Ni-MH battery today is one of the most widely used secondary battery type because of its properties like secure use at high voltages, excellent thermal properties and consisting of environmentally acceptable materials. LaNi5, as an anode material, is the dominant commercial active material for the Ni-MH battery industry. CaNi5, belonging to same crystal structure, is an alternative for LaNi5, due to higher hydrogen storage capacity, higher theoretical discharge capacity, light weight and low cost. However, low cycle life is the main restriction for the use of CaNi5. In this study, effects of alloying was studied using an ab initio pseudo potential method. In this regard, formation energies of the CaNi5 compounds having different alloying elements were calculated for the understanding of the effect of the alloying element on the stability of the compound. It was found that, all lanthanides and actinides and early transition metals (Sc, Y, Zr, Hf) replacing Ca and early transition metals (Sc, Ti, Zr, Hf) plus elements like Al, Si, P, Ge, Zn, Sn and Sb replacing Ni, decrease the formation energy of CaNi5. Lower formation energy, compared to the pure compound, increases the stability which could improve the cyclic durability of CaNi5 to be used as an anode in Ni-MH batteries. In addition, in order to investigate effects of alloying on Ca diffusion in CaNi5, activation energies of Ca diffusion for different alloys were calculated by Nudged Elastic Band method (NEB) method.

Une alternative aux énergies fossiles comme vecteur énergétique peut se présenter sous la forme de l'hydrogène et de son stockage. Les hydrures métalliques sont une des options possibles pour le stockage de l'hydrogène. Les accumulateurs alcalins Ni-MH présentent une technologie intéressante pour les applications portables et pour le développement des véhicules électriques hybrides (HEV). Afin de répondre à la demande d'augmentation de la capacité massique des accumulateurs, de nouveaux composés intermétalliques hydrurables de type ABx (3etlt;xetlt;5) sont étudiés. Le groupe A est constitué de terres rares partiellement substituées par du magnésium, le groupe B contient du Ni. Après un état de l'art sur ce type de composés, le travail de cette thèse consiste à rechercher les conditions d'élaboration des composés A1-yMgyNix (3etlt;xetlt;5, 0etlt;yetlt;1, A= La, Pr, Nd) ainsi que de les caractériser d'un point de vue structural et physico-chimique (DRX, microsonde électronique, ICP) et de déterminer leurs propriétés vis-à-vis de l'hydrogène (réac tion solide-gaz et électrochimique). Durant ce travail de nouvelles phases ont été découvertes et caractérisées : les phases (A1-yMgy)5Ni19 / One solution to overcome the diminution of fossil fuel resources is to use hydrogen as an energy vector. The main issue concerning hydrogen systems is its storage. NiMH batteries are promising candidates for portable devices and hybrid vehicles (HEV) applications. In order to answer to growing need for higher capacity, new compounds such as ABx (3etlt;xetlt;5) are under investigation. A is a rare earth element that can be partially substituted by Mg. B is Ni. After careful examination of the state of the art on this family of compound, the synthesis routes to prepare A1-yMgyNix (3etlt;xetlt;5, 0etlt;yetlt;1, A= La, Pr, Nd) alloys were investigated and optimized during this PhD work. The structure and chemical composition of the samples were determined using X-ray diffraction, microprobe analysis and ICP. The hydrogen sorption properties (solid-gas and electrochemical reactions) were studied as well. During this work the (A1-yMgy)5Ni19 new phase s have been reported and characterized

Les applications portables et stationnaires des accumulateurs Ni-MH nécessitent sans cesse des autonomies de plus en plus importantes. Cet accroissement d’autonomie peut être obtenu en développant de nouveaux composés intermétalliques hydrurables de type ABx (3<x<4) de plus grande capacité massique. Le groupe A de ces composés est constitué de La partiellement substitué par du Mg, qui est beaucoup plus léger et diminue la masse molaire de l’alliage, et le groupe B contenant du Ni partiellement substitué par d’autres éléments de transition. Après une étude bibliographique approfondie, le travail de cette thèse consiste à rechercher tout d’abord les conditions optimales d’élaboration d’intermétalliques de composition La1-yMgyNix (0<y<1 ; 3<x<4). Puis ces composés sont caractérisés du point de vue structural et physico chimique (diffraction des rayons X et microsonde électronique), et leurs propriétés vis-à-vis de l’hydrogène (réaction solide-gaz et électrochimique) sont étudiées / Mobile and stationary applications for Ni-MH batteries require continuously more and more energy density. This increased autonomy can be obtained by developing new hydride-forming compounds of ABx-type (3<x<4) with larger weight capacities. The A element of these compounds is constituted of La partially substituted by light Mg, allowing a reduced molar weight. The B element is made of Ni that can be partially substituted by other transition metals. After an extensive bibliographic study, this thesis presents the research work to find optimum conditions for the synthesis of Mg-containing intermetallic compounds La1-yMgyNix (0<y<1; 3<x<4). These compounds are then characterized from the structural and chemical point of views (X-ray diffraction and microprobe analysis) and their hydrogen-related properties are studied and compared (solid-gas and electrochemical reactions)

Les batteries Ni-MH sont utilisées dans diverses applications, aussi bien stationnaires (panneaux solaires) que mobiles (véhicules hybrides). La matière active des électrodes négatives des batteries actuellement commercialisées est un alliage intermétallique de type AB5 (A = terres rares, B = métaux de transition). La demande croissante en énergie nécessite d'améliorer la capacité massique de ces accumulateurs. Pour cette raison, nous étudions de nouveaux matériaux d'électrode de type ABy (y = 3,5 ou 3,8). La structure d'empilement particulière de ces alliages composés d'unités [AB5] et [A2B4] leur confère une capacité plus importante. L'unité [A2B4] est en effet capable d'absorber davantage d'hydrogène que l'unité [AB5]. Cependant, sa stabilité au cyclage lui fait défaut. Dans cette thèse nous avons, dans un premier temps, mené une étude sur les composés binaires de type ANi3,5 et ANi3,8 (A Æ Gd, Sm ou Y) puis nous avons étudié l'évolution des propriétés thermodynamiques, électrochimiques et de corrosion et après substitutions successives de la terre rare (ou yttrium) par du magnésium puis du lanthane / Ni-MH batteries are used in both stationary (solar panels) and mobile (hybrid vehicles) applications. The active material of negative electrodes currently on the market is an AB5-type alloy (A = rare earth, B = transition metal). The continuously increasing demand for energy requires improving the mass capacity of these batteries. For this reason, we study new type of electrode materials ABy (y Æ 3.5 or 3.8). The particular stacking structure of these alloys composed of [AB5] and [A2B4] units give them more capacity. Indeed, [A2B4] unit is able to absorb more hydrogen than [AB5] unit. However, stability in cycling is lowered. In this phD work we have, at first, conducted a study of binary compounds type ANi 3.5 and ANi3.8 (A = Gd, Sm ou Y), then we studied the evolution of the thermodynamic properties, electrochemical and corrosion after successive substitutions of the rare earth (or yttrium) with magnesium and lanthanum

Neste trabalho avaliou-se a ação positiva da substituição de lantânio por praseodímio e de lantânio por magnésio na performance eletroquímica de eletrodos de ligas de armazenamento de hidrogênio em estado bruto de fusão e com tratamento térmico. O La foi substituído por Mg nas ligas La0,7-xMgxPr0,3Al0,3Mn0,4Co0,5Ni3,8 (x=0,0-0,7) e por Pr nas ligas La0,7-yPryMg0,3Al0,3Mn0,4Co0,5Ni3,8 (y=0,0-0,7). Os parâmetros eletroquímicos analisados foram ativação, capacidade de descarga, retenção da capacidade de descarga, autodescarga e alta taxa de descarga. As ligas apresentaram comportamento passivo em relação à corrosão. As análises por MEV/EDS e por DRX com refinamento por Rietveld revelaram a presença majoritária de fases similares às fases LaNi5, PrNi5, LaMg2Ni9 e PrMg2Ni9 em função das composições das ligas estudadas. Os parâmetros de rede e os volumes da célula unitária das fases diminuíram com a substituição crescente de La por Mg e de La por Pr. As capacidades de descarga máxima decresceram com a substituição crescente de La por Mg e de La por Pr, acompanhando o decréscimo da abundância da fase similar à fase LaNi5 e o aumento da abundância da fase similar à fase LaMg2Ni9. Comparativamente, menores taxas de autodescarga e maior estabilidade cíclica foram observadas para o eletrodo da liga na condição x=0,1, ao passo que o eletrodo da liga na condição y=0,0 apresentou maiores valores de alta taxa de descarga, indicando melhor performance cinética. / In this work, the positive action of the substitution of lanthanum by praseodymium and lanthanum by magnesium in the electrochemical performance of the as-cast and annealed hydrogen storage alloys electrodes had been evaluated. La was replaced by Mg in La0.7-xMgxPr0.3Al0.3Mn0.4Co0.5Ni3.8 (x=0.0-0.7) alloys and by Pr in La0.7-yPryMg0.3Al0.3Mn0.4Co0.5Ni3.8 (y=0.0-0.7) alloys. The electrochemical parameters analyzed were activation, discharge capacity, discharge capacity retention, self-discharge rate and high-rate dischargeability. The alloys showed a passive corrosion behavior. The analyses by SEM/EDS and XRD with Rietveld refinement revealed the majority presence of LaNi5, PrNi5, LaMg2Ni9 and PrMg2Ni9 similar reference phases depending on the compositions of the studied alloys. The lattice parameters and cell volumes of the component phases decreased with increasing substitution of La for Mg and with La for Pr. The maximum discharge capacity decreased with increasing substitution of La for Mg and with La for Pr, following the decrease in the abundance of LaNi5 similar phase and the increase in the abundance of to the LaMg2Ni9 similar phase. Lower self-discharge rates were observed for the alloy electrode when x=0.1, while higher high-rate dischargeability for the alloy electrode when y=0.0 indicated better kinetic performance, comparatively.

Neste trabalho, avaliou-se o efeito da substituição parcial do Ni pelos elementos Co, Cu e Sn, e do La e Mg pelo Pr em ligas do tipo AB5 para as ligas nominais La0,7Mg0,3Al0,3Mn0,4Cu0,5Ni3,8, La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 e La0,7Mg0,3Al0,3Mn0,4Sn0,5Ni3,8, La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8, Pr0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 sem e com tratamento térmico de 750° e 850°C por 9 e 16 horas. Estas ligas absorvedoras de hidrogênio foram utilizadas como material ativo em eletrodos negativos de baterias de Ni-HM. Avaliou-se a influência destas substituições e do tratamento térmico na microestrutura e nas propriedades eletroquímicas nas ligas. A substituição parcial do Ni pelo Co com o tratamento térmico de 750°C por 16 horas apresentou duas novas fases Al6Mn e PrCo13. Na substituição parcial do Ni pelo Sn formou a fase LaNi2Sn2 na liga. Utilizou-se caracterização de raios-X com refinamento de Rietveld para quantificar as fases em cada composição. Mediu-se a absorção de hidrogênio utilizando um Aparato Sieverts para obtenção das curvas PCT. Observou-se que as ligas La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 e La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 apresentaram as melhores capacidades de absorção de hidrogênio. Verificou-se o comportamento destas ligas na capacidade de descarga, estabilidade cíclica das baterias de Ni-HM. Comparando as ligas, a maior capacidade de descarga medida foi para a substituição parcial do Ni pelo Co, alcançando 406,1 mAh após o tratamento térmico de 850° C por 16 horas. A melhor capacidade de absorção obtida na analise de PCT, foi para a liga La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 com valor de H/M de 0,980. Também, foi avaliada uma correlação das propriedades eletroquímicas com a capacidade de absorção obtida na analise da curva PCT. / In this work, it was evaluated the effect of the partial substitution of Ni by the elements Co, Cu and Sn and of the La and Mg by the Pr in type AB5 alloys to the nominal alloys La0,7Mg0,3Al0,3Mn0,4Cu0,5Ni3,8, La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8, La0,7Mg0,3Al0,3Mn0,4Sn0,5Ni3,8, La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 and Pr0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8, as castting and with annealing treatment of 750 °C and 850 °C for 9 and 16 hours. These hydrogen-absorbing alloys were used as active material on negative electrodes of Ni-HM batteries. The influence of these substitutions and the annealing treatment on the microstructure and on the electrochemical properties in the alloys was evaluated. The partial substitution of Ni by Co with the annealing treatment of 750 °C for 16 hours presented two new phases Al6Mn and PrCo13. In the partial substitution of Ni by Sn formed the LaNi2Sn2 phase in the alloy. It was characterized by X-ray diffraction using Rietveld\'s refinement to quantify the phases in each composition. Hydrogen absorption was measured using the Sieverts apparatus to obtain the PCT curves. It was observed that the alloys La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 and La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8, presented the best capacities of hydrogen absorption. The behavior of these alloys in the discharge capacity, the cyclic stability of the Ni-HM batteries, was verified. Comparing the alloys, the biggest discharge capacity measured was for the partial substitution of Ni by Co alloy, reaching 406.1 mAh after the annealing treatment of 850 °C for 16 hours. The finest absorption capacity obtained in the PCT analysis was for the La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 alloy with an H/M value of 0.980. Also, a correlation of the electrochemical properties with the absorption capacity obtained in the analysis of the PCT curve was evaluated.

Neste trabalho avaliou-se a ação positiva da substituição de lantânio por praseodímio e de lantânio por magnésio na performance eletroquímica de eletrodos de ligas de armazenamento de hidrogênio em estado bruto de fusão e com tratamento térmico. O La foi substituído por Mg nas ligas La0,7-xMgxPr0,3Al0,3Mn0,4Co0,5Ni3,8 (x=0,0-0,7) e por Pr nas ligas La0,7-yPryMg0,3Al0,3Mn0,4Co0,5Ni3,8 (y=0,0-0,7). Os parâmetros eletroquímicos analisados foram ativação, capacidade de descarga, retenção da capacidade de descarga, autodescarga e alta taxa de descarga. As ligas apresentaram comportamento passivo em relação à corrosão. As análises por MEV/EDS e por DRX com refinamento por Rietveld revelaram a presença majoritária de fases similares às fases LaNi5, PrNi5, LaMg2Ni9 e PrMg2Ni9 em função das composições das ligas estudadas. Os parâmetros de rede e os volumes da célula unitária das fases diminuíram com a substituição crescente de La por Mg e de La por Pr. As capacidades de descarga máxima decresceram com a substituição crescente de La por Mg e de La por Pr, acompanhando o decréscimo da abundância da fase similar à fase LaNi5 e o aumento da abundância da fase similar à fase LaMg2Ni9. Comparativamente, menores taxas de autodescarga e maior estabilidade cíclica foram observadas para o eletrodo da liga na condição x=0,1, ao passo que o eletrodo da liga na condição y=0,0 apresentou maiores valores de alta taxa de descarga, indicando melhor performance cinética. / In this work, the positive action of the substitution of lanthanum by praseodymium and lanthanum by magnesium in the electrochemical performance of the as-cast and annealed hydrogen storage alloys electrodes had been evaluated. La was replaced by Mg in La0.7-xMgxPr0.3Al0.3Mn0.4Co0.5Ni3.8 (x=0.0-0.7) alloys and by Pr in La0.7-yPryMg0.3Al0.3Mn0.4Co0.5Ni3.8 (y=0.0-0.7) alloys. The electrochemical parameters analyzed were activation, discharge capacity, discharge capacity retention, self-discharge rate and high-rate dischargeability. The alloys showed a passive corrosion behavior. The analyses by SEM/EDS and XRD with Rietveld refinement revealed the majority presence of LaNi5, PrNi5, LaMg2Ni9 and PrMg2Ni9 similar reference phases depending on the compositions of the studied alloys. The lattice parameters and cell volumes of the component phases decreased with increasing substitution of La for Mg and with La for Pr. The maximum discharge capacity decreased with increasing substitution of La for Mg and with La for Pr, following the decrease in the abundance of LaNi5 similar phase and the increase in the abundance of to the LaMg2Ni9 similar phase. Lower self-discharge rates were observed for the alloy electrode when x=0.1, while higher high-rate dischargeability for the alloy electrode when y=0.0 indicated better kinetic performance, comparatively.