Hierarchically porous nitrogen-doped graphene frameworks (N-GFs) are fabricated through the ice-templating of GO with polyethylenimine and the thermal treatment of the resultant hybrids. As cathode materials in lithium ion batteries (LIBs), the obtained N-GFs exhibit an outstanding specific capacity of 379 mA h g−1 at 0.5 A g−1 for 2500 cycles. Even at an ultrahigh current density of 5 A g−1, the N-GFs maintain a capacity of 94 mA h g−1, superior to that of most reported LIB cathode materials. The experimental results and quantum mechanics calculations suggest that pyridinic-like N and pyridinic N-oxide in graphene are responsible for the excellent cathodic performance of the bipolar N-GFs by providing fast surface faradaic reactions with both p- and n-doped states.

Hierarchically porous nitrogen-doped graphene frameworks (N-GFs) are fabricated through the ice-templating of GO with polyethylenimine and the thermal treatment of the resultant hybrids. As cathode materials in lithium ion batteries (LIBs), the obtained N-GFs exhibit an outstanding specific capacity of 379 mA h g−1 at 0.5 A g−1 for 2500 cycles. Even at an ultrahigh current density of 5 A g−1, the N-GFs maintain a capacity of 94 mA h g−1, superior to that of most reported LIB cathode materials. The experimental results and quantum mechanics calculations suggest that pyridinic-like N and pyridinic N-oxide in graphene are responsible for the excellent cathodic performance of the bipolar N-GFs by providing fast surface faradaic reactions with both p- and n-doped states.

The environmental concerns over the use of fossil fuels, and their resource constraints, as well as energy security concerns, have spurred great interest in generating electric energy from renewable sources. Solar and wind energy are abundant and potentially readily available. However, the generation of sustainable energies is generally intermittent and these energies have geographical limits which are relative to current large-scale energy generation facilities. To smooth out the intermittency of renewable energy production, low-cost electrical energy storage (EES) devices are becoming highly necessary. Among these EES technologies, lithium ion batteries are one of the most promising EES devices in terms of the characteristics of high gravimetric, volumetric energy density and environmentally friendly compared to lead-acid batteries and Ni-Cd batteries. Other advantages of Li-ion batteries are the ability of being recharged hundreds of times and high stability. Moreover, the dramatically growing market share of hybrid electrical and electrical vehicles in automobiles has motivated the development of high energy and power density LIBs with high mass loading. However, there are still several remaining challenges in LIBs for their further application in grid-scale ESSs. One of the global issues to date is the high costs including the cost of raw materials such as lithium and cobalt, production, machining, and transportation, etc. In addition, the increasing energy demand thereby leads to the pressures on the resource supply chains and thus increasing the cost of LIBs. Therefore, it is urgent to find a complementary or alternative EES device in a short term to satisfy the growing energy demand. Under the background of fast development of LIBs technology as well as the establishment of Li chemistry fundamentals in the last 40 years, rechargeable battery systems utilizing Na element have been extensively studied to develop less expensive and more sustainable ESSs. The sodium resource is abundantly existed in the planet. According to the periodic table, sodium is the most possible alternative to lithium, because it has the similar chemical and physical properties towards to lithium. As a consequence, the established fundamentals in LIBs can be reasonably analogized to SIBs. Moreover, Sodium is readily available from various sources-foods that contain sodium naturally, foods containing salt and other sodium-containing ingredients. Therefore, The study of SIBs technology and sodium chemistry are gaining increasing interests and attentions both in the scientific researchers and battery industry. However, theoretically speaking, the energy density of SIBs is lower than that of LIBs by using same electrode materials because sodium is more than 3 times heavier than Li as well as the standard electrode potential of Na (-2.71 V) is higher than Li (-3.04 V). Therefore, SIBs are not thought as an ideal candidate to substitute LIBs in the fields of small or middle-size portable devices, but are more favorable in a large grid support where the operation cost is the primary choice. Negative electrode is important component in a single cell. Exploring negative electrode materials with high electrochemical performance in LIBs and SIBs is indeed required for fulfilling the spreading energy demand. Among various negative electrode materials, layered transition metal sulfides (MSs) are reckoned as a promising class with high theoretical specific capacity and power capability due to their intrinsically layered structure which is beneficial to the diffusion of Li+ and Na+ . However, layered transition metal sulfides are suffering from intrinsically poor electrical conductivity, volume changes, high irreversibility and sluggish kinetics during Li+ /Na+ storage process. To address these issues, numerous strategies are applied to explore high performance LIBs and SIBs negative electrode materials in this PHD thesis. / Die ökologischen Bedenken hinsichtlich der Nutzung fossiler Brennstoffe und deren Ressourcenbeschränkungen sowie Bedenken hinsichtlich der Energiesicherheit haben großes Interesse an der Erzeugung elektrischer Energie aus erneuerbaren Quellen geweckt. Sonnen- und Windenergie sind im Überfluss vorhanden und potenziell leicht verfügbar. Die Erzeugung nachhaltiger Energien ist jedoch in der Regel intermittierend, und diese Energien haben geographische Grenzen, die im Vergleich zu den derzeitigen großen Energieerzeugungsanlagen relativ begrenzt sind. Um die Unterbrechungen in der Produktion erneuerbarer Energien auszugleichen, werden kostengünstige elektrische Energiespeicher (EES) dringend notwendig. Unter diesen EES-Technologien sind Lithium-Ionen-Batterien eines der vielversprechendsten EES-Geräte hinsichtlich der Eigenschaften einer hohen gravimetrischen, volumetrischen Energiedichte und umweltfreundlich im Vergleich zu Blei-Säure-Batterien und Ni-Cd-Batterien. Weitere Vorteile von Lithium-Ionen-Batterien sind die Fähigkeit, hunderte Male wieder aufgeladen werden zu können, und die hohe Stabilität. Darüber hinaus hat der dramatisch wachsende Marktanteil von Hybrid- und Elektrofahrzeugen in Automobilen die Entwicklung von LIBs mit hoher Energie- und Leistungsdichte und hoher Massenbelastung motiviert. Es gibt jedoch noch einige Herausforderungen in den LIBs, die für die weitere Anwendung in den ESSs im Rastermaßstab erforderlich sind. Eine der bisherigen globalen Fragen sind die Gesamtkosten einschließlich der Kosten für Rohstoffe wie Lithium und Kobalt, Produktion, Bearbeitung und Transport usw. Darüber hinaus führt die steigende Energienachfrage dadurch zu einem Druck auf die Ressourcenversorgungsketten und damit zu einer Verteuerung der LIBs. Daher ist es dringend erforderlich, kurzfristig eine ergänzende und alternative EES-Technologie zu finden, um den wachsenden Energiebedarf zu decken. Vor dem Hintergrund der schnellen Entwicklung der LIBs-Technologie sowie der Etablierung der Grundlagen der Li-Chemie in den letzten 40 Jahren wurden wiederaufladbare Batteriesysteme, die das Na-Element verwenden, umfassend untersucht, um kostengünstigere und nachhaltigere ESSs zu entwickeln. Die Natriumressource ist auf der Erde im Überfluss vorhanden. Nach dem Periodensystem ist Natrium die möglichste Alternative, da es die ähnlichen chemischen und physikalischen Eigenschaften von Lithium hat. Folglich lassen sich die etablierten Grundlagen der LIBs in vernünftiger Weise mit denen der SIBs vergleichen. Darüber hinaus ist Natrium aus verschiedenen Quellen leicht erhältlich - aus Lebensmitteln, die von Natur aus Natrium enthalten, aus Lebensmitteln, die Salz und andere natriumhaltige Zutaten enthalten. Daher gewinnt das Studium der SIBs-Technologie und Natriumchemie sowohl in der wissenschaftlichen Forschung als auch in der Batterieindustrie zunehmend an Interesse und Aufmerksamkeit. Theoretisch gesehen ist jedoch die Energiedichte von SIBs bei Verwendung der gleichen Elektrodenmaterialien niedriger als die von LIBs, da Natrium mehr als dreimal schwerer als Li ist und das Standardelektrodenpotential von Na (-2,71 V) höher als Li (-3,04 V) ist. Daher werden SIBs nicht als idealer Kandidat für den Ersatz von LIBs im Bereich kleiner oder mittelgroßer tragbarer Geräte angesehen, sondern sie sind günstiger bei einer großen Netzunterstützung, bei der die Betriebskosten die primäre Wahl sind. Die negative Elektrode ist ein notwendiger und wichtiger Teil in einer einzelnen Zelle. In der Tat ist es zur Erfüllung des sich ausbreitenden Energiebedarfs erforderlich, negative Elektroden-Materialien mit hoher elektrochemischer Leistung in LIBs und SIBs zu untersuchen. Unter den verschiedenen Materialien für negative Elektroden gelten geschichtete Übergangsmetallsulfide (MS) als eine vielversprechende Klasse mit hoher theoretischer spezifischer Kapazität und Leistungskapazität aufgrund ihrer intrinsisch geschichteten Struktur, die der Diffusion von Li+ und Na+ förderlich ist. Allerdings leiden schichtförmige Übergangsmetallsulfide unter inhärent schlechter elektrischer Leitfähigkeit, Volumenänderungen, hoher Irreversibilität und träger Kinetik während des Li+ /Na+ -Speicherprozesses. Um diese Probleme anzugehen, werden in dieser Doktorarbeit zahlreiche Strategien zur Untersuchung von Hochleistungs-LIBs und SIBs für negative Elektrodenmaterialien angewandt.

Developed rechargeable batteries are urgently required to make more efficient use of renewable energy sources to support our modern way of life. Among all battery types, lithium batteries have attracted the most attention because of the high energy density (both gravimetric and volumetric), long cycle life, reasonable production cost and the ease of manufacturing flexible designs. Indeed, electrode material characteristics need to be improved urgently to fulfil the requirements for high performance lithium ion batteries. TiO2-based anodes are highly promising materials for LIBs to replace carbon due to fast lithium insertion/extraction kinetics, environmentally-friendly behavior, low cost and low volume change (less than 4%) therewith, high structural stability as well as improved safety issues are obtained. Nevertheless, the low ionic and electric conductivity (≈ 10−12 S m−1) of TiO2 represent the main challenge. In short, the present work aims at developing, optimization and construction of novel anode materials for lithium ion batteries using materials that are stable, abundant and environmentally friendly. Herein, both of two-phase Ti80Co20 and single phase Ti-Sn alloys (with different Sn contents of 1 to 10 at.%) were used to fabricate highly ordered, vertically oriented and dimension-controlled 1D nanotubes of mixed transition metal oxides (TiO2-CoO and TiO2-SnO2) via a straight-forward anodic oxidation step in organic electrolytes containing NH4F. Surface morphology and current density for the initial nanotube formation are found to be dependent on the crystal structure of the alloy phases. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. The results reveal the successful formation of mixed TiO2-CoO and TiO2-SnO2 nanotubes under the selected voltage ranges. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at different current densities. The results revealed that TiO2-CoO nanotubes prepared at 60 V exhibited the highest areal capacity of ~ 600 µAh cm–2 (i.e. 315 mAh g–1) at a current density of 10 µA cm–2. At higher current densities TiO2-CoO nanotubes showed nearly doubled lithium ion intercalation and a coulombic efficiency of 96 % after 100 cycles compared to lower effective TiO2 nanotubes prepared under identical conditions. To further improve the electrochemical performance of the TiO2-CoO nanotubes, a novel ternary carbon nanotubes (CNTs)@TiO2-CoO nanotubes composite was fabricated by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO2-CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO2 and TiO2-CoO NTs without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li+ ion diffusivity promoting a strongly favored lithium insertion into the TiO2-CoO NT framework, and hence results in high capacity and extremely reproducible high rate capability. On the other hand, the results demonstrate that TiO2-SnO2 nanotubes prepared at 40 V on a Ti-Sn alloy with 1 at.% Sn display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. The thesis is organized as follows: Chapter 1: General introduction, in which the common situation of energy demand, along with the importance of lithium ion batteries in renewable energy systems and portable devices are discussed. A brief introduction to TiO2-based anode in lithium ion batteries and the genera strategies for developing TiO2 anodes are also presented. The scope of this thesis as well as the main tasks are summarized. Chapter 2: The basic concepts of lithium ion batteries with an overview about their main components are discussed, including a brief information about the anode materials and the crystal structure of TiO2 anode. A detailed review for TiO2 nanomaterials for LIBs including the fabrication methods and the electrochemical performance of various TiO2 nanostructures (nanoparticles, nanorods, nanoneedles, nanowires and nanotubes) as well as porousTiO2 nanostructures is presented. The fabrication of TiO2 nanotubes by anodic oxidation, along with the growth mechanism are highlighted. The factors affecting the electrochemical performance of anodically fabricated pure TiO2, TiO2/carbon composites and TiO2-mixed with another metal oxide are reviewed. Chapter 3: In this chapter, the synthesis of TiO2-CoO, (CNTs)@TiO2-CoO and TiO2-SnO2 nanotubes, along with the characterization techniques and the electrochemical basics and concepts are discussed. Chapter 4: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-CoO nanotubes and ternary (CNTs)@TiO2/CoO nanotube composites are presented. Chapter 5: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of ternary (CNTs)@TiO2-CoO nanotube composites are explained. Chapter 6: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-SnO2 nanotubes are presented. Chapter 7: Summarizes the results presented in this work finishing with realistic conclusions, and highlights interesting work for the future.:1. Introduction and scope of the thesis 15 1.1 Batteries for renewable energy systems and portable devices 15 1.2 TiO2-based anodes in lithium ion batteries 17 1.3 Strategies for developing TiO2 anodes 17 1.4 Scope of work 19 1.5 Tasks 20 2. Basics and literature review 23 2.1 Lithium ion battery system 23 2.2 Anode materials 26 2.3 Crystal structure of TiO2 28 2.4 TiO2 nanomaterials for LIBs 30 2.4.1 TiO2 nanoparticles 30 2.4.2 TiO2 nanoneedles 36 2.4.3 Porous TiO2 nanostructures 39 2.5 TiO2 nanotubes prepared by electrochemical anodization 44 2.6 The mechanism of nanotube formation by anodic oxidation 47 2.7 Anodically fabricated TiO2 nanotubes as anodes in LIBs 49 2.7.1 Anodization electrolyte 50 2.7.2 Amorphous and crystalline TiO2 anodes 50 2.7.3 Influence of the nnealing atmospheres of TiO2 52 2.7.4 Free-standing TiO2 nanotube membranes 54 2.7.5 TiO2 nanotubes/carbon composites 55 2.7.6 Mixed oxide nanotubes 55 3. Materials and methods 61 3.1 Methodology 61 3.1.1 Synthesis of TiO2-CoO and TiO2 nanotubes 61 3.1.2 Synthesis of CNTs@TiO2-CoO NT composite 62 3.1.3 Synthesis of TiO2-SnO2 and TiO2 nanotubes 63 3.2 Characterization techniques 64 3.2.1 X-ray diffraction (XRD 64 3.2.2 Scanning electron microscopy (SEM 65 3.2.3 Energy-dispersive X-ray spectroscopy (EDXS 65 3.2.4 Transmission electron spectroscopy (TEM 66 3.2.5 X-ray photoelectron spectroscopy (XPS 66 3.2.6 Raman spectroscopy 67 3.2.7 Nitrogen sorption isotherms 67 3.2.8 Inductively coupled plasma optical emission spectroscopy (ICP–OES 68 3.3 Basic definitions and electrochemical concepts 68 3.3.1 Faraday’s law 68 3.3.2 Capacity 69 3.3.3 Discharging 69 3.3.4 Charging 69 3.4 Electrochemical techniques 70 3.4.1 Cyclic voltammetry 70 3.4.2 Galvanostatic discharging/charging cycling 70 3.4.3 Electrochemical impedance spectroscopy (EIS 71 3.5 Electrode preparation and measurement conditions 71 3.5.1 TiO2-CoO nanotube electrodes 71 3.5.2 CNTs@TiO2 and CNTs@TiO2/CoO NTs electrodes 72 3.5.3 TiO2-SnO2 nanotube electrodes 73 4. TiO2-CoO as anodes in lithium ion batteries 75 4.1 Introduction 76 4.2 Characterization 76 4.2.1 Phase identification of as cast Ti-Co alloy 76 4.2.2 Time-current density relationship 79 4.2.3 Morphology of the fabricated TiO2-CoO nanotubes 81 4.2.4 Phase identification of the fabricated TiO2-CoO nanotubes 85 4.2.5 Specific surface area of the fabricated TiO2-CoO nanotubes 87 4.2.6 Chemical state in the grown TiO2-CoO nanotubes 89 4.2.7 Raman spectroscopy of TiO2-CoO nanotubes 91 4.3 Electrochemical testing of TiO2-CoO electrodes 92 4.3.1 Cyclic voltammetry 92 4.3.2 Galvanostatic cycling with potential limitation 93 4.3.3 Electrochemical impedance spectroscopy (EIS) 97 4.3.4 Structural stability TiO2-CoO anodes over cycling 98 4.4 Summary of chapter 4 99 5. Ternary CNTs@TiO2-CoO nanotube composites: improved anode materials for LIBs 101 5.1 Introduction 102 5.2 Characterization 103 5.2.1 Morphology and Raman analysis of the fabricated CNTs@TiO2-CoO NTs 103 5.2.2 XRD analysis of the fabricated TiO2-CoO NTs before and after CNTs coating 106 5.3 Electrochemical properties 107 5.3.1 Cyclic voltammetry 107 5.3.2 Galvanostatic cycling with potential limitation 109 5.3.2 Electrochemical impedance spectroscopy (EIS 112 5.4 Summary of chapter 5 114 6. TiO2-SnO2 nanotubes as anodes in lithium ion batteries 115 6.1 Introduction 116 6.2 Characterization 117 6.2.1 ICP-OES analysis of the as-cast Ti-Sn alloys 117 6.2.2 SEM analysis of the as-cast Ti-Sn alloys 117 6.2.3 Phase analysis of the as-cast Ti-Sn alloys 118 6.2.4 Morphology of the fabricated TiO2-SnO2 nanotubes 121 6.2.5 XPS investigation of the grown TiO2-SnO2 nanotubes 127 6.2.6 Raman spectroscopy of TiO2-SnO2 nanotubes 129 6.3 Electrochemical Testing 130 6.3.1 Cyclic voltammetry 130 6.3.2 Galvanostatic cycling with potential limitation132 6.3.3 Specific surface area of the fabricated TiO2-SnO2 nanotubes135 6.3.4 Electrochemical impedance spectroscopy (EIS) and rate performance tests of the fabricated TiO2-SnO2 nanotubes 137 6.4 Summary of chapter 6140 7. Summary and outlook 141 7.1 Summary 141 7.2 Outlook 143 Appendix 145 Bibliography 157 List of figures 183 Glossary 191 Publications 193 Curriculum vitae 195 Acknowledgment 199 Declaration 201 / Um die zur Aufrechterhaltung unserer modernen Lebensweise unabdingbaren erneuerbaren Energiequellen effizient nutzen zu können, werden hochentwickelte wiederaufladbare Batterien dringend benötigt. Lithium-Ionenbatterien gelten aufgrund ihrer hohen Energiedichte (sowohl gravimetrisch als auch volumetrisch), ihrer langen Lebensdauer, moderater Produktionskosten und aufgrund der Möglichkeit, vielfältige Konzepte einfach herstellen zu können, als vielversprechend. Dennoch müssen die Elektrodenmaterialien dringend verbessert werden, um den Ansprüchen an zukünftige hochentwickelte Lithium-Ionenbatterien gerecht zu werden. TiO2-basierte Anoden gelten aufgrund ihrer schnellen Lade- und Entladekinetik, ihres umweltfreundlichen Verhaltens und niedriger Kosten als aussichtsreiche Alternativen zu Kohlenstoffen. Durch die geringe Volumenänderung beim Lithiumeinbau (unter 4%) werden außerdem eine hohe strukturelle Stabilität und erhöhte Sicherheit gewährleistet. Die hauptsächlichen Herausforderungen stellen die niedrige ionische und elektrische Leitfähigkeit (≈ 10−12 S m−1) von TiO2 dar. Zusammengefasst liegt das Ziel der vorliegenden Arbeit in der Entwicklung, Optimierung und Herstellung neuartiger Anodenmaterialien für Lithium-Ionenbatterien unter Verwendung stabiler, verfügbarer und umweltfreundlicher Materialien. In dieser Arbeit wurden sowohl zweiphasiges Ti80Co20 und einphasige Ti-Sn-Legierungen (mit verschiedenen Sn-Gehalten zwischen 1 und 10 at-%) zur Herstellung hochgeordneter, vertikal orientierter eindimensionaler Nanoröhren aus gemischten Übergangsmetalloxiden (TiO2–CoO und TiO2–SnO2) mittels anodischer Oxidation in NH4F-haltigen organischen Elektrolyten genutzt. Dabei wurden Abhängigkeiten der Oberflächenmorphologie und der Stromdichte für die Bildung der Nanoröhren von der Kristallstruktur der zugrundeliegenden Legierung beobachtet. Vielfältige Methoden wie REM, EDXS, TEM, XPS und Ramanspektroskopie wurden genutzt, um die Nanoröhren zu charakterisieren. Die Ergebnisse zeigen, dass gemischte TiO2-CoO und TiO2-SnO2 Nanoröhren in den gewählten Spannungsfenstern erfolgreich gebildet werden konnten. Die so hergestellten Nanoröhren sind amorph und in ihren Dimensionen präzise durch die Wahl der Spannung einstellbar. Eine elektrochemische Beurteilung der Nanoröhren erfolgte durch Tests gegen eine Li/Li+-Elektrode bei veschiedenen Stromdichten. Die Resultate zeigen, dass TiO2-CoO-Nanoröhren, welche bei 60 V hergestellt wurden, die höchsten Flächenkapazitäten von ~ 600 µAh cm–2 (d.h. 315 mAh g–1) bei einer Stromdichte von 10 µA cm–2 aufweisen. Bei höheren Stromdichten zeigen TiO2-CoO-Nanoröhren nahezu verdoppelte Lithiuminterkalation und eine Coulomb-Effizienz von 96 % nach 100 Zyklen, verglichen mit weniger effektiven TiO2–Nanoröhren, welche unter identischen Bedingungen hergestellt wurden. Um die elektrochemischen Eigenschaften der TiO2-CoO-Nanoröhren weiter zu verbessern, wurde ein neuer Komposit aus Kohlenstoff-Nanoröhren und TiO2-CoO-Nanoröhren ((CNT)s@TiO2/CoO) durch eine zweistufige Synthese hergestellt. Die Herstellung beinhaltet zunächst die anodische Bildung geordneter TiO2/CoO-Nanoröhren, ausgehend von einer Ti-Co-Legierung, gefolgt von einem horizontalen Kohlenstoff-Nanoröhren-Wachstum auf dem Oxid mittels einer simplen Sprühpyrolyse. Die einzigartige 1D-Struktur einer solchen hybriden Nanostruktur mit eingebundenen CNTs zeigt deutlich erhöhte Flächenkapazitäten und Belastbarkeiten im Vergleich zu Nanoröhren aus TiO2 und TiO2/CoO-Nanoröhren ohne CNTs, die unter identischen Bedingungen getestet wurden. Die Ergebnisse zeigen, dass die CNTs ein hochleitfähiges Netzwerk bilden, welches die Diffusion von Lithium-Ionen und deren Einbau in die TiO2/CoO-Nanoröhren begünstigt und somit hohe Kapazitäten und reproduzierbare hohe Belastbarkeiten bewirkt. Außerdem zeigen die Resultate, dass TiO2-SnO2 Nanoröhren, welche bei 40 V auf einer Ti-Sn-Legierung mit 1 at.% Sn hergestellt wurden, im Mittel eine 1,4-fache Erhöhung der Flächenkapazität und eine exzellente Zyklenstabilität über mehr als 400 Zyklen, verglichen mit unter identischen Konditionen hergestellten und getesteten TiO2-Nanoröhren, zeigen. Die Arbeit ist wie folgt organisiert: Kapitel 1: Allgemeine Einführung, in der die Energienachfrage und die Bedeutung von Lithium-Ionenbatterien in erneuerbaren Energiesystemen und tragbaren Geräten diskutiert wird. Eine kurze Einleitung zu TiO2-basierten Anoden in Lithium-Ionenbatterien und allgemeine Strategien zur Entwicklung von TiO2-Anoden werden ebenfalls gezeigt. Das Ziel der Arbeit und hauptsächliche Aufgaben werden zusammengefasst. Kapitel 2: Das grundlegende Konzept der Lithium-Ionenbatterie mit einem Überblick über ihre Hauptkomponenten wird diskutiert. Dies beinhaltet auch eine kurze Darstellung der Anodenmaterialien und der Kristallstruktur von TiO2-Anoden. Eine detaillierte Übersicht über TiO2-Nanomaterialien für LIB, welche Herstellungsmethoden und die elektrochemische Performance verschiedener TiO2-Nanostrukturen (Nanopartikel, Nanostäbe, Nanonadeln, Nanodrähte und Nanoröhren) und poröser TiO2-Nanostrukturen beinhaltet, wird gezeigt. Die Bildung von TiO2-Nanoröhren durch anodische Oxidation und der Wachstumsmechanismus werden hervorgehoben. Faktoren, welche die elektrochemische Performance anodisch hergestellter TiO2-Materialien, TiO2/Kohlenstoff-Komposite und TiO2 als Gemisch mit anderen Metalloxiden beeinflussen, werden diskutiert. Kapitel 3: In diesem Kapitel werden die Synthese von TiO2-CoO, (CNTs)@TiO2/CoO und TiO2-SnO2-Nanoröhren, die Charakterisierungsmethoden, elektrochemische Grundlagen und Konzepte diskutiert. Kapitel 4: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der TiO2-CoO- Nanoröhren und der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden gezeigt. Kapitel 5: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden diskutiert. Kapitel 6: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance von TiO2-SnO2-Nanoröhren werden gezeigt. Kapitel 7: Eine Zusammenfassung der Resultate, die in dieser Arbeit gezeigt wurden und Schlussfolgerungen, sowie interessante Ansatzpunkte für zukünftige Arbeiten werden präsentiert.:1. Introduction and scope of the thesis 15 1.1 Batteries for renewable energy systems and portable devices 15 1.2 TiO2-based anodes in lithium ion batteries 17 1.3 Strategies for developing TiO2 anodes 17 1.4 Scope of work 19 1.5 Tasks 20 2. Basics and literature review 23 2.1 Lithium ion battery system 23 2.2 Anode materials 26 2.3 Crystal structure of TiO2 28 2.4 TiO2 nanomaterials for LIBs 30 2.4.1 TiO2 nanoparticles 30 2.4.2 TiO2 nanoneedles 36 2.4.3 Porous TiO2 nanostructures 39 2.5 TiO2 nanotubes prepared by electrochemical anodization 44 2.6 The mechanism of nanotube formation by anodic oxidation 47 2.7 Anodically fabricated TiO2 nanotubes as anodes in LIBs 49 2.7.1 Anodization electrolyte 50 2.7.2 Amorphous and crystalline TiO2 anodes 50 2.7.3 Influence of the nnealing atmospheres of TiO2 52 2.7.4 Free-standing TiO2 nanotube membranes 54 2.7.5 TiO2 nanotubes/carbon composites 55 2.7.6 Mixed oxide nanotubes 55 3. Materials and methods 61 3.1 Methodology 61 3.1.1 Synthesis of TiO2-CoO and TiO2 nanotubes 61 3.1.2 Synthesis of CNTs@TiO2-CoO NT composite 62 3.1.3 Synthesis of TiO2-SnO2 and TiO2 nanotubes 63 3.2 Characterization techniques 64 3.2.1 X-ray diffraction (XRD 64 3.2.2 Scanning electron microscopy (SEM 65 3.2.3 Energy-dispersive X-ray spectroscopy (EDXS 65 3.2.4 Transmission electron spectroscopy (TEM 66 3.2.5 X-ray photoelectron spectroscopy (XPS 66 3.2.6 Raman spectroscopy 67 3.2.7 Nitrogen sorption isotherms 67 3.2.8 Inductively coupled plasma optical emission spectroscopy (ICP–OES 68 3.3 Basic definitions and electrochemical concepts 68 3.3.1 Faraday’s law 68 3.3.2 Capacity 69 3.3.3 Discharging 69 3.3.4 Charging 69 3.4 Electrochemical techniques 70 3.4.1 Cyclic voltammetry 70 3.4.2 Galvanostatic discharging/charging cycling 70 3.4.3 Electrochemical impedance spectroscopy (EIS 71 3.5 Electrode preparation and measurement conditions 71 3.5.1 TiO2-CoO nanotube electrodes 71 3.5.2 CNTs@TiO2 and CNTs@TiO2/CoO NTs electrodes 72 3.5.3 TiO2-SnO2 nanotube electrodes 73 4. TiO2-CoO as anodes in lithium ion batteries 75 4.1 Introduction 76 4.2 Characterization 76 4.2.1 Phase identification of as cast Ti-Co alloy 76 4.2.2 Time-current density relationship 79 4.2.3 Morphology of the fabricated TiO2-CoO nanotubes 81 4.2.4 Phase identification of the fabricated TiO2-CoO nanotubes 85 4.2.5 Specific surface area of the fabricated TiO2-CoO nanotubes 87 4.2.6 Chemical state in the grown TiO2-CoO nanotubes 89 4.2.7 Raman spectroscopy of TiO2-CoO nanotubes 91 4.3 Electrochemical testing of TiO2-CoO electrodes 92 4.3.1 Cyclic voltammetry 92 4.3.2 Galvanostatic cycling with potential limitation 93 4.3.3 Electrochemical impedance spectroscopy (EIS) 97 4.3.4 Structural stability TiO2-CoO anodes over cycling 98 4.4 Summary of chapter 4 99 5. Ternary CNTs@TiO2-CoO nanotube composites: improved anode materials for LIBs 101 5.1 Introduction 102 5.2 Characterization 103 5.2.1 Morphology and Raman analysis of the fabricated CNTs@TiO2-CoO NTs 103 5.2.2 XRD analysis of the fabricated TiO2-CoO NTs before and after CNTs coating 106 5.3 Electrochemical properties 107 5.3.1 Cyclic voltammetry 107 5.3.2 Galvanostatic cycling with potential limitation 109 5.3.2 Electrochemical impedance spectroscopy (EIS 112 5.4 Summary of chapter 5 114 6. TiO2-SnO2 nanotubes as anodes in lithium ion batteries 115 6.1 Introduction 116 6.2 Characterization 117 6.2.1 ICP-OES analysis of the as-cast Ti-Sn alloys 117 6.2.2 SEM analysis of the as-cast Ti-Sn alloys 117 6.2.3 Phase analysis of the as-cast Ti-Sn alloys 118 6.2.4 Morphology of the fabricated TiO2-SnO2 nanotubes 121 6.2.5 XPS investigation of the grown TiO2-SnO2 nanotubes 127 6.2.6 Raman spectroscopy of TiO2-SnO2 nanotubes 129 6.3 Electrochemical Testing 130 6.3.1 Cyclic voltammetry 130 6.3.2 Galvanostatic cycling with potential limitation132 6.3.3 Specific surface area of the fabricated TiO2-SnO2 nanotubes135 6.3.4 Electrochemical impedance spectroscopy (EIS) and rate performance tests of the fabricated TiO2-SnO2 nanotubes 137 6.4 Summary of chapter 6140 7. Summary and outlook 141 7.1 Summary 141 7.2 Outlook 143 Appendix 145 Bibliography 157 List of figures 183 Glossary 191 Publications 193 Curriculum vitae 195 Acknowledgment 199 Declaration 201

Indiana University-Purdue University Indianapolis (IUPUI) / Since 1990s, rechargeable Li-ion batteries have been widely used in consumer electronics such as cell phones, global positioning systems (GPS), personnel digital assistants (PDA), digital cameras, and laptop computers. Recently Li-ion batteries received considerable attention as a major power source for electric vehicles. However, significant technical challenges still exist for widely deploying Li-ion batteries in electric vehicles. For instance, the energy density of Li-ion batteries is not high enough to support a long-distance commute. The Li-ion batteries used for the Nissan Leaf and Chevy Volt only can support 50 – 100 miles per charge. The cost of Li-ion battery packs in electric vehicles is still high. The battery pack for the Chevy Volt costs about $8,000, and the larger one in the Nissan Leaf costs about $12,000. To address these problems, new Li-ion battery electrode materials with high energy density and low cost should be developed. Among Li-ion battery cathode materials, vanadium pentoxide, V2O5, is one of the earliest oxides studied as a cathode for Li-ion batteries because of its low cost, abundance, easy synthesis, and high energy density. However, its practical reversible capacity has been limited due to its irreversible structural change when Li insertion is more than x = 1. Tremendous efforts have been made over the last twenty years to improve the phase reversibility of LixV2O5 (e.g., 0 ≤ x ≤ 2) because of vanadium pentoxides’ potential use as high capacity cathodes in Li-ion batteries. In this thesis, a new strategy was studied to develop vanadium pentoxide cathode materials with improved phase reversibility. The first study is to synthesize vanadium oxide cathodes via a new chemical route – creating a phase transformation from the vanadium sulfide to oxide. The β-Na0.33V2O5 was prepared via a new method of chemical synthesis, involving the chemical transformation of NaVS2 via heat-treatment at 600 °C in atmospheric air. The β-Na0.33V2O5 particles were well crystalized and rod-shaped, measuring 7–15 μm long and 1–3 μm wide with the formation of the crystal defects on the surface of the particles. In contrast to previous reports contained in the literature, Na ions were extracted, without any structural collapse, from the β -Na0.33V2O5 structure and replaced with Li ions during cycling of the cell in the voltage range, 1.5 V to 4.5 V. This eventually resulted in a fully reversible Li intercalation into the LixV2O5 structure when 0.0 ≤ x ≤ 2.0. The second study is to apply the synthesis method to LiVS2 for the synthesis of β׳-LixV2O5 for use as a high performance cathode. The synthesis method is based on the heat treatment of the pure LiVS2 in atmospheric air. By employing this method of synthesis, well-crystalized, rod-shaped β׳-LixV2O5 particles 20 – 30 μm in length and 3 – 6 μm in width were obtained. Moreover, the surface of β׳-LixV2O5 particles was found to be coated by an amorphous vanadium oxysulfide film (~20 nm in thickness). In contrast to a low temperature vanadium pentoxide phase (LixV2O5), the electrochemical intercalation of lithium into the β׳-LixV2O5 was fully reversible where 0.0 < x < 2.0, and it delivered a capacity of 310 mAh/g at a current rate of 0.07 C between 1.5 V and 4 V. Good capacity retention of more than 88% was also observed after 50 cycles even at a higher current rate of 2 C. The third study is the investigation of NaVS2 as a cathode intercalation material for sodium ion batteries. We have shown that reversible electrochemical deintercalation of x ~ 1.0 Na per formula unit of NaxVS2, corresponding to a capacity of ~200 mAh/g, is possible. And a stable capacity of ~120 mAh/g after 30 cycles was observed. These studies show that the new chemical synthesis route for creating a phase transformation from the vanadium sulfide to oxide by heat treatment in air is a promising method for preparing vanadium oxide cathode material with high reversibility. Although this sample shows a relatively low voltage range compared with other cathodes such as LiCoO2 (3.8 V) and LiFePO4 (3.4 V), the large capacity of this sample is quite attractive in terms of increasing energy density in Li-ion batteries. Also, NaVS2 could be a promising cathode material for sodium ion batteries.

Lithium ion batteries (LIBs) have attracted considerable interest due to their wide range of applications, such as portable electronics, electric vehicles (EVs) and aerospace applications. Particularly, the emergence of a variety of nanostructured materials has driven the development of LIBs towards the next generation, which is featured with high specific energy and large power density. Herein, rolled-up nanotechnology is introduced for the design of strain-released materials as anodes of LIBs. Upon this approach, self-rolled nanostructures can be elegantly combined with different functional materials and form a tubular shape by relaxing the intrinsic strain, thus allowing for enhanced tolerance towards stress cracking. In addition, the hollow tube center efficiently facilitates electrolyte mass flow and accommodates volume variation during cycling. In this context, such structures are promising candidates for electrode materials of LIBs to potentially address their intrinsic issues. This work focuses on the development of superior structures of Si and SnO2 for LIBs based on the rolled-up nanotech. Specifically, Si is the most promising substitute for graphite anodes due to its abundance and high theoretical gravimetric capacity. Combined with the C material, a Si/C self-wound nanomembrane structure is firstly realized. Benefiting from a strain-released tubular shape, the bilayer self-rolled structures exhibit an enhanced electrochemical behavior over commercial Si microparticles. Remarkably, this behavior is further improved by introducing a double-sided carbon coating to form a C/Si/C self-rolled structure. With SnO2 as active material, an intriguing sandwich-stacked structure is studied. Furthermore, this novel structure, with a minimized strain energy due to strain release, exposes more active sites for the electrochemical reactions, and also provides additional channels for fast ion diffusion and electron transport. The electrochemical characterization and morphology evolution reveal the excellent cycling performance and stability of such structures.

The growing urgency of climate change has led to growth in the electrification technology field, where batteries have emerged as an essential role in the renewable energy transition, supporting the implementation of environmentally friendly technologies such as smart grids, energy storage systems, and electric vehicles. Battery cell degradation is a common occurrence indicating battery usage. Optimizing lithium-ion battery degradation during operation benefits the prediction of future degradation, minimizing the degradation mechanisms that result in power fade and capacity fade. This degree project aims to investigate battery degradation prediction based on capacity using deep learning methods. Through analysis of battery degradation and health prediction for lithium-ion cells using non-destructive techniques. Such as electrochemical impedance spectroscopy obtaining ECM and three different deep learning models using multi-channel data. Additionally, the AI models were designed and developed using multi-channel data and evaluated performance within MATLAB. The results reveal an increased resistance from EIS measurements as an indicator of ongoing battery aging processes such as loss o active materials, solid-electrolyte interphase thickening, and lithium plating. The AI models demonstrate accurate capacity estimation, with the LSTM model revealing exceptional performance based on the model evaluation with RMSE. These findings highlight the importance of carefully managing battery charging processes and considering factors contributing to degradation. Understanding degradation mechanisms enables the development of strategies to mitigate aging processes and extend battery lifespan, ultimately leading to improved performance.

<p>This work focuses on the collection and analysis of Lithium-ion battery operational and temperature data during nail penetration testing through two different experimental approaches. Raman spectroscopy, machine learning, and internal temperature sensors are used to collect and analyze data to further investigate the effects on cell operation during and after nail penetrations, and the feasibility of using this data to predict future performance.</p> <p><br></p> <p>The first section of this work analyzes the effects on continued operation of a small Lithium-ion prismatic cell after nail penetration. Raman spectroscopy is used to examine the effects on the anode and cathode materials of cells that are cycled for different amounts of time after a nail puncture. Incremental capacity analysis is then used to corroborate the findings from the Raman analysis. The study finds that the operational capacity and lifetime of cells is greatly reduced due to the accelerated degradation caused by loss of material, uneven current distribution, and exposure to atmosphere. This leads into the study of using the magnitude and corresponding voltage of incremental capacity peaks after nail puncture to forecast the operation of damaged cells. A Gaussian process regression is used to predict discharge capacity of different cells that experience the same type of nail puncture. The results from this study show that the method is capable of making accurate predictions of cell discharge capacity even with the higher rate of variance in operation after nail puncture, showing the method of prediction has the potential to be implemented in devices such as battery management systems.</p> <p><br></p> <p>The second section of this work proposes a method of inserting temperature sensors into commercially-available cylindrical cells to directly obtain internal temperature readings. Characterization tests are used to determine the effect on the operability of the modified cells after the sensors are inserted, and lifetime cycle testing is implemented to determine the long-term effects on cell performance. The results show the sensor insertion causes a small reduction in operational performance, and lifetime cycle testing shows the cells can operate near their optimal output for approximately 100-150 cycles. Modified cells are then used to monitor internal temperatures during nail penetration tests and how the amount of aging affects the temperature response. The results show that more aging in a cell causes higher temperatures during nail puncture, as well as a larger difference between internal and external temperatures, due mostly to the larger contribution of Joule heating caused by increased internal resistance.</p>

The increasing adoption of electric vehicles (EVs) brings forth the challenge of effectively managing the second-life and end-of-life cycles for lithium-ion batteries. Augmented Reality (AR) offers a promising solution to sustainably and efficiently dismantle these batteries. This thesis explores the development and evaluation of an AR mobile app specifically designed for guiding the dismantling process of a Volkswagen (VW) ID.4 lithium-ion EV battery. Subsequently, a detailed end-to-end development pipeline is presented, spanning from identifying the correct dismantling steps and building complete 3D reconstructions of the ID.4 battery using photogrammetry and CAD or 3D modelling, to creating an AR mobile application in Unity with the help of Vuforia allowing users to visualize the disassembly steps through an interactive guide. Tracking recognition testing results for each model indicates that simpler models exhibit a higher chance of producing false positives, while composite models have a greater minimum recognition distance compared to the faithfulto-real-life one-piece counterparts. User testing is conducted using a hybrid approach, combining a Figma prototype with video recordings to replicate the app’s behavior in a safe environment, without the physical presence of a high voltage battery. Results show positive user feedback, demonstrating the app’s usability and effectiveness in guiding the dismantling process. Furthermore, the thesis evaluates the app’s performance through the System Usability Scale (SUS) and the Technology Acceptance Model. The obtained SUS score of 80 (Grade B - Good) indicates favorable usability, while the Technology Acceptance Model provides insights into potential users’ perceptions. / Den ökande användningen av elektriska fordon (EV) frambringar utmaningen att effektivt hantera andra livscykler och slutlivscykler för litiumjonbatterier. För att hållbart och effektivt demontera dessa batterier erbjuder Augmented Reality (AR) en lovande lösning. Denna uppsats utforskar utvecklingen och utvärderingen av en AR-mobilapplikation som specifikt är utformad för att guida demonteringsprocessen av ett Volkswagen (VW) ID.4 litiumjon EVbatteri. Därefter presenteras en detaljerad genomgående utvecklingsprocess, som sträcker sig från att identifiera korrekta demonteringssteg och skapa kompletta 3D-rekonstruktioner av ID.4-batteriet med hjälp av fotogrammetri och CAD eller 3D-modellering, till att skapa en AR-mobilapplikation i Unity med hjälp av Vuforia, som tillåter användare att visualisera demonteringsstegen genom en interaktiv guide. Resultaten bättre identifieringstester för varje modell indikerar att enklare modeller har större chans att producera falska positiva resultat, medan komplexa modeller har större minsta igenkänningsavstånd jämfört med helhetsmodeller som är trogna verkligheten. Användartester genomförs med hjälp av en hybridmetod som kombinerar en Figma-prototyp med videoinspelningar för att återskapa appens beteende i en säker miljö, utan att behöva ha ett högspänningsbatteri fysiskt närvarande. Resultaten visar positivt användarfeedback och bekräftar appens användarvänlighet och effektivitet vid guidning av demonteringsprocessen. Uppsatsen utvärderar också appens prestanda genom System Usability Scale (SUS) och Technology Acceptance Model. Den erhållna SUS-poängen på 80 (Betyg B - Bra) indikerar en god användbarhet, medan Technology Acceptance Model ger insikter om potentiella användares uppfattningar.

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.