Matching Items (8)
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- All Subjects: Lithium ion batteries
- All Subjects: Nanostructured materials
- Creators: Sieradzki, Karl
Description
This work investigates in-situ stress evolution of interfacial and bulk processes in electrochemical systems, and is divided into two projects. The first project examines the electrocapillarity of clean and CO-covered electrodes. It also investigates surface stress evolution during electro-oxidation of CO at Pt{111}, Ru/Pt{111} and Ru{0001} electrodes. The second project explores the evolution of bulk stress that occurs during intercalation (extraction) of lithium (Li) and formation of a solid electrolyte interphase during electrochemical reduction (oxidation) of Li at graphitic electrodes. Electrocapillarity measurements have shown that hydrogen and hydroxide adsorption are compressive on Pt{111}, Ru/Pt{111}, and Ru{0001}. The adsorption-induced surface stresses correlate strongly with adsorption charge. Electrocatalytic oxidation of CO on Pt{111} and Ru/Pt{111} gives a tensile surface stress. A numerical method was developed to separate both current and stress into background and active components. Applying this model to the CO oxidation signal on Ru{0001} gives a tensile surface stress and elucidates the rate limiting steps on all three electrodes. The enhanced catalysis of Ru/Pt{111} is confirmed to be bi-functional in nature: Ru provides adsorbed hydroxide to Pt allowing for rapid CO oxidation. The majority of Li-ion batteries have anodes consisting of graphite particles with polyvinylidene fluoride (PVDF) as binder. Intercalation of Li into graphite occurs in stages and produces anisotropic strains. As batteries have a fixed size and shape these strains are converted into mechanical stresses. Conventionally staging phenomena has been observed with X-ray diffraction and collaborated electrochemically with the potential. Work herein shows that staging is also clearly observed in stress. The Li staging potentials as measured by differential chronopotentiometry and stress are nearly identical. Relative peak heights of Li staging, as measured by these two techniques, are similar during reduction, but differ during oxidation due to non-linear stress relaxation phenomena. This stress relaxation appears to be due to homogenization of Li within graphite particles rather than viscous flow of the binder. The first Li reduction wave occurs simultaneously with formation of a passivating layer known as the solid electrolyte interphase (SEI). Preliminary experiments have shown the stress of SEI formation to be tensile (~+1.5 MPa).
ContributorsMickelson, Lawrence (Author) / Friesen, Cody (Thesis advisor) / Sieradzki, Karl (Committee member) / Buttry, Daniel (Committee member) / Venables, John (Committee member) / Arizona State University (Publisher)
Created2011
Description
Dealloying induced stress corrosion cracking is particularly relevant in energy conversion systems (both nuclear and fossil fuel) as many failures in alloys such as austenitic stainless steel and nickel-based systems result directly from dealloying. This study provides evidence of the role of unstable dynamic fracture processes in dealloying induced stress-corrosion cracking of face-centered cubic alloys. Corrosion of such alloys often results in the formation of a brittle nanoporous layer which we hypothesize serves to nucleate a crack that owing to dynamic effects penetrates into the un-dealloyed parent phase alloy. Thus, since there is essentially a purely mechanical component of cracking, stress corrosion crack propagation rates can be significantly larger than that predicted from electrochemical parameters. The main objective of this work is to examine and test this hypothesis under conditions relevant to stress corrosion cracking. Silver-gold alloys serve as a model system for this study since hydrogen effects can be neglected on a thermodynamic basis, which allows us to focus on a single cracking mechanism. In order to study various aspects of this problem, the dynamic fracture properties of monolithic nanoporous gold (NPG) were examined in air and under electrochemical conditions relevant to stress corrosion cracking. The detailed processes associated with the crack injection phenomenon were also examined by forming dealloyed nanoporous layers of prescribed properties on un-dealloyed parent phase structures and measuring crack penetration distances. Dynamic fracture in monolithic NPG and in crack injection experiments was examined using high-speed (106 frames s-1) digital photography. The tunable set of experimental parameters included the NPG length scale (20-40 nm), thickness of the dealloyed layer (10-3000 nm) and the electrochemical potential (0.5-1.5 V). The results of crack injection experiments were characterized using the dual-beam focused ion beam/scanning electron microscopy. Together these tools allow us to very accurately examine the detailed structure and composition of dealloyed grain boundaries and compare crack injection distances to the depth of dealloying. The results of this work should provide a basis for new mathematical modeling of dealloying induced stress corrosion cracking while providing a sound physical basis for the design of new alloys that may not be susceptible to this form of cracking. Additionally, the obtained results should be of broad interest to researchers interested in the fracture properties of nano-structured materials. The findings will open up new avenues of research apart from any implications the study may have for stress corrosion cracking.
ContributorsSun, Shaofeng (Author) / Sieradzki, Karl (Thesis advisor) / Jiang, Hanqing (Committee member) / Peralta, Pedro (Committee member) / Arizona State University (Publisher)
Created2012
Description
Lithium-ion batteries can fail and catch fire when overcharged, exposed to high temperatures or short-circuited due to the highly flammable organic liquid used in the electrolyte. Using inorganic solid electrolyte materials can potentially improve the safety factor. Additionally, nanostructured electrolyte materials may further enhanced performance by taking advantage of their large aspect ratio. In this work, the synthesis of two promising nanostructured solid electrolyte materials was explored. Amorphous lithium niobate nanowires were synthesized through the decomposition of a niobium-containing complex in a structure-directing solvent using a reflux method. Lithium lanthanum titanate was obtained via solid state reaction with titanium oxide nanowires as the titanium precursor, but the nanowire morphology could not be preserved due to high temperature sintering. Hyperbranched potassium lanthanum titanate was synthesized through hydrothermal route. This was the first time that hyperbranched nanowires with perovskite structure were made without any catalyst or substrate. This result has the potential to be applied to other perovskite materials.
ContributorsYang, Ting (Author) / Chan, Candace K. (Thesis advisor) / Crozier, Peter A. (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2012
Description
The electrochemical behavior of nanoscale solids has become an important topic to applications, such as catalysis, sensing, and nano–electronic devices. The electrochemical behavior of elemental metal and alloy particles was studied in this work both theoretically and experimentally. A systematic thermodynamic derivation for the size–dependent Pourbaix Diagram for elemental metal particles is presented. The stability of Pt particles was studied by in situ electrochemical scanning tunneling microscopy (ECSTM). It is shown that small Pt particles dissolve at a lower potential than the corresponding bulk material. For the alloy particles, two size ranges of AuAg particles, ∼4 nm and ∼45 nm in diameter, were synthesized by co–reduction of the salts of Au and Ag from an aqueous phase. The alloy particles were dealloyed at a series of potential by chronoamperometry in acid, and the resulting morphology and composition were characterized by electron microscopy, energy dispersive X–ray spectroscopy (EDX). In the case of the smaller particles, only surface dealloying occurred yielding a core–shell structure. A porous structure was observed for the larger particles when the potential was larger than a critical value that was within 50 mV of the thermodynamic prediction.
ContributorsLi, Xiaoqian (Author) / Sieradzki, Karl (Thesis advisor) / Crozier, Peter (Committee member) / Buttry, Daniel (Committee member) / Friesen, Cody (Committee member) / Arizona State University (Publisher)
Created2012
Description
Lithium-ion batteries are one of the most widely used energy storage solutions today. As renewable energy sources proliferate to meet growth in worldwide energy consumption, it is important that lithium-ion batteries be improved to help capture this energy for use when the demand arises. One way to boost the performance of lithium-ion batteries is to replace the electrode active materials with materials of higher specific capacity. Silicon is one material that has been widely touted as a potential replacement for the graphite used in commercial anodes with a theoretical capacity of 3500 mAh/g as opposed to graphite's 372 mAh/g. However, bulk silicon is known to pulverize after experiencing large strains during lithiation. Here, silicon clathrates are investigated as a potential structure for accommodation of these strains. Silicon clathrates consist of covalently bonded silicon host cages surrounding a guest alkali or alkaline earth metal ion. Previous work has looked at silicon clathrates for their superconducting and thermoelectric properties. In this study, electrochemical properties of type I and II silicon clathrates with sodium guest ions (NaxSi46 and NaxSi136) and type I silicon clathrates with copper framework substitution and barium guest ions (Ba8CuxSi46-x) are examined. Sodium clathrates showed very high capacities during initial lithiation (>2500 mAh/g), but rapidly lost capacity thereafter. X-ray diffraction after lithiation showed conversion of the clathrate phase to lithium silicide and then to amorphous silicon after delithiation, indicating destruction of the clathrate structure as a possible explanation for the rapid capacity fade. Ba8CuxSi46-x clathrates were found to have their structures completely intact after 50 cycles. However, they had very low reversible capacities (<100 mAh/g) and potentially might not be electrochemically active. Further work is needed to better understand exactly how lithium is inserted into clathrates and if copper impurities detected during wavelength-dispersive X-ray spectroscopy could be inhibiting lithium transport into the clathrates.
ContributorsWagner, Nicholas Adam (Author) / Chan, Candace (Thesis director) / Sieradzki, Karl (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2014-05
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
This research examines several critical aspects of the so-called "film induced cleavage" model of stress corrosion cracking using silver-gold alloys as the parent-phase material. The model hypothesizes that the corrosion generates a brittle nanoporous film, which subsequently fractures forming a high-speed crack that is injected into the uncorroded parent-phase alloy. This high speed crack owing to its kinetic energy can penetrate beyond the corroded layer into the parent phase and thus effectively reducing strength of the parent phase. Silver-gold alloys provide an ideal system to study this effect, as hydrogen effect can be ruled out on thermodynamic basis. During corrosion of the silver-gold alloy, the less noble metal i.e. silver is removed from the system leaving behind a nanoporous gold (NPG) layer. In the case of polycrystalline material, this corrosion process proceeds deeper along the grain boundary than the matrix grain. All of the cracks with apparent penetration beyond the corroded (dealloyed) layer are intergranular. Our aim was to study the crack penetration depth along the grain boundary to ascertain whether the penetration occurs past the grain-boundary dealloyed depth. EDS and imaging in high-resolution aberration corrected scanning transmission electron microscope (STEM) and atom probe tomography (APT) have been used to evaluate the grain boundary corrosion depth.
The mechanical properties of monolithic NPG are also studied. The motivation behind this is two-fold. The crack injection depth depends on the speed of the crack formed in the nanoporous layer, which in turn depends on the mechanical properties of the NPG. Also NPG has potential applications in actuation, sensing and catalysis. The measured value of the Young's modulus of NPG with 40 nm ligament size and 28% density was ~ 2.5 GPa and the Poisson's ratio was ~ 0.20. The fracture stress was observed to be ~ 11-13 MPa. There was no significant change observed between these mechanical properties on oxidation of NPG at 1.4 V. The fracture toughness value for the NPG was ~ 10 J/m2. Also dynamic fracture tests showed that the NPG is capable of supporting crack velocities ~ 100 - 180 m/s.
The mechanical properties of monolithic NPG are also studied. The motivation behind this is two-fold. The crack injection depth depends on the speed of the crack formed in the nanoporous layer, which in turn depends on the mechanical properties of the NPG. Also NPG has potential applications in actuation, sensing and catalysis. The measured value of the Young's modulus of NPG with 40 nm ligament size and 28% density was ~ 2.5 GPa and the Poisson's ratio was ~ 0.20. The fracture stress was observed to be ~ 11-13 MPa. There was no significant change observed between these mechanical properties on oxidation of NPG at 1.4 V. The fracture toughness value for the NPG was ~ 10 J/m2. Also dynamic fracture tests showed that the NPG is capable of supporting crack velocities ~ 100 - 180 m/s.
ContributorsBadwe, Nilesh (Author) / Sieradzki, Karl (Thesis advisor) / Peralta, Pedro (Committee member) / Oswald, Jay (Committee member) / Mahajan, Ravi (Committee member) / Arizona State University (Publisher)
Created2014
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