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- All Subjects: Materials Science
- Genre: Masters Thesis
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Description
Tin (Sn) has a high-specific capacity (993 mAhg-1) as an anode material for Li-ion batteries. To overcome the poor cycling performance issue caused by its large volume expansion and pulverization during the charging and discharging process, many researchers put efforts into it. Most of the strategies are through nanostructured material design and introducing conductive polymer binders that serve as matrix of the active material in anode. This thesis aims for developing a novel method for preparing the anode to improve the capacity retention rate. This would require the anode to have high electrical conductivity, high ionic conductivity, and good mechanical properties, especially elasticity. Here the incorporation of a conducting polymer and a conductive hydrogel in Sn-based anodes using a one-step electrochemical deposition via a 3-electrode cell method is reported: the Sn particles and conductive component can be electrochemically synthesized and simultaneously deposited into a hybrid thin film onto the working electrode directly forming the anode. A well-defined three dimensional network structure consisting of Sn nanoparticles coated by conducting polymers is achieved. Such a conductive polymer-hydrogel network has multiple advantageous features: meshporous polymeric structure can offer the pathway for lithium ion transfer between the anode and electrolyte; the continuous electrically conductive polypyrrole network, with the electrostatic interaction with elastic, porous hydrogel, poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) (PAMPS) as both the crosslinker and doping anion for polypyrrole (PPy) can decrease the volume expansion by creating porous scaffold and softening the system itself. Furthermore, by increasing the amount of PAMPS and creating an interval can improve the cycling performance, resulting in improved capacity retention about 80% after 20 cycles, compared with only 54% of that of the control sample without PAMPS. The cycle is performed under current of 0.1 C.
ContributorsGao, Tianxiang (Author) / He, Ximin (Thesis advisor) / Sieradzki, Karl (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2015
Description
This research seeks to answer the question if there is a singular relationship between stishovite nucleation and the atomistic structure of the preshocked amorphous SiO$_2$. To do this a stishovite manufacturing method is developed in which 1,152 samples were produced. The majority of these samples did crystallize. The method was produced through two rounds of experiments and fine-tuning with the pressure damp, temperature damp, shock pressure using an NPHug fix, and sample origin. A new random atomic insertion method was used to generate a new and different SiO$_2$ amorphous structure not before seen within the research literature. The optimal values for shock were found to be 60~GPa for randomly atom insertion samples and 55~GPa for quartz origin samples. Temperature damp appeared to have a slight effect optimizing at 0.05~ps and the pressure damp had no visible effect, testing was done with temperature damp from 0.05 to 0.5~ps and pressure damp from 0.1 to 10.0~ps. There appeared to be significant randomness in crystallization behavior. The preshocked and postnucleated samples were transformed into Gaussian fields of crystal, mass, and charge. These fields were divided and classified using a cut-off method taking the number of crystals produced in portions of each simulation and classifying each potion as nucleated or non-nucleated. Data in which some nucleation but not a critical amount was present was removed constituting 2.6\% to 20.3\% of data in all tests. A max method was also used which takes only the maximum portions of each simulation to classify as nucleating. There are three other variables tested within this work, a sample size of 18,000 or 72,728~atoms, Gaussian variance of 1 or 4~\AA, and Convolutional neural network (CNN) architecture of a garden verity or all convolution along with the portioning classification method, sample origination, and Gaussian field type. In total 64 tests were performed to try every combination of variable. No significant classifications were made by the CNNs to nucleation or non-nucleation portions. The results clearly confirmed that the data was not abstracting to atomistic structure and was random by all classifications of the CNNs. The all convolution CNN testing did show smoother outcomes in training with less fluctuations. 59\% of all validation accuracy was held at 0.5 for a random state and 84\% was within $\pm0.02$ of 0.5. It is conclusive that prenucleation structure is not the sole predictor of nucleation behavior. It is not conclusive if prenucleation structure is a partial or non-factor within nucleation of stishovite from amorphous SiO$_2$.
ContributorsChristen, Jonathan Scorr (Author) / Oswald, Jay (Thesis advisor) / Muhich, Christopher (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2021
Description
Nanostructured (NS, grain size (d) <100nm) and ultrafine grained (UFG, d<500nm) metals possess superior mechanical and electrical properties over coarse grained (CG, d≫1μm) metals. The strength of metals like copper (Cu) has been shown to be significantly improved when engineered to have fine and ultrafine grain sizes via processes such as cryomilling, Cold Isostatic Pressing (CIP) and Continuous Equal Channel Angular Pressing (C-ECAP). This study investigates the mechanical and electrical properties of laboratory scale copper (Cu) conductors manufactured through several steps including cryomilling followed by cold isostatic pressing and finally C-ECAP and how its strength is affected by a variety of parameters when tested in uniaxial tension. The copper material is fabricated through cryomilling, cold isostatic pressing and (C-ECAP). Mechanical characterization is conducted using uniaxial tensile tests, nanoindentation and hardness tests. Pre and Post fabrication examination of the material with 3D-xray tomography, optical and electron microscope were conducted to gain deeper understanding of the effects of the processing parameters on the material during fabrication and the evolution of the microstructure as the powders go through the manufacturing process. Electrical testing is conducted to evaluate the electrical conductivity of the manufactured copper.
While the material showed improved strength and hardness compared to conventional copper material at room temperature, its ductility decreased. Also, higher ECAP temperatures produced materials with higher electrical and mechanical properties.
ContributorsOpoku, Jackson Abankwa (Author) / Ladani, Leila LJL (Thesis advisor) / Razmi, Jafar JR (Committee member) / Li, Xiangjia XL (Committee member) / Arizona State University (Publisher)
Created2022
Description
Vanadium-dioxide-based devices show great switchability in their optical properties due to its dramatic thermochromic phase transition from insulator to metal, but generally have concerns due to its relatively high transition temperature at 68 °C. Doping the vanadium dioxide with tungsten has been shown to reduce its transition temperature at the cost lower optical property differences between its insulating and metallic phases. A recipe is developed through parametric experimentation to fabricate tungsten-doped vanadium dioxide consisting of a novel dual target co-sputtering deposition, a furnace oxidation process, and a post-oxidation annealing process. The transmittance spectra of the resulting films are measured via Fourier-transform infrared spectroscopy at different temperatures to confirm the lowered transition temperature and analyze their thermal-optical hysteresis behavior through the transition temperature range. Afterwards, the optical properties of undoped sputtered vanadium films are modeled and effective medium theory is used to explain the effect of tungsten dopants on the observed transmittance decrease of doped vanadium dioxide. The optical modeling is used to predict the performance of tungsten-doped vanadium dioxide devices, in particular a Fabry-Perot infrared emitter and a nanophotonic infrared transmission filter. Both devices show great promise in their optical properties despite a slight performance decrease from the tungsten doping. These results serve to illustrate the excellent performance of the co-sputtered tungsten-doped vanadium dioxide films.
ContributorsChao, Jeremy (Author) / Wang, Liping (Thesis advisor) / Wang, Robert (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2022
Description
Alkali-activated aluminosilicates, commonly known as "geopolymers", are being increasingly studied as a potential replacement for Portland cement. These binders use an alkaline activator, typically alkali silicates, alkali hydroxides or a combination of both along with a silica-and-alumina rich material, such as fly ash or slag, to form a final product with properties comparable to or better than those of ordinary Portland cement. The kinetics of alkali activation is highly dependent on the chemical composition of the binder material and the activator concentration. The influence of binder composition (slag, fly ash or both), different levels of alkalinity, expressed using the ratios of Na2O-to-binders (n) and activator SiO2-to-Na2O ratios (Ms), on the early age behavior in sodium silicate solution (waterglass) activated fly ash-slag blended systems is discussed in this thesis. Optimal binder composition and the n values are selected based on the setting times. Higher activator alkalinity (n value) is required when the amount of slag in the fly ash-slag blended mixtures is reduced. Isothermal calorimetry is performed to evaluate the early age hydration process and to understand the reaction kinetics of the alkali activated systems. The differences in the calorimetric signatures between waterglass activated slag and fly ash-slag blends facilitate an understanding of the impact of the binder composition on the reaction rates. Kinetic modeling is used to quantify the differences in reaction kinetics using the Exponential as well as the Knudsen method. The influence of temperature on the reaction kinetics of activated slag and fly ash-slag blends based on the hydration parameters are discussed. Very high compressive strengths can be obtained both at early ages as well as later ages (more than 70 MPa) with waterglass activated slag mortars. Compressive strength decreases with the increase in the fly ash content. A qualitative evidence of leaching is presented through the electrical conductivity changes in the saturating solution. The impact of leaching and the strength loss is found to be generally higher for the mixtures made using a higher activator Ms and a higher n value. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) is used to obtain information about the reaction products.
ContributorsChithiraputhiran, Sundara Raman (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniyam D (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2012
Description
Integrating advanced materials with innovative manufacturing techniques has propelled the field of additive manufacturing into new frontiers. This study explores the rapid 3D printing of reduced graphene oxide/polymer composites using Micro-Continuous Liquid Interface Production (μCLIP), a cutting-edge technology known for its speed and precision. A printable ink is formulated with reduced graphene oxide for μCLIP-based 3D printing. The research focuses on optimizing μCLIP parameters to fabricate reduced graphene composites efficiently. The study encompasses material synthesis, ink formulation and explores the resulting material's structural and electrical properties. The marriage of graphene's unique attributes with the rapid prototyping capabilities of μCLIP opens new avenues for scalable and rapid production in applications such as energy storage, sensors, and lightweight structural components. This work contributes to the evolving landscape of advanced materials and additive manufacturing, offering insights into the synthesis, characterization, and potential applications of 3D printed reduced graphene oxide/polymercomposites.
ContributorsRavishankar, Chayaank Bangalore (Author) / Chen, Xiangfan (Thesis advisor) / Bhate, Dhruv (Committee member) / Azeredo, Bruno (Committee member) / Arizona State University (Publisher)
Created2024