<p>The formation of surface films on electrodes in contact with non-aqueous electrolytes in lithium-ion batteries has a vital impact on battery performance. A basic understanding of such films is essential to the development of next-generation power sources. The surface chemistry, morphology and thermal stability of two typical anode and cathode materials, graphite and LiNi_0.8Co_0.2O₂, have here been evaluated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, and placed in relation to the electrochemical performance of the electrodes. </p><p>Chemical and morphological information on electrochemically formed graphite surface films has been obtained accurately by combining XPS measurements with Ar⁺ ion etching. An improved picture of the spatial organisation, including thickness determination of the surface film and characterisation of individual component species, has been established by a novel sputtering calibration procedure. The stability of the surface films has been shown to depend strongly on temperature and choice of lithium salt. Decomposition products from elevated-temperature storage in different electrolyte systems were identified and coupled to effects such as capacity loss and increase in electrode resistance. Different decomposition mechanisms are proposed for surface films formed in electrolytes containing LiBF₄, LiPF₆, LiN(SO₂CF₃)₂ and LiCF₃SO₃ salts.</p><p>Surface film formation due to electrolyte decomposition has been confirmed on LiNi_0.8Co_0.2O₂ positive electrodes. An overall surface-layer increase with temperature has been identified and provides an explanation for the impedance increase the material experiences on elevated-temperature storage. </p><p>Surface phenomena are clearly major factors to consider in selecting materials for practical Li-ion batteries.</p>

The formation of surface films on electrodes in contact with non-aqueous electrolytes in lithium-ion batteries has a vital impact on battery performance. A basic understanding of such films is essential to the development of next-generation power sources. The surface chemistry, morphology and thermal stability of two typical anode and cathode materials, graphite and LiNi0.8Co0.2O2, have here been evaluated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, and placed in relation to the electrochemical performance of the electrodes. Chemical and morphological information on electrochemically formed graphite surface films has been obtained accurately by combining XPS measurements with Ar+ ion etching. An improved picture of the spatial organisation, including thickness determination of the surface film and characterisation of individual component species, has been established by a novel sputtering calibration procedure. The stability of the surface films has been shown to depend strongly on temperature and choice of lithium salt. Decomposition products from elevated-temperature storage in different electrolyte systems were identified and coupled to effects such as capacity loss and increase in electrode resistance. Different decomposition mechanisms are proposed for surface films formed in electrolytes containing LiBF4, LiPF6, LiN(SO2CF3)2 and LiCF3SO3 salts. Surface film formation due to electrolyte decomposition has been confirmed on LiNi0.8Co0.2O2 positive electrodes. An overall surface-layer increase with temperature has been identified and provides an explanation for the impedance increase the material experiences on elevated-temperature storage. Surface phenomena are clearly major factors to consider in selecting materials for practical Li-ion batteries.

Demands for high energy-density batteries have sharpened with the increased use of portable electronic devices, as has the focus global warming is now placing on the need for electric and electric-hybrid vehicles. Li-ion battery technology is superior to other rechargeable battery technologies in both energy- and power-density. A remaining challenge, however, is to find an alternative candidate to graphite as the commercial anode. Several metals can store more lithium than graphite, e.g., Al, Sn, Si and Sb. The main problem is the large volume changes that these metals undergo during the lithiation process, leading to degradation and pulverization of the anode with resulting limitations in cycle-life. The Li-ion battery is studied in this thesis with the goal of better understanding the critical parameters determining high and stable electrochemical performance when using a metal or a metal-alloy anode. Various antimony-containing systems will be presented. These represent different routes to circumvent the problems caused by volume change. Sb-compounds exhibit a high lithium storage capability. At most, three Li-ions can be stored per Sb atom, leading to a theoretical gravimetric capacity of 660 mAh/g. Model systems with stepwise increasing complexity have been designed to better understand the factors influencing lithium insertion/extraction. It is demonstrated that the microstructure of the anode material is crucial to stable cycling performance and high reversibility. The relative importance of the various factors controlling stability, such as particle-size, oxide content and morphology, varies strongly with the type of system studied. The cycling performance of pure Sb is improved dramatically by incorporating a second component, Sb2O3. With a critical oxide concentration of ~25%, a stable capacity close to the theoretical value of 770 mAh/g is obtained for over 50 cycles. Cu2Sb shows stable cycling performance in the absence of oxide. Cu9Sb2 has been presented for the first time as an anode material in a Li-ion battery context. Studies of the Solid Electrolyte Interphase (SEI) formed on AlSb composite electrodes show an SEI layer thinner than graphite, and with a clearly dynamic character.

This research proposes a method for estimating the residual capacity of Li-ion batteries. The charging and discharging characteristics of Li-ion batteries are investigated and analyzed by a battery test system. The measurement of the initial capacity is based on the improved open-circuit voltage measurement, which compensates the effects of battery aging and self-discharging. The measurement of the used capacity is based on the improved coulomb counting measurement, which compensates the effects of output current and environmental temperature. The designed system provides various functions for battery charging and discharging, battery voltage measuring and recording, battery capacity estimation and calculation, and the log files can be used for further battery characteristics analysis.

Environmental and economic reasons have lead automotive companies towards the direction of EVs and HEVs. Stricter emission legislations along with the consumer needs for more cost-efficient and environmental friendly vehicles have increased immensely the amount of hybrid and electric vehicles available in the market. It is essential though for Li-ion batteries, the main propulsion force of EVs and HEVs, to be able to read the battery characteristics in a high accuracy manner, predict life expectancy and behaviour and act accordingly. The following thesis constitutes a concept study of a battery diagnostics method. The method is based on the notion of a pseudo-random binary signal used as the current input and from its voltage response, the impedance is used for the estimation of parameters such as the state of charge and more. The feasibility of the PRBS method at a battery cell has been examined through various tests, both in an experimental manner at the lab but also in a simulation manner. The method is compared for validation against the electrochemical impedance spectroscopy method which is being used as a reference. For both the experimental and the simulation examinations, the PRBS method has been validated and proven to work. No matter the change in the parameters of the system, the method behaves in a similar manner as in the reference EIS method. The level of detail in the research and the performed experiments is what makes the significance of the results of high importance. The method in all ways has been proven to work in the concept study and based on the findings, if implemented on an EV’s or HEV’s electric drive line and the same functionality is observed, be used as a diagnostics method of the battery of the vehicle.

The improvement of volumetric energy density remains a key area of research to opti-mize Li-ion batteries for applications such as extending the range of electric vehicles. There is still improvement to be made in the energy density in the positive elec-trode materials. The current thesis deals with determining the phase diagrams of the Li-Mn-Ni-O and Li-Co-Mn-O systems in order to better understand the structures and the electrochemistry of these materials. The phase diagrams were made through careful analysis of hundreds of X-ray di raction patterns taken of milligram-scale combinatorial samples. A number of bulk samples were also investigated. The Li-Mn-Ni-O system is of particular interest as avoiding cobalt lowers the cost of the material. However, this system is very complex: there are two large solid-solution regions separated by three two-phase regions as well as two three-phase regions. Comparing quenched and slow cooled samples shows that the system trans-form dramatically when cooled at rates typically used to make commercial materials. The consequences of these results are that much of the system must be avoided in order to guarantee that the materials remain single phase during cooling. This work should therefore impact signi cantly researchers working on composite electrodes. Two new structures were found. The first was Li-Ni-Mn oxide rocksalt structures with vacancies and ordering of manganese which were previously mistakenly identi ed as LixNi2xO2. The other new structure was a layered oxide with metal site vacancies allowing manganese to order on two superlattices. The electrochemistry of both these materials is presented here. Finally, the region where layered-layered composites form during cooling has been determined. These materials were long looked for along the composition line from Li2MnO3 to LiNi0.5Mn0.5O2 and the most significant consequence of the actual locations of the end-members is that one of the structures contains a high concentration of nickel on the lithium layer. Layered-layered nano-composites formed in this system are therefore not ideal positive electrode materials and it will be demonstrated that single-phase layered materials lead to better electrochemistry.

Les batteries lithium-ion sont présentes dans de nombreuses applications portables ou embarquées car leurs énergies massique et volumique et leur cyclabilité les placent en tête des autres technologies de stockage. Cependant, elles ne résistent pas aux fonctionnements abusifs et peuvent subir des emballements thermiques avec risque d’explosion. Par ailleurs, l’état des composants internes évoluant au cours du vieillissement de la batterie, son comportement en sécurité doit être considéré pour n'importe quel état de santé afin de mieux concevoir la gestion thermique des cellules et du pack batterie. Dans ce contexte, il est donc primordial de comprendre les mécanismes de dégradation de l’ensemble des composants internes d’un élément (matériaux d'électrodes, collecteurs, séparateur et électrolyte) lors d’un vieillissement en fonctionnement normal et le déroulement des évènements en conditions abusives pouvant aboutir à un scénario accidentel.Le séparateur doit alors être considéré comme le premier dispositif de sécurité intrinsèque car il assure la séparation physique entre l’électrode positive et négative. Il doit alors être étudié sur le plan de ses propriétés électrochimiques, mécaniques et thermiques. Pour cela, une méthodologie de caractérisation a été développée, mettant en œuvre un large panel de techniques de caractérisation physique et chimique, et appliquée sur des séparateurs issus de vieillissements en conditions normales et après surcharge. Différentes méthodes de lavage ont permis de discréditer l’évolution morphologique et électrochimique du polymère poreux sans l’interaction des résidus solides associées aux produits de dégradation de l’électrolyte. Ainsi, la porosité et la tortuosité de la matrice polymère, associées à la conductivité ionique du système séparateur/électrolyte, ont été pleinement étudiées.Il a pu être montré que, en accord avec la croissance de la SEI sur l’électrode négative graphite, sa porosité de surface se dégrade avec un encrassement des pores par accumulation de composés solides de la SEI. Aucune conséquence sur les propriétés mécaniques n’a été observée, mais les performances électrochimiques en puissance se dégradent fortement. Une évaluation face aux risques de court-circuit interne par percée dendritique a permis de montrer que la formation de dendrite est favorisée. Le séparateur en tant qu’organe de sécurité face aux risques mécaniques garde donc son efficacité tout au long de la vie de la batterie lithium-ion mais le risque de court-circuit est plus élevé. / Lithium-ion batteries have undeniable assets to meet several of the requirements for embedded applications. They provide high energy density and long cycle life. Nevertheless, they can face irreversible damage during their lives which could cause safety issues like the thermal runaway of the battery and its explosion. It is then essential to understand the degradation mechanisms of all the internal components of an accumulator (i.e. electrode materials, collectors, separator and electrolyte) and the progress of events in abusive conditions that can lead to an accident scenario. The aim of this thesis is to work on the security aspects of Lithium-ion batteries in order to understand these degradation mechanisms and to help to prevent future incidents.Even if the degradation mechanisms of all the internal components are studied in this work, a special attention is given to the separator. This component is indeed one of the most important safety devices of a battery and have to be electrochemically, mechanically and thermally characterized after ageing. Different washing methods have been study in order to characterize the separator without any degradation product of the electrolyte which could interfere. Porosity and tortuosity associated with the ionic conductivity of the separator have been tested.The results show that even if the separator is electrochemically inactive, its porosity can decrease because of the degradation of the negative graphite electrode. Indeed, SEI components obstruct the surface porosity of the separator. This porosity change do not cause any mechanical degradation but decrease separator performances at high current rate and promote lithium dendrite growth.

Ce travail de thèse, débuté en 2015, a pour but de développer et d'étudier les propriétés de nouveaux liants polymères pour batteries Li-ion. Les synthèses organiques ainsi que leurs caractérisations associées et les tests électrochimiques ont été réalisées à Delft. Puis, des études de spectroscopie photo-électronique par rayons X (XPS) ont été réalisées à Pau pour déterminer et comprendre la réactivité de certain de ces nouveaux matériaux vis-à-vis du lithium. / This PhD work started in 2015, aimed to develop and investigate the properties of new polymers as binders for Li-ion batteries. Organic syntheses with associated characterizations and electrochemical tests were performed in Delft. Then, X-ray photoelectron spectroscopy studies were performed in Pau, to determine and understand the reactivity of some of these new materials toward lithium ions in coin cells.

The recent discovery of layered transition metal carbides (MXenes) is one of the most important developments in two-dimensional (2D) materials. Preliminary theoretical and experimental studies suggest a wide range of potential applications for MXenes. The MXenes are prepared by chemically etching ‘A’-layer element from layered ternary metal carbides, nitrides and carbonitrides (MAX phases) through aqueous acid treatment, which results in various surface terminations such as hydroxyl, oxygen or fluorine. It has been found that surface terminations play a critical role in defining MXene properties and affects MXene performance in different applications such as electrochemical energy storage, electromagnetic interference shielding, water purification, sensors and catalysis. Also, the electronic, thermoelectric, structural, plasmonic and optical properties of MXenes largely depend upon surface terminations. Thus, controlling the surface chemistry if MXenes can be an efficient way to improve their properties. This research mainly aims to perform surface modifications of two commonly studied MXenes; Ti2C and Ti3C2, via chemical, thermal or physical processes to enhance electrochemical energy storage properties. The as-prepared and surface modified MXenes have been studied as electrode materials in Li-ion batteries (LIBs) and supercapacitors (SCs). In pursuit of desirable MXene surface, we have developed an in-situ room temperature oxidation process, which resulted in TiO2/MXene nanocomposite and enhanced Li-ion storage. The idea of making metal oxide and MXene nanocomposites was taken to the next level by combining a high capacity anode materials – SnO2 – and MXene. By taking advantage of already existing surface functional groups (–OH), we have developed a composite of SnO2/MXene by atomic layer deposition (ALD) which showed enhanced capacity and excellent cyclic stability. Thermal annealing of MXene at elevated temperature under different atmospheres was carried out and detailed surface chemistry was studied to analyze the change in surface functional groups and its effect on electrochemical performance. Also, we could replace surface functional groups with desirable heteroatoms (e.g., nitrogen) by plasma processing and studied their effect on energy storage properties. This work provides an experimental baseline for surface modification of MXene and helps to understand the role of various surface functional groups in MXene electrode electrochemical performance.

Rechargeable lithium-ion batteries are a staple of modern society, providing power to a significant portion of the world's electronics and rapidly replacing older power sources. The advent of widely available electric cars with batteries of up to 200 kWh, with an increasing emphasis on fast charging, has only increased their importance. Lithium-ion battery electronic and ionic properties are largely determined by the microstructure of the battery electrode film and can be heavily influenced by relatively small variations in film makeup, including the formation of voids or distribution of carbon and binder. Prior to this research, electrical properties, which are some of the most important characteristics to battery cost, performance, and safety, were either difficult or, in the case of contact resistance, impossible to directly measure. This dissertation focuses on the development and use of a micro-surface probe for measurement and mapping of lithium-ion battery film electronic characteristics. The measurement apparatus, inversion and mapping routines, and experimental data presented provide manufacturers and researchers with a better understanding of battery heterogeneity and the influence of microstructure on electrical properties. The micro-surface probe was used to map spatial variation on both a macro and micro scale; compare physical, electrical, and ionic properties; and validate tests that were previously used to estimate electronic parameters. Experiments on commercial-quality battery electrode films showed higher micro-heterogeneity than was previously assumed by a significant margin. Additionally, electronic and ionic properties were shown to not always be inversely related and some physical explanations for observed variation were explored. Macro-variations were measured and shown to exist across electrode films which were previously assumed to be uniform. Finally a comparison to the mechanical peel test, a common test used in industry as a proxy measurement of electrical contact resistance, proved the peel test to be inconclusive and showed that it will not always accurately reflect electrical properties of films. Direct measurements of both electrical conductivity and contact resistance provide a new and important tool to advance understanding and development of lithium-ion batteries. The magnitude of the measured resistivities and their significant variation demonstrates that a better understanding of film properties is needed and will significantly influence our understanding of modern battery parameters and the effects of manufacturing techniques on battery performance.