Dissertations / Theses on the topic 'Li/Na-Ion batteries'

Developing a sustainable energy infrastructure for the 21st century requires the large scale development of renewable energy resources. Fully exploiting these inherently intermittent supplies will require advanced energy storage technologies, with rechargeable Li-ion and Na-ion batteries considered highly promising for both vehicle electrification and grid storage applications. However, the performance required of battery materials has not been achieved, and significant improvements are needed. Modern computational techniques allow the elucidation of structure-property relationships at the atomic level and are valuable tools in providing fundamental insights into novel materials. Therefore, in this thesis a combination of atomistic simulation and ab initio density functional theory (DFT) techniques have been used to study a number of potential battery cathode materials. Firstly, Na2FePO4F and NaFePO4 are interesting materials that have been reported recently as attractive positive electrodes for Na-ion batteries. Here, we report their Na-ion conduction behaviour and intrinsic defect properties using atomistic simulation methods. Na+ ion conduction in Na2FePO4F is predicted to be two-dimensional (2D) in the interlayer plane. Na ion migration in NaFePO4 is restricted to the [010] direction along a curved trajectory, leading to quasi-1D Na+ diffusion. Furthermore, Na/Fe antisite defects are predicted to have a lower formation energy in NaFePO4 than Na2FePO4F. The higher probability of tunnel occupation with a relatively immobile Fe2+ cation - along with a greater volume change on redox cycling - contributes to the poor electrochemical performance of NaFePO4. Secondly, work on the Na2FePO4F system is extended to include investigation of the surface structures and energetics. The equilibrium morphology is found to be essentially octagonal, compressed slightly along the [010] direction, and is dominated by the (010), (021), (122) and (110) surfaces. The calculated growth morphology is a more ``rod-like'' nanoparticle, with the (021), (023), (110) and (112) planes predominant. The (010) surface lies parallel to the Na layers in the ac plane and is unlikely to facilitate Na+ intercalation. As such, its prominence in the equilibrium morphology, and absence from the growth morphology, suggests nanoparticles synthesised in a kinetically limited regime should provide higher rate performance than those synthesised in close to equilibrium conditions. Surface redox potentials for Na2FePO4F derived using DFT vary between 2.76 - 3.37 V, in comparison to a calculated bulk cell voltage of 2.91 V. Most significantly, the lowest energy potentials are found for the (130) and (001) planes suggesting that upon charging Na+ will first be extracted from these surfaces, and inserted lastly upon discharging. Thirdly, the mixed phosphates Na4M3(PO4)2P2O7 (M=Fe, Mn, Co, Ni) are explored as a fascinating new class of materials reported to be attractive Na-ion cathodes, displaying low volume changes upon cycling indicative of long lifetime operation. Key issues surrounding intrinsic defects, Na-ion migration mechanisms and voltage trends have been investigated through a combination of atomistic energy minimisation, molecular dynamics and DFT simulations. The MD results suggest Na+ diffusion extends across a 3D network of migration pathways with an activation barrier of 0.20-0.24 eV, and diffusion coefficients (DNa) of 10-10-10-11 cm2s-1 at 325 K, suggesting high rate capability. The cell voltage trends, explored using DFT methods, indicate that doping the Fe-based cathode with Ni can significantly increase the voltage, and hence energy density. Finally, DFT simulations of K+-stabilised α-MnO2 have been combined with aberration corrected-STEM techniques to study the surface energetics, particle morphologies and growth mechanism. α-K0.25MnO2 grown through a hydrothermal synthesis method is found to produce primary nanowires with preferential growth along the [001] direction. Primary nanowires attach through a shared (110) interface to form larger secondary nanowires. This is in agreement with DFT simulations with the {100}, {110} and {211} surfaces displaying the lowest surface energies. The ranking of surface energies is driven by Mn coordination environments and surface relaxation. The calculated equilibrium morphology of α-K0.25MnO2 is consistent with the observed primary nanowires from high resolution electron microscopy images.

De nos jours, les batteries jouent un rôle clé dans presque toutes les technologies qui entourent le genre humain. Afin de répondre à la demande croissante, la conception d'appareils plus efficaces avec une densité d'énergie et une durée de vie plus élevées est cruciale. Dans ce contexte, le silicium et le germanium apparaissent comme des candidats prometteurs pour les matériaux d'électrodes en raison de leurs capacités théoriques élevées. Bien avant une mise en œuvre de ces matériaux au niveau industriel, plusieurs défis doivent être relevés. Les capacités élevées délivrées se font au détriment d'une expansion volumique lors de l'insertion des ions lithium par exemple. Ces changements de volume dans les particules de Si et de Ge entraînent la pulvérisation des particules, le détachement du collecteur de courant, la formation excessive et incontrôlée de la couche de SEI et une chute de la capacité. Différentes stratégies ont été rapportées dans la littérature pour surmonter les défis susmentionnés. Dans ce travail, deux approches ont été considérées, d'une part l'étude des alliages Si1-xGex et d'autre part l'étude de composés lamellaires. Dans le premier cas, la formation de la solution solide Si1-xGex améliore la rétention de capacité et la conductivité électronique. Dans le second, les matériaux lamellaires Siloxene et germanane, dérivés des phases de Zintl CaSi2 et CaGe2, amortissent les changements de volume et améliorent la cinétique du système. Une étude fondamentale des mécanismes électrochimiques a été réalisée pour comprendre les processus mis en jeu dans ces deux approches
Nowadays, the batteries play a key role in almost all of the technologies that surround human kind. In order to satisfy the increasing demand, the design of more efficient devices with higher energy density and cycle life is crucial. In this context, silicon and germanium appear as promising candidates for electrode materials due to their high theoretical capacities. Although, prior to the implementation of these materials at an industrial level, several challenges must be addressed. The high delivered capacities come at the expense of a volume expansion and contraction upon alkali insertion and deinsertion. These volume changes in the Si and Ge particles, lead to particle pulverization, detachment from the current collector, excessive and uncontrolled formation of SEI layer and eventual capacity fade. Different strategies have been reported in the literature to overcome the aforementioned challenges. In this work, two approaches are considered, the study of the Si1-xGex alloys and the use of a layered morphology. In the first one, the formation of the Si1-xGex solid solution improves the capacity retention and the electronic conductivity. In the second one, the layered Siloxene and germanane, derived from the CaSi2 and CaGe2 Zintl phases buffers the volume changes and improves the kinetics of the system. On the other hand, the fundamental study of their electrochemical mechanism is crucial to understand the reasons behind an improvement and a failure. Thus, in this work we have studied the electrochemical lithiation mechanism of the Si- and Ge- based materials in an attempt to identify the different phases that are formed during cycling

This thesis uses first principles techniques, mainly the ab initio random structure searching method (AIRSS), to study anode materials for lithium- and sodium- ion batteries (LIBs and NIBs, respectively). Initial work relates to a theoretical structure prediction study of the lithium and sodium phosphide systems in the context of phosphorus anodes as candidates for LIBs and NIBs. The work reveals new Li-P and Na-P phases, some of which can be used to better interpret previous experimental results. By combining AIRSS searches with a high-throughput screening search from structures in the Inorganic Crystal Structure Database (ICSD), regions in the phase diagram are correlated to different ionic motifs and NMR chemical shielding is predicted from first principles. An electronic structure analysis of the Li-P and Na-P compounds is performed and its implication on the anode performance is discussed. The study is concluded by exploring the addition of aluminium dopants to the Li-P compounds to improve the electronic conductivity of the system. The following work deals with a study of tin anodes for NIBs. The structure prediction study yields a variety of new phases; of particular interest is a new NaSn$_2$ phase predicted by AIRSS. This phase plays a crucial role in understanding the alloying mechanism of high-capacity tin anodes, work which was done in collaboration with experimental colleagues. Our predicted theoretical voltages give excellent agreement with the experimental electrochemical cycling curve. First principles molecular dynamics is used to propose an amorphous Na$_1$Sn$_1$ model which, in addition to the newly derived NaSn$_2$ phase, provides help in revealing the electrochemical processes. In the subsequent work, we study Li-Sn and Li-Sb intermetallics in the context of alloy anodes for LIBs. A rich phase diagram of Li-Sn is present, exhibiting a variety of new phases. The calculated voltages show excellent agreement with previously reported cycling measurements and a consistent structural evolution of Li-Sn phases as Li concentration increases is revealed. The study concluded by calculating NMR parameters on the hexagonal- and cubic-Li$_3$Sb phases which shed light on the interpretation of reported experimental data. We conclude with a structure prediction study of the pseudobinary Li-FeS$_2$ system, where FeS$_2$ is considered as a potential high-capacity electrochemical energy storage system. Our first principles calculations of intermediate structures help to elucidate the mechanism of charge storage observed by our experimental collaborators via $\textit{in operando}$ studies.

Ce travail vise à étudier les matériaux d'électrodes pour batteries Li-ion et Na-ion lors qu’ils fonctionnent à l'intérieur des batteries. Afin de comprendre l'évolution structurelle des matériaux alors que les ions Li+ ou Na+ sont insérés/extraits de leur cadre, on utilise principalement la diffraction, exploitant neutrons, rayons X et le rayonnement synchrotron (SR). Nous avons adopté une approche combinée des mesures ex situ, in situ et operando. Au début, nous avons conçu une cellule électrochimique pour mesures in situ de diffraction de neutrons sur poudre (NPD), avec un alliage en (Ti,Zr) "transparent aux neutrons"; cette cellule s'est ajoutée à l’ensemble de nos outils pour effectuer des études de type operando. Nous avons démontré leur faisabilité en utilisant LiFePO4, montrant de bonnes performances électrochimiques et des données NPD de haute qualité pour affinements structurales Rietveld. Ensuite, nous avons réalisé des études des spinelles Li1+xMn2-xO4 (x=0,0.05,0.10) et LiNi0.4Mn1.6O4: pendant le cyclage, nous avons rapporté des évolutions structurelles, des diagrammes de phases et paramètres subtils tels que le comportement du Li, ou les facteurs de température. L’utilisation complémentaire du SR a clarifié la nature de la phase ordonnée Li0.5Mn2O4. Nos études combinées ont concernées d’autres matériaux d'électrodes prometteurs: LiVPO4O et Na3V2(PO4)2F3. Les 2 révèle des comportements complexes pendant la (de)intercalation du Li+/Na+. Les données de haute qualité ont permis des analyses quantitatives, dévoilant la structure d'un grand nombre des phases ordonnées et menant à la compréhension du comportement des cations dans ces matériaux
This work aims at studying electrode materials for Li-ion and Na-ion batteries as they function inside batteries. Diffraction is the mainly used technique, exploiting neutrons, X-Rays and synchrotron radiation (SR), to obtain insights on the structural evolution of such materials as Li+ or Na+ are inserted/extracted from their framework. We adopted a combined approach of ex situ, in situ and operando measurements to extract a maximum of information from our studies. At first, we designed an electrochemical cell for in situ neutron powder diffraction (NPD) measurements, featuring a “neutron-transparent” (Ti,Zr) alloy; this cell, joined to others previously developed in our group, gave us a complete set of tools to perform our studies. We demonstrated the feasibility of operando NPD using LiFePO4, showing good electrochemical performances and high-quality NPD patterns for Rietveld structural refinements. Then we carried out detailed studies of spinels Li1+xMn2-xO4 (x = 0, 0.05, 0.10) and LiNi0.4Mn1.6O4: we reported phase diagrams, structural evolutions and subtle parameters as lithium's behavior inside the spinel framework, or thermal displacement parameters, directly upon cycling. Complementary use of SR shed light on other features, as the nature of the ordered phase Li0.5Mn2O4. Our combined studies concerned other promising electrode materials: LiVPO4O and Na3V2(PO¬4)2F3. Both revealed complex behaviors upon Li+/Na+

Ce travail consiste en l’étude par RMN multinoyaux de matériauxparamagnétiques d’électrodes positives pour batteries Li ou Na-ion. La RMN du solidepermet une caractérisation de l’environnement local du noyau sondé grâce à l’exploitationdes interactions hyperfines dues à la présence d’une certaine densité d’électrons célibataires(déplacement de contact de Fermi) sur ce noyau (densité transférée selon des mécanismesplus ou moins complexes). Les matériaux étudiés sont des fluoro ou oxy phosphates devanadium de formules générales AVPO4X (A= Li ou Na; X = F, OH, ou OF) (structure typeTavorite), et Na3V2(PO4)2F1-xOx. Tous ces matériaux ont été caractérisés par RMN du 7Li ou23Na, 31P et 19F combiné à des calculs DFT, afin de mieux comprendre les structure etstructure électroniques locales. Notamment, ces études nous ont permis de mettre enévidence la présence de défauts dans certains matériaux et donc de discuter leur impact surles propriétés électrochimiques. L’utilisation de la méthode PAW nous a permis de modéliserdes défauts dilués dans des supermaille. Ensuite, l’impact de ces défauts sur la structurelocale a été étudié afin d’envisager les mécanismes de transfert de spin possibles etreproduire leur déplacements de RMN
Paramagnetic materials for positive electrodes for Li or Na-ion batteries havebeen studied by multinuclear NMR. The local environment of the probed nucleus can becharacterized by solid state NMR making use of hyperfine interactions due to transfer ofsome electron spin density (Fermi contact shift) on this nucleus, via more or less complexmechanisms. The materials studied are vanadium fluoro or oxy phosphates of generalformulas AVPO4X (A= Li or Na; X = F, OH, or OF) belonging to the Tavorite family and theNa3V2(PO4)2F1-xOx . All these materials have been characterized by 7Li or 23Na, 31P and 19F,combined with DFT calculations to better understand local electronic structures andstructures. In particular, these studies have enabled us to highlight the presence of defects incertain materials and to discuss their impact on the electrochemical properties. The use ofthe PAW method allowed us to model diluted defects in large supercells, to calculate theFermi contact shifts of the surrounding nuclei and to study the mechanisms of electron spintransfer. This allowed us to better understand the nature of defects in materials.For some systems, the mechanisms related to the intercalation or deintercalation of Li+ orNa+ ions have also been studied by NMR

Cette thèse est centrée sur l'étude du composé AxIrO3 en tant qu'hôte polyvalent pour Li+, Na+ et H+. Sa structure tridimensionnelle représente un terrain intéressant pour l’étude fondamentale de l’oxydoréduction du réseau anionique dans les oxydes pour les batteries à ions Li+ et Na+. La phase lithiée peut être obtenue par synthèse céramique à haute température selon deux étapes alors que la phase sodiée n’a pu être obtenue que par voie électrochimique en passant par IrO3. La phase protonée peut être obtenue par échange cationique de la phase lithiée ou par réaction de l’eau avec IrO3. Ces deux dernières phases n’avaient encore pas été reportées auparavant. Les processus d’insertion ont été caractérisés par diverses techniques telles que la diffraction des rayons X et des neutrons et par spectroscopies d’absorption et de photoémission X afin de déterminer les changements structuraux associés aux processus d’oxydoréduction cationique et anionique. Les résultats obtenus permettent d’approfondir notre compréhension d’un mécanisme de compensation de charge encore mal compris. De plus, l’étude de la réactivité d’IrO3 avec un milieu aqueux acide a permis de décrire un mécanisme de catalyse de la réaction d’oxydation de l’eau à la surface des oxydes d’iridium et apporte des pistes pour le développement de nouveaux électrocatalyseurs à base d’iridium
This thesis focuses on the study of the compound AxIrO3 as a versatile host for Li+, Na+ and H+. Its three-dimensional structure represents an interesting playing field for the fundamental study of the redox activity of the anionic network in oxides for Li+ and Na+ ion batteries. The lithiated phase can be obtained by high temperature ceramic synthesis in two stages whereas the sodiated phase could only be obtained electrochemically via IrO3. The protonated phase can be obtained by cation exchange of the lithiated phase or by reaction of water with IrO3. These last two phases had not been previously reported. The insertion processes were characterized by various techniques such as X-ray and neutron diffraction as well as X-ray absorption and photoemission spectroscopies to determine the structural changes associated with cationic and anionic oxidation processes. The results obtained allow us to deepen our understanding of a charge compensation mechanism that is still poorly understood. In addition, the study of the reactivity of IrO3 with an acidic aqueous media has made it possible to describe a mechanism for the electrocatalysis of the oxygen evolution reaction on the surface of iridium oxides and provides avenues for the development of new electrocatalysts based on iridium

Ce travail de thèse a pour but d'explorer de nouveaux matériaux de type structural Tavorite et de revisiter certains déjà bien connus. Dans un premier temps, les synthèses de compositions ciblées ont été réalisées selon des procédures variées (voies tout solide, hydrothermale, céramique assistée par sol-gel, broyage mécanique) afin de stabiliser d'éventuelles phases métastables et d'ajuster la microstructure impactant fortement les performances électrochimiques de tels matériaux polyanioniques. Ces matériaux ont ensuite été décrits en profondeur, dans leurs états originaux, depuis leurs structures moyennes, grâce aux techniques de diffraction (diffraction des rayons X sur poudres ou sur monocristaux et diffraction des neutrons) jusqu'aux environnements locaux, en utilisant des techniques de spectroscopie (résonance magnétique nucléaire à l'état solide, absorption des rayons X, infra-rouge et Raman). Par la suite, les diagrammes de phases et les processus d'oxydoréduction impliqués pendant l'activité électrochimique des matériaux ont été étudiés grâce à des techniques operando (diffraction et absorption des rayons X). La compréhension des mécanismes impliqués pendant le cyclage permet de mettre en évidence les raisons de leurs limitations électrochimiques : La synthèse de nouveaux matériaux (composition, structure, microstructure) peut maintenant être développée afin de contrepasser ces limitations et de tendre vers de meilleures performances
This PhD work aims at exploring new Tavorite-type materials and at revisiting some of the well-known ones. The syntheses of targeted compositions were firstly performed using various ways (all solid state, hydrothermal, sol-gel assisted ceramic, ball milling) in order to stabilize eventual metastable phases and tune the microstructure impacting strongly the electrochemical performances of such polyanionic compounds. The materials were then described in-depth, at the pristine state, from their average long range structures, thanks to diffraction techniques (powder X-rays, single crystal X-rays and neutrons diffraction), to their local environments, using spectroscopy techniques (solid state Nuclear Magnetic Resonance, X-rays Absorption Spectroscopy, Infra-Red and/or Raman). Thereafter, the phase diagrams and the redox processes involved during electrochemical operation of the materials were investigated thanks to operando techniques (SXRPD and XAS). The in-depth understanding of the mechanisms involved during cycling allows to highlight the reasons of their electrochemical limitations: the synthesis of new materials (composition, structure and microstructure) can now be developed to overcome these limitations and tend toward better performance

Alkali-ion batteries have revolutionized modern life through enabling the widespread application of portable electronic devices. The call for adapting renewable energy in many applications will also see an increase in the demand of alkali-ion batteries, specially to account for the intermittent nature of the renewable energy sources. However, the advancement of such technologies will require innovation on the forefront of materials development as well as fundamental understanding on the physical and chemical processes from atomic to device length scales. Herein, we focus on advancing energy storage devices such as alkali-ion batteries through cathode materials development and discovery as well as fundamental understanding through multiscale advanced synchrotron spectroscopic and microscopic characterizations. Multiscale electrochemical properties of cathode materials are unraveled through complementary characterizations and design principles are developed for stable cathode materials for alkali-ion batteries. In Chapter 1, we provide a comprehensive background on alkali-ion batteries and cathode materials. The future prospect of Li-ion and beyond Li-ion batteries are summarized. Surface to bulk chemistry of alkali-ion cathode materials is introduced. The prospect of combined cationic and anionic redox processes to enhance the energy density of cathode materials is discussed. Structural and chemical complexities in cathode materials during electrochemical cycling as well as due to anionic redox are summarized. In Chapter 2, we explain an inaugural effort on tuning the 3D nano/mesoscale elemental distribution of cathode materials to positively impact the electrochemical performance of cathode materials. We show that engineering the elemental distribution can take advantage of depth dependent redox reactions and curtail harmful side reactions at cathode-electrolyte interface which can stabilize the electrochemical performance. In Chapter 3, we show that the surface to bulk chemistry of cathode particles is distinct under applied electrochemical potential. We show that the severe surface degradation at the beginning stages of cycling can impact the long-term cycling performance of cathode materials in alkali-ion batteries. In Chapter 4, we utilize the structural and chemical complexities of sodium layered oxide materials to synthesize stable cathode materials for half cell and full cell sodium-ion batteries. Meanwhile, challenges with enabling long term cycling (more than 1000 cycles) are deciphered to be transition metal dissolution and local and global structural transformations. In Chapter 5, we utilize anionic redox in conjunction with conventional cationic redox of cathode materials for alkali-ion batteries to enhance the energy density. We show that the stability of anionic redox is closely related to the local transition metal environment. We also show that a reversible evolution of local transition metal environment during cycling can lead to stable anionic redox. In Chapter 6, we provide design principles for cathode materials for advanced alkali-ion batteries for application under extreme environments (e.g., outer space and nuclear power industries). For the first time, we systematically study the microstructural evolution of cathode materials under extreme irradiation and temperature to unravel the key factors affecting the stability of battery cathodes. Our experimental and computational studies show that a cathode material with smaller cationic antisite defect formation energy than another is more resilient under extreme environments.
Doctor of Philosophy
Alkali-ion batteries are finding many applications in our life, ranging from portable electronic devices, electric vehicles, grid energy storage, space exploration and so on. Cathode materials play a crucial role in the overall performance of alkali-ion batteries. Reliable application of alkali-ion batteries requires stable and high-energy cathode materials. Hence, design principles must be developed for high-performance cathode materials. Such design principles can be benefited from advanced characterizations that can reveal the surface-to-bulk properties of cathode materials. Herein, we focus on formulating design principles for cathode materials for alkali-ion batteries. Aided by advanced synchrotron characterizations, we reveal the surface-to-bulk properties of cathodes and their role on the long-term stability of alkali-ion batteries. We present tuning structural and chemical complexities as a method of designing advanced cathode materials. We show that energy density of cathode materials can be enhanced by taking advantage of a combined cationic and anionic redox. Lastly, we show design principles for stable cathode materials under extreme conditions in outer space and nuclear power industries (under extreme irradiation and temperature). Our study shows that structurally resilient cathode materials under extreme irradiation and temperature can be designed if the size of positively charged cations in cathode materials are almost similar. Our study provides valuable insights on the development of advanced cathode materials for alkali-ion batteries which can aid the future development of energy storage devices.

Au cours des dernières années, de nombreuses recherches se sont concentrées sur les batteries afin de satisfaire leur demande croissante pour de nombreuses applications. Les matériaux hybrides métal/carbone ont fait l'objet d'une grande attention en tant qu'anodes pour les batteries ioniques Li et Na en raison de leur capacité plus élevée par rapport aux anodes graphite/carbone dur. Cependant, l'expansion de la taille des NPs métalliques et la forte capacité irréversible pendant le 1ercycle sont les principaux inconvénients à surmonter et représentent l'objectif principal de cette thèse. Trois types d'hybrides ont été étudiés (C@Sn et C@SiO2pour les LIBs, et C@Sb pour les NIBs) et des voies de synthèse originales ont été développées qui ont permis d'obtenir des matériaux avec des NPs petites et homogènes distribuées dans le réseau de carbone. Plusieurs paramètres expérimentaux ont été optimisés, conduisant à une vaste palette de matériaux avec des porosités, des structures et des granulométries différentes. La température et la charge de particules se sont avérées être les principaux paramètres affectant la porosité et la taille des particules ainsi que les performances électrochimiques. L'augmentation de la température et de la charge de NPs ont conduit à une porosité plus faible qui a permis de diminuer la capacité irréversible et d'améliorer la capacité réversible. En même temps, le cycle à long terme a été affecté négativement en raison de la formation de particules non confinées et agglomérées. Un compromis entre la charge de carbone/porosité/structure a été déterminé pour chaque système et les mécanismes électrochimiques traités sur la base d'analyses post-mortem
During the last years a lot of research has been focused on batteries to satisfy their increasing demand for a broad application. Metal-based/carbon hybrid materials received great attention as anodes for Li and Na ion batteries due to their higher capacity compared to graphite/hard carbons anodes. However, the metal particle size expansion and the high irreversible capacity during cycling are the main inconvenients to be overcome and represent the main goal of this thesis. Three type of hybrids were studied(C@Sn and C@SiO2for LIBs, and C@Sb for NIBs) and original synthesis pathways were developed which allowed to obtain materials with small and homogeneous distributed particles in the carbon network. Several experimental parameters were tuned leading to a large pallet of materials exhibiting different porosities, structures and particle size/distribution. The temperature and the particle loading were found to be the main parameters affecting the porosity and the particle size and further the electrochemical performances. The increase of both temperature and particle loading lead to smaller porosity which successfully allowed to diminish the irreversible capacity and to improve the reversible capacity. In the same time, the long-term cycling was negatively affected due to the formation of un-confined and agglomerated particles. The extent of particle agglomeration and consequently of capacity fading was found to depend on the type of metal and synthesis route. A compromise between the carbon loading/porosity/structure was determined for each system and the electrochemical mechanisms addressed based on post-mortem analyses

L’amélioration des systèmes de stockage d’énergie représente un défi majeur de la transition vers les véhicules électriques et les énergies renouvelables. Les accumulateurs Li-ion, qui ont déjà conquis le marché de l’électronique portatif, constitueront la technologie dominante pour réaliser cet objectif, et sont donc l’objet d’intense recherches afin d’améliorer leurs performances, en particulier en termes de capacité. Parmi les stratégies les plus prometteuse pour augmenter la capacité des matériaux de cathodes, beaucoup d’espoir est placé dans la préparation de matériaux riches en lithium, qui combinent l’activité électrochimique des cations (métaux de transitions) et des anions (oxygène). Cependant, l’activation des propriétés redox de l’oxygène est accompagnée de plusieurs problèmes qui freinent le développement industriel de ces matériaux. Il est donc nécessaire d’obtenir de solides connaissances fondamentales sur le phénomène de redox anionique pour résoudre ces problèmes. En utilisant des matériaux modèles à base d’iridium, ce travail explore comment l’activité de l’oxygène est influencé par son environnement local. Les propriétés électrochimiques des composés Na2IrO3 et Na(Li1/3Ir2/3)O2 sont étudiés afin de comprendre l’impact de la nature de l’ion alcalin. L’influence du ratio Li/M dans les oxydes de structure NaCl est étudié à travers la synthèse d’un nouveau composé de formule Li3IrO4, qui présente la plus haute capacité réversible parmi les matériaux d’insertion utilisés comme cathode. Cette famille de matériau est finalement étendue à des phases contenant des protons par une simple méthode d’échange cationique, et les propriétés électrochimiques d’un nouveau composé H3+xIrO4 sont étudiées, dévoilant de très bonnes propriétés de stockage de puissance en milieu aqueux
Improving energy storage stands as a key challenge to facilitate the transition to electric vehicles and renewable energy sources in the next years. Li-ion batteries, which have already conquered the portable electronic market, will be the leading technology to achieve this goal and are therefore the focus of intense research activities to improve their performances, especially in terms of capacity. Among the most promising strategies to obtain high capacity cathode materials, the preparation of Li-rich materials combining the redox activity of cations (transition metals) and anions (oxygen) attracts considerable interest. However, activation of anionic redox in these high capacity materials comes with several issues that need to be solved prior their implementation in the energy storage market. Deep fundamental understanding of anionic redox is therefore required to go forward. Using model systems based on iridium, this work explores how the oxygen local environment can play a role on the activation of anionic redox. The electrochemical properties of Na2IrO3 and Na(Li1/3Ir2/3)O2 phases are studied to understand the impact of the alkali nature. The influence of the Li/M ratio in rocksalt oxides is investigated with the synthesis of a new material Li3IrO4, which presents the highest reversible capacity among intercalation cathode materials. The rich electrochemical properties of this family of iridate materials are finally extended by preparing proton-based materials through a simple ion-exchange reaction and the electrochemical properties of a new H3+xIrO4 material are presented, with high rate capability performances

L’amélioration des systèmes de stockage d’énergie représente un défi majeur de la transition vers les véhicules électriques et les énergies renouvelables. Les accumulateurs Li-ion, qui ont déjà conquis le marché de l’électronique portatif, constitueront la technologie dominante pour réaliser cet objectif, et sont donc l’objet d’intense recherches afin d’améliorer leurs performances, en particulier en termes de capacité. Parmi les stratégies les plus prometteuse pour augmenter la capacité des matériaux de cathodes, beaucoup d’espoir est placé dans la préparation de matériaux riches en lithium, qui combinent l’activité électrochimique des cations (métaux de transitions) et des anions (oxygène). Cependant, l’activation des propriétés redox de l’oxygène est accompagnée de plusieurs problèmes qui freinent le développement industriel de ces matériaux. Il est donc nécessaire d’obtenir de solides connaissances fondamentales sur le phénomène de redox anionique pour résoudre ces problèmes. En utilisant des matériaux modèles à base d’iridium, ce travail explore comment l’activité de l’oxygène est influencé par son environnement local. Les propriétés électrochimiques des composés Na2IrO3 et Na(Li1/3Ir2/3)O2 sont étudiés afin de comprendre l’impact de la nature de l’ion alcalin. L’influence du ratio Li/M dans les oxydes de structure NaCl est étudié à travers la synthèse d’un nouveau composé de formule Li3IrO4, qui présente la plus haute capacité réversible parmi les matériaux d’insertion utilisés comme cathode. Cette famille de matériau est finalement étendue à des phases contenant des protons par une simple méthode d’échange cationique, et les propriétés électrochimiques d’un nouveau composé H3+xIrO4 sont étudiées, dévoilant de très bonnes propriétés de stockage de puissance en milieu aqueux
Improving energy storage stands as a key challenge to facilitate the transition to electric vehicles and renewable energy sources in the next years. Li-ion batteries, which have already conquered the portable electronic market, will be the leading technology to achieve this goal and are therefore the focus of intense research activities to improve their performances, especially in terms of capacity. Among the most promising strategies to obtain high capacity cathode materials, the preparation of Li-rich materials combining the redox activity of cations (transition metals) and anions (oxygen) attracts considerable interest. However, activation of anionic redox in these high capacity materials comes with several issues that need to be solved prior their implementation in the energy storage market. Deep fundamental understanding of anionic redox is therefore required to go forward. Using model systems based on iridium, this work explores how the oxygen local environment can play a role on the activation of anionic redox. The electrochemical properties of Na2IrO3 and Na(Li1/3Ir2/3)O2 phases are studied to understand the impact of the alkali nature. The influence of the Li/M ratio in rocksalt oxides is investigated with the synthesis of a new material Li3IrO4, which presents the highest reversible capacity among intercalation cathode materials. The rich electrochemical properties of this family of iridate materials are finally extended by preparing proton-based materials through a simple ion-exchange reaction and the electrochemical properties of a new H3+xIrO4 material are presented, with high rate capability performances

The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One considerable bottleneck is the cathode energy density, the Li-rich layered oxide compounds xLi₂MnO₃.(1-x)LiMO ₂ (M= Ni, Mn, Co) (0.5= Co) (0.5=discharge capacities greater than 280 mAh g^-1 (almost twice the practical capacity of LiCoO ₂).

In this work, neutron diffraction under operando battery cycling is developed to study the lithium and oxygen dynamics of Li-rich compounds that exhibits oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show movement of oxygen and lattice contractions during the high voltage plateau until the end of charge. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer and transition metal layer are related to the different charge and discharge characteristics.

In the second part, a combination of multi-modality surface sensitive tools was applied in an attempt to obtain a complete picture to understand the role of NH4F and Al₂O₃ surface co-modification on Li-rich. The enhanced discharge capacity of the modified material can be primary assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material was facilitated with pre-activated Mn³⁺ on the surface, and stabilization of the Ni redox pair. These insights will provide guidance for the surface modification in high voltage cathode battery materials of the future.

In the last part, the idea of Li-rich has transferred to the Na-ion battery cathode. A new O3 - Na_0.78Li_0.18Ni_0.25Mn _0.583O_w is prepared as the cathode material for Na-ion batteries, delivering exceptionally high energy density and superior rate performance. The single-slope voltage profile and ex situ synchrotron X-ray diffraction data demonstrate that no phase transformation happens through a wide range of sodium concentrations (0.8 Na removed). Further optimization could be realized by tuning the combination and ratio of transition metals.

In questa tesi di dottorato, diversi materiali anodici per batterie agli ioni Li e Na con caratteristiche complementari sono stati studiati per avere una gamma di possibili candidati come materiali per batterie di nuova generazione. L’ossido ternario ZnFe2O4 ad alta densità di energia ha una reazione complessa e irreversibile con il Li, che è stata studiata con tecniche elettrochimiche e diffrazione operando, per comprenderne la ciclabilità. Alligazione e conversione-alligazione di Sn e SnOx sono altre reazioni elettrochimiche ad alta densità di energia, che possono essere sfruttate sia in batterie al Li che al Na. Sono stati ottenuti risultati promettenti (anche a correnti elevate) da un elettrodo composito self-standing elettrospinnato. Alte densità di potenza sono la caratteristica prevalente di FeNb11O29, le cui sorprendenti caratteristiche cinetiche sono state studiate insieme al meccanismo di reazione, grazie a diffrazione operando e spettroscopia Raman in situ.
In this PhD thesis, different anode materials for Li- and Na-ion batteries with complementary features were investigated to obtain a wide spectrum of candidate materials for next-generation batteries. The ternary transition metal oxide ZnFe2O4 offers high energy density, and its complex and irreversible reaction with Li was studied with electrochemical techniques and operando X-ray diffraction in order to understand the cycling behaviour of the material. Alloying and conversion-alloying of tin and tin oxides are also high energy density electrochemical reactions, that can be exploited in both Li- and Na-ion batteries. Promising results were obtained from an electrospun self-standing tin/carbon composite with enhanced rate capability. Higher power densities are shown by complex niobium oxides such as FeNb11O29, whose enhanced kinetic features were studied alongside the reaction mechanism, that was unravelled with operando X-ray diffraction and in situ Raman spectroscopy.

Le cœur de technologie d'une batterie réside principalement dans les matériaux actifs des électrodes, qui est fondamental pour pouvoir stocker une grande quantité de charge et garantir une bonne durée de vie. Le dioxyde d'étain (SnO₂) a été étudié en tant que matériau d'anode dans les batteries Li-ion (LIB) et Na-ion (NIB), en raison de sa capacité spécifique élevée et sa bonne tenue en régimes de puissance élevés. Cependant, lors du processus de charge/décharge, ce matériau souffre d'une grande expansion volumique qui entraîne une mauvaise cyclabilité, ce qui empêche la mise en oeuvre de SnO₂ dans des accumulateurs commerciaux. Aussi, pour contourner ces problèmes, des solutions pour surmonter les limites de SnO₂ en tant qu'anode dans LIB / NIB seront présentées dans cette thèse. La partie initiale de la thèse est dédié à la production de SnO₂ et de RGO (oxyde de graphène réduit)/SnO₂ par pyrolyse laser puis à sa mise en oeuvre en tant qu'anode. La deuxième partie s'attarde à étudier l'effet du dopage de l'azote sur les performances et permet de démontrer l'effet positif sur le SnO₂ dans les LIB, mais un effet néfaste sur les NIB. La partie finale de la thèse étudie l'effet de l'ingénierie matricielle à travers la production d'un composé ZnSnO₃. Enfin, les résultats obtenus sont comparés avec l'état de l'art et permettent de mettre en perspectives ces travaux
The heart of battery technology lies primarily in the electrode material, which is fundamental to how much charge can be stored and how long the battery can be cycled. Tin dioxide (SnO₂) has received tremendous attention as an anode material in both Li-ion (LIB) and Na-ion (NIB) batteries, owing to benefits such as high specific capacity and rate capability. However, large volume expansion accompanying charging/discharging process results in poor cycleability that hinders the utilization of SnO₂ in commercial batteries. To this end, engineering solutions to surmount the limitations facing SnO₂ as an anode in LIB/NIB will be presented in this thesis. The initial part of the thesis focuses on producing SnO₂ and rGO (reduced graphene oxide)/SnO₂ through laser pyrolysis and its application as an anode. The following segment studies the effect of nitrogen doping, where it was found to have a positive effect on SnO₂ in LIB, but a detrimental effect in NIB. The final part of the thesis investigates the effect of matrix engineering through the production of a ZnSnO₃ compound. Finally, the obtained results will be compared and to understand the implications that they may possess

Le besoin accru de stockage d'énergie via Li- et batteries Na-ion nécessite une recherche continue de nouveaux matériaux de cathode ayant une densité énergétique plus élevée et étant sûr et durable. Ainsi, nous avons exploré des composés à base de borate capables de réagir avec Li/ Na-ions de manière réversible, soit par le biais de réactions topotactic- ou de conversion. Nous nous sommes concentrés sur les candidats avec des anions polyborate, qui devraient montrer des potentiels redox élevés par rapport aux matériaux à base BO3. Li6CuB4O10 utilisant comme composé modèle, nous avons montré la possibilité d'obtenir des potentiels d'oxydo-réduction de 4.2 et 3.9 V par rapport à Li pour l'α- et ß polymorphes. L'activité redox a été rationalisée par spectroscopie EPR et calculs DFT. Nous révélons en outre la relation structurelle / synthétique entre les deux polymorphes et montrons une conductivité ionique élevée de 1.4 mS / cm à 500 °C pour une forme de HT d'-Li6CuB4O10. De plus, nous avons pu préparer deux pentaborates 3d-métal nouveau sodium Na3MB5O10 (M = Fe, Co). M = Fe, nous avons observé une intercalation Na réversible à un potentiel moyen de 2.5 V par rapport à Na, alors Na3CoB5O10 avéré être inactif électrochimique. Dévier à partir de composés d'insertion / désinsertion classiques, nous avons étudié la électrochimique entraîné la réaction d'un oxyborate bismuth Bi4B2O9 contre Li par des mesures électrochimiques combinées avec XRD et TEM. Nous avons constaté qu'il est possible de faire défiler ce matériau réversible entre 1.7 et 3.5 V avec un potentiel redox d'environ 2.3 V par rapport à Li avec seulement 5% en poids de carbone et une faible polarisation ~ 300 mV
The increased need of energy storage via Li- and Na-ion batteries requires a continuous search for new cathode materials having higher energy density and being safe and sustainable. Thus, we explored borate based compounds capable of reacting with Li/ Na-ions in a reversible way either through topotactic- or conversion reactions. We focused on candidates with polyborate anions, that are expected to show elevated redox potentials compared to BO3 based materials. Using Li6CuB4O10 as a model compound we showed the possibility to achieve redox potentials of 4.2 and 3.9 V vs Li for the α- and β-polymorphs. The redox activity was rationalized through EPR spectroscopy and DFT calculations. We further reveal the structural/ synthetic relation between the two polymorphs and show a high ionic conductivity of 1.4 mS/cm at 500°C for a HT form of α-Li6CuB4O10. Moreover we were able to prepare two new sodium 3d-metal pentaborates Na3MB5O10 (M = Fe, Co). For M = Fe we observed a reversible Na intercalation at an average potential of 2.5 V vs Na, whereas Na3CoB5O10 turned out to be electrochemical inactive. Deviating from classical insertion/ deinsertion compounds, we studied the electrochemical driven reaction of a bismuth oxyborate Bi4B2O9 versus Li through electrochemical measurements combined with XRD and TEM. We found that it is possible to reversible cycle this material between 1.7 and 3.5 V with an redox potential of ~2.3 V vs Li with only 5wt% carbon and a small polarization ~300 mV. Owing to the complexity of 3d-metal borate chemistry encountered through this PhD, the chances of having a borate based positive electrode for next generation Li-ion batteries is rather slim

Le réchauffement climatique, provoqué par l’augmentation de la concentration de CO2 dans l’atmosphère, est un problème majeur du 21ème siècle. C’est pourquoi, il est d’une importance capitale de valoriser l’utilisation des énergies renouvelables et des technologies de stockage d’énergie telles que les batteries Li-ion. Suivant ce but, les chercheurs ont mis au point un nouveau matériau d’électrode, le Li-rich NMC, dont l’utilisation permet d’augmenter significativement la capacité des batteries Li-ion grâce à la participation des oxygènes de l’oxyde dans la réaction électrochimique. Cependant, ce nouveau phénomène va de pair avec une hystérésis de potentiel qui empêche la commercialisation du Li-rich NMC. Afin de proposer une solution à l’hystérésis de potentiel tout en continuant à augmenter la capacité des électrodes, des études fondamentales sont nécessaires, notamment: la redox anionique a-t-elle une limite de capacité ? et, quelle est l’origine de l’hystérésis ? Pour répondre à la première question, nous avons conçu des matériaux, de composition chimique A3MO4 (A étant du Li ou Na, et M un mix de Ru, Sb, Nb, Ta ou Ir), ayant une redox anionique exacerbée. Après avoir caractérisé la structure de ces nouveaux matériaux, nous avons étudié leur mécanisme électrochimique et montré que la redox anionique est limitée par la décomposition de l’électrode via formation de O2 ou dissolution. Dans un second temps, par l’étude de deux nouveaux matériaux, Li1.3Ni0.27Ta0.43O2 et Li1.3Mn0.4Ta0.3O2 ayant des hystérésis de potentiel très différentes, nous avons montré le lien entre la redox anionique, la taille de la bande interdite, et l’hystérésis de potentiel
Global warming, due to the increasing CO2 concentration in the atmosphere, is a major issue of the 21th century, hence the need to move towards the use of renewable energies and the development of electrical storage devices, such as Li-ion batteries. Along that line, a new electrode material called Li-rich NMCs have been developed, having higher capacity, 290 mAh/g, than commercial materials, like LiCoO2 (150 mAh/g), thanks to participation of oxygen anions into the redox reaction. This process, called anionic redox, unfortunately comes with voltage hysteresis preventing the commercialization of Li-rich NMC. To alleviate this issue while increasing the capacity, fundamental understanding on anionic redox is needed, specifically concerning two points: is anionic redox limited in terms of capacity? And what is the origin of the voltage hysteresis? In a first part, with the aim to assess the limit of anionic redox capacity, we designed new compounds, having enhanced oxygen oxidation behavior, belonging to the A3MO4 family (A being Li or Na and with M a mix of Ru, Ir, Nb, Sb or Ta). We performed their synthesis, deeply characterized their structure, and, by studying their charge compensation mechanism, we showed that anionic redox is always limited by either O2 release or metal dissolution. In a second part, we designed two new materials, Li1.3Ni0.27Ta0.43O2 and Li1.3Mn0.4Ta0.3O2, having different voltage hysteresis, in order to identify the origin of this phenomenon. Coupling spectroscopic techniques with theoretical calculations, we suggest that the electronic structure, namely the size of the charge transfer band gap, plays a decisive role in voltage hysteresis

Le besoin accru de stockage d'énergie via Li- et batteries Na-ion nécessite une recherche continue de nouveaux matériaux de cathode ayant une densité énergétique plus élevée et étant sûr et durable. Ainsi, nous avons exploré des composés à base de borate capables de réagir avec Li/ Na-ions de manière réversible, soit par le biais de réactions topotactic- ou de conversion. Nous nous sommes concentrés sur les candidats avec des anions polyborate, qui devraient montrer des potentiels redox élevés par rapport aux matériaux à base BO3. Li6CuB4O10 utilisant comme composé modèle, nous avons montré la possibilité d'obtenir des potentiels d'oxydo-réduction de 4.2 et 3.9 V par rapport à Li pour l'α- et ß polymorphes. L'activité redox a été rationalisée par spectroscopie EPR et calculs DFT. Nous révélons en outre la relation structurelle / synthétique entre les deux polymorphes et montrons une conductivité ionique élevée de 1.4 mS / cm à 500 °C pour une forme de HT d'-Li6CuB4O10. De plus, nous avons pu préparer deux pentaborates 3d-métal nouveau sodium Na3MB5O10 (M = Fe, Co). M = Fe, nous avons observé une intercalation Na réversible à un potentiel moyen de 2.5 V par rapport à Na, alors Na3CoB5O10 avéré être inactif électrochimique. Dévier à partir de composés d'insertion / désinsertion classiques, nous avons étudié la électrochimique entraîné la réaction d'un oxyborate bismuth Bi4B2O9 contre Li par des mesures électrochimiques combinées avec XRD et TEM. Nous avons constaté qu'il est possible de faire défiler ce matériau réversible entre 1.7 et 3.5 V avec un potentiel redox d'environ 2.3 V par rapport à Li avec seulement 5% en poids de carbone et une faible polarisation ~ 300 mV
The increased need of energy storage via Li- and Na-ion batteries requires a continuous search for new cathode materials having higher energy density and being safe and sustainable. Thus, we explored borate based compounds capable of reacting with Li/ Na-ions in a reversible way either through topotactic- or conversion reactions. We focused on candidates with polyborate anions, that are expected to show elevated redox potentials compared to BO3 based materials. Using Li6CuB4O10 as a model compound we showed the possibility to achieve redox potentials of 4.2 and 3.9 V vs Li for the α- and β-polymorphs. The redox activity was rationalized through EPR spectroscopy and DFT calculations. We further reveal the structural/ synthetic relation between the two polymorphs and show a high ionic conductivity of 1.4 mS/cm at 500°C for a HT form of α-Li6CuB4O10. Moreover we were able to prepare two new sodium 3d-metal pentaborates Na3MB5O10 (M = Fe, Co). For M = Fe we observed a reversible Na intercalation at an average potential of 2.5 V vs Na, whereas Na3CoB5O10 turned out to be electrochemical inactive. Deviating from classical insertion/ deinsertion compounds, we studied the electrochemical driven reaction of a bismuth oxyborate Bi4B2O9 versus Li through electrochemical measurements combined with XRD and TEM. We found that it is possible to reversible cycle this material between 1.7 and 3.5 V with an redox potential of ~2.3 V vs Li with only 5wt% carbon and a small polarization ~300 mV. Owing to the complexity of 3d-metal borate chemistry encountered through this PhD, the chances of having a borate based positive electrode for next generation Li-ion batteries is rather slim

Les batteries Li-ion sont cruciales pour la transition énergétique, tant pour la mobilité que pour l’intégration des EnR. La densité d’énergie de ces batteries est déterminée par le nombre d’électrons disponibles dans la cathode, principalement issus de l’oxydation du métal. Toutefois, l’oxygène peut lui aussi être oxydé, ce qui permet d’augmenter la densité d’énergie au détriment de la stabilité du matériau. Le modèle théorique actuel distingue deux mécanismes de stabilisation de la redox anionique : i) l’appariement de l’oxygène qui dégrade le matériau via la formation des peroxydes ou le dégazage de dioxygène et ii) le couplage réducteur entre l’oxygène et le métal, qui réduit l’instabilité structurale. Bien que ce modèle binaire décrive correctement les oxydes métalliques ordonnés, il ne peut expliquer le comportement plus nuancé des matériaux décrits plus récemment, tels que les oxydes désordonnés, les matériaux d’insertion de sodium (Na-ion) ou les sulfures métalliques. Cette limitation est due à la description uniforme du réseau d’oxygène, réduit à un seul site cristallographique
Li-ion batteries are key to the energy transition, both for electric mobility and for renewable energies development. Their energy density is limited by the cathode, a lithium metal oxide where electrons come from the metal oxidation. Interestingly, the anions (e.g. oxygen, O) can also be oxidized thus increasing the energy density at the expense of stability. The existing theoretical framework of the anionic redox (A.R.) distinguishes two mechanisms: i) the oxygen pairing, causing quick degradation due to peroxide formation or oxygen release and ii) the metal-oxygen reductive coupling which mitigates the structural instability. While this binary model correctly describes the ordered lithium oxides, it fails to account for the more subtle behavior that has been recently reported in A.R. materials such as disordered compounds, Na-ion oxides or Li-rich sulfides. This shortcoming is due to the uniform description of the oxygen network (all O sites are considered equivalent). In this Ph.D., we refine this initial model by integrating non-equivalent oxygen sites to the previously described mechanisms. This allows describing the charge disproportionation necessary to oxygen pairing and the cooperative distortion caused by the metal-oxygen reductive coupling. Using this refined framework, we then revisit the understanding of Na-ion oxides and Li-rich sulfides. Finally, we propose two computational methods to predict the maximal reversible A.R. capacity, one based on the bandgap of the pristine and the other based on the magnetic signature of each A.R. mechanisms

Les prochaines générations de batteries à ions lithium et sodium seront basées sur le développement de nouveaux matériaux d'électrode positive durables, peu chers et sûrs. Dans ce but, nous avons exploré le monde des minéraux à la recherche de structures présentant les pré-requis pour l'insertion et la désinsertion d'ions alcalins. Nous avons alors entrepris l'étude de sulfates bimétalliques dérivés du minéral bloedite, ayant pour formule générale AxM(SO4)2*nH2O (A = Li, Na, M = métal de transition 3d, et n = 0, 4). Ces systèmes présentent une cristallochimie riche, montrant des transitions structurales en fonction de la température ainsi qu'avec le départ des molécules d'eau. Les nouvelles structures ont été déterminées en combinant les techniques de diffraction des rayons X, neutrons et électrons. Nous avons également montré que les composés à base de lithium LixM(SO4)2 présentent des propriétés antiferromagnétiques intéressantes, du fait notamment de leurs structures particulières qui permettent seulement des interactions de super-super-échange. Enfin et surtout, nous avons, parmi les composés isolés, identifié trois sulfates à base de fer, à savoir Na2Fe(SO4)2*4H2O, Na2Fe(SO4)2 et Li2Fe(SO4)2, qui présentent des propriétés électrochimiques intéressantes face au lithium et au sodium. Avec un potentiel de 3,83 V vs. Li+/Li0, la nouvelle phase marinite Li2Fe(SO4)2 affiche le plus haut potentiel jamais observé pour le couple redox FeIII+/FeII+ dans un composé inorganique à base de fer et dépourvu de fluor, et est en fait seulement dépassé par celui de la forme triplite de LiFeSO4F.

The research work presented in this thesis regarded the structural study of different materials employed as battery electrodes (for both Li and Na ion cells) by means of X-ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS) and RamanSpectroscopy. The main purpose of the thesis was to provide better insight, at a microscopic and atomic level, of all the mechanisms related to the insertion/de-insertion of lithium or sodium ions in the electrode structure at the electrolyte interface and the bulk. In particular we have tackled three main open problems concerning: i) the evolution of the local structure in zinc-ferrite conversion-alloying materials used in lithium-ion batteries, ii) the study of formation and evolution of the solid electrolyte interphase (SEI) in carbon-based anodes again used for lithium-ion cells, iii) the relationship between local structure distortion and electrochemical performances in a class of cathode materials for sodium-ion batteries. By using X-ray absorption spectroscopy, we have shown that in the very early stages of Li+ insertion (until 0.3Li+ per formula unit) carbon-coated zinc-ferrite nanoparticles anode retain the spinel structure while at higher level of Li uptake (> 0.3 Li+ per formula unit), Zn atoms migrate to vacant crystallographic sites. In this initial stage, Fe is found to be gradually reduced from Fe3+ to Fe2+ upon lithium insertion and remains in the original octahedral sites. Our EXAFS study indicates an increase in structural disorder upon lithiation. Lithiation proceeds with a continuous reduction of the Zn and Fe until those species are fully metallized in the form of nano-sized particles. Finally, we could provide direct proof of the reversible lithium-zinc alloying mechanism occurring in the very final stage of the lithiation. The evolution and stability of the SEI were studied using an arsenic-containing compound as electrolyte. Arsenic acts as local probe for SEI formation for XAS and XPS, giving an insight into the oxidation state and structure of the SEI. Both XAS and XPS revealed the presence of arsenic with oxidation state 3+ and 5+, possibly in the form of arsenic oxides (As2O5, As2O3) and arsenic-fluorine compounds (AsF3, AsF6–, LixAsF3-x). Moreover, XPS revealed the presence of As0 (not detected by XAS) that could be present, in a small quantity, only on the outer layer of the SEI. The organic fraction of the SEI has been also studied with XPS, showing the presence of different lithium alkyls species and carbonates as a result of the degradation of the electrolyte organic solvents. Those species may contain lithium atoms contributing to the total capacity of the cell, in agreement with recent results. In-situ microRaman experiments, specifically developed during this thesis, were attempted showing the modifications of the graphitic host structure during lithium insertion in the material. Finally, the structure of Mn-based layered oxides for sodium-ion cathodes, doped with Ti and Fe, was studied by X-ray Absorption Spectroscopy. We have verified that the oxidation states of Mn and Ti in P2-Na2/3Mn0.8Fe0.2-xTixO2 are in agreement with the expected theoretical values. Our structural XAS refinement, compared with the results of DFT calculations and XRD data, confirmed experimentally the Jahn-Teller induced distortion of the structure for all the materials under consideration. A slight decrease of the local structural disorder is observed in the material where both Fe and Ti are present with equal proportions. Most of the results presented in this thesis have been published in international journals, and the reader is referred to the published papers for further details.

This article deals with properties of cathode material of lithium-ion cells study in term of active layer dependence. Aim of the work is to get familiar with problematics of cathode material production and diagnostics and to compare different active layer production methods. The opening of the work is concentrating on rechargeable batteries, mainly lithium-ion batteries and their electrode materials. Practical part is describing method of cathode material production and its characteristics.

Manganese Hexacyanoferrate (MnHCF) and nickel doped manganese hexacyanoferrate were synthesized by simple co-precipitation method. The water content and chemical formula was obtained by TGA and MP-AES measurements, functional groups by FT-IR analysis, the crystal structure by PXRD and a local geometry by XAS. Elemental species of cycled samples were further investigated by TXM and 2D XRF. Electrochemical tests were performed in the glass cell. With addition of nickel, vacancies and water content increased in the sample. Crystal structure changed from monoclinic to cubic. Ni disturbed the local structure of Mn, site, however, almost no change was observed in Fe site. After charge/discharge cycling of MnHCF intercalation was already found in the peripheries of charged species after 20 cycle in 2D XRF analysis and randomly distributed intercalated regions after 50 cycles in TXM analysis. Cyclic voltammetry showed that peak-to-peak separation is increasing in case of the addition of Ni to MnHCF.

Les prochaines générations de batteries à ions lithium et sodium seront basées sur le développement de nouveaux matériaux d'électrode positive durables, peu chers et sûrs. Dans ce but, nous avons exploré le monde des minéraux à la recherche de structures présentant les pré-requis pour l'insertion et la désinsertion d'ions alcalins. Nous avons alors entrepris l'étude de sulfates bimétalliques dérivés du minéral bloedile, ayant pour formule générale. (,. \/(S04):«H;0 {A = L i , Na, \t= métal de transition 3d, et « = 0, 4). Ces systèmes présentent une cristallochimie riche, montrant des transitions structurales en fonction de la température ainsi qu'avec le départ des molécules d'eau. Les nouvelles structures ont été déterminées en combinant les techniques de diffraction des rayons X. Neutrons et électrons. Nous avons également montré que les composés à base de lithium Liv. V/(S04): présentent des propriétés antiferromagnétiques intéressantes, du fait notamment de leurs structures particulières qui permettent seulement des interactions de super-super-échange. Enfin et surtout, nous avons, parmi les composés isolés, identifié trois sulfates à base de fer, à savoir Na:Fe(S04)2-4H;0, Na2Fe(S04)2 et Li2Fe(S04):, qui présentent des propriétés électrochimiques intéressantes face au lithium et au sodium. Avec un potentiel de 3,83 V vs. L i 7 L i ° , la nouvelle phase marinite Li2Fe(S04)2 affiche le plus haut potentiel jamais observé pour le couple redox Fe"''/Fe"* dans un composé inorganique à base de fer et dépourvu de fluor, et est en fait seulement dépassé par celui de la forme iriplite de LiFeS04F
The next générations of Li- and Na-ion batteries will rely on the development of new sustainable, low-cost and safe positive électrode materials. To this end, we explored the world of minerais with an emphasis on spotting structures having the prerequisites for insertion and deinsertion of alkaline ions. From this survey, we embarked on the investigation of bimetallic sulfates derived from the bloedite minerai and having the gênerai formula /4,/W(S04)2 nHzO {A = Li, Na, M = 3d transition métal and n = 0, 4). Thèse Systems présent rich crysta chemistry, undergoing phase transitions upon heating and removal of water. The new structures were determined by combining X-ray, neutron and électron diffraction techniques. We have aiso shown that lithium-based compounds LixM(S04)2 présent interesting antiferromagnetic properties resulting from their peculiar structures, which solely enable super-super-exchange interactions. Finally, and more importantly, we identified among the isolated compounds three iron-based sulfates, namely Na2Fe(S04)2 4H2O, Na2Fe(S04)2 and Li2Fe(S04)2, which présent attractive electrochemical properties against both lithium and sodium. With a potentiel of 3. 83 V vs. L'C/U°, the new marinite phase Li2Fe(S04)2 displays the highest potentiel ever observed for the Fe"'VFe"* redox couple in e fluorine-free iron-based inorgenic compound, only riveled by the triplite form of LiFeS04F

The aim of this work is to describe final properties of the electrodes based on the amount of pressure used during its production. In the theoretical part of this work, secondary electrochemical accumulators are described, with the focus on Li-ion accumulators. In the main part of this work, the production of Li-ion accumulators, with usage of different pressures during its production is described. In the final part of this work, the examination of these created cells for the classification of the optimal production pressure is described.

The purpose of this diploma thesis is to describe the impact of compaction pressure on the electrochemical parameters of lithium-sulfur batteries. Theoretical part of this thesis contains briefly described terminology and general issues of batteries and their division. Every kind of battery is provided with a closer description of a specific battery type. A separate chapter is dedicated to lithium cells, mainly lithium-ion batteries. Considering various composition of lithium-ion batteries, this chapter deeply analyzes mostly used active materials of electrodes, used electrolytes and separators. Considering that the electrochemical principle of Li-S and Li-O batteries is different to Li-ion batteries, these accumulators of new generation are included in individual subhead. In the experimental part of this thesis are described methods used to measure electrochemical parameters of Li-S batteries. Next chapter contains description of preparing individual electrodes and their composition. Rest of the experimental part of my thesis is dedicated to the description of individual experiments and achieved results.

U ovoj doktorskoj disertaciji ispitivani su elektroliti na bazi jonskih tečnosti pogodni zaprimenu u litijum  jonskim baterijama. Fizičko-hemijska svojstva binarnih smešajonskih tečnosti sa dicijanamidnim i bis(trifluorometilsulfonil)imidnim anjonima imolekulskih rastvarača ispitana su u celom opsegu molskih udela i na različitimtemperaturama. Na osnovu izmerenih gustina, viskoznosti i električne provodljivostiizračunati su različiti fizičko hemijski parametri i diskutavne interakcije između komponenata smeša. Ispitana je termička i elektrohemijska stabilnost odabranihelektrolita. Dodatkom litijumove soli u odabrane binarne smeše dobijeni su ternarnisistemi koji su okarakterisani u zavisnoti od koncentracije litijumove soli. Odabranielektroliti upotrebljeni su za  ispitivanje performansi litijum  jonske ćelije sa anatasTiO2  nanotubularnim elektrodama.Cikličnom voltametrijom i galvanostatskimcikliranjem su ispitane performanse ćelije u toku 150 ciklusa punjenja i pražnjenja. Naosnovu ciklovoltametrijskih merenja izračunati su koeficijenti difuzije i energija aktivacije za difuziju.
In this doctoral dissertation, Ion liquid-based electrolytes were tested for use in  lithium-ion batteries. The physicochemical properties of binary mixtures of ionic  liquids with dicyanamide and bis (trifluoromethylsulfonyl) imide anions and  molecular solvents were examined throughout the range of molar proportions and at different temperatures. Based on the measured densities, viscosity and electrical conductivity, various physical chemical parameters and discrete interactions between  the components of the mixture are calculated. Thermal and electrochemical stability of selected electrolytes was examined. By addition of lithium salt to the selected binary mixtures, ternary systems were characterized which were characterized by the concentration of lithium salt. The selected electrolytes were used to test the performance of the lithium-ion cell with anatomic TiO2 nanotubular electrodes. Cyclic voltammetry and galvanostatic cycling tested the cell's performance during the 150 charge and discharge  cycles. Based on cyclotoltametric  measurements, the diffusion coefficients and activation energies for diffusion were calculated.

Neste trabalho foram estudadas diferentes modificações superficiais do titânio (Ti) como método de preparação de superfícies de eletrodos para baterias de íons lítio (Li+) Inicialmente, as modificações foram produzidas pelas micro-indentações, com posterior corrosão eletroquímica por pites em soluções de brometo. As superfícies polidas, tratadas termicamente e modificadas através de micro-indentações foram avaliadas em diferentes parâmetros, tais como o potencial aplicado, concentração dos íons agressivos no eletrólito, temperatura, tempo dos testes e principalmente, sobre o impacto das deformações causadas pela força indentações para localização de orifícios produzidos por pites. Filmes porosos de titânia (TiO2) crescidos sobre o Ti puro, foram produzidos por anodização a plasma (anodização por centelhamento ou sparking) em 1M H3PO4 e em 1M Na2SO4 e por anodização nanotubular em 1M H3PO4 + 1M NaOH + 0,4 %(peso) HF. Os resultados mostraram, em óxidos tipo “esponja” formados na anodização a plasma em 1M H3PO4 e 1M Na2SO4, a incorporação de elementos do eletrólito contendo, respectivamente, P e S, numa relação de P/O > S/O e em óxidos nanotulares, a predominante incorporação de elemento de F. Posteriormente, as superfícies corroídas por pites e as superfícies de óxidos crescidos por anodização a plasma foram convertidas por sulfetação em diferentes materiais micro e nanoestruturados compostos por sulfetos e oxisulfetos de titânio, ajustando-se as condições de processo. O desenvolvimento proposto mostrou que é possível modificar a composição química do óxido formado por anodização a plasma para nanocristais de TiS2, nanofitas de TiS3 e TiOxSy, sem danificar a morfologia original dos nanoporos de TiO2. Os compostos formados podem ser usados como eletrodos nanoarquiteturados tridimensionais (3D) para microbaterias de íons lítio (Li+) com alta densidade de potência. A síntese desses compostos é realmente promissora, porque eles têm a capacidade de inserir mais íons lítio do que TiO2 puro, resultando em uma melhoria na capacidade das microbaterias.
In this study, different surface modifications of titanium (Ti) were studied as a method of surface preparation of electrodes for ion lithium batteries (Li+). Initially, the modifications were produced by micro-indentation with subsequent electrochemical pitting corrosion in solutions of bromide. The polished surfaces, heat treated and modified through micro indentations were evaluated for different values of parameters, such as applied potential, concentration of aggressive ions in the electrolyte, temperature, polarization time, and mainly intensity of the deformation caused by indentations for localizing holes produced by pitting. It was expected the adjust of location of these parameter settings promotes nucleation of pits, according to the pattern of indentations and growth of pitting depth for increased surface area. Porous films of titania (TiO2) were produced on pure Ti by plasma anodization (or sparking) in 1M H3PO4 and 1M Na2SO4. Nanotubes were synthesized by porous anodization in 1M NaOH + 1M H3PO4 + 0.4 (wt%) HF. The results showed oxide "sponge" like formed by plasma anodization, incorporating elements of the electrolyte containing respectively, P and S in a ratio P/O> S/O and, in nanotubular oxides, with predominant incorporation of F. Subsequently, the pitted surfaces and the surfaces of oxides grown by plasma anodization were converted by sulfidation into different micro and nanostructured materials consisting of titanium sulfide and oxisulfides by adjusting the process conditions. The proposed development has shown that it is possible to modify the chemical composition of the oxide formed by plasma anodizing to nanocrystals of TiS2 and nanobelts of TiS3 and TiOxSy without damaging the original morphology of the nanoporous TiO2. The formed compounds can be used as three-dimensional (3D) nanoarchitectured electrodes for ion lithium batteries (Li+) with high power density. The synthesis of these compounds is promising due to a higher ability to intercalate more ions lithium than pure TiO2, resulting in an improvement in the capacity of microbatteries.

Este trabalho apresenta um estudo exploratório do potencial do Paraguai e da Bolívia para o desenvolvimento de uma indústria de mobilidade elétrica, avaliando a viabilidade de substituição da frota convencional de veículos leves, propulsados atualmente por motores à combustão interna (VCI), por veículos elétricos (VE) equivalentes. O estudo leva em consideração critérios econômicos, energéticos, ambientais, geopolíticos e disponibilidade de recursos naturais. Por tanto, são consideradas duas situações de substituição. No primeiro, por veículos elétricos disponíveis no mercado internacional (VE) e, alternativamente, por veículos elétricos com baterias de Li-ion, resultado da implantação e desenvolvimento de uma indústria de VE`s e outra de baterias de íons de lítio (Li-ion). Aproveitando assim, as vantagens estratégicas de recursos naturais proveniente do Salar de Uyuni Bolívia e da disponibilidade de energia elétrica no Paraguai, considerando a utilização de parte da potência da usina de Itaipu, propriedade do Paraguai e atualmente cedida a seu sócio no empreendimento, o Brasil, bem como a partir das abundantes reservas de gás natural boliviano e o potencial de ambos os países para o desenvolvimento de projetos de fontes renováveis. A indústria de baterias para os automóveis elétricos pode ser localizada na Bolívia, perto dos recursos e com grandes avanços tecnológicos e investimentos do governo na área nos últimos anos, enquanto a de VEL pode ser sediada no Paraguai que na atualidade possui um grande interesse de investidores estrangeiros. Os governos poderiam fomentar o projeto com iniciativas, como subsídios no custo da energia utilizada para o abastecimento de VE`s, ou no custo de investimento inicial do veículo. Poderia também fornecer financiamento para a aquisição de VE`s a taxas menores as do mercado. As estimativas conduzidas neste trabalho mostram que uma eventual substituição da frota de veículos leves VCI por VE no período de 10 anos, geraria benefícios econômicos cumulativos para o Paraguai de US$ 1.031 milhões e para Bolívia de US$ 1.373 milhões. Essa substituição permitiria uma redução das emissões de Gases de Efeito estufa (GEE) de 8.398 GgCO2 para o Paraguai e 9.420 7 GgCO2 para a Bolívia. Inicialmente seriam produzidos 40 mil veículos por ano em cada país para atingir a escala necessária para a redução dos custos das BIL`s. A ideia subjacente é ganhar escala local para a cadeia de produção inicial e, em seguida, acessar os mercados de América latina e o mundo.
This document presents an exploratory study of the potential of Paraguay and Bolivia for the development of an electric mobility industry, assessing the viability of replacing conventional light vehicle fleet, currently driven by internal combustion engines (ICE), for electric vehicles (EV) equivalent. The study takes into account economic, energy, environmental, geopolitical, and availability of natural resources criteria. Therefore, two replacement situations are considered. In the first, for EV`s currently available in the international market and, alternatively, for electric vehicles with Li-ion batteries, due to the implementation and development of both, an electric vehicle and a lithium-ion batteries industry. Leveraging so, the strategic advantages of natural resources from the Salar de Uyuni - Bolivia and the availability of electricity. This considering the use of part of the over-potential of the Itaipu power plant, owned by Paraguay and currently assigned to his associated in the undertaken, Brazil, and from Bolivian natural gas abundant reserves and the potential of both countries for the development of renewable projects. The battery industry for electric cars could be located in Bolivia, because of the proximity of the lithium resources and the technological breakthroughs and investments in the area of the Bolivian government in recent years, while the LEV industry could be based in Paraguay, which currently has a great appeal for foreign investors. Governments could promote the project with incentives such as subsidies in the cost of energy used to supply EV`s, or the cost of the initial investment vehicle, it also could provide funding for the acquisition of EV`s at lower rates. Estimates conducted in this study in a ten year basis show that any replacement of the ICE light vehicle fleet for EV would generate cumulative economic benefits to Paraguay for US$ 1,031 million, and for Bolivia US$ 1,373 million. This substitution would reduce Greenhouse Gases emissions (GHG) in 8,398 GgCO2 for Paraguay and 9,420 GgCO2 for Bolivia. Initially, 40,000 vehicles per year in each country would be produced to achieve the scale required for reducing BIL`s costs. The underlying idea is to make local scale for initial production chain and then access the Latin America markets and the world.

The demand for electrical energy storage has increased tremendously in recent years, especially in the applications of portable electronic devices, transportation and renewable energy. The performances of lithium-ion and sodium-ion batteries depend on their electrode materials. In commercial Li-ion batteries with graphite anodes the intercalation potential of lithium in graphite is close to the reversible Li/Li⁺ half-cell potential. The proximity of the potentials can result in unintended electroplating of metallic instead of intercalation of lithium in the graphite anode and frequently leads to internal shorting and overheating, which constitute unacceptable hazards, especially when the batteries are large, as they are in cars and airplanes. Moreover, graphite cannot be readily used as the anode material of Na-ion batteries, because electroplating of metallic sodium on graphite is kinetically favored over sodium intercalation in graphite. This dissertation examines safer Li-ion and Na-ion battery anode materials.
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碩士
國立中正大學
化學工程研究所
107
At present, there are many kinds of anode materials for lithium ion batteries, and each anode material has its own advantages and disadvantages. Among them, titanium-based materials have stable electrochemical performance and high safety, which makes it gradually applied to sodium ion batteries. But its poor conductivity and low lithium ion diffusion coefficient limited its performance in lithium-ion batteries and sodium-ion battery. In this study, Li4Ti5O12 anode material was prepared by sol-gel method. It had a suitable particle size and crystallinity after calcination at 750oC. At a rate of 1C charge rate, the reversible capacity of Li4Ti5O12 was 142.5 mAh/g. As the charge-discharge rate increased to 5C charge rate, its capacity still remained 121.6 mAh/g. We successfully synthesized Li4Ti5O12 anode material with the highly stable electrochemical performance. Furthermore, graphene oxide (GO) was prepared by Hummers method and then it was reduced to reduced graphene oxide (rGO) by thermal treatment. And rGO was coated on Li4Ti5O12 anode material to improve the conductivity of Li4Ti5O12. At a rate of 5C charge rate, the reversible capacity of LTO@3.7 wt.%rGO was 146.1 mAh/g. After 300 cycles of cycling test, the capacity retention rate was 89.2%. Moreover, it remained 101.5 mAh/g at 20C charge rate. As a result, rGO successfully enhanced the conductivity of Li4Ti5O12 in electrochemical performance. This study also used hydrothermal synthesis of Li4Ti5O12 anode materials and doped Na ions to prepared Li4-xNaxTi5O12(x=0.05, 0.10, 0.15, 0.20) by adding NaOH aqueous solution for sodium ion batteries. The reversible capacity of Li4-xNaxTi5O12(x=0.1) was 80.7 mAh/g after 0.1C cycle test, and the capacity retention rate was 83.0% after 300 cycles. In order to improve its electrochemical performance, we prepared Li4Ti5O12 nanosheets by changing the hydrothermal solvent to reduce the path of sodium ion diffusion. At a rate of 0.1C, the reversible capacity of Li4Ti5O12 nanosheets were as high as 130.1 mAh/g, and the first cycle Coulomb efficiency was 64.1%. In addition, Na ions were doped into Li4Ti5O12 nanosheets by adding NaOH aqueous solution. The results of XRD analysis showed that the lattice constant was enlarged to 8.345 Å, and the thickness was about 30~50 nm. In the electrochemical analysis, the reversible capacity of Li4-xNaxTi5O12(x=0.1) nanosheets were 154.4 mAh/g at a rate of 0.1 C, and the capacity was 115.5 mAh/g after 100 cycles. Furthermore, the Li4-xNaxTi5O12(x=0.1) nanosheets exhibited a reversible capacity of 76.0 mAh/g at the high of 1C.

An alternate family of “high” voltage (where the equilibrium voltage lies between 3.6 V and 4.2 V) polyanion cathode materials is reported in this thesis with the objective of improving specific energy density (Wh/kg) and developing a better understanding of polyanion electrochemistry. The electrochemical properties, synthesis and the structure of novel fluorosulfate materials crystallizing in the tavorite and the triplite type mineral structures are described. These materials display highest discharge voltages reported for any Fe2+/Fe3+ redox couple. LiFeSO4F was prepared in both the tavorite and the triplite polymorphs using inexpensive and scalable methods. Complete structural characterization was performed using X-ray and neutron based diffraction methods. A rapid synthesis of fluorosulfates can be achieved by using microwave heating. The local rapid heating created by the microwaves generates nanocrystalline LiFeSO4F tavorite with defects that induce significant microstrain. To date, this is unique to the microwave synthesis method. Phase transformation to the more stable triplite framework, facilitated by the lattice defects which include hydroxyl groups, is therefore easily triggered. The formation of nanocrystalline tavorite leads to nanocrystalline triplite, which greatly favors its electrochemical performance because of the inherently disordered nature of the triplite structure. Direct synthesis of the electrochemically active triplite type compound can be carried out either by extending the duration of the solvothermal reactions or by the partial substitution of Fe by Mn to produce LiFe1-xMnxSO4F. This study, overall, has led to a better understanding of the transformation of tavorite to the triplite phase. To examine Li and the Na ion conduction and their correlation with the electrochemical performance of 3-D, 2-D and 1-D ion conductors, atomistic scale simulations have been used to investigate tavorite type LiFeSO4F, NaFeSO4F, olivine type NaMPO4 (M= Fe, Mn, Fe0.5Mn0.5) and layered Na2FePO4F. These calculations predict high mobility of the Li-ion in the tavorite type LiFeSO4F but sluggish Na-ion transport in iso-structural NaFeSO4F. High mobility of the Na-ion is predicted for phosphate layered and olivine structures. Finally, the synthesis and structural details of NaMSO4F (M=Fe, Mn) and NH4MSO4F (M=Fe, Mn) are presented in the last chapter to show the structural diversity present in the fluorosulfate family.

碩士
國立中正大學
化學暨生物化學研究所
107
β12 Borophene is a new type of two-dimensional material which has been successfully synthesized on Ag (111) surface under ultrahigh-vacuum conditions. Borophenes are unstable when they are separated from Ag(111) substrates, but it can be improved by doping nitrogen to change the electronic properties by breaking the lattice periodicity. In this work, N-doped β12 borophenes were considered as the anode material of Li-ion and Na-ion batteries. Theoretical methods were adopted to calculate the structures, total energies, cohesive energies, electronic properties, adsorption behavior, migration barrier and maximal capacity at GGA-PBE level based on first-principle calculations using Vienna ab initio simulation package (VASP). N4-doped β12 borophene is more stable than primitive β12 borophene. The most favorable adsorption sites for Li-ion and Na-ion on N4-doped β12 borophene are hole sites with the adsorption energy of -2.315 eV and -1.710 eV, respectively. Comparing to primitive β12 borophene, the band structure converts from metallic into semiconducting due to the non-crossing band on Fermi level and thus lower adsorption energy. The migration barrier of Li and Na are 0.239 eV and 0.089 eV, much lower than that of primitive β12 borophene. Finally, the maximum capacity for Li and Na cations on N4-doped β12 borophene are 602 and 482 mA h/g, respectively. Therefore, our results suggest that N-doped β12 borophene has a higher charge-discharge performance than primitive borophene.

碩士
大同工學院
材料工程研究所
87
In this study, NaxMnO2 (x<1) and NaxLiyMnO2 were prepared by calcining 800℃ 4 hours, 800℃ 100 hours, and 1000℃ 4 hours. Electrical properties and structure evolutions were examined. From the results in the system of Na-Mn-O, the diffraction patterns of NaxMnO2 show that structure is orthorhombic for x< 0.4, hexagonal-orthorhombic mixture between 0.4 and 0.59, hexagonal structure for x between 0.6 and 1.0. In the system of Na-Li-Mn-O NaxMnO2 (x<1) system structures and LiMn2O4 spinel structure appear simultaneously. From the tests of charge and discharge, Na0.2Li0.2MnO2 has the best capacity and the least power loss. The capacity will decrease as the content of sodium increases to form hexagonal and spinel mixture. Comparing of different heat treatments, we can see that increasing calcining time and temperature will benefit the capacity and the calcining time is much more helpful than calcining temperature.

As for borohydrides, the alanate family promises very interesting capacities due to the light molar weight of aluminum and the high hydrogen content of these complex hydrides. In fact, in view of a full conversion reaction in LiH and metal elements, they can theoretically achieve more than 1000 mAhg-1 exchanging at least 3 electrons for redox center. Furthermore, their thermal stability makes these compounds feasible candidates for practical applications (details are in chapter 3). The interest in them has been supported from pioneering DFT calculation performed in our laboratory few years ago [25,26], with the task to theoretically demonstrate the feasibility of alanates conversion reaction and its exploitability for application in lithium ion batteries. Besides our investigations, also Trepovich et al. [24] recently reported the use of LiAlH4 and NaAlH4 as anodes in lithium cells, furnishing a reference for comparison of our results and conclusions. This PhD thesis provides the experimental evidences of the electrochemical activity of sodium and lithium alanates in lithium cells. The focus is on the properties and reaction mechanism of tetrahydro-alluminates (LiAlH4 and NaAlH4). Beside them, further three hexa-alanates phases (Li3AlH6, Na3AlH6 and Li Na2AlH6) have been investigated. In fact, the electrochemical reaction mechanism is expected to involve the formation of these compounds in the intermediate steps. Therefore, their behavior in electrochemical cells have been used to delineate a full picture of the conversion mechanism of the corresponding tetrahydro-alluminates compounds. The work has been structured in three sections. The first section is focused on lithium alanates (LiAlH4 and Li3AlH6). Chapter 4 reports the studies conducted on LiAlH4. After confirming the electrochemical activity of this compound, mechanochemical treatments have been used to improve its performance. It's well known that mechanical grinding causes the reduction of the particles and induces strains that could lead to a better diffusion of hydrogen and lithium by increasing the number of diffusion paths. Comparisons with pristine sample have been made to evaluate the effects of the performed treatments on the structure, morphology and electrochemical performance. The electrochemical reaction mechanism has been elucidated by ex-situ diffraction experiments on LiAlH4 based electrodes at different state of charge. The chapter ends with the study of the reactivity of LiAlH4 with the carbonate based electrolyte used for electrochemical tests. Chapter 5 provides the results for Li3AlH6. In this case, mechanochemistry has been used to synthesize the compound. Second section describes the sodium alanates compounds (NaAlH4, Na3AlH6 and LiNa2AlH6). As already did for lithium alanates, mechanochemical treatments have been used both to activate the bare NaAlH4 (chapter 6) and to synthesize hexa-alanates phases (chapter 7). Then, for the obtained samples the chemical-physical and the electrochemical properties have been studied. Finally, in the chapter 8, the conversion reactions of the three phases have been described by in situ diffraction experiments during discharge/charge cycling. Further investigations have been addressed on NaAlH4, in view of the encouraging results obtained. In conclusion, the last section is dedicated to the performance improvements of the alanates based electrodes. In fact, for all the samples poor cell efficiency and cyclability have been observed. This could be mainly ascribed to the big volumetric expansion observed with conversion reaction as well to the high reactivity of this materials with the common solvents used as electrolytes, due to the high reducing power of alanates. Two main strategies have been adopted to reduce these effects: the nanoconfinement in a nanoporous carbon matrix, as described in chapter 9 and the replacement of carbonates based electrolyte with an ionic liquid, as in chapter 10.

The commercialization of Li-ion battery (LIB) in 1990s by Sony Corporation has led to its applications in portable electronic devices such as mobile phones, cameras, laptop computers, etc. Initially, the energy density of commercial LIB was only about 120 Wh Kg-1. However, with sustained improvements in properties of various cell components, the present-day LIB provides energy density of about 250 Wh Kg-1. With future use envisaged for mobility applications such as electric vehicles, research activities have gained momentum for development of high energy density Li-S and Li-O2 batteries. However, due to limited sources of lithium (0.007 % in earth’s crust and 0.2 ppm in sea water) and uneven distribution, concerns arise about its cost and availability which would inhibit bulk production and utilization of lithium-based batteries. Hence, there is an urgent need to switch over to battery systems employing earth abundant and environmentally benign materials. Sodium and potassium-based batteries have received attention in research laboratories as alternatives to lithium-based batteries due to their natural abundance and low cost. Na and K are the metals below Li in the periodic table and their physical and chemical properties are similar to those of Li. Na and K are the sixth and seventh most abundant elements, constituting 2.6 % and 2.4 %, respectively of the earth’s crust. Sea water contains about 10800 ppm Na and 400 ppm K. Although, the standard potentials of Na/Na+ (-2.71 V vs. standard hydrogen electrode (SHE)) and K/K+ (-2.93 V vs. SHE) are less than Li/Li+ (-3.04 V vs. SHE) by about 300 and 100 mV, respectively, the cost and availability factors overweigh the marginal reduction in energy density. The quest for new electrode materials for Na- and K-based batteries, their physicochemical characterizations and electrochemical investigations are described in the thesis. It consists of a comprehensive review of the literature on the evolution of battery systems with a focus on the next generation Na- and K-based batteries. The cathode and anode materials for Na- and K-ion batteries are reviewed along with the current research activities in Na- and K-sulphur, and Na- and K-O2 batteries. It furnishes a brief description of various experimental techniques and procedures adopted at different stages of the present thesis. The amorphous MnO2 has been prepared by two different methods: (i) reduction of KMnO4 using ethylene glycol (EG) and (ii) the redox reaction between KMnO4 and MnSO4.H2O at ambient conditions. The as prepared MnO2 samples in both cases are amorphous in nature and on heating in the temperature range of 300 – 800 °C, they convert to α-MnO2. The MnO2 prepared by reduction by EG has been studied for Na/MnO2 and Li/MnO2 laboratory scale primary cells in non-aqueous electrolytes. The specific capacity of amorphous MnO2 is 300 mAh g-1 in both Na/MnO2 and Li/MnO2 cells. Na/MnO2 cell shows a nominal voltage less than Li/MnO2 cell by 0.35 V, as expected. MnO2 prepared by the redox reaction between KMnO4 and MnSO4.H2O has a specific surface area of 184 m2 g-1 with narrowly distributed mesopores of 3.5 nm pore diameter. The crystallinity increases and specific surface area decreases upon heating. The as prepared sample provides the first discharge capacity of about 300, 200 and 80 mAh g-1 for Li-, Na- and K-MnO2 cells, respectively, at a specific current of 50 mA g-1. The attractively high discharge capacity of the as prepared amorphous MnO2 is attributed to the large specific surface area and mesoporosity. However, the crystalline samples exhibit low specific discharge capacity in comparison with amorphous samples. It deals with electrochemical impedance spectroscopy (EIS) study of Na/MnO2 primary cell fabricated in a non-aqueous electrolyte of Na salt. The EIS data provides a high resistance of Na metal due to the surface passive film. On subjecting the cell for discharge, the surface film causes a delay response of the cell voltage and the closed-circuit voltage reaches the normal discharge level following dielectric break-down of the film. The EIS data measured at different stages of cell discharge are subjected to non-linear least squares fitting with the aid of an appropriate equivalent circuit. The impedance parameters are examined to throw light on state-of-charge of Na/MnO2 primary cells. The study has been further extended to analyze the delay-time behaviour of the non-aqueous Na/MnO2 cells and quantifying the film resistance and break-down field for the film formed on the Na surface. P2-type Na0.67Mn0.65Fe0.20Ni0.15O2 is studied as a cathode material for Na-ion battery and presented. It is synthesized in microspherical and disc-like morphologies using two different synthetic procedures. Microspheres of FeCO3 are first prepared and used as a template to synthesize Mn0.65Fe0.20Ni0.15CO3, followed by its thermal decomposition to the corresponding oxide and finally, thermal fusion of the oxide with Na2CO3 to produce P2-type Na0.67Mn0.65Fe0.20Ni0.15O2. However, disc-like Na0.67Mn0.65Fe0.20Ni0.15O2 is synthesized by sintering the product obtained using a low temperature solution combustion method using aqueous solution of stoichiometric quantities of corresponding metal nitrates and sucrose as the fuel at 800 °C. Cyclic voltammograms in both the samples are characterized by well-defined two pairs of current peaks corresponding to the oxidation and reduction processes in two different stages. The sodiated microspherical oxide provides an initial discharge capacity of about 216 mAh g-1 at C/15 rate cycling with an excellent cycling stability (Fig. 3a). The rate capability is also high, and the discharge capacity is about 100 mAh g-1 at 2C rate. The high discharge capacity and high rate capability are attributed to porous microspherical morphology. When the cells with disc-like morphology cathode sample are cycled at a current density of 35 mA g-1, a specific discharge capacity of 178 mAh g-1 is obtained with close to 100 % coulombic efficiency. Capacity retention of more than 70 % is observed after 50 charge-discharge cycles Potassium tetratitanate (K2Ti4O9) is synthesized by solid-state method using K2CO3 and TiO2 and studied as an anode material for potassium ion batteries (KIB) for the first time. A discharge capacity of 97 mAh g-1 has been obtained at a current density of 30 mA g-1 (0.2 C rate) and 80 mAh g-1 at 100 mA g-1 (0.8 C rate), initially (Fig. 4a). The proposed mechanism of charging involves reduction of two Ti ions from 4+ oxidation state to 3+ oxidation state, which facilitates insertion of two K+ ions per formula unit in the zig-zag layer of TiO6 octahedra separated with K+ ions with interlayer spacing of 0.85 nm. For KIB cathode, K0.27Mn0.65Fe0.35-xNixO2 (0.00 ≤ x ≤ 0.35) is synthesized in microspherical morphology. The potassiated mixed metal oxide formed in microspherical morphology is in pure crystalline phase. The oxide with the composition x = 0.35 i.e., K0.27Mn0.65Ni0.35O2 provides the highest first specific discharge capacity of 97 mAh g-1 at C/10 rate (Fig. 4b). A good cycling stability is observed. It deals with carbonization of milk-free coconut kernel pulp carried out at low temperatures. The carbon samples are activated using KOH and electrical doublelayer capacitor (EDLC) properties are studied (Fig. 5a). Among the several samples prepared, activated carbon prepared at 600 °C has a large specific surface area (1200 m2 g-1). Cyclic voltammetry and galvanostatic charge-discharge studies suggest that activated carbons derived from coconut kernel pulp are appropriate materials for EDLC studies in acidic, alkaline and non-aqueous electrolytes. Specific capacitance (SC) of 173 F g-1 is obtained in 1 M H2SO4 electrolyte for the activated carbon prepared at 600 °C. The supercapacitor properties of activated carbon sample prepared at 600 °C are superior to the samples prepared at higher temperatures. Electrochemical studies are also undertaken for the prepared and activated samples for sodium ion intercalation/deintercalation. It is found that various factors such as surface area, mesoporosity, inter-layer spacing, electrolyte diffusion, solid electrolyte interface formation for high surface area carbon, etc. contribute to the capacity and cycle life of the material. Carbon sample synthesized at 600 °C and having a specific surface area of about 280 m2 g-1 provides the highest discharge capacity of about 200 mAh g-1 with good cycling stability. The thesis ends with a short summary and prospects of the investigations described here in. The work presented in it is carried out by the candidate as a part of Int. Ph.D. program. Some of the results are published in the literature and some more manuscripts are in preparation. A list of publications is enclosed. It is hoped that the studies reported in the thesis are worthy contributions.

In this thesis, we have attempted to understand the working principle of Li(Na)-S(Se) battery and following such understandings we have attempted towards the design of various S(Se)- cathode materials for the alkali based chalcogen batteries. In the final chapter, we have focussed on the development of anode materials for full Li-ion cell. The summary of the various chapters is as follows. Chapter 2 discusses about NaY-xS-PAni exhibiting remarkable electrochemical performance as a cost-effective sulfur cathode for rechargeable Li-S batteries. The superior electrochemical stability and performance of the NaY-xS-PAni is directly correlated to the novel NaY electrode structure in combination with the host polarity and ionic conductivity. The zeolite provides an optimum geometrical and chemical environment for precise confinement of the sulfur while the polyaniline coating provides electron conduction pathway along with extra polysulfide confinements. This cathode material exhibits very stable cycling for more than 200 cycles with relatively low specific capacity and modest rate capability. To develop a material for obtaining high specific capacity value we moved to carbon based host and the details are covered in chapter 3 and 4. To summarize Chapter 3, we have successfully extended the pressure induced capillary filling method for confinement of sulfur and selenium in the interior core of the MWCNTs. This method results in ultra-high loading yields of the chalcogens inside the MWCNTs. The ensuing composites S-CNT have been convincingly demonstrated as prospective cathodes in Li-S rechargeable batteries exhibiting very high specific capacities ~ 1000 mAh g-1 at C/10 current rates. The novelity of this host has been established by extending the work in encapsulating Se with the similar protocol and studying its electrochemical activity. The high efficiency of the Li-S/Se electrochemical reaction observed here is directly attributed to the efficacy of the encapsulation protocol of S/Se inside the CNTs. The polyselenides/polysulfides are completely confined within the precincts of the CNT cavity leading to an exceptionally stable battery performance at widely varying current densities. With the success of this encapsulation technique for the carbon based host, we developed another interconnected mesoporous microporous carbon host for sulfur encapsulation the details of which constitute the next chapter. In chapter 4, we have discussed here a novel S-cathode where the sulfur confining hierarchical carbon host synthesized using a sacrificial template can be very effectively employed for in Li-S rechargeable battery. The hierarchical mesoporous-microporous architecture comprising of both mesopores and micropores provide an optimal potential landscape which in turn traps high amounts of sulfur as well as polysulfides formed during successive charge-discharge cycles. The uniqueness of the carbon matrix translates to exceptionally stable reversible cycling and rate capability for Li. Such promising result with Li-S battery compelled us to check the performance with Na anode. This led to the development of intermediate temperature Na-S battery with JNC-S as the prospective cathode. It is envisaged that such materials design will be very promising in general for battery chemists especially for higher valent metal-sulfur systems (e.g. magnesium, aluminum). The host discussed here will be ideally suitable for introduction of dopants such as nitrogen, boron, thus enhancing it’s versatility as a heterodoped mesoporous-microporous host for varied applications. In all the preceding chapters, the focus was to encapsulate sulfur in some host structures. Chapter 5 deals with an alternative configuration for the Li-S battery that uses an oxide based interlayer to restrict the polysulfides. From the study discussed here, it can be concluded that NiOH-np/NiO-np can act as an efficient interlayer material for superior anode protection. The interlayer provides an anchor to hold back the polysulfides primarily on the cathode side by forming intermediates such as NiS3(OH) and NiS4(OH). Although, the specific capacity is less compared to the theoretically estimated value for S-cathode, the high cyclability coupled with extremely good rate capability performance makes this a very promising configuration of Li-S cell assembly for practical applications and deployment. The success of this strategy is expected to decrease the need for design of sophisticated S-scaffolds and lead to simpler Li-S rechargeable batteries. After an extensive discussion on development of cathodes for alkali based chalcogen batteries, we shifted gears and tried our hands in developing some eco-friendly anode materials. The details of graphitic carbonitride as an anode material for Li-ion cell has been discussed in chapter 6. To conclude, we have discussed here in detail the unique layered structure of the as-synthesized gCN and its impact on the intrinsic charge transport properties. Both factors eventually determine their electrochemical performance. The gCN discussed here is obtained using a very simple synthesis protocol in large yields from a very cheap organic precursor. The work highlights again the important role of chemical composition and structure on the functionality of the intercalation host. These have a strong bearing on the electronic charge distribution in the host and its eventual interaction with the intercalating ions. Compared to several non-trivial layered carbonaceous structures, the gCN interestingly displays 3-D ion transport. Additionally, it also sustains facile electron transport (2-D) despite the low concentration of carbon. In spite of the modest specific capacities as observed in case of the half cells, the gCN when assembled with (high) voltage cathodes in full Li-ion cells, the performance is quite encouraging. To the best of our knowledge this is for the first time that graphitic carbon nitrides have been demonstrated as an anode in full Li-ion cells. The potential of majority of the reported high surface area and high capacity complex carbonaceous structures in Li-ion cells are inconclusive. This is mainly due to the fact that the percentage of reports on full Li-ion cell performance is very rare. The full cell analysis of the gCN discussed here conclusively rules out the necessity of the requirement of high specific capacity materials in practical/commercial full cells. We envisage that the work discussed here will pave the way for synthesis of many such electrode materials from renewable resources resulting in the development of green and sustainable batteries. Overall we have been able to address some of the potential problems of Li-S and Li-ion battery systems. There is further scope of betterment with extensive study and this work opens the scope for it in future.

The present Thesis explores a few novel anode materials for both lithium-ion and sodium-ion rechargeable batteries. A series of layered metal titanium niobates have been synthesised and their electrochemical energy storage properties, ion transport, and reaction mechanisms are studied in detail. Alkali-titanium niobates such as Li-Ti-niobate (and it’s sodium counterpart) store lithium (sodium) via the conventional intercalation mechanism. Detailed experimental and theoretical investigations reveal interesting and non trivial ion transport, which are found to be strongly correlated to the electrochemical properties. Apart from intercalation, where amount of energy storage is limited by the crystal structure, energy storage via an alloying reaction is an important alternative strategy to boost specific capacities and energy densities of various battery systems. However, drastic volume changes during alloying/dealloying is detrimental for stable electrochemical function of the cell. The volume expansion problem associated with alloying anodes materials e.g. Sn for alkali-ion batteries have been tackled here via two different strategies. While one uses a flexible layered structure resulting in simultaneous intercalation and alloying process, the other approach uses a porous electrospun carbon fiber encapsulation for alloying compounds. The electrochemical properties as a function of Sn-content in a binary SnX (X: Sb) compound anode have been explicitly probed. This study provided invaluable information on alloying reaction mechanisms as well as identified the most optimum Sn-content for the long term stable battery operations. Usage of graphite as an anode in high energy density Li-ion cell has already been shown to be associated with severe safety issues. The thesis demonstrates a novel and very simple strategy to develop a stable non-carbonaceous anode for operation in the Li-ion (full) cell configuration. The thesis comprises of six chapters and a brief discussion of the content and highlights of the individual chapters are discussed below: Chapter 1 briefly reviews the different materials (mainly anodes) and storage mechanisms in the context of lithium-ion and sodium-ion rechargeable batteries. Energy storage via different mechanisms in metal-ion batteries has it’s own advantages and disadvantages. Thus, design of alternative novel materials is absolutely essential to nullify the detrimental factors associated with various storage methods leading to highly efficient and safe alkali metal-ion rechargeable battery systems. Development of materials for efficient alkali metal-ion batteries are very pertinent even today as the next generation high energy density rechargeable batteries based on metal-S/metal-O2 are still in the stages of infancy. They are far away from widespread commercialization and thus, do not pose any threat to the rechargeable alkali metal-ion batteries. This chapter discusses the importance of diffusion of ions inside the electrode materials, which essentially determines the rate capability of half/full cells. Chapter ends with discussion on galvanostatic intermittent titration technique (GITT) which has been used extensively for calculating the diffusion coefficients of the electrodes. Chapter 2 comprises of synthesis, characterization and investigation of electrochemical properties of novel Ti-based anode materials, namely Li-Ti-niobate and Na-Ti-niobate. These compounds are synthesized using a simple ion-exchange reaction from aqueous medium using KTiNbO5 (potassium titanium niobate) as the parent compound. Li-Ti-niobate and Na-Ti-niobate are tested in Li and Na-battery respectively as an anode material. The effects of Ti3+/Ti2+ redox couple in the electrochemical performances are also investigated in the case of Li-Ti-niobate by altering the working potential window of the battery. The electrochemical performances of Li-Ti-niobate are further improved by downsizing the particle size followed by carbon coating through hydrothermal carbonization method. Scheme 1: Layered structure of metal-titanium niobate. Electrochemical performance of Li-Ti-niobate in the voltage ranges (1-3) V and (0.2-2.75) V. The specific capacity of Li-Ti-niobate has been increased by downsizing the particles followed by carbon coating (cd-Li-Ti-niobate) in the voltage range (0.2-2.75) V. In Chapter 2 we investigated the electrochemical properties of Li-Ti-niobate as an anode material for Li-ion battery. In Chapter 3 we probed the ion diffusion inside the material, an important physical property that determines the possibility of battery operation at higher current densities. Layered Li-Ti-niobate shows pesudo-1-D Li+ ion diffusion, with ion transport taking place mainly along the crystallographic b-direction. Presence of line defects along crystallographic b-direction assists the diffusion to be pesudo-1-D in nature. Removal of line defects via sintering followed by studies on electrochemical properties suggests that presence of high density dislocation defects is crucial for superior rate performance of Li-Ti-niobate. Scheme 2: Preferential direction of ion diffusion in Li-Ti-niobate In the previous Chapters, the lithium ion intercalation behavior and its diffusion properties into titanium niobate layers have been investigated in detail. In Chapter 4, the same layered geometry has been explored to tackle the drastic volume expansion problem typically associated with anodes storing energy via the alloying method. Unique flexible non-carbonaceous layered host viz. M-Ti-niobate (Ti: Titanium; M: Al3+, Pb2+, Sb3+, Ba2+, Mg2+) has been designed which can synergistically store both lithium-ions and sodium-ions via simultaneous intercalation and alloying mechanisms. M-Ti-niobate is formed by ion-exchange of the K-ions, which are specifically located in the galleries between the layers formed by edge and corner sharing TiO6 and NbO6 octahedral units in the sol-gel synthesized potassium titanium niobate (KTiNbO5). The detrimental issues such as drastic volume changes (approximately 300-400%) typically associated with alloying mechanism of storage are completely tackled chemically viz. by the unique chemical composition and structure of the M-Ti-niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the drastic volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50-75% of total K-ions) in the M-Ti-niobate, efficient alloying reaction takes place directly with the ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M-Ti-niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li+ and Na+ ion cyclability (> 2 Li+/Na+ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms demonstrated by the experiments is studied within the framework of density functional theory (DFT). DFT expectedly shows a very small variation in the volume of Al-titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively endorse the occurrence of the alloying process of Li-ions with the Al-ions along with the intercalation process during discharge. The M-Ti-niobates studied here demonstrates a paradigm shift in chemical design of electrodes and will pave the way for development of multitude of improved electrodes for different battery chemistries Scheme 3: Scheme depicts the synergistic approach of charge storage in M-Ti-niobate anodes for alkali-ion rechargeable batteries. Colour changes in the layers indicate that the layers are electrochemically active. Chapter 5 mainly focuses on a fully Li-alloy based anode such as SnSb for prospective application in rechargeable Li-ion batteries. The Sn-content variation in SnSb nanoparticles confined inside electrically conducting carbon nanofiber is observed to significantly influence the electrochemical performance. It is a major challenge to minimize the detrimental effects arising as a result of drastic volume changes (≈ few hundred times) occurring during repeated alloying-dealloying of lithium with Group IV elements e.g. tin (Sn). An important design strategy is to have Sn as a component in a binary compound. SnSb, is an important example where the antimony (Sb) itself is redox active at a potential higher than that of Sn. The ability of Sb to alloy with Li reduces the Li uptake amount of Sn in SnSb compared to bare Sn. Thus, the volume changes of Sn in SnSb will expectedly be much lower compared to bare Sn leading to greater mechanical stability and cyclability. As revealed recently, complete reformation of SnSb (for molar ratio Sn:Sb= 1:1) during charging is not achieved due to loss of some fraction of Sn. Thus, molar concentration of Sn and Sb in SnSb is also absolutely important for the optimization of battery performance. We discuss here SnSb with varying compositions of Sn encapsulated inside an electrospun carbon-nanofiber (abbreviated as CF). The carbon-nanofiber matrix not only provides electron transport pathways for the redox process but also provides ample space to accommodate the drastic volume changes occurring during successive charge and discharge cycles. The systematic changes in the chemical composition of SnSb minimize the instabilities in the SnSb structure as well as replenish any loss in Sn during repeated cycling. The composition plays a very crucial role as magnitude of specific capacities and cyclability of SnSb is observed to depend on the variable percentage of Sn. SnSb-75-25-CF, which contains excess Sn, exhibits the highest specific capacity of 550 mAh g-1 after 100 cycles in a comparison with pure SnSb (1:1) anode material at current density (0.2 A/g) and shows excellent rate capability over widely varying current densities (0.2-5 A g-1). Scheme 4: Schematic depiction of lithiation and delithiation mechanism in SnSb. Bar diagram of specific capacity versus percentage of Sn present in SnSb-series of compounds. Percentage of Sn present is 0 %, 25%, 50%, 75% and 100% in Sb-CF, SnSb-25-75-CF, SnSb-50-50-CF, SnSb-75-25-CF and Sn-CF respectively. In Chapter 6 we discuss a binary mixture of two non-carbon coated electroactive compounds viz. anatase-titanium dioxide (TiO2) and vanadium pentoxide (V2O5) as a potential electrode for Li-based batteries. The binary mixture, whose components are synthesized using sol-gel methods and not carbon coated, can be reversibly cycled in the potential range (1.0-3.5) V against Li-metal. The physical mixture of the as-synthesized TiO2 and V2O5 (w/w = 1:1) provides a high specific capacity (≈ 190 mAh g-1 after 100 cycles at 100 mA g-1) and higher compared to the bare anatase-TiO2 and V2O5. Thus, this simple strategy enhances the operational potential of anatase-TiO2 by 0.5 V to 3.5 V against lithium and also nullifies greatly the complexities of carbon electronic wiring of electroactive particles. A Li-ion cell, comprising of the non-carbon coated binary mixture as anode and lithium manganese oxide (LiMn2O4) as the cathode, cycled in the potential range (0.2-3.5) V delivers a high specific capacity of nearly 80 mAh g-1 at 100 mA g-1 and is higher compared to the full cell capacities using the individual components as anodes. No signatures of SEI formation is observed from the cyclic voltammetry results. The presence of a second electroactive material may strongly suppress the SEI formation typically observed for Ti-oxide based materials when cycled to such a low potential (≈ 0.2 V). This may also account for the high percentage of reversibility and specific capacity of the full cell in this wide potential range. This simple approach enables the possibility of using Ti-oxide based anodes against the commercial intercalation cathodes without any compromise in the cell performance and also reduces the need for design of novel high voltage cathode materials. Scheme 5: Scheme shows a design strategy for improvement in specific capacity as a result of presence of an additional redox active species in the Li-ion configuration.