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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
There has been much interest in photoelectrochemical conversion of solar energy in recent years due to its potential for low-–cost, sustainable and renewable production of fuels. Despite the huge potential, there are still a number of technical barriers due to the many constraints needed in order to drive photoelectrochemical reactions such as overall water splitting and the identification of efficient and effective semiconductor materials. To this end, the search for novel semiconductors that can act as light absorbers is still needed. The copper hydroxyphosphate mineral libethenite (CHP), which has a chemical formula of Cu2(OH)PO4, has been recently shown to be active for photocatalytic degradation of methylene blue under UV-–irradiation, indicating that photo-excited electrons and holes can effectively be generated and separated in this material. However, CHP has not been well studied and many of its fundamental electrochemical and photoelectrochemical properties are still unknown. In this work, the synthesis of different morphologies of CHP using hydrothermal synthesis and precipitation methods were explored. Additionally, a preliminary investigation of the relevant fundamental characteristics such as the bandgap, flatband potential, band diagram, electrochemical and photoelectrochemical properties for CHP was performed. Better understanding of the properties of this material may lead to the development of improved catalysts and photocatalysts from natural sources.
ContributorsLi, Man (Author) / Chan, Candace K. (Thesis advisor) / O'Connell, Michael (Committee member) / Crozier, Peter (Committee member) / Arizona State University (Publisher)
Created2013
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
ContributorsGlenn, Erica (Conductor) / Evans, Bartlett R. (Conductor) / Oh, Eun-Mi (Conductor) / Thompson, Jason D. (Conductor) / Schildkret, David (Conductor) / Concert Choir (Performer) / Arizona Statesmen (Performer) / Women's Chorus (Performer) / Gospel Choir (Performer) / Barrett Choir (Performer) / Chamber Singers (Performer) / Choral Union (Performer) / ASU Library. Music Library (Publisher)
Created2017-11-30
ContributorsStocker, David, 1939- (Conductor) / Kempton, Randall (Conductor) / Hickman, Miriam, 1955- (Performer) / Concert Choir (Performer) / ASU Library. Music Library (Publisher)
Created1999-03-07
ContributorsBailey, Donald (Performer) / Qualls, Karla J. (Performer) / Concert Choir (Performer) / ASU Library. Music Library (Publisher)
Created1989-10-15
ContributorsBailey, Donald (Performer) / Qualls, Karla J. (Performer) / Stocker, David, 1939- (Performer) / Wiest-Parthun, Karen (Performer) / Concert Choir (Performer) / University Choir (Performer) / ASU Library. Music Library (Publisher)
Created1993-02-21
ContributorsBruffy, Charles (Conductor) / Amerind, Gregory (Contributor) / Gorton, William (Contributor) / Huff, Vernon (Contributor) / Cole, Nina (Performer) / Kraft, John (Performer) / Schildkret, Miriam (Performer) / Lange, Michelle (Performer) / Rynex, Carolyn (Performer) / Morgan, Philip (Performer) / Concert Choir (Performer) / ASU Library. Music Library (Publisher)
Created2012-11-04
ContributorsHill, Gary W. (Conductor) (Conductor) / Schildkret, David (Conductor) / Forkner, Christina (Performer) / Frank, Elijah (Performer) / Gustafson, Erik (Performer) / Miller, Max (Performer) / Sample, Michael (Performer) / Chamber Winds (Performer) / Concert Choir (Performer) / ASU Library. Music Library (Publisher)
Created2003-10-09
ContributorsSchildkret, David (Conductor) / Downey, Ryan (Performer) / Jeffers, Brian (Performer) / Willmer, Asleif (Performer) / Lempke, Arijana (Performer) / Kim, Sehoon (Performer) / Barrett Choir (Performer) / Chamber Singers (Performer) / Choral Union (Performer) / Concert Choir (Performer) / Symphony Orchestra (Performer) / ASU Library. Music Library (Publisher)
Created2015-04-29