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Description
Novel materials for Li-ion batteries is one of the principle thrust areas for current research in energy storage, more so than most, considering its widespread use in portable electronic gadgets and plug-in electric and hybrid cars. One of the major limiting factors in a Li-ion battery's energy density is the low specific capacities of the active materials in the electrodes. In the search for high-performance anode materials for Li-ion batteries, many alternatives to carbonaceous materials have been studied. Both cubic and amorphous silicon can reversibly alloy with lithium and have a theoretical capacity of 3500 mAh/g, making silicon a potential high density anode material. However, a large volume expansion of 300% occurs due to changes in the structure during lithium insertion, often leading to pulverization of the silicon. To this end, a class of silicon based cage compounds called clathrates are studied for electrochemical reactivity with lithium. Silicon-clathrates consist of silicon covalently bonded in cage structures comprised of face sharing Si20, Si24 and/or Si28 clusters with guest ions occupying the interstitial positions in the polyhedra. Prior to this, silicon clathrates have been studied primarily for their superconducting and thermoelectric properties. In this work, the synthesis and electrochemical characterization of two categories of silicon clathrates - Type-I silicon clathrate with aluminum framework substitution and barium guest ions (Ba8AlxSi46-x) and Type-II silicon clathrate with sodium guest ions (Nax Si136), are explored. The Type-I clathrate, Ba8AlxSi46-x consists of an open framework of aluminium and silicon, with barium (guest) atoms occupying the interstitial positions. X-ray diffraction studies have shown that a crystalline phase of clathrate is obtained from synthesis, which is powdered to a fine particle size to be used as the anode material in a Li-ion battery. Electrochemical measurements of these type of clathrates have shown that capacities comparable to graphite can be obtained for up to 10 cycles and lower capacities can be obtained for up to 20 cycles. Unlike bulk silicon, the clathrate structure does not undergo excessive volume change upon lithium intercalation, and therefore, the crystal structure is morphologically stable over many cycles. X-ray diffraction of the clathrate after cycling showed that crystallinity is intact, indicating that the clathrate does not collapse during reversible intercalation with lithium ions. Electrochemical potential spectroscopy obtained from the cycling data showed that there is an absence of formation of lithium-silicide, which is the product of lithium alloying with diamond cubic silicon. Type II silicon clathrate, NaxSi136, consists of silicon making up the framework structure and sodium (guest) atoms occupying the interstitial spaces. These clathrates showed very high capacities during their first intercalation cycle, in the range of 3,500 mAh/g, but then deteriorated during subsequent cycles. X-ray diffraction after one cycle showed the absence of clathrate phase and the presence of lithium-silicide, indicating the disintegration of clathrate structure. This could explain the silicon-like cycling behavior of Type II clathrates.
ContributorsRaghavan, Rahul (Author) / Chan, Candace K. (Thesis advisor) / Crozier, Peter (Committee member) / Petuskey, William T (Committee member) / Arizona State University (Publisher)
Created2013
Description
This work focuses on simulation of electrical resistivity and optical behaviors of thin films, where an Ag or Au thin layer is embedded in zinc oxide. Enhanced conductivity and transparency were earlier achieved with multilayer structured transparent conducting oxide (TCO) sandwich layer with metal (TCO/metal/TCO). Sputtering pattern of metal layer is simulated to obtain the morphology, covered area fraction, and the percolation strength. The resistivity as a function of the metal layer thickness fits the modeled trend of covered area fraction beyond the percolation threshold. This result not only presents the robustness of the simulation, but also demonstrates the influence of metal morphology in multilayer structure. Effective medium coefficients are defined from the coverage and percolation strength to obtain simulated optical transmittance which matches experimental observation. The coherence of resistivity and optical transmittance validates the simulation of the sputtered pattern and the incorporation of percolation theory in the model.
ContributorsFang, Chia-Ling (Author) / Alford, Terry L. (Thesis advisor) / Crozier, Peter (Committee member) / Theodore, David (Committee member) / Arizona State University (Publisher)
Created2012
Description
As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode.
ContributorsCavendish, Rio (Author) / Crozier, Peter (Thesis advisor) / Adams, James (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2012
Description
Lithium titanium oxide (LTO), is a crystalline (spinel) anode material that has recently been considered as an alternative to carbon anodes in conventional lithium-ion batteries (LIB), mainly due to the inherent safety and durability of this material. In this paper commercial LTO anode 18650 cells with lithium cobalt oxide (LCO) cathodes have been cycled to simulate EV operating condition (temperature and drive profiles) in Arizona. The capacity fade of battery packs (pack #1 and pack#2), each consisting 6 such cells in parallel was studied. While capacity fades faster at the higher temperature (40°C), fading is significantly reduced at the lower temperature limit (0°C). Non-invasive techniques such as Electrochemical Impedance Spectroscopy (EIS) show a steady increase in the high-frequency resistance along with capacity fade indicating Loss of Active Material (LAM) and formation of co-intercalation products like Solid Electrolyte Interface (SEI). A two-stage capacity fade can be observed as previously reported and can be proved by differential voltage curves. The first stage is gradual and marks the slow degradation of the anode while the second stage is marked by a drastic capacity fade and can be attributed to the fading cathode. After an effective capacity fading of ~20%, the battery packs were disassembled, sorted and repackaged into smaller packs of 3 cells each for second-life testing. No major changes were seen in the crystal structure of LTO, establishing its electrochemical stability. However, the poor built of the 18650-cell appears to have resulted in failures like gradual electrolytic decomposition causing prominent swelling and failure in a few cells and LAM from the cathode along with cation dissolution. This result is important to understand how LTO batteries fail to better utilize the batteries for specific secondary-life applications.
ContributorsWadikar, Harshwardhan (Author) / Crozier, Peter (Thesis advisor) / Wang, Qing H (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2019
Description
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.
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.
ContributorsCheng, Qian (Author) / Chan, Candace Kay (Thesis advisor) / Sieradzki, Karl (Committee member) / Crozier, Peter (Committee member) / He, Ximin (Committee member) / Arizona State University (Publisher)
Created2016
Description
Solid electrolytes have great potential to address the safety issues of Li-ion batteries, but better synthesis methods are still required for ceramics electrolytes such as lithium lanthanum titanate (LLTO) and lithium lanthanum zirconate (LLZO). Pellets made from ceramic nanopowders using conventional sintering can be porous due to the agglomeration of nanoparticles (NPs). Electrospinning is a simple and versatile technique for preparing oxide ceramic nanowires (NWs) and was used to prepare electrospun LLTO and LLZO NWs. Pellets prepared from the electrospun LLTO NWs had higher density, less void space, and higher Li+ conductivity compared to those comprised of LLTO prepared with conventional sol-gel methods, which demonstrated the potential that electrospinning can provide towards improving the properties of sol-gel derived ceramics. Cubic phase LLZO was stabilized at room temperature in the form of electrospun NWs without extrinsic dopants. Bulk LLZO with tetragonal structure was transformed to the cubic phase using particle size reduction via ball milling. Heating conditions that promoted particle coalescence and grain growth induced a transformation from the cubic to tetragonal phase in both types of nanostructured LLZO. Composite polymer solid electrolyte was fabricated using LLZO NWs as the filler and showed an improved ionic conductivity at room temperature. Nuclear magnetic resonance studies show that LLZO NWs partially modify the polymer matrix and create preferential pathways for Li+ conduction through the modified polymer regions. Doping did not have significant effect on improving the overall conductivity as the interfaces played a predominant role. By comparing fillers with different morphologies and intrinsic conductivities, it was found that both NW morphology and high intrinsic conductivity are desired.
ContributorsYang, Ting (Author) / Chan, Candace K. (Thesis advisor) / Crozier, Peter (Committee member) / Lin, Jerry Ys (Committee member) / Arizona State University (Publisher)
Created2017
Description
Nanocrystalline (nc) thin films exhibit a wide range of enhanced mechanical properties compared to their coarse-grained counterparts. Furthermore, the mechanical behavior and microstructure of nc films is intimately related. Thus, precise control of the size, aspect ratio and spatial distribution of grains can enable the synthesis of thin films with exceptional mechanical properties. However, conventional bottom-up techniques for synthesizing thin films are incapable of achieving the microstructural control required to explicitly tune their properties. This dissertation focuses on developing a novel technique to synthesize metallic alloy thin films with precisely controlled microstructures and subsequently characterizing their mechanical properties using in situ transmission electron microscopy (TEM). Control over the grain size and distribution was achieved by controlling the recrystallization process of amorphous films by the use of thin crystalline seed layers. The novel technique was used to manipulate the microstructure of structural (TiAl) and functional (NiTi) thin films thereby exhibiting its capability and versatility. Following the synthesis of thin films with tailored microstructures, in situ TEM techniques were employed to probe their mechanical properties. Firstly, a novel technique was developed to measure local atomic level elastic strains in metallic glass thin films during in situ TEM straining. This technique was used to detect structural changes and anelastic deformation in metallic glass thin films. Finally, as the electron beam (e-beam) in TEMs is known to cause radiation damage to specimen, systematic experiments were carried out to quantify the effect of the e-beam on the stress-strain response of nc metals. Experiments conducted on Al and Au films revealed that the e-beam enhances dislocation activity leading to stress relaxation.
ContributorsSarkar, Rohit (Author) / Rajagopalan, Jagannathan (Thesis advisor) / Peralta, Pedro (Committee member) / Sieradzki, Karl (Committee member) / Crozier, Peter (Committee member) / Arizona State University (Publisher)
Created2017
Description
Lithium conducting garnets in the family of Li7La3Zr2O12 (LLZO) are promising lithium conductors for solid-state batteries, due to their high ionic conductivity, thermal stability, and electrochemical stability with metallic lithium. Despite these advantages, LLZO requires a large energy input to synthesize and process. Generally, LLZO is synthesized using solid-state reaction (SSR) from oxide precursors, requiring high reaction temperatures (900-1000 °C) and producing powder with large particle sizes, necessitating high energy milling to improve sinterability. In this dissertation, two classes of advanced synthesis methods – sol-gel polymer-combustion and molten salt synthesis (MSS) – are employed to obtain LLZO submicron powders at lower temperatures. In the first case, nanopowders of LLZO are obtained in a few hours at 700 °C via a novel polymer combustion process, which can be sintered to dense electrolytes possessing ionic conductivity up to 0.67 mS cm-1 at room temperature. However, the limited throughput of this combustion process motivated the use of molten salt synthesis, wherein a salt mixture is used as a high temperature solvent, allowing faster interdiffusion of atomic species than solid-state reactions. A eutectic mixture of LiCl-KCl allows formation of submicrometer undoped, Al-doped, Ga-doped, and Ta-doped LLZO at 900 °C in 4 h, with total ionic conductivities between 0.23-0.46 mS cm-1. By using a highly basic molten salt medium, Ta-doped LLZO (LLZTO) can be obtained at temperatures as low as 550 °C, with an ionic conductivity of 0.61 mS cm-1. The formation temperature can be further reduced by using Ta-doped, La-excess pyrochlore-type lanthanum zirconate (La2Zr2O7, LZO) as a quasi-single-source precursor, which convert to LLZTO as low as 400 °C upon addition of a Li-source. Further, doped pyrochlores can be blended with a Li-source and directly sintered to a relative density up to 94.7% with high conductivity (0.53 mS cm-1). Finally, a propensity for compositional variation in LLZTO powders and sintered ceramics was observed and for the first time explored in detail. By comparing LLZTO obtained from combustion, MSS, and SSR, a correlation between increased elemental inhomogeneity and reduced ionic conductivity is observed. Implications for garnet-based solid-state batteries and strategies to mitigate elemental inhomogeneity are discussed.
ContributorsWeller, Jon Mark (Author) / Chan, Candace K (Thesis advisor) / Crozier, Peter (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2021