This thesis is interested in new materials for lithium – ion batteries. Two different samples were investigated, one intercalation and one conversion cathode material. The theoretical part is focused to the structure of cells, their advantages and disadvantages compared to other secondary batteries. Also other materials used in batteries are described. The practical part describes the preparation of cathode materials for subsequent testing by scanning elektron microscopy and thermogravimetric analysis. In conclusions two different materials were evaluated and compared with each other.

Die vorliegende Arbeit liefert einen Beitrag für ein besseres Verständnis über die zyklische Alterung von Siliciumnanopartikel (Si-NP) als Anodenmaterial in Lithium-Ionen- und Lithium-Schwefel-Batterien. Im Fokus der Studie stand der Einfluss der Partikelgröße, des Elektrodendesigns und der Elektrolytzusammensetzung auf die elektrochemische Reversibilität des Siliciums zur Lithiumspeicherung. Über umfangreiche strukturelle Charakterisierungstechniken mittels Röntgenbeugung, Elektronenmikroskopie und der Röntgenphotoelektronenspektroskopie in Verbindung mit elektrochemischen Untersuchungsmethoden, konnten wesentliche Mechanismen zur Degradation aufgeklärt und die Funktion diverser Oberflächenverbindungen auf der Siliciumanode identifiziert werden. Als Hauptursache der Degradation von Si-NP mit einer Partikelgröße unter 20 nm konnte das Wachstum der Solid-Electrolyte-Interface (SEI) identifiziert werden. Pulverisierung und die Bildung neuer kristalliner Phasen kann ausgeschlossen werden. Es wurde ein kostengünstiges und flexibles Verfahren zur Herstellung eines nanostrukturierten Silicium-Kohlenstoff-Komposites entwickelt, welches unter optimierten Bedingungen eine spezifische Kapazität von 1280 mAh/g(Elektrode) und einen Kapazitätserhalt von 81 % über 500 Tiefentladungszyklen liefert. Es konnten erfolgreich hoch reversible Flächenkapazitäten von 5 mAh/cm^2 bei nur 4,4 mg/cm^2 Elektrodengewicht nachgewiesen werden. Für die Arbeit wurde zunächst ein Verfahren zur Herstellung von monodispersen Si-NP mit einer Größe von 5 nm – 20 nm angewendet. Die galvanostatische Zyklierung gegen Lithiummetall hat ergeben, dass mit abnehmender Partikelgröße die Reversibilität des Siliciums zunimmt. Über in situ Synchrotron XRD und post mortem XPS konnte eine stabilere Solid-Electrolyte-Interface (SEI) mit abnehmender Partikelgröße als Hauptursache identifiziert werden. Im weiteren Verlauf der Arbeit wurden Si-NP im porösen Kohlenstoffgerüst durch ein leicht modifiziertes Herstellungsverfahren abgeschieden und untersucht. Durch das veränderte Elektrodendesign konnte die Reversibilität bei gleichem Kohlenstoffgehalt deutlich verbessert werden, da der Kontaktverlust des Siliciums zum leitfähigen Gerüst durch SEI Wachstum verzögert wird. Die Elektrolytadditive Fluoroethylencarbonat und Vinylencarbonat führen zu einer weiteren Verbesserung der Reversibilität, wobei Vinylencarbonat die höchste Reversibilität zur Folge hat, jedoch einen hohen Filmwiderstand verursacht. Weiterhin wurden etherbasierte Elektrolyte, welche typischerweise in Lithium-Schwefel-Batterien zum Einsatz kommen, untersucht. Hierbei wurde eine positive Wirkung von Lithiumnitrat auf die Reversibilität von Silicium festgestellt. Es konnten erfolgreich Si-Li-S (SLS) Vollzellen getestet werden, welche eine höhere Lebensdauer als vergleichbare Zellen mit Lithiummetall als Anode aufweisen. Aus den elektrochemischen und post mortem Untersuchungen konnte ein positiver Einfluss von Polysulfiden auf die SEI von Silicium nachgewiesen werden. Durch die umfangreichen post mortem Analysen konnte die Funktion diverser, in der SEI des Siliciums auftretender Verbindungen in Abhängigkeit der Elektrolytzusammensetzung aufgeklärt werden. Es wurde ein anschaulicher Mechanismus des SEI Wachstums in Abhängigkeit des Elektrolyts erstellt. / The results of this work provide a better understanding about the cyclic aging of silicon nanoparticles (Si-NP) as anode material in Lithium-ion- and Lithium-sulfur batteries. Subject of investigation was the influence of particle size, electrode design and electrolyte composition on the electrochemical reversibility of Si-NP for lithium storage. The main characterization techniques used in this study were XRD, SEM, TEM and XPS combined with electrochemical analysis and in situ synchrotron XRD. Bare silicon nanoparticles ranging from 5 – 20 nm and silicon nanoparticles embedded within a porous carbon scaffold were prepared through a cost-effective and novel synthesis technique including the hydrolysis of trichlorosilane as feedstock. The dominant degradation mechanism of these silicon nanoparticles was identified to be the continuous growth the solid-electrolyte-interphase (SEI). Other phenomena such as pulverisation or new evolving crystalline phases are excluded. It was found that a reduction of the particle size from 20 nm to 5 nm increases the reversibility due to a thicker and therewith more stable SEI. The deposition of the silicon nanoparticles into a porous carbon scaffold caused a significant improvement of the reversibility at constant carbon content. The effect of the electrolyte additives Fluoroethylene carbonate and Vinylene carbonate was analysed in detail. Furthermore, typical electrolyte compositions used for lithium-sulfur-batteries were tested and studied. Si-Li-S (SLS) full cells were demonstrated which outperform conventional lithium-sulfur batteries in terms of life time. The systematic analysis and the rational optimization process of the particle size, electrode design and electrolyte composition allowed to provide a nanostructured silicon electrode with a specific capacity of up to 1280 mAh/g(Electrode) and 81 % capacity retention after 500 deep discharge cycles. Reversible areal capacities of 5 mAh/cm^2 at 4.4 mg/cm^2 electrode weight were demonstrated.

Plusieurs structures hiérarchisées des fluorures de fer et de nickel avec des matrices carbonées ou métalliques ont été obtenues par deux voies de fluoration : fluoration gaz-solide de nanoparticules par le fluor moléculaire pur ou par fluoration en milieu liquide via l’agent fluorant NH 4 F. Les différentes nanostructures des matériaux ainsi préparées ont été caractérisées par les techniques classiques de microscopies électroniques, de spectroscopies vibrationnelles (infrarouge et Raman) ou encore d’analyse thermogravimétrique. En complément, la diffraction des rayons X a permis d’étudier les matériaux tant à l’ordre global, qu’à l’ordre local par affinement et analyse PDF sous rayonnement synchrotron. Ainsi, les conditions de synthèse et les mécanismes de formation de différents assemblages de type 0D avec des structures core-shell nickel/fluorure de nickel ; mais aussi 1D avec des nanotubes de carbone double parois remplis par du fluorure de fer, ou encore 3D (« flower-like ») avec le greffage de nanoparticules de fluorures de nickel en surface de nanotubes de carbone simple ou multi parois ont pu être appréhendés. Finalement, les nanostructures les plus adaptées à la diffusion des ions lithium (particules core-shell et flower-like) ont finalement été testées comme matériaux de cathode. / Some hierarchized structures made of iron or nickel fluorides together with carbonaceous or metallic matrix were obtained owing to two fluorination ways : solid-gas fluorination proceeding by pure molecular fluorine gas or fluorination in liquid media using NH 4 F in solution. The different nanostructures have been characterized thanks to classical technics such as electronic microscopies, vibrational spectroscopies (infrared and Raman) or thermogravimetric analysis. Many attentions have been paid to determine the global and local structures by using X-ray diffraction, refinement of the diffraction pattern by Rietveld analysis or Pair Distribution Function analysis on pattern registered on synchrotron. So, the synthesis conditions and the formation mechanism of various assemblies have been carried out on 0D core-shell nickel/ nickel fluoride, 1D double-walled carbon nanotubes filled with iron fluoride or 3D single and multi-walled carbon nanotubes decorated with flower-like nickel fluoride. Finally, the nanostructures the most favorable to lithium-ion diffusion (core-shell and flower like nanostructures) have been used as electrode in secondary lithium batteries.

The present thesis deals with the beneficial influence of nanostructuring on electrochemical performance of certain promising electrode and electrolyte materials for lithium-ion batteries (LIBs). Electrochemical performances of chosen electrodes and electrolytes have been presented in a systematic and detailed manner via studies related to both transport and lithium storage. Titanium dioxide (TiO2) or titania, a promising non-carbonaceous anode material for LIBs was chosen for the study. As part of the study, variety of nanostructured titania were synthesized. In general, all materials exhibited high lithium storage ( theoretical value for lithium storage in titania) and some of them showed exemplary rate capability, typically desired for modern lithium-ion batteries. Studies related to performance of these materials and mechanistics of lithium storage and kinetics are presented in Chapters 2-5. “Soggy sand” electrolyte, a promising soft matter electrolyte for LIBs was studied on the electrolyte side. Ion transport, mechanical strength and electrochemical properties of “soggy sand” electrolytes synthesized via dispersion of various surface chemically functionalized silica particles dispersed in model as well as LIB relevant electrolytes were studied in this thesis. Extensive physico-chemical and battery performance studies of “soggy sand” electrolytes are discussed in Chapters 6-8. A brief discussion of the contents and highlights of the individual chapters are described below: Chapter 1 briefly discusses the importance of electrochemical power sources as a viable green alternative to the combustion engine. Various facets of rechargeable LIBs, one of the most important electrochemical storage devices, are presented following the general discussion on electrochemical power devices. The importance of nanostructuring of electrodes with special emphasis on anodes for high lithium storage capacities and rate capabilities are also discussed in the opening chapter. The various advantages and disadvantages of the most commonly used electrolytes in LIB i.e. the liquid electrolytes are also discussed in Chapter 1. Suggestions for improvement of the physico-chemical properties of liquid electrolytes especially via nanostructuring (demonstrated via dispersions of fine oxide particles in liquid electrolytes in Chapters 6-8) using the concept of Heterogeneous doping are discussed in detail. A brief description on the importance of rheology for comprehension of soft matter microstructure is also provided in this chapter. Chapter 2 discusses composite of anatase titania (TiO2) nanospheres and carbon grown and self-assembled into micron-sized mesoporous spheres via a solvothermal synthesis route as prospective anode for rechargeable lithium-ion battery. The morphology and carbon content and hence the electrochemical performance are observed to be significantly influenced by the synthesis parameters. Synthesis conditions resulting in a mesoporous arrangement of an optimized amount of carbon and TiO2 exhibited the best lithium battery performance. The first discharge cycle capacity of carbon-titania mesoporous spheres (solvothermal reaction at 150 oC at 6 h, calcination at 500 oC under air, BET surface area 80 m2g-1) was 334 mAhg-1 (approximately 1 Li) at current rate of 66 mAg-1. High storage capacity and good cyclability is attributed to the nanostructuring (i.e. mesoporosity) of TiO2 as well as due to formation of a percolation network of carbon around the TiO2 nanoparticles. The micron-sized mesoporous spheres of carbon-titania composite nanoparticles also show good rate cyclability in the range (0.066-6.67) Ag-1. The electrochemical performance of the mesoporous carbon-TiO2 spheres has been compared with nonporous TiO2 spheres, normal mesoporous TiO2 and bulk TiO2. Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics in nanoparticles of anatase polymorph of titania is discussed in Chapter 3. Sol-gel synthesized nanoparticles of titania (particle size ~ 6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2-5 nm) and calcined at a temperature much higher than the sol-gel synthesis temperature. The carbon-titania composite particles (resulting size  10 nm) displayed immensely superior cyclability and rate capability (higher current rates  4 Ag-1) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystals enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of un-modified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in decrease in the irreversible capacity observed in case of nanoparticles without any carbon coating. Chapter 4 discusses the morphology and electrochemical performance of mixed crystallographic phase titania nanotubes and nanosheets for prospective application as anode in rechargeable lithium-ion batteries. Hydrothermally grown nanotubes/nanosheets of titania (TiO2) and carbon/silver-titania (C/Ag-TiO2) comprise a mixture of both anatase and TiO2(B) crystallographic phases. The first cycle capacity (at current rate = 10 mAg-1) for bare TiO2 nanotubes was 355 mAhg-1 (approximately 1.06 Li), which is higher than both the theoretical capacity (335 mAhg-1) as well as reported values for pure anatase and TiO2(B) nanotubes. Higher capacity is attributed to a combination of presence of mixed crystallographic phases of titania as well as trivial size effects. The surface area of bare TiO2 nanotubes was very high being equal to 340 m2g-1. Surface modification of the TiO2 nanotubes via amorphous carbon and Ag nanoparticles resulted in significant improvement in battery performance. The first cycle irreversible capacity loss can be minimized via effective coating of the surface. Carbon coated TiO2 nanotubes showed superior performance than Ag nanoparticle coated TiO2 nanotubes in terms of long term cyclability. Unlike Ag nanoparticles which are randomly distributed over the TiO2 nanotubes, the effective homogeneous carbon coating forms an efficient percolation network for the conducting species thus exhibiting better battery performance. The C-TiO2 and Ag-TiO2 nanotubes showed a better rate capability i.e. higher capacities compared to bare TiO2 nanotubes in the current range 0.055-2 Ag-1. Although titania nanosheets retains mixed crystallographic phases, the lithium battery performance (first cycle capacity = 225 mAhg-1) is poor compared to TiO2 nanotubes. It is attributed to lower surface area (22 m2g-1) which resulted in lesser electrode/electrolyte contact area and inefficient transport pathways for Li+ and e-. Implications of iron on electrochemical lithium insertion/removal capacity of iron (Fe3+) doped anatase TiO2 is discussed in Chapter 5. Iron doped anatase TiO2 nanoparticles with different doping concentrations were synthesized by simple sol-gel method. The electrochemistry of anatase TiO2 is observed to be a strong function of concentration of iron (Fe3+). A high 1st cycle discharge capacity of 704 mAhg−1 (2.1 mol of Li) and 272 mAhg−1 (0.81 mol of Li) at the 30th discharge cycle with Coulombic efficiency greater than 96% has been observed for 5% iron (Fe3+) doped TiO2 at a current density of 75 mAg−1. Additional increase in the iron (Fe3+) concentrations deteriorates the lithium storage of TiO2. An improvement in lithium storage of more than 50% is noticed for 5% iron (Fe3+) doped TiO2 compared to pure anatase TiO2 which shows an initial discharge capacity of 279 mAhg−1. The anomalous lithium storage behavior in all the iron (Fe3+) doped TiO2 has been accounted, in addition to homogeneous Li insertion in the octahedral sites, on the basis of formation of metallic Fe and Li2O during initial lithiation process and subsequent heterogeneous interfacial storage between Fe and Li2O interface. Chapter 6 discusses in a systematic manner the crucial role of oxide surface chemical composition on ion transport in “soggy sand” electrolytes. A “soggy sand” electrolytic system comprising of aerosil silica functionalized with various hydrophilic and hydrophobic moeities dispersed in lithium perchlorate ethylene glycol solution ( = 37.7) was used for the study. Detailed rheology studies show that the attractive particle network in case of the composite with unmodified aerosil silica (with surface silanol groups) is most favorable for percolation in ionic conductivity as well as rendering the composite with beneficial elastic mechanical properties. Though weaker in strength compared to the composite with unmodified aerosil particles, attractive particle networks are also observed in composites of aerosil particles with surfaces partially substituted with hydrophobic groups. However, ionic conductivity is observed to be dependent on the size of the hydrophobic moiety. No spanning attractive particle network was formed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol) and as a result no percolation in ionic conductivity was observed. The composite with hydrophilic particles was a sol contrary to gels obtained in case of unmodified aerosil and partially substituted with hydrophobic groups. Chapter 7 also discusses the influence of oxide surface chemical composition but additionally the role of solvent on ion solvation and ion transport of “soggy sand” electrolytes. Compared to the liquid electrolyte in Chapter 6, a lower dielectric constant liquid electrolyte was employed for the study in this chapter. A “soggy sand” electrolyte system comprising of dispersions of hydrophilic/hydrophobic functionalized aerosil silica in lithium perchlorate-methoxy polyethylene glycol solution ( = 10.9) was employed for the study. Static and dynamic rheology measurements again showed formation of an attractive particle network in case of the composite with unmodified aerosil silica (i.e. with surface silanol groups) as well as composites with hydrophobic alkane groups. While particle network in the composite with hydrophilic aerosil silica (unmodified) were due to hydrogen bonding, hydrophobic aerosil silica particles were held together via van der Waals forces. The network strength in the latter case (i.e. for hydrophobic composites) were weaker compared with the composite with unmodified aerosil silica. Both unmodified silica as well as hydrophobic silica composites displayed solid-like mechanical strength. However, this time around no enhancement in ionic conductivity compared to the liquid electrolyte was observed in case of the unmodified silica. This is attributed to the existence of a very strong particle network which leads to the “expulsion” of all conducting entities from the interfacial region between adjacent particles. The ionic conductivity for composites with hydrophobic aerosil particles displayed ionic conductivity as a function of the size of the hydrophobic chemical moiety. No spanning attractive particle network was observed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol). The composite resembled a sol and no percolation in ionic conductivity was observed. Chapter 8 describes the influence of dispersion of uniformly sized mono-functional or bi-functional (“Janus”) particles on ionic conductivity in lithium battery solutions and it’s implications on battery performance. Mono-functionalized (hydrophilic or hydrophobic) and bi-functionalized Janus (hydrophilic and hydrophobic) particles form physical gels of varying strength over a wide range of concentration (0.1    0.4; , oxide volume fraction). While the composites with mono-functionalized particles display shear thinning typical of gels (due to gradual breaking up spanning particle network held together by hydrogen/van der Walls force), the bi-functionalized “Janus” particles exhibit both complementary properties of gel and sol. The latter observation is interpreted in terms of existence of both hydrogen and van der Waals force arising out of the particle arrangement which get perturbed under the influence of external shear. Composites with homogeneous hydrophilic surface group show the highest ionic conductivity whereas the homogeneous hydrophobic surfaces exhibit superior electrode/electrolyte interface stability and battery cyclability. The Janus particles did not show any enhancement in ionic conductivity however, battery performance is highly satisfactory taking intermediate values between the homogeneously functionalized hydrophilic and hydrophobic particle composites.

Les batteries lithium-ion dominent le marché des appareils nomades et celui des véhicules électriques. Néanmoins elles posent des problèmes de sécurité liés à leur électrolyte, contenant des carbonates inflammables et volatils. Pour sécuriser ces systèmes, les liquides ioniques (LI) sont étudiés comme électrolytes alternatifs. Ce sont des sels liquides à température ambiante, réputés stables thermiquement et non inflammables. Ce caractère sécuritaire des LI, souvent avancé, est pourtant peu étayé par des expériences probantes. Les travaux de cette thèse visent à comprendre le comportement de ces LI en situations abusives, telles qu'un échauffement de la batterie, un feu ou une surcharge. Les températures de décomposition de LI contenant les cations imidazolium ou pyrrolidinium différemment substitués et l'anion bis(trifluoromethanesulfonyl)imide ont été déterminées par analyse thermogravimétrique (ATG). Une analyse critique des données (de la littérature et de nos mesures) a permis de définir une procédure optimisée, pour obtenir des résultats reproductibles et comparables. Des électrolytes constitués de mélanges de carbonates ou de LI et de sels de lithium ont été analysés par ATG dynamique et isotherme, et leurs produits de décomposition ont été identifiés. Leur comportement au feu a été testé par la mesure des chaleurs de combustion, des délais d'inflammation et l'identification des gaz générés. Des tests de cyclage électrochimique ont été menés avec ces mêmes électrolytes dans des systèmes lithium-ion constitués des électrodes Li4Ti5O12 et LiNi1/3Mn1/3Co1/3O2. L'évolution des électrolytes et des surfaces des électrodes en situation de surcharge a été examinée / Lithium-ion batteries are dominating both the nomad device and electric vehicle markets. However they raise safety concerns related to their electrolyte, which consists of flammable and volatile carbonate mixtures and toxic salts. The replacement of the latter by ionic liquids (IL), liquid salts claimed to be thermally stable and non-flammable, could provide a safer alternative. Yet this often claimed feature has been poorly examined by experiments. The work of this thesis investigates IL behaviour under abuse conditions such as overheating, fire or overcharge. Decomposition temperatures of IL based on differently substituted imidazolium or pyrrolidinium cations and the bis(trifluoromethanesulfonyl)imide anion were determined by thermogravimetric analysis (TGA). A critical study of gathered data (from literature and our work) led to the determination of an optimised procedure to obtain reproducible and comparable results. Electrolytes based on carbonates mixtures or IL and containing lithium salt were studied by dynamic and isothermal TGA, and their decomposition products were identified. Their combustion behaviour was also tested by measuring heats of combustion and ignition delays. Emitted gases were analysed and quantified. Electrochemical cycling tests were carried out with these electrolytes in lithium-ion systems based on Li4Ti5O12 and LiNi1/3Mn1/3Co1/3O2 electrodes. The evolution of the electrolytes and electrodes surface was also examined under overcharge

This diploma thesis deals with an issue of lithium-ion batteries, primarily with negative (anode) electrode materials. Natural graphite in two forms, namely flake and expanded graphite, is used in the thesis as active electrode material. It is concerned with study of their capacity and output characteristics depending on the pressing pressure and discharging current. The first part of thesis consists of theory and describes basic principles and the composition of lithium-ion batteries. Materials, their characteristics used in production and theoretical description of measurement techniques are presented then. The second part of the thesis is focused on production, assembling and measurement of the characteristics of the produced electrodes. The aim of the thesis is finding the effects of changes of pressing pressure on the capacity, stability during cycling and stability at higher loads.

The thesis deals with the influence of low-flammable electrolytes on negative electrodes. The thesis describes materials used in lithium-ion batteries and functions of individual components. There is also a description of conductometry and electron microscopy, which is used in the practical part, ie during measurement. All findings are summarized at the end of the thesis.

No description available.

The diploma thesis deals with electrode materials for lithium-ions accumulators, concretely layered materials prepared via new methods. The main objective of this work is dealing with new procedures prepare electrodes of newly developed layered electrode materials and subsequently their measure. Another challenge was a theoretical analysis of newly developed layered electrode materials for positive and negative electrodes and their preparation of new procedures. In this work the detailed procedures for the preparation of individual electrodes, electrolytes and other issues associated with these preparations. There were describing batteries of general, primary and secondary lithium cells, fuel cells, Lithium-ion batteries, layered materials forming the electrodes and of course the history these cells. Practical work is focused on separate measurements layered electrode materials prepared by new processes and assessment of results for individual layered materials. In the practical part has been made that the newly prepared layered electrode materials offer higher capacity and voltage.

This thesis is interested in new materials for lithium – ion batteries. Two different samples were investigated, one intercalation and one conversion cathode material. The theoretical part is focused to the structure of cells, their advantages and disadvantages compared to other secondary batteries. Also other materials used in batteries are described. The practical part describes the preparation of cathode materials for subsequent testing by scanning elektron microscopy and thermogravimetric analysis. In conclusions two different materials were evaluated and compared with each other.