Silicon has emerged as a promising alternative to traditional graphite as an anode material in battery technology, primarily due to its high theoretical capacity and abundance. However, its application is hindered by significant challenges, including severe volume expansion in the active material (~275%) during cycling, which can lead to a series of electrode failure issues. Polymer binder plays an essential role in addressing these challenges as it accommodates silicon's volume expansion and the rearrangement of particles. This work conducted an analysis of how different binders influence mechanical and electrochemical properties of silicon electrodes. Our findings are supported by a series of experiments, aimed at addressing the challenge of silicon volume expansion and improving the durability and efficiency of silicon-based anodes. Water-soluble polyacrylic acid (PAA) has emerged as a promising binder material for silicon anodes, with lithium hydroxide (LiOH) frequently added to improve the rheological properties of the slurry. However, literature presents varying results regarding the electrochemical performance of batteries incorporating LiOH in PAA binders. In addressing these discrepancies, our research investigates the role of LiOH in PAA, defining its impact through two primary factors: lithium-ion concentration and pH level. Our analysis involved conducting cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests, which confirmed our hypothesis that the addition of Li+ ions improves ion transport. Regarding pH, an optimal middle-ground pH level is identified, balancing the advantages shown at both lower and higher pH ranges. Despite the observed benefits of water-soluble PAA binder, such binders frequently result in uneven carbon distribution in coating, attributed to the poor wettability of nano-carbon in water. Consequently, the next portion of this work revisits the use of a traditional NMP (N-Methyl-2-pyrrolidone) soluble binder, PVDF (polyvinylidene fluoride), known for its widespread application in battery technology. However, PVDF-based silicon anodes often exhibit poor cycling performance. To address this issue and enhance the binder's flexibility, we attempted to chemically modify PVDF by incorporating carboxylic acid (-COOH) groups and reducing the polymer chain length. Despite these efforts, the experimental results did not show an improvement in cycling performance. The findings suggest that the deteriorated performance may be due to a weakened adhesion to the current collector for short-chain polymers. We then explore additional binder systems in an attempt to improve Si electrode performance. Our previous research suggests a trade-off between flexibility and adhesion in shortened polymers. To further verify this, we investigate the effect of two commercially available short-chain polymer binders, namely Jeffamine D-2000 and PAA(2000). Next, in order to mitigate the adverse effects of short polymer chain lengths on mechanical performance, we adopt an adhesion layer between the bulk electrode layer and the current collector. Finally, we evaluate several binders known for their promising results in other battery systems, including polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyimide (PI). A series of mechanical and electrochemical characteristics of the as-mentioned binders are investigated. The findings confirm that shorter polymer chain length leads to a weaker adhesion between the electrode coating and the current collector. Additionally, we discovered that introducing an adhesion layer can enhance the cycling stability of silicon anodes.

Recent experiments revealed micrometer (µm)-sized Selenium (Se)-doped Germanium (Ge) particles forming a network of inactive phase (Li-Ge-Se) bring superior performance in cycling stability and capacity over un-doped Ge particles. Therefore, based on two states of Li (one for diffusion and another for alloyed reaction), a phaseield model (PFM) is developed incorporating both chemical reaction and Li diffusion to investigate remaining elusive underpinning mechanism. The reaction-diffusion PFM enables us to directly determine the conditions under which the lithiation process is diffusion- and/or reaction-controlled. Moreover, coupling the elasto-plastic deformation, the model allows us to investigate the role of the inactive phase in morphology and stress variation of Se-doped Ge electrode upon lithiation. The numerical results reveal that the tensile hoop stress at the surface of the particles is significantly suppressed due to softness of the inactive Li-Ge-Se phase, in line with the experimental observation of surface fractureree behavior. Further, we find that the soft Li-Ge-Se phase reduces a compressive mean stress at the reaction front, thus alleviating the stress retardation effect on the lithiation kinetics. And, the high Li diffusivity of the amorphous Li-Ge-Se network provides an effective Li diffusion path for inter-particle diffusion, reducing stress difference between the surfaces of neighboring particles. Besides, the constraint between the adjacent particles induces a higher compressive stress at the reaction front impeding the mobile Li insertion during lithiation. Though small c-Ge nano-particle in the Ge0.9Se0.1 microparticle is lithiated faster than large one, the compressive stress is generated at the center of small one for stress equilibrium which causes more retardation effect. Meanwhile, the size difference between adjacent particles increases the principle and shear stresses in the inactive Li-Ge-Se network near adjacent surfaces, which could potentially lead to mechanical failure and debonding of the amorphous network. We believe that the results of this investigation can shed some light on the optimization design of electrodes.

No description available.

Ce mémoire est consacré à l'étude de deux matériaux d'électrodes négatives pour batteries Li-ion : NiSb2 et TiSnSb. Ces matériaux de conversion possèdent des capacités presque deux fois supérieures à celle du graphite, actuellement utilisé, mais ils souffrent i) d'une faible cyclabilité causée par les variations volumiques caractéristiques de ce type d'électrode et ii) d'une grande perte de lithium irréversible lors de la 1ère insertion due à la réactivité de surface avec l'électrolyte. Les mécanismes réactionnels avec le lithium ont été étudiés en profondeur par diffraction des rayons X, spectrométrie Mössbauer (119Sn et 121Sb). Les études in situ et ex situ en spectroscopie d'absorption X ont permis d'identifier la formation de nanoparticules de métal de transition très réactives et dont l'instabilité est probablement à l'origine des phénomènes de relaxation observés dans l'électrode à l'état déchargé. L'amélioration des performances a été réalisée grâce à l'élaboration d'électrodes composites contenant des fibres de carbone et de la CMC. Cette formulation d'électrodes permet d'atteindre une cyclabilité de 250 cycles pour TiSnSb à régimes variables entre 4C et C. L'ajout de FEC dans l'électrolyte apparait également comme une solution pour augmenter la durée de vie des électrodes.L'interface électrode/électrolyte a été analysée par Résonance Magnétique Nucléaire, Spectroscopie Photoéletronique à rayonnement X et spectroscopie infrarouge. Li2CO3 est l'espèce majoritairement formée lors de la réduction de l'électrolyte en 1ère décharge (lié à la création de nouvelles surfaces lors de la réaction et à expansion volumique). Lors de la charge, une restructuration (ou fragmentation) de la SEI (couche de passivation) est probable à cause de la contraction de l'électrode. L'épaisseur de la couche de SEI à l'interface continue de croitre après 15 cycles. / The thesis is devoted to the study of two negative electrode materials for Li-ion batteries: NiSb2 and TiSnSb. These conversion type materials have high capacities greater than graphite electrode used in current devices. However, these compounds suffer from i) a low cyclability caused by volumetric variations which are characteristic of this type of electrode, and ii) a loss of lithium (irreversible process) during the 1st insertion due to the reduction of the liquid electrolyte on the surface of active material.The mechanisms have been studied by X-Ray Diffraction, Mössbauer Spectroscopy (119Sn and 121Sb). The in situ and ex situ X-ray Absorption Spectroscopy analysis have allowed identifying both the formation of highly reactive Ti and Ni nanoparticles and a relaxation effect in the discharged electrode at 0V. The improvement of performances is based on the composite electrodes formulation using carbon fibers as conductive additive and Carboxymethyl cellulose CMC as binder. A cyclability of 250 cycles at C and 4C rate is reached for TiSnSb electrodes. The addition of Fluoro Ethylene Carbonate (FEC) in the electrolyte is another way to increase the life span of electrodes.The electrode/electrolyte interface has been analyzed by Nuclear Magnetic Resonance, X-ray Photoelectron Spectroscopy and Infrared Spectroscopy. During the discharge, among the species produced from the reduction of electrolyte Li2CO3 is in the majority because new surfaces are created (volumetric expansion). On charge, a fragmentation of the Solid Electrolyte Interphase (SEI) deposited on the surface of the active material grains is observed. Moreover, first XPS investigations have shown that the SEI thickness continuously increases on cycling.

The Lithium-ion (Li-ion) battery is one of the major topics currently studied as a potential way to help in reducing greenhouse gas emissions. Major car manufacturers are interested in adapting the Li-ion battery in the power trains of Plug-in Hybrid Electric Vehicles (PHEV) to improve fuel efficiency. Materials currently used for Li-ion batteries are LiCoO2 (LCO) and graphite—the first materials successfully integrated by Sony into Li-ion batteries. However, due to the high cost and polluting effect of cobalt (Co), and the low volumetric capacity of graphite, new materials are being sought out. LiFePO4 (LFP) and SnO2 are both good alternatives for the cathode and anode materials in Li-ion batteries. But, to create high-performance batteries, nano-sized carbon-coated particles of LFP and SnO2 are required. The present work attempts to develop a new synthesis method for these materials: organic template-assisted synthesis for three-dimensionally ordered macroporous (3DOM) LFP and porous SnO2. With the newly developed synthesis, highly pure materials were successfully synthesized and tested in Li-ion batteries. The obtained capacity for LFP was 158m Ah/g, which is equivalent to 93% of the theoretical capacity. The obtained capacity for SnO2 was 700 mAh/g, which is equivalent to 90% of the theoretical capacity. Moreover, Hybrid Pulse Power Characterization (HPPC) was used to test LFP and LCO for comparison and feasibility in PHEVs. HPPC is generally used to test the feasibility and capacity fade for PHEVs. It simulates battery use in various driving conditions of PHEVs to study pulse energy consumption and regeneration. In this case, HPPC was conducted on a half-cell battery for the first time to study the phenomena on a single active material, LFP or LCO. Based on the HPPC results, LFP proved to be more practical for use in PHEVs.

The Lithium-ion (Li-ion) battery is one of the major topics currently studied as a potential way to help in reducing greenhouse gas emissions. Major car manufacturers are interested in adapting the Li-ion battery in the power trains of Plug-in Hybrid Electric Vehicles (PHEV) to improve fuel efficiency. Materials currently used for Li-ion batteries are LiCoO2 (LCO) and graphite—the first materials successfully integrated by Sony into Li-ion batteries. However, due to the high cost and polluting effect of cobalt (Co), and the low volumetric capacity of graphite, new materials are being sought out. LiFePO4 (LFP) and SnO2 are both good alternatives for the cathode and anode materials in Li-ion batteries. But, to create high-performance batteries, nano-sized carbon-coated particles of LFP and SnO2 are required. The present work attempts to develop a new synthesis method for these materials: organic template-assisted synthesis for three-dimensionally ordered macroporous (3DOM) LFP and porous SnO2. With the newly developed synthesis, highly pure materials were successfully synthesized and tested in Li-ion batteries. The obtained capacity for LFP was 158m Ah/g, which is equivalent to 93% of the theoretical capacity. The obtained capacity for SnO2 was 700 mAh/g, which is equivalent to 90% of the theoretical capacity. Moreover, Hybrid Pulse Power Characterization (HPPC) was used to test LFP and LCO for comparison and feasibility in PHEVs. HPPC is generally used to test the feasibility and capacity fade for PHEVs. It simulates battery use in various driving conditions of PHEVs to study pulse energy consumption and regeneration. In this case, HPPC was conducted on a half-cell battery for the first time to study the phenomena on a single active material, LFP or LCO. Based on the HPPC results, LFP proved to be more practical for use in PHEVs.

In this thesis, a number of clean-energy materials for hydrogen generation, hydrogen storage, and Li-ion battery energy storage applications have been investigated through state-of-the-art density functional theory. As an alternative fuel, hydrogen has been regarded as one of the promising clean energies with the advantage of abundance (generated through water splitting) and pollution-free emission if used in fuel cell systems. However, some key problems such as finding efficient ways to produce and store hydrogen have been hindering the realization of the hydrogen economy. Here from the scientific perspective, various materials including the nanostructures and the bulk hydrides have been examined in terms of their crystal and electronic structures, energetics, and different properties for hydrogen generation or hydrogen storage applications. In the study of chemisorbed graphene-based nanostructures, the N, O-N and N-N decorated ones are designed to work as promising electron mediators in Z-scheme photocatalytic hydrogen production. Graphene nanofibres (especially the helical type) are found to be good catalysts for hydrogen desorption from NaAlH4. The milestone nanomaterial, C60, is found to be able to significantly improve the hydrogen release from the (LiH+NH3) mixture. In addition, the energetics analysis of hydrazine borane and its derivative solid have revealed the underlying reasons for their excellent hydrogen storage properties.  As the other technical trend of replacing fossil fuels in electrical vehicles, the Li-ion battery technology for energy storage depends greatly on the development of electrode materials. In this thesis, the pure NiTiH and its various metal-doped hydrides have been studied as Li-ion battery anode materials. The Li-doped NiTiH is found to be the best candidate and the Fe, Mn, or Cr-doped material follows. / <p>QC 20130925</p>

The Lithium-ion (Li-ion) battery is one of the major topics currently studied as a potential way to help in reducing greenhouse gas emissions. Major car manufacturers are interested in adapting the Li-ion battery in the power trains of Plug-in Hybrid Electric Vehicles (PHEV) to improve fuel efficiency. Materials currently used for Li-ion batteries are LiCoO2 (LCO) and graphite—the first materials successfully integrated by Sony into Li-ion batteries. However, due to the high cost and polluting effect of cobalt (Co), and the low volumetric capacity of graphite, new materials are being sought out. LiFePO4 (LFP) and SnO2 are both good alternatives for the cathode and anode materials in Li-ion batteries. But, to create high-performance batteries, nano-sized carbon-coated particles of LFP and SnO2 are required. The present work attempts to develop a new synthesis method for these materials: organic template-assisted synthesis for three-dimensionally ordered macroporous (3DOM) LFP and porous SnO2. With the newly developed synthesis, highly pure materials were successfully synthesized and tested in Li-ion batteries. The obtained capacity for LFP was 158m Ah/g, which is equivalent to 93% of the theoretical capacity. The obtained capacity for SnO2 was 700 mAh/g, which is equivalent to 90% of the theoretical capacity. Moreover, Hybrid Pulse Power Characterization (HPPC) was used to test LFP and LCO for comparison and feasibility in PHEVs. HPPC is generally used to test the feasibility and capacity fade for PHEVs. It simulates battery use in various driving conditions of PHEVs to study pulse energy consumption and regeneration. In this case, HPPC was conducted on a half-cell battery for the first time to study the phenomena on a single active material, LFP or LCO. Based on the HPPC results, LFP proved to be more practical for use in PHEVs.

NMR spectroscopy of paramagnetic solids provides detailed information about the local configuration and the chemical environment of the NMR observed center, as well as about the structural, magnetic and electronic properties of the coordianted paramagnetic centres. In the case of complex paramagnetic solids such as cathode materials for (rechargeable) batteries, NMR represents an invaluable tool to provide insight into the structural and electronic properties of the systems, which are at the base of the electrochemical performance of these materials. However, the paramagnetism makes the interpretation of the NMR data very challenging. This is primarily due to the interactions of the unpaired electrons with the NMR observed nucleus, and the interpretation of the NMR spectra often requires the aid of reliable theoretical and computational methods. Often the dominant interaction contributing to the measured isotropic shifts is the hyperfine interaction between the unpaired electrons and the observed nucleus, which results from the transfer of unpaired electrons from the paramagnetic centre(s) to the NMR observed site. In systems such as the ones studied here, in which the paramagnetic ions are a major constituent of the lattice, the multitide of different local environments results in a complex distribution of resonances. As in the case of the Li$_x$V$_6$O$_{13}$ cathode material, a methodical investigation of the configurational stability from first principles gives insight into the preferred site configurations. The combination of experimental $^7$Li NMR spectra and hyperfine shift DFT calculations of the so-found stable Li environments allows to unravel the complex lithiation mechanism of this material. In the other case of the LiTi$_x$Mn$_{2-x}$O$_4$ cathode materials, the $^7$Li hyperfine shifts calculated from first principles for a variety of Li environments are combined in a lattice model which allows to assign the isotropic regions of the experimental $^7$Li NMR spectra, helping to resolve the complex cation ordering as a function of Mn/Ti content in the series. For paramagnetic centres with an unquenched orbital component of the electron magnetic moment(s), the spin-orbit coupling effects also contribute to the paramagnetic NMR shift and shift anisotropy. A first principles model is derived, which describes how spin-orbit coupling and the single-ion $g$-tensor are defined and calculated in periodic paramagnetic solids, and how they can be coupled with the hyperfine interaction to model their effects on the NMR spectrum. The method is applied to a series of olivine-type LiTMPO$_4$ cathode materials (with TM = Mn, Fe, Co, and Ni) and the respective $^7$Li and $^{31}$P NMR spectra are simulated and compared with the experiments. The other paramagnetic effect considered in this thesis involves the bulk magnetic susceptibility (BMS), which is particularly important for paramagnetic single crystals and solids of complex shape. The BMS effect results from the discontinuity of the bulk susceptibility at the surface of the crystal, inducing a demagnetizing field throughout the sample which changes the measured NMR shift and shift anisotropy. A method to analytically calculate the demagnetising field and the BMS shift in crystals of different shapes is derived, and it is applied to a series of LiFePO$_4$ single crystals for which the $^7$Li NMR spectra are also measured experimentally. The study confirms that, particularly for $^7$Li NMR, the macroscopic shape-dependent BMS shift can indeed be a significant contribution to the measured resonances, determining the large variation in shift measured for the crystals of different shapes.

The electrolyte is a crucial part of any lithium battery, strongly affecting longevity and safety. It has to survive rather severe conditions, not the least at the electrode/electrolyte interfaces. Current commercial electrolytes based on 1 M LiPF 6 in a mixture of organic solvents balance the requirements on conductivity and electrochemical stability, but they are volatile and degrade when operated at temperatures above ca. 70°C. The salt could potentially be replaced with e.g. LiTFSI, but corrosion of the aluminium current collector is an issue. Replacing the graphite negative electrode by Li metal for large gains in energy density challenges the electrolyte further by exposing it to freshly deposited Li, leading to poor coulombic efficiency (CE) and consumption of both Li and electrolyte. Highly concentrated electrolytes (up to &gt; 4 M) have emerged as a possible remedy, by a changed solvation structure such that all solvent molecules are coordinated to cations – leading to a lowered volatility and melting point, an increased charge carrier density and electrochemical stability, but a higher viscosity and a lower ionic conductivity. Here two approaches to highly concentrated electrolytes are evaluated. First, LiTFSI and acetonitrile electrolytes with respect to increased electrochemical stability and in particular the passivating solid electrolyte interphase (SEI) on the anode is studied using electrochemical techniques and X-ray photoelectron spectroscopy. Second, lowering the liquidus temperature by high salt concentration is utilized to create an electrolyte solely of LiTFSI and ethylene carbonate, tested for application in Li metal batteries by characterizing the morphology of plated Li using scanning electron microscopy and the CE by galvanostatic polarization. While the first approach shows dramatic improvements, the inherent weaknesses cannot be completely avoided, the second approach provides some promising cycling results for Li metal based cells. This points towards further investigations of the SEI, and possibly long-term safe cycling of Li metal anodes. / Elektrolyten är en fundamental del av ett litiumbatteri som starkt påverkar livslängden och säkerheten. Den måste utstå svåra förhållanden, inte minst vid gränsytan mot elektroderna. Dagens kommersiella elektrolyter är baserade på 1 M LiPF 6 i en blandning av organiska lösningsmedel. De balanserar kraven på elektrokemisk stabilitet och jonledningsförmåga, men de är lättflyktiga och bryts ned när de används vid temperaturer över ca. 70°C. Saltet skulle kunna bytas ut mot t.ex. LiTFSI, vilket ökar värmetåligheten avsevärt, men istället uppstår problem med korrosion på den strömsamlare av aluminium som används för katoden. Genom att byta ut grafitanoden i ett Li-jonbatteri mot en folie av litiummetall kan man öka energitätheten, men då litium pläteras bildas ständigt nya Li-ytor som kan reagera med elektrolyten. Detta leder till en låg coulombisk effektivitet genom nedbrytning av både Li och elektrolyt. Högkoncentrerade elektrolyter har en mycket hög saltkoncentration, ofta över 4 M, och har lags fram som en möjlig lösning på många av de problem som plågar denna och nästa generations batterier. Dessa elektrolyter har en annorlunda lösningsstruktur, sådan att alla lösningsmedelsmolekyler koordinerar till katjoner – vilket leder till att de blir mindre lättflyktiga, får en ökad täthet av laddningsbärare, och en ökad elektrokemisk stabilitet. Samtidigt får de en högre viskositet och lägre jonledningsförmåga. Här har två angreppssätt för högkoncentrerade elektrolyter utvärderats. I det första har acetonitril, som har begränsad elektrokemisk stabilitet och ett högt ångtryck, blandats med LiTFSI för en uppsättning av elektrolyter med varierande koncentration. Dessa har testats i Li-jonbatterier och i synnerhet den passiverande ytan på grafitelektroder har undersökts med både röntgen-fotoelektronspektroskopi (XPS) och elektrokemiska metoder. En markant förbättring av den elektrokemiska stabiliteten observeras, men de inneboende bristerna hos elektrolyten kan inte kompenseras fullständigt, vilket skapar tvivel på hur väl detta kan fungera i en kommersiell cell. Med det andra angreppssättet har hög saltkoncentration nyttjats för sänka smältpunkten för en elektrolyt baserad på etylenkarbonat, som annars inte kan används som enda lösningsmedel. Dessa elektrolyter har testats för användning i Limetall-batterier genom långtidstest, mätning av den coulombiska effektiviteten och analys av deponerade Li-ytor med svepelektronmikroskop. Resultaten är lovande, med över 250 cykler på 0.5 mAh/cm2 och en effektivitet på över 94%, men framförallt observeras en mycket jämnare deponerad Li-yta, vilket kan möjliggöra säker cykling av Li-metall-batterier. Ett logiskt nästa steg är studier av Liytan med t.ex. XPS för att utröna vad som skiljer den från ytan som bildats i en 1 M referenselektrolyt.