This thesis aims to provide insight into the fundamental electrochemical processes taking place when cycling SnO2 in lithium-ion batteries (LIBs). Special attention was paid to the partial reversibility of the tin oxide conversion reaction and how to enhance its reversibility. Another main effort was to pinpoint which limitations play a role in tin based electrodes besides the well-known volume change effect in order to develop new strategies for their improvement. In this aspect, Li+ mass transport within the electrode particles and the large first cycle charge transfer resistance were studied. Li+ diffusion was proven to be an important issue regarding the electrochemical cycling of SnO2. It was also shown that it is the Li+ transport inside the SnO2 particles which represents the largest limitation. In addition, the overlap between the potential regions of the tin oxide conversion and the alloying reaction was investigated with photoelectron spectroscopy (PES) to better understand if and how the reactions influence each other`s reversibility. The fundamental insights described above were subsequently used to develop strategies for the improvement of the performance and the cycle life for SnO2 electrodes in LIBs. For instance, elevated temperature cycling at 60 oC was employed to alleviate the Li+ diffusion limitation effects and, thus, significantly improved capacities could be obtained. Furthermore, an ionic liquid electrolyte was tested as an alternative electrolyte to cycle at higher temperatures than 60 oC which is the thermal stability limit for the conventional LP40 electrolyte. In addition, cycled SnO2 nanoparticles were characterized with transmission electron microscopy (TEM) to determine the effects of long term high temperature cycling. Also, the effect of vinylene carbonate (VC) as an electrolyte additive on the cycling behavior of SnO2 nanoparticles was studied in an effort to improve the capacity retention. In this context, a recently introduced intermittent current interruption (ICI) technique was employed to measure and compare the development of internal cell resistances with and without VC additive.

Many material properties depend on specific details of microstructure and both optimal material performance and material reliability often correlate directly to microstructure. In nano- and micro-systems, the material's microstructure has a characteristic length scale that approaches that of the device in which it is used. Fundamental understanding and prediction of material behavior in nano- and micro-systems depend critically on methods for computing the effect of microstructure. Methods for including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) rechargeable lithium ion battery microstructures, 2) photonic composites with anisotropic particulate morphologies, 3) crack deflection in partially devitrified metallic glasses. / Singapore-MIT Alliance (SMA)

The role of nanohybrid materials in the fields of polymer composites and electrochemical energy systems is significant since they affect the enhanced physical properties and improved electrochemical performance, respectively. As basic nanomaterials, carbon nanotubes and graphene were utilized due to their outstanding physical properties. With these materials, hybrid nanostructures were generated through a novel synthesis method, modified sol-gel process; namely, carbon nanotubes (CNTs)-maghemite and reduced graphene oxide (rGO)-maghemite nanohybrid materials were developed. In the study on polymer composities, developed CNTs-maghemite (magnetic carbon nanotbues (m-CNTs)) were readily aligned under an externally applied magnetic field, and due to the aligned features of m-CNTs in polymer matrices, it showed much enhanced anisotropic electrical and mechanical properties. In the study on electrochemical energy system (Li-ion batteries), rGO-maghemite were used as anode materials; as a result, they showed improved electrochemical performance for Li-ion batteries due to their specific morphology and characteristics.

Electric vehicles (EVs) offer an exciting opportunity in China both in terms of the potential to build a domestic manufacturing base and the potential to create a strong domestic market for the product. The Chinese nation stands to benefit from both supply-side and demand-side promotion due to the economic stimulus from EV manufacturing and export, the environmental benefits of reduced air pollution and reduced greenhouse gas emissions, and the energy security benefits of transitioning away from foreign oil dependence. The Chinese have several advantages when it comes to stimulating EV industry development and EV deployment, including: leadership in battery technology, great potential for cost competitiveness, an enormous and emerging number of new car buyers, and high level government support. Yet a number of challenges must be taken into account as well, including: shortfalls in overall automobile R&D spending, consumer concerns about Chinese cars’ safety and reliability, enhancing the appeal of the Chinese brand, and heavy national infrastructure demands. This paper will seek to examine the opportunities and challenges associated with EV deployment in China and identify industry actions and policy measures to facilitate the process.

The rechargeable lithium ion batteries (LIB) are playing increasingly important roles in powering portal commercial electronic devices. They are also the potential power sources of electric mobile vehicles. The first kind of the cathode materials, LiXCoO2, was commercialized by Sony Company in 1980s, and it is still widely used today in LIB. However, the high cost of cobalt source, its environmental unfriendliness and the safety issue of LiXCoO2 have hindered its widespread usage today. Searching for alternative cathode materials with low cost of the precursors, being environmentally benign and more stable in usage has become a hot topic in LIB research and development. In the first part of this study, lithium nickel manganese cobalt oxide (LiNi0.6Mn0.35Co0.05O2) is studied as the electrode. The materials are synthesized at high temperatures by solid state reaction method. The effect of synthesis temperature on the electrochemical performance is investigated, where characterizations by, for example, X-ray diffraction (XRD) and scanning electron microscopy (SEM), for particle size distribution, specific surface area, and charge-discharge property, are done over samples prepared at different conditions for comparison. The electrochemical tests of the rechargeable Li ion batteries using LiNi0.6Mn0.35Co0.05 cathode prepared at optimum conditions are carried out in various voltage ranges, at different discharge rates and at high temperature. In another set of experiments, the material is adopted as anode with lithium foil as the cathode, and its capacitance is tested. In the second part of this study, the iron based cathode material is investigated. Lithium iron orthosilicate with carbon coating is synthesized at 700℃ by solid state reaction, which is assisted by high energy ball milling. Characterizations are done for discharge capacities of the samples with different carbon weight ratio coatings. / published_or_final_version / Physics / Master / Master of Philosophy

Vertically aligned multi walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysis in anodized aluminum oxide (AAO) templates without the use of a catalyst, were integrated into a resistive sensor design. The steady state sensitivities as high as 5% and 10% for 100 ppm of NH3 and NO2 respectively at a flow rate of 750 sccm were observed. A study was undertaken to elucidate (i) the dependence of sensitivity on the thickness of amorphous carbon layers, (ii) the effect of UV light on gas desorption characteristics and (iii) the dependence of room temperature sensitivity on different NH3 and NO2 flow rates. An equivalent circuit model was developed to understand the operation and propose design changes for increased sensitivity. Multi Walled Carbon NanoTubes (MWCNTs) – Polymer composite based hybrid sensors were fabricated and integrated into a resistive sensor design for gas sensing applications. Thin films of MWCNTs were grown onto Si/SiO2 substrates via xylene pyrolysis using chemical vapor deposition technique. Polymers like PEDOT:PSS and Polyaniline (PANI) mixed with various solvents like DMSO, DMF, 2-Propanol and Ethylene Glycol were used to synthesize the composite films. These sensors exhibited excellent response and selectivity at room temperature when exposed to low concentrations (100ppm) of gases like NH3 and NO2. Effect of various solvents on the sensor response imparting selectivity to CNT – Polymer nanocomposites was investigated extensively. Sensitivities as high as 28% was observed for a MWCNT – PEDOT:PSS composite sensor when exposed to 100ppm of NH3 and -29.8% sensitivity for a MWCNT-PANI composite sensor to 100ppm of NO2. A novel nanostructured electrode design for Li based batteries and electrochemical capacitor applications was developed and tested. High density and highly aligned metal oxide nanowire arrays were fabricated via template assisted electrochemical deposition. Nickel and Molybdenum nanowires fabricated via cathodic deposition process were converted into respective oxides via thermal treatments and were evaluated as electrodes for batteries and capacitor applications via Cyclic Voltammetery (CV). Several chemical baths were formulated for the deposition of pristine molybdenum nanowires. Superior electrochemical performance of metal (Ni and Mo) oxide nanowires was observed in comparison to the previously reported nano-particle based electrodes.

Three-dimensional macroporous structures (‘opals’ and ‘inverse opals’) can be produced by colloidal crystal templating, one of the most intensively studied areas in materials science today. There are several potential advantages of lithium-ion battery electrodes based on inverse opal structures. High electrode surface, easier electrolyte access to the bulk of electrode and reduced lithium diffusion lengths allow higher discharge rates. Highly open structures provide for better mechanical stability to volume swings during cycling. Silicon is one of the most promising anode materials for lithium-ion batteries. Its theoretical capacity exceeds capacities of all other materials besides metallic lithium. Silicon is abundant, cheap, and its use would allow for incorporation of microbattery production into the semiconductor manufacturing. Performance of silicon is restricted mainly by large volume changes during cycling. The objective of this work was to investigate how the inverse opal structures influence the performance of silicon electrodes. Several types of silicon-based inverse opal films were synthesised, and their electrochemical performance was studied. Amorphous silicon inverse opals were fabricated via chemical vapour deposition and characterised by various techniques. Galvanostatic cycling of these materials confirmed the feasibility of the approach taken, since the electrodes demonstrated high capacities and decent capacity retentions. The rate performance of amorphous silicon inverse opals was unsatisfactory due to low conductivity of silicon. The conductivity of silicon inverse opals was improved by crystallisation. Nanocrystalline silicon inverse opals demonstrated much better rate capabilities, but the capacities faded to zero after several cycles. Silicon-carbon composite inverse opal materials were synthesised by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals in an attempt to further increase conductivity and achieve mechanical stabilisation of the structures. The amount of carbon deposited proved to be insufficient to stabilise the structures, and silicon-carbon composites demonstrated unsatisfactory electrochemical behaviour. Carbon inverse opals were coated with amorphous silicon producing another type of macroporous composites. These electrodes demonstrated significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increased the material conductivity, but also resulted in lower silicon pulverisation during cycling.

Titanium dioxide, TiO₂, materials have received much attention in recent years due to their potential use as intercalation negative electrodes for rechargeable lithium-ion batteries. The aim of this doctoral work was to synthesise and characterise new titanium dioxide nanomaterials and to investigate their electrochemical behaviour. Three morphologies of TiO₂(B) phase: micro-sized (bulk), nanowires and nanotubes, were synthesised. All three exhibit properties which make them excellent hosts for lithium intercalation. The nanotubes show the best capability of accommodating lithium in the structure, being able to host over one molar equivalent of lithium at low current rates (5 mA g⁻¹). The lithium insertion mechanism in the TiO₂(B) was studied using powder neutron diffraction. In addition, the nature of the irreversible capacity of the nanotubes was studied and ways of reducing it proposed. Nanotubes of another titanium dioxide polymorph, anatase, were synthesised and characterised. Their electrochemical performance was compared with that of commercially available counterparts with different morphologies and particle sizes. The interrelation between particle size/morphology and electrochemical properties has been established. The insertion of lithium which leads to phase variations was studied using in situ Raman microscopy and neutron powder diffraction. It has been demonstrated that doping of the TiO₂(B) nanotubes with vanadium improves their electronic conductivity which is essential for practical applications. Remarkably good electrochemical performance is exhibited by the 6% V-doped TiO₂(B) nanotubes.

abstract: There is a fundamental attractiveness about harnessing renewable energy in an age when sustainability is an ethical norm. Lithium ion batteries and hydrogen fuels are considered the most promising energy source instead of fossil fuels. This work describes the investigation of new cathode materials and devices architectures for lithium ion batteries, and photocatalysts for their usage in water splitting and waste water treatment. LiCoO2 and LiNi1/3Mn1/3Co1/3O2 were exfoliated into nanosheets using electrochemical oxidation followed by intercalation of tetraethylammonium cations. The nanosheets were purified using dialysis and electrophoresis. The nanosheets were successfully restacked into functional cathode materials with microwave hydrothermal assistance, indicating that new cathodes can be obtained by reassembling nanosheets. This method can pave the way for the synthesis of materials with novel structures and electrochemical properties, as well as facilitate the fabrication of hybrid and composite structures from different nanosheets as building blocks. Paper folding techniques are used in order to compact a Li-ion battery and increase its energy per footprint area. Full cells were prepared using Li4Ti5O12 and LiCoO2 powders deposited onto current collectors consisting of paper coated with carbon nanotubes. Folded cells showed higher areal capacities compared to the planar versions. Origami lithium-ion battery made in this method that can be deformed at an unprecedented high level, including folding, bending and twisting. Spray pyrolysis was used to prepare films of AgInS2 with and without Sn as an extrinsic dopant. The photoelectrochemical performance of these films was evaluated after annealing under a N2 or S atmosphere with different amounts of the Sn dopant. Density Function Theory (DFT) was used to calculate the band structure of AgInS2 and understand the role of Sn doping in the observed properties. Cr(VI) removal was investigated using multiple oxide photocatalyst and additives. The efficiency for Cr(VI) removal using these photocatalysts was investigated in synthetic neutral and alkaline water, as well as in cooling tower blowdown water. While sulfite alone can chemically reduce Cr(VI), sulfite in combination with a photocatalyst resulted in faster and complete removal of Cr(VI) in 10 min using a SO32−/Cr(VI) ratio >35 in pH ∼ 8 solutions. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2016

abstract: Lithium ion batteries prepared with a ceramic separator, have proven to possess improved safety, reliability as well as performance characteristics when compared to those with polymer separators which are prone to thermal runaway. Purely inorganic separators are highly brittle and expensive. The electrode-supported ceramic separator permits thinner separators which are a lot more flexible in comparison. In this work, it was observed that not any α-alumina could be used by the blade coating process to get a good quality separator on Li4Ti5O12 (LTO) electrode. In this work specifically, the effect of particle size of α-alumina, on processability of slurry was investigated. The effect of the particle size variations on quality of separator formation was also studied. Most importantly, the effect of alumina particle size and its distribution on the performance of LTO/Li half cells is examined in detail. Large-sized particles were found to severely limit the ability to fabricate such separators. The α-alumina slurry was coated onto electrode substrate, leading to possible interaction between α-alumina and LTO substrate. The interaction between submicron sized particles of α-alumina with the substrate electrode pores, was found to affect the performance and the stability of the separator. Utilizing a bimodal distribution of submicron sized particles with micron sized particles of α-alumina to prepare the separator, improved cell performance was observed. Yet only a specific ratio of bimodal distribution achieved good results both in terms of separator formation and resulting cell performance. The interaction of α-alumina and binder in the separator, and its effect on the performance of substrate electrode was investigated, to understand the need for bimodal distribution of powder forming the separator. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2017