Neste trabalho, foi desenvolvido um material híbrido inédito carvão ativado/nanotubos de carbono/nanopartículas de prata para as aplicações em bateria de íons de lítio e capacitor eletroquímico de dupla camada. O compósito foi preparado por crescimento dos nanotubos de carbono diretamente sobre o carvão ativado via deposição química de vapor e depois nanopartículas de prata foram incorporadas no carvão ativado/nanotubos de carbono. A morfologia do compósito foi analisada por microscopia eletrônica de varredura. Investigação das propriedades de intercalação de lítio no carvão ativado (CA), carvão ativado/nanotubos de carbono (CA/NTC), carvão ativado/prata (CA/Ag) e carvão ativado/nanotubos de carbono/prata (CA/NTC/Ag) foi conduzida por voltametria cíclica e ciclos de carga/descarga, utilizando dois diferentes eletrólitos. Verificou-se que o ânodo de CA/NTC/Ag apresenta mais elevado valor de capacidade específica reversível que a grafita em eletrólito comercial, provavelmente devido à rede tridimensional com elevada condutividade eletrônica formada por nanotubos de carbono e nanopartículas de prata nos poros e nas rugosidades do substrato. Além disso, os nanotubos de carbono podem exibir elevada capacidade de armazenamento de lítio. Outra vantagem do CA/NTC/Ag é que a rede de nanotubos de carbono acomoda a expansão de volume das partículas de prata durante a ciclagem do eletrodo, mantendo-as bem adsorvidas na superfície do CA/NTC. Os resultados confirmaram a existência do sinergismo entre os componentes do CA/NTC/Ag, que promove características eletroquímicas superiores àquelas dos constituintes isolados. / In this work, an unpublished hybrid material activated carbon/carbon nanotubes/silver nanoparticles was developed for lithium ion battery and electrochemical double layer capacitor applications. The composite was prepared by growing carbon nanotubes directly on the activated carbon via chemical vapor deposition and after silver nanoparticles were incorporated on the activated carbon/carbon nanotubes. The composites morphology was analyzed by scanning electron microscopy. Investigation of lithium intercalation properties in activated carbon (AC), activated carbon/carbon nanotubes (AC/CNT), activated carbon/silver (AC/Ag) and activated carbon/carbon nanotubes/silver (AC/CNT/Ag) was carried out by cyclic voltammetry and charge/discharge cycles by making use of two different electrolytes. It was found that the AC/CNT/Ag anode presents higher reversible specific capacity value in comparison with graphite in commercial electrolyte, probably due to the three dimensional network with high electronic conductivity formed by carbon nanotubes and silver nanoparticles in the substrates pores and roughness. Furthermore, carbon nanotubes can exhibit high lithium storage capacity. Another advantage of the AC/CNT/Ag is that the network of carbon nanotubes accommodates volume expansion of the silver particles during electrode cycling, keeping them well adsorbed on the surface of the AC/CNT. The results confirmed the existence of synergism between the components of the AC/CNT/Ag, which promotes electrochemical characteristics that are higher than those of the individual constituents.

O aumento no consumo energético e a crescente preocupação ambiental frente à emissão de gases poluentes criam um apelo mundial favorável para pesquisas de novas tecnologias não poluentes de fontes de energia. Baterias recarregáveis de lítio-ar em solventes não aquosos possuem uma alta densidade de energia teórica (5200 Wh kg-1), o que as tornam promissoras para aplicação em dispositivos estacionários e em veículos elétricos. Entretanto, muitos problemas relacionados ao cátodo necessitam ser contornados para permitir a aplicação desta tecnologia, por exemplo, a baixa reversibilidade das reações, baixa potência e instabilidades dos materiais empregados nos eletrodos e dos solventes eletrolíticos. Assim, neste trabalho um modelo cinético foi empregado para os dados experimentais de espectroscopia de impedância eletroquímica, para a obtenção das constantes cinéticas das etapas elementares do mecanismo da reação de redução de oxigênio (RRO), o que permitiu investigar a influência de parâmetros como o tipo e tamanho de partícula do eletrocatalisador, o papel do solvente utilizado na RRO e compreender melhor as reações ocorridas no cátodo dessa bateria. A investigação inicial se deu com a utilização de sistemas menos complexos como uma folha de platina ou eletrodo de carbono vítreo como eletrodos de trabalho em 1,2-dimetoxietano (DME)/perclorato de lítio (LiClO4). A seguir, sistemas complexos com a presença de nanopartículas de carbono favoreceu o processo de adsorção das moléculas de oxigênio e aumentou ligeiramente (uma ordem de magnitude) a etapa de formação de superóxido de lítio (etapa determinante de reação) quando comparada com os eletrodos de platina e carbono vítreo, atribuída à presença dos grupos laterais mediando à transferência eletrônica para as moléculas de oxigênio. No entanto, foi observada uma rápida passivação da superfície eletrocatalítica através da formação de filmes finos de Li2O2 e Li2CO3 aumentando o sobrepotencial da bateria durante a carga (diferença de potencial entre a carga e descarga > 1 V). Adicionalmente, a incorporação das nanopartículas de platina (Ptnp), ao invés da folha de platina, resultou no aumento da constante cinética da etapa determinante da reação em duas ordens de magnitude, o qual pode ser atribuído a uma mudança das propriedades eletrônicas na banda d metálica em função do tamanho nanométrico das partículas, e estas modificações contribuíram para uma melhor eficiência energética quando comparado ao sistema sem a presença de eletrocatalisador. Entretanto, as Ptnp se mostraram não específicas para a RRO, catalisando as reações de degradação do solvente eletrolítico e diminuindo rapidamente a eficiência energética do dispositivo prático, devido ao acúmulo de material no eletrodo. O emprego de líquido iônico como solvente eletrolítico, ao invés de DME, promoveu uma maior estabilização do intermediário superóxido formado na primeira etapa de transferência eletrônica, devido à interação com os cátions do líquido iônico em solução, o qual resultou em um valor de constante cinética da formação do superóxido de três ordens de magnitude maior que o obtido com o mesmo eletrodo de carbono vítreo em DME, além de diminuir as reações de degradação do solvente. Estes fatores podem contribuir para uma maior potência e ciclabilidade da bateria de lítio-ar operando com líquidos iônicos. / The increasing in energetic consumption and environmental concerning toward rising in the emission of pollutant gases create a favorable scenario to develop non-pollutant technologies and more efficient energy storages. Rechargeable non-aqueous lithium-air batteries possess high theoretical energy density (5200 Wh kg-1), characterizing as a promising system to stationary and electric vehicles applications. However, many issues on the cathode electrode should be addressed to enable this technology, for example, low reversibility of the reactions, low rate-capability and instabilities issues from cathode materials and electrolytic solvents. Here, a kinetic model was employed for modulate the experimental impedance data in order to obtain the rate constants of elementary steps from oxygen reduction reaction (ORR), which allows the investigation of the role of some parameters such as, type and grain size of electrocatalysts, and the solvent influence. The initial investigation were with less complexes systems of platinum bulk or glassy carbon as the working electrode in 1,2-dimethoxyethane (DME)/lithium perchlorate (LiClO4). Based on that, the role of carbon nanoparticles in the ORR was an increasing the oxygen adsorption process, and by slightly increasing (one order of magnitude) the superoxide formation (rate determining step) as when compared with platinum and glassy carbon electrodes due to the presence of side groups acting as mediators to the electron transfer. Nonetheless, a fast surface passivation was observed in function of Li2O2 and Li2CO3 thin films formations, and these films increase the battery overpotential during the charge process (potential difference between charge/discharge >1V). In addition, dispersed platinum nanoparticles (Ptnp) resulted in an increase of two orders of magnitude on the rate constant of the rate determining step when compared to platinum bulk. This can be explained due to changes in electronic properties of metallic d-bands in function of nanometric size. These changes contributed to enhance the energetic efficiency of the practical device when compared to the non-catalyzed system. However, the Ptnp were non-specific toward the ORR catalyzing the electrolyte degradation reactions, and decreasing the energy efficiency faster than the non-catalyzed system. The ionic liquid rather than DME promoted better stabilization process for intermediary superoxide due to interaction between cations present in solution, resulting in an outstanding enhancement of the rate constant for rate determining step (three orders of magnitude) when compared to the same working electrode in DME. In addition, decrease the electrolyte degradation reaction. These factors can improve a higher rate-capability and cycle life of the practical lithium-air batteries.

Materiais auto-organizados constituídos de V2O5 xerogel, poli(etilenoimina) (PEI) e nanopartículas de carbono (NpCs) foram obtidos por meio da técnica camada-por-camada (LbL). A metodologia aplicada permitiu a obtenção de filmes finos com elevado controle de espessura além de permitir um crescimento linear dos filmes, denominados neste trabalho V2O5/PEI e V2O5/PEI/NpCs. Além disso, o desempenho eletroquímico dos materiais auto-organizados foi comparado a um eletrodo de V2O5. Análises de FTIR mostraram que interações específicas entre os grupos amina do PEI e os grupos carboxila do V2O5 são responsáveis pelo crescimento do filme. Estas interações permitem a formação de um campo eletrostático capaz de blindar as interações entre os íons lítio e os oxigênios da vanadila (V=O) e, por consequência, são responsáveis pelo aumento na mobilidade iônica dos íons lítio no interior da matriz hospedeira e, portanto, um aumento na capacidade de armazenamento de carga. Resultados obtidos através de medidas de carga/descarga mostram que o V2O5/PEI/NpCs apresenta uma melhor desempenho do que os demais materiais estudados neste trabalho. Estes resultados mostram que a capacidade específica do V2O5/PEI/NpCs foi de 137 mA h g-1 para a menor densidade de corrente aplicada e aproximadamente 1,6 vezes maior do que os valores de capacidade específica para os outros materiais para a maior densidade de corrente aplicada. Além disso, estas medidas permitiram a observação de uma menor variação na razão estequiométrica máxima (xmáx) em função das densidades de corrente aplicadas para os filmes auto-organizados, fato este relacionado a uma maior mobilidade iônica dos íons lítio no interior dessas matrizes. Os resultados obtidos a partir de espectroscopia de impedância eletroquímica (EIS) mostraram que a difusão dos íons lítio no interior das matrizes auto-organizadas é maior do que no caso do V2O5, cujos valores do coeficiente de difusão foram de 1,64 x 10-15, 1,21 x 10-14 e 2,26 x 10-14 cm2 s-1 para os filmes V2O5, V2O5/PEI e V2O5/PEI/NpCs, respectivamente. Sendo assim, o polímero e as NpCs promoveram novos caminhos condutores e permitiram a conexão elétrica entre camadas isoladas da matriz V2O5. Dessa forma, novos nanocompósitos foram obtidos visando demonstrar o método de auto-organização empregado para melhorar o transporte de carga em matrizes hospedeiras. / Self-assembled materials constituted of V2O5 xerogel, poly (ethyleneimine) (PEI), and carbon nanoparticles (CNPs) were obtained by the layer-by-layer (LbL) technique. The applied methodology permitted the obtainment of thin films with high thickness control and also permitted a linear growth of the films, which will be named V2O5/PEI and V2O5/PEI/CNPs. Besides, the electrochemical performance of the self-assembled materials was compared to a V2O5 electrode. FTIR analyses showed that the specific interactions between the amine groups of PEI and the vanadyl groups of the V2O5 are responsible for the film growth. These interactions permitted the formation of an electrostatic shield capable of hindering the interactions between the lithium ions and the vanadyl oxygen atoms (V=O) and are consequently responsible for the enhancement on the ionic mobility of the lithium ions within the host matrix, leading to a higher energy storage capability. Results obtained by the charge/discharge measurements showed that V2O5/PEI/CNPs presents a better performance than the other materials studied for this research. These results demonstrated that the specific capacity of the V2O5/PEI/CNPs was 137 mA h g-1 under the lowest current density applied and approximately 1.6 times higher than the specific capacity values obtained for the other materials under the highest current density applied. Moreover, it was observed that the variation of the maximum stoichiometric ratio (xmax) as a function of the current density is lower for the self-assembled materials than for the V2O5 electrode, which can be related to the higher ionic mobility of the lithium ion within the self-assembled materials. Electrochemical Impedance Spectroscopy (EIS) data demonstrated that the diffusion of the lithium ions within the self-assembled materials is higher than within the V2O5 electrode, and the diffusion coefficients were 1.64 x 10-15, 1.21 x 10-14 e 2.26 x 10-14 cm2 s-1 for V2O5, V2O5/PEI and V2O5/PEI/CNPs, respectively. Thus, the polymer and the CNPs provided new conducting pathways and connected isolated V2O5 chains in the host matrix. Therefore, novel spontaneous nanocomposites were formed, aiming to demonstrate the self-assembled method adopted for improving charge transport within host matrices.

Neste trabalho, avaliou-se inicialmente o efeito da substituição de elementos em ligas à base de LaMgAlMnCoNi do tipo AB5 com adição de estanho (Sn) e cobre (Cu) em substituição ao cobalto (Co), para utilização em ligas absorvedoras de hidrogênio e em eletrodos negativos de baterias de Ni-HM. Avaliou-se a influência desta substituição na microestrutura do material. Notou-se que o aumento da concentração de estanho promove a formação da fase LaNiSn nas ligas, bem como a diminuição das duas fases principais: LaNi5 e (La,Mg)Ni3. Adicionalmente, utilizou-se o refinamento de Rietveld para quantificar as fases em cada composição. Posteriormente, propôs-se um estudo da absorção de hidrogênio. Notou-se que a liga com cobalto apresentou a melhor capacidade de absorção de hidrogênio. Ademais, verificou-se o comportamento destas ligas na capacidade de descarga, estabilidade cíclica e na alta taxa de descarga de baterias de Ni-HM. A maior capacidade de descarga medida foi para a liga de cobalto, atingindo 337,1 mAh/g. Notou-se, posteriormente uma melhora na estabilidade cíclica das baterias com o aumento do teor de cobre. Além disso, observou-se que a alta taxa de descarga apresenta melhores valores com a adição de cobre na composição. Por fim, avaliou-se o efeito da susceptibilidade a corrosão. Notou-se que o estanho promove um aumento na resistência à corrosão das ligas em eletrólito alcalino. / In this work, it has firstly been evaluated the effect of tin (Sn) and copper (Cu) substituting cobalt (Co) in LaMgAlMnCoNi AB5-type alloys for use in hydrogen storage materials and negative electrodes of Ni-MH batteries. The influence of this substitution on the microstructure of these materials has been evaluated. It could be noted that increasing the tin concentration promotes the formation of LaNiSn phase and decrease of two main phases of these alloys: LaNi5 and (La,Mg)Ni3. Additionally, the Rietveld refinement has been evaluated to quantify phases in each composition. Subsequently, it has been proposed a study of the hydrogen absorption in these alloys. It could be observed that the cobalt alloy showed the best hydrogen absorption capacity. Moreover, the behavior of these alloys has been investigated in the discharge capacity, cyclic stability and high rate dischargeability of Ni-MH batteries. The highest discharge capacity has been measured for cobalt alloy, reaching 337.1 mAh/g. It has been noted, further improvement in the cyclic stability batteries with increasing copper content in the alloys. Furthermore, it has been observed that the high rate dischargeability has better values with the addition of copper in the composition. Finally, it has been evaluated the effect of susceptibility to corrosion. It has been noted that tin promotes an increase in corrosion resistance of the alloys in an alkaline electrolyte.

Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges. Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium  mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased. Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one. Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface. During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed. The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium. During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence. / Litiumsyrebatteriet, även känt som litiumluftbatteriet, kan potentiellt revolutionera vårt förhållande till energilagring. Genom att låta litium reagera med syrgas från luften kan teoretiskt höga energitätheter uppnås. Dock så behöver många problem lösas, så som att hitta lämpliga elektrod- och elektrolytmaterial samt att få en ökad förståelse för reaktionsmekanismen, innan litiumsyrebatteriet kan kommersialiseras. Den här avhandlingen behandlar de sistnämnda av dessa problem. För att ett batteri ska kunna leverera hög effekttäthet och energieffektivitet krävs en effektiv jontransport mellan elektroderna. Här utvärderades masstransporten hos flera olika elektrolyter. Resultatet visade att masstransporten av litium i en litiumsyrebatterielektrolyt (baserad på dimetylsulfoxid (DMSO)) är likvärdig med en konventionell litiumjonbatterielektrolyt. När elektrolyter baserade på jonvätskor användes uppvisades väldigt stora energiförluster. När litiumsalt tillsattes påverkades lösligheten av syre i DMSO-baserade elektrolyter. Vilken sorts litiumsalt som användes påverkade om lösligheten av syre ökade eller minskade. Vid en saltkoncentration på en molar var den högsta syrelösligheten 68 \% större än den lägsta. Två olika modellsystem används för att studera den elektrokemiska reaktionen: En elektrokemisk kvartskristallmikrovåg och en cylindrisk ultramikroelektrod. Vid kombinerad användning av dessa system påvisades att löslig litiumsuperoxid bildades vid urladdningen. Följden av detta blev att endast delar av urladdningsprodukten hamnade på elektroden. Vid urladdning visade ultramikroelektroderna tecken på passivering som inte kunde beskrivas av tidigare teori. Här föreslås att passiveringen uppstår på grund av en blockering av de aktiva säten där reaktionen fortskrider. För denna process föreslås även en detaljerad mekanism. Urladdningsprocessens koncentrationsberoende utvärderades genom att bestämma reaktionsordningen för syre och litium under kinetisk- och masstransport kontroll. Under kinetisk kontroll fanns inga heltalsreaktionsordningar, för syre var reaktionsordningen nära 0.5 vilket föreslår att det reaktionssteg som bestämmer strömstorleken innefattar en adsorption av syre. Vid högre överpotentialer, då systemet var under masstransportkontroll, var reaktionsordningarna för litium och syre noll respektive ett. Detta föreslår att ändringar i syrekoncentration påverkar strömmen betydligt mer än vad det gör för litium. Under uppladdning kunde inte all reaktionsprodukt avlägsnas från elektroden. Detta ledde till en ackumulation då flera cykler studerades. Uppladdningens delsteg innefattade en delitiering följt av en oxidation av reaktionsproduktbulken. Denna process uppvisade även ett syrekoncentrationsberoende. / <p>QC 20171114</p>

Electric double layer capacitors (EDLCs) are an important class of electrical energy storage devices which store energy in the form of electric double layers. The charging mechanism is highly reversible physical adsorption of ions into the porous electrodes, which empower these devices to show a remarkable power performance (15kW/kg) and greater life expectancy (> 1 million cycles). However, they store a small amount of energy (5Wh/kg) when compared with batteries. Optimization of the performance of EDLCs based on porous activated carbons is highly challenging due to complex charging process prevailing in the Nano pores of electrodes. Molecular simulations provide information at the molecular scale which in turn can be used to develop insights that can explain experimental results and design improved EDLCs. The conventional approach to simulate EDLCs places both the electrodes and electrolyte region in a single simulation box. With present day computers, however, this one-box method limits us to system sizes of the order of nanometres whereas the size of a typical EDLC is at least of the order of micrometres. To overcome this system size limitation, a Gibbs-ensemble based Monte Carlo (MC) method was recently developed, where the electrodes are simulated in a separate simulation boxes and each box is subjected to periodic boundary conditions in all the three directions. This allows us to eliminate the electrode-electrolyte interface. The simulation of the bulk electrolyte is avoided through the use of the grand canonical ensemble. The electrode atoms in the electrode are maintained at an equal constant electric potential likewise the case in a pure conductor with the use of the constant voltage ensemble. In this thesis, the Gibbs-ensemble based MC simulations are performed for an EDLC consisting of porous electrodes. The simulations are performed with aqueous electrolytes of type MX and DX2 (where M=Na+, K+; D=Ca+2; X=Cl , F ) for a wide variety of operating conditions. The water is modelled as a continuum background with a dielectric constant value of 30. The electrodes are silicon carbide-derived carbon, whose microstructure generated from reverse MC technique, is used in the simulations. The results from these simulations help us understand the charge storage mechanism, the effect of size and valence of ions on the performance of nonporous carbon based EDLCs when the hydration effects are indignant. The thesis first demonstrates the presence of finite size effects in the simulations performed with the one-box method for KCl electrolyte. The capacitance (ratio of the charged stored on the positive electrode to the voltage applied) values obtained for KCl electrolyte with the one-box method are significantly higher than the corresponding values obtained from the Gibbs-ensemble method. This shows the presence of finite size effects in the one-box method simulations and justices the use of the Gibbs-ensemble based method in our simulations. The fundamental characteristics of aqueous electrolytes in the EDLC are analyzed with the simulation results for KCl electrolyte. In agreement with experiments and modern mean held theory, the capacitance monotonically decreases with voltage (bell-shaped curve) due to overcrowding of ions near the electrode surface. The charge storage mechanism in both the electrodes is mainly a combination of countering (ions oppositely charged to that of the electrode) adsorption and ion exchange, where coins (ions identically charged to that of the electrode) are replaced with countering. However, at higher voltages, the mechanism is predominantly counter ion adsorption because of the scarcity of coins in the electrodes. The mechanism is preferentially more ion exchange for the positive electrode because of its relatively bulky countering, Cl . The shifting of mechanism towards counter ion adsorption at higher voltages and preferential ion exchange process for the positive electrode are in qualitative agreement with the recent experimental results. The constraint of equal electric potential on all the electrode atoms of the amorphous electrode in the simulations resulted in a non-uniform average charge distribution on the electrodes. It shows that the Gibbs-ensemble simulation approach can account for the polarization effects which arises due to a complex topology of the electrodes. In agreement with earlier experiments and simulation studies, the local structure analyses of the electrodes shows that the highly conned ions store charge more efficiently. On the application of voltage difference between the electrodes, the electrolyte ions move towards higher degree of con ned regions of the electrodes indicating the charging process involves local rearrangement and rescuing of electrolyte ions. The thesis also discusses the effect of temperature and bulk concentration on the performance of EDLCs. The Gibbs-ensemble based simulations are performed for the EDLC with varying temperature and bulk concentration for the KCl electrolyte independently. In agreement with the Guo -Chapman theory and experiments, the capacitance decreases with the temperature and increases with the bulk concentration. This is because the concentration of countering in the electrodes decreases with an increase in the temperature but increases with an increase in the bulk concentration. Lastly, the effect of ion size and valency on the performance of EDLCs is analyzed. The capacitance monotonically decreases with voltage (bell-shaped curve) for all the electrolytes, except for NaF, where a maximum is observed at a non-zero finite voltage (camel-shaped curve). The capacitances of NaCl and NaF are greater than that for KCl and KF, respectively. This is because the smaller Na+ ions have more accessibility to narrow con ned regions, where the charge storage efficiency is high. As expected, the capacitance for CaCl2 and CaF2 are highest among their monovalent counterparts, NaCl and KCl; NaF and KF, respectively. This is attributed to the relatively smaller double layer thickness of the bivalent Ca+2 ions. Interestingly, at higher voltages, the capacitance for the bivalent electrolytes approaches the capacitance for the monovalent electrolytes because the concentration of Ca+2 ions in the negative electrode increases sluggishly with voltage due to a strong electrostatic repulsion between Ca+2 ions.

Rechargeable lithium-ion batteries are now attracting great attention for applications in portable electronic devices and electrical vehicles, because of their high energy density, long cycle and great convenience. For new generations of rechargeable lithium-ion batteries, they applied not only to consumer electronics but also especially to clean energy storage and hybrid electric vehicles. Therefore, further breakthroughs in electrode materials that open up a new important avenue are essential. Graphite, the most commonly used commercial anode material, has a limited reversible lithium intercalation capacity (372 mAh g-1). In this regard, tremendous efforts have been made towards even further improving high capacity, excellent rate capability, and cycling stability by developing advanced anode materials. This work focuses on the lithium storage properties of nickel oxide (NiO) and germanium (Ge) nanomembranes anodes mainly fabricated by electron-beam evaporation. Specifically, NiO is selected for conversion-type material because of high theoretical specific capacity of 718 mAh g-1 and easily obtained material. The resultant curved NiO nanomembranes anodes exhibit ultrafast power rate of 50 C (1 C = 718 mA g-1) and good capacity retention (721 mAh g-1, 1400 cycles). Remarkably, multifunctional Ni/NiO hybrid nanomembranes were further fabricated and investigated. Benefiting from the advantages of the intrinsic architecture and the electrochemical catalysis of metallic nickel, the hybrid Ni/NiO anodes could be tested at an ultrahigh rate of ~115 C. With Ge as active alloying-type material (1624 mAh g-1), the effect of the incorporated oxygen to the lithium storage properties of amorphous Ge nanomembranes is well studied. The oxygen-enabled Ge (GeOx) nanomembranes exhibit improved electrochemical properties of highly reversible capacity (1200 mAh g-1), and robust cycling performance.

Li-O2 batteries have attracted world-wide research interest as an appealing candidate for future energy supplies because they possess the highest energy density of any battery technology. However, such system still face some challenges for the practical application. One of the key issues is exploring highly efficient cathode materials for Li-O2 batteries. Here, a rolled-up technology associated with other physical or chemical methods are applied to prepare architectural nanomembranes for the cathode materials in Li-O2 batteries. The strain-release technology has recently proven to be an efficient approach on the micro/nanoscale to fabricate composite nanomembranes with controlled thickness, versatile chemical composition and stacking sequence. This dissertation first focuses on the synthesis of trilayered Pd/MnOx/Pd nanomembranes. The incorporation of active Pd layers on both sides of the poor conductive MnOx layer commonly used in energy storage systems greatly enhances the conductivity and catalytic activity. Encouraged by this design, Pd nanoparticles functionalized MnOx-GeOy nanomembranes are also fabricated, which not only improve the conductivity but also facilitate the transport of Li+ and oxygen-containing species, thus greatly enhancing the performance of Li-O2 batteries. Similarly, Au and Pd arrays decorated MnOx nanomembranes act as bifunctional catalysts for both oxygen reduction reaction and oxygen evolution reaction in Li-O2 batteries. Moreover, by introducing hierarchical pores on the nanomembranes, the performance of Li-O2 batteries is further promoted by porous Pd/NiO nanomembranes. The macropores created by standard photolithography facilitate the rolling process and the nanopores in the nanomembranes induced by a novel template-free method supply fast channels for the reactants diffusion. In addition, a facile thermal treatment method is developed to fabricate Ag/NiO-Fe2O3/Ag hybrid nanomembranes as carbon-free cathode materials in Li-O2 batteries. A competing scheme between the intrinsic strain built in the oxide nanomembranes and an external driving force provided by the metal nanoparticles is introduced to tune the morphology of the 3D tubular architectures which greatly improve the performance by providing continuous tunnels for O2 and electrolyte diffusion and mitigating the side reactions produced by carbonaceous materials.

Philosophiae Doctor - PhD / Aqueous ion-intercalation batteries (AIB’s) have the potential to provide both high power for hybrid-electric transport, and low cost bulk energy storage for electric grid supply. However, a major setback to AIB development is the instability of suitable ionintercalation anode material in aqueous electrolyte. To counter this problem, the use of activated carbon (AC) (a supercapacitor anode) paired against the low cost ionintercalation cathode spinel LiMn2O4 (LMO) provides a stable alternative. This thesis comprises two novel areas of investigation concerning: (1) the development of the AC/LMO cell for high power applications, and (2) the introduction of PbSO4 as a high capacity alternative anode material paired against LMO for low cost bulk energy storage. The study on AC/LMO explores the electrode combination’s practical specific energy and power capability at high P/E (power to energy ratio) of 50:1 suitable for hybrid electric vehicle batteries. To study the relationship between electrode material loading density, active material performance, and current collector mass contribution, a specially designed cell was constructed for galvanic cycling of different thicknesses of electrode. Between a loading density range of 25 – 100 mg, ~50 mg of total active material between two 1 cm2 current collectors produced the highest 50:1 P/E ratio values of 4 Wh/kg and 200 W/kg, constituting a 4-fold reduction of the active material values of thin films at 50:1 P/E. The cycling potentials of the individual electrodes revealed that doublings of electrode film loading density increased the LMO electrode’s polarization and voltage drop to similar levels as doublings in applied current density. However, by increasing the charging voltage from 1.8 V to 2.2 V, 6 Wh/kg and 300 W/kg was obtainable with minimal loss of energy efficiency. Finally a large-format cell of a calculated 3 Ah capacity at 50:1 P/E was constructed and tested. The cell produced ~60% of the anticipated capacity due to a suspected high level of resistance in the electrode contact points. The overall conclusion to the study was that AC/LMO holds promise for high power applications, and that future use of higher rate capability forms of LMO offers a promising avenue for further research. v The second part of this thesis presents the development of a novel cell chemistry, PbSO4/LMO, that has yet to be reported elsewhere in existing literature. The cell uses aqueous pH 7, 1 M, Li2SO4 electrolyte, and forms an electrode coupling where the PbSO4 anode charge/discharge is analogous to that in Pb-acid batteries. The average discharge voltage of the cell was 1.4 V and formed a flat charge/discharge plateau. The use of a low cost carbon coating method to encapsulate PbSO4 microparticles had a marked improvement on cell performance, and compared to uncoated PbSO4 improved both rate capability and specific capacity of the material. The active materials of the carbon-coated PbSO4/LMO cell produced a specific energy 51.1 Wh/kg, which, if a 65% yield is possible for a practical cell format, equals 38.4 Wh/kg, which is 15 Wh/kg higher than AC/LMO bulk storage cells at 23 Wh/kg, but lower than Pb-acid batteries at ~25-50 Wh/kg. Interestingly, the specific capacity of PbSO4 was 76 mAh/g compared to 100 mAh/g in Pb-acid cells. The predicted cost of the cell, providing a 65% value of the active material specific energy for a practical cell can be realized, is on par with Pb-acid battery technology and, importantly, uses 2.3 × less Pb/kWh. The cycling stability achieved thus far is promising, but will require testing over comparable cycle life periods to commercial batteries, which could be anywhere between 5 – 15 years.

Les piles au lithium tiennent une place importante dans de nombreuses applications, notamment dans le secteur industriel à forte valeur ajoutée. Les oxyfluorures de graphites et graphènes, ainsi que leurs précurseurs oxydes, ont été identifiés comme des matériaux de cathode pouvant permettre d’augmenter la densité d'énergie de ces piles. Durant cette thèse, afin d’obtenir des nouveaux oxyfluorures de graphite, deux voies de synthèse ont été prospectées. Lors de la synthèse enchainant oxydation de Hummers puis fluoration gaz-solide, le paramètre température d’oxydation a été modulé et a donné lieu à des composés contenant des proportions différentes de fonctions oxygénées de type OH, COOH, COC. Lors de la synthèse débutant par la fluoration, différentes méthodes de fluoration ont été mise en oeuvre faisant agir soit le fluor moléculaire soit le fluor radicalaire à deux échelles de synthèse (laboratoire et micropilote). Une caractérisation minutieuse des matériaux issus de chaque voie, croisant les analyses structurales (DRX, ATG, diffusion Raman...) et analyses chimiques (IR, RMN, XPS...) a permis de cerner les modularités sur les effets de structure et de distribution de fonctions à l'échelle locale. Ce panel de composés a été testé en décharge galvanostatique en pile au lithium afin de corréler activité électrochimique des fonctions et gain en performances. / Primary Lithium Batteries are substantial in many applications, particularly in industrial niche sectors. Graphite oxifluorides and their precursors, graphite oxides, are promising materials for the cathodes. We explored two-step synthesis combining Hummers' oxidation and solid-gas fluorination. Temperature of oxidation was key parameter to control OH, COC and COOH ratio. Direct fluorination and controlled fluorination were processed at laboratory and scaled-up. Because of complexity of the materials and specificity at each scale, we cross-checked the data from several techniques for structure (XRD, TGA, Raman spectroscopy...) and chemistry (IR, MAS NMR, XPS...) for an accurate picture. We tested the broad set of materials. Galvanostatic discharges enabled us to understand the electrochemical activity of functions at stake and key factors of design for better performances.