que as associações ítalo-brasileiras têm em difundir a LI em escolas públicas pertencentes às suas respectivas áreas de atuação. De forma específica, apoiados na Metodologia da História Oral (MEIHY e HOLANDA, 2011; ALBERTI, 2005), analisamos o percurso da Associação Cultural Ítalo-Brasileira do Rio de Janeiro (ACIB-RJ), que fornecia professores para a escola pública foco desta pesquisa, mas que encerrou suas atividades em 2012 devido a uma crise financeira. Com este trabalho, esperamos contribuir para uma melhor compreensão da sala de aula de italiano em escolas públicas e também, para uma cartografia do ensino de italiano no Brasil em contextos públicos. / This research aims to investigate how educational practices are characterized and how social representations are built by a teacher who has taught Italian at a state school, but that, from a labor standpoint, has been connected to an Italian Association. In relation to the methodological procedures, this research is a qualitative study, whose data acquisition was made through the recording of ten meetings between the researcher and the teacher of Italian. For the purpose of analyzing data, there have been identified three thematic axes: (1) the relationship between the teacher and the principal of the school, (2) the teachers representations about the state school students and (3) the representations about the teaching of the Italian language in this educational context. We have considered associating each of the thematic axes to various concepts, such as: authority (ADORNO, 2006), social representations (MOSCOVICI, 2011) and communicative language teaching (WIDDOWSON, 1991; ALMEIDA FILHO, 1993). As we will see in this study, the data reveal a conflicting relationship between the teacher and the state school principal. They also indicate that the teachers representations about the state school context as well as his university training have affected his teaching practice. At the same time, the data pointed out that these representations are not static, but dynamic, because they were reformulated as the teacher faced unexpected situations and lived new experiences. Since this study is part of a state school context, we have decided to map the Brazilian districts whose state schools teach Italian, something unique in the area of studies of the Italian language in Brazil until then. One of the results of this mapping was to see the relevant role of the Italian-Brazilian associations in disseminating the Italian language at the state schools under their responsibility. In a specific way, based on the Oral History Methodology (Meihy e Holanda, 2011: Alberti, 2005), we analyzed the journey of the Associação Cultural Ítalo-Brasileira do Rio de Janeiro (ACIB-RJ), which provided teachers of Italian to the state school that was the focus of this research, but ended its activities in 2012 due to a financial crisis. With this work, we hope to promote a better understanding of the Italian language classroom at state schools, as well as a mapping of the teaching of Italian at state schools in Brazil.

Une compréhension précise de la géométrie de coordination et de la structure électronique autour d’un ion métallique à l’intérieur des catalyseurs et des matériaux de batteries est essentielle pour contrôler ces systèmes complexes, modifier leur fonctionnement, et permettre la conception logique de sites améliorés. Cependant, la structure de ces systèmes n’est pas toujours accessible par des techniques de diffraction, et même si elle l’est, la structure électronique ne peut alors être déduite qu’indirectement des coordonnées atomiques. De ce fait, il est essentiel d’avoir une sonde directe de la structure électronique. L’objectif de cette thèse est l’étude des propriétés structurales et électroniques des sites mé- talliques de catalyseurs et de matériaux de batteries par Résonance Magnétique Nucléaire en rotation à l’angle magique (MAS NMR). La MAS NMR est une technique très performante pour l’étude des effets locaux dans les matériaux à l’état solide et permet de sonder directement la structure électronique des matériaux paramagnétiques à haute résolution. Néanmoins, cette ap- proche souffre d’une pauvre résolution et d’une sensibilité limitée pour les noyaux proches d’un site paramagnétique. Pour dépasser ces limitations, nous avons levé des verrous dans l’acquisition et l’interprétation de la MAS NMR en développant et appliquant de nouvelles méthodes pour l’étude de solides paramagnétiques basées sur des hautes fréquences de rotation (60-111 kHz MAS). Pour ce faire, un répertoire de séquences d’impulsion a été développé pour la détection et l’interprétation des effets paramagnétiques dans des solides cristallins et non cristallins. Le potentiel de cette méthodologie a été examiné pour l’élucidation de la géométrie locale et de la structure électronique autour des sites paramagnétiques de catalyseurs homogènes ou hétérogènes, et des matériaux de cathodes en phase mixte pour des batteries au Lithium. Nous voyons dans les méthodes présentées ici, un ensemble d’outils indispensables pour l’élucidation de nombreuses questions de la chimie moderne relatives à la structure et la fonction des sites métalliques. / A precise understanding of the coordination geometry and electronic structure around metal cen- ters in catalysts and battery materials is crucial in order to control these complex systems, modify their behavior, and allow rational design of improved sites. However, such systems are not al- ways amenable for diffraction-based structural determination, and even if they are, obtaining atom-specific electronic structure can only be inferred indirectly from the atomic coordinates. As such, a direct probe of the electronic structure is highly desired. The aim of the present thesis is the investigation of structural and electronic properties of metal sites in catalysts and battery materials by magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. MAS NMR is a powerful technique for the investigation of local effects in solid materials, and offers a direct probe of highly resolved electronic structures in paramagnetic solids. However, it suffers from limited sensitivity and resolution for nuclei lying close to a paramagnetic center in general. We address these limitations by first tackling some of the bottlenecks in the acquisition and interpretation of MAS NMR by developing and applying new methodologies to paramagnetic solids using ultra-fast (60-111) kHz MAS rates. A "toolkit" of suitably designed pulse sequences is assembled for broadband detection and interpretation of paramagnetic shifts in crystalline and non-crystalline solids. The potential of this methodology is explored for the elucidation of local geometry and electronic structure around paramagnetic metal sites in homogeneous and heterogeneous catalysts, and a set of mixed-phase Li-ion battery cathode materials. We anticipate that the approaches described herein form an essential tool to elucidate many outstanding questions about the structure and function of metal sites in modern chemistry.

<p>Li-ion batteries is a system that dynamically couples electrochemistry and mechanics. The electrochemical processes occurring during battery operation induces a wealth of elemental mechanics such as deformation, plasticity, and fracture. Likewise, mechanics influences the electrochemical processes via modulating the thermodynamics of Li reactions and kinetics of ionic transport. These complex interrelated phenomena are far from being well understood and need to be further explored. This thesis studies the couplings between the mechanical phenomena and electrochemical processes in Li-ion batteries using integrated theories and experiments. </p> <p>A continuum model coupling the kinetics of Li diffusion and kinematics of large elasto-plastic deformation is established to investigate the coupling between Li transport and stress evolution in electrodes of Li-ion batteries. Co-evolutions of Li distribution, stress field and deformation in the electrodes with multiple components are obtained. It is found that the Li profile and stress state in a composite electrode are significantly different from <a></a><a>that </a>in a free-standing configuration, mainly due to the regulation from the mechanical interactions between different components. Chemomechanical behaviors of the heterogeneous electrodes in real batteries are further explored. Three-dimensional reconstructed models are employed to investigate the mechanical interactions of the constituents and their influence on the accessible capacity of batteries. </p> <p>Structural disintegration of the state-of-art cathode materials LiNi_xMn_yCo_zO₂ (x+y+z=1, NMC) during electrochemical cycling is experimentally revealed. Microstructural evolution of different marked regimes in electrodes are tracked before and after lithiation cycles. It is found that the decohesion of primary particles constitutes the major mechanical degradation in the NMC materials. Electrochemical impedance spectroscopy (EIS) measurement confirms that the mechanical disintegration of NMC secondary particle causes the electrochemical degradation of the battery. To reveal the reasons for particle disintegration, the dynamic evolution of mechanical properties of NMC during electrochemical cycling is explored by using instrumented nanoindentation. It is found that the elastic modulus, hardness, and interfacial fracture strength of NMC secondary particle significantly depend on the lithiation state and degrade as the electrochemical cycles proceed, which may cause the damage accumulation during battery cycling.</p> <p>Corrosive fracture of electrodes in Li-ion batteries is investigated. Li reaction causes embrittlement of the host material and typically results in a decrease of fracture toughness. The dynamics of crack growth depends on the chemomechanical load, kinetics of Li transport, and the Li embrittlement effect. A theory of coupled diffusion, large deformation, and crack growth is implemented into finite element program and the corrosive fracture of electrodes under concurrent mechanical and chemical load is simulated. The competition between energy release rate and fracture resistance as crack grows during both Li insertion and extraction is examined in detail, and it is found that the corrosive fracture behaviors of the electrodes rely on the chemomechanical load and the supply of Li to the crack tip. The theory is further applied to model corrosive behavior of intergranular cracks in NMC upon Li cycles. The evolving interfacial strength at different states of charge and different cycle numbers measured by in-situ nanoindentation is implemented in the numerical simulation.</p>