1,721,179 research outputs found
STEPWISE COLLOIDAL CRYSTALLIZATION DUE TO CONFINED THERMAL LATTICE VIBRATIONS
No full textMaster'sMASTER OF SCIENCE IN ADVANCED MATERIALS FOR MICRO- & NANO- SYSTEMS1. Assoc. Prof. Wong Chee Cheong, SMA Fellow, NTU. 2. Prof. Yet-Ming Chiang, SMA Fellow, MI
Shape morphing structures via intercalation compounds
Get PDFThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (leaves 35-36).Recent research has allowed the use of electrode-active materials as actuators by harnessing reversible volumetric change due to intercalation during charging and discharging. These actuators provide a relatively large strain, 2-3%, while requiring less than ten volts to operate with a cycle time on the order of one hundred seconds. This technology can be used in any moderate bandwidth, high-force, high-strain application, including shape-morphing helicopter blades, boat hulls, satellites, and any other structure that benefits from shape change. An analysis is performed on the state of the technology, the intellectual property held, and the potential markets that exist. A recommendation is made to pursue the technology, while cognizant of the fact that it is still in a seed stage and requires significant time and financial investment before entering production. Two business models are proposed and rough market calculations are also presented. The basis of this project is work done at the Massachusetts Institute of Technology by Professor Yet-Ming Chiang and Professor Steven Hall. Industrialists, including but not limited to, William Fallon and Dan Ursenbach of Sikorsky Aircraft in Stratford, Connecticut are also involved in the project.by John T. Wong.M.Eng
High-strain actuation of lead-free perovskites : compositional effects, phenomenology and mechanism
Get PDFThesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.Includes bibliographical references.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.An experimental study was carried out to map the compositional dependence of electromechanical behavior and ferroelectric phase stability in the barium, zirconium-codoped sodium bismuth titanate (BNBZT) system for barium concentrations up to 18 mol.% and zirconium concentrations up to 4 mol.%. A number of polycrystalline BNBZT samples has been electromechanically tested under applied electric fields of different frequencies (0.2-47 Hz). A novel model of electromechanical response capable of describing both dynamic and static hysteresis for pure and mixed cases of ferroelectric, antiferroelectric, ferroelastic and paraelectric behavior has been developed. Major electromechanical properties of polycrystalline BNBZT have been identified and compositionally mapped. The peak of electromechanical response (d33 = 400 pC/N) has been found at the composition (Bil/2Nal/2)0.93Bao.07Zro.02Tio.9803. The compositional dependence of ferroelectric phase stability has been mapped by means of a Landau type free energy expansion. A nanodomain relaxation mechanism of frequency dependent electromechanical response of BNBZT has been suggested and is supported by optical and transmission electron microscopy.by Andrey N. Soukhojak.Ph.D
Implementations of electric vehicle system based on solar energy in Singapore assessment of lithium ion batteries for automobiles
Get PDFThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 142-150).In this thesis report, both quantitative and qualitative approaches are used to provide a comprehensive analysis of lithium ion (Li-ion) batteries for plug-in hybrid electric vehicle (PHEV) and battery electric vehicle (BEV) from technological and economical perspectives. Five key factors including power density, energy density, safety, durability, and cost are employed to compare four types of Li-ion batteries. Utility analysis indicates that all the Li-ion batteries are able to satisfy both power density and energy density targets, but only two of them are able to meet safety and durability requirements. Currently, the main challenge for their automotive application is cost reduction, since the cheapest LiFePO₄ battery costs 4,270 and $7,726 of U.S. government subsidizations to an individual user are needed for PHEV and BEV to breakeven. Lastly, the lithium ion battery based electric vehicle systems have also been evaluated in the implementation models in Singapore. The conclusion is that it is not feasible to adopt electric vehicle system in Singapore under current government incentives.by Haitao Fu.M.Eng
Self-assembly of conformal polymer electrolyte film for lithium ion microbatteries
Get PDFThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (leaves 37-39).I apply the theory of polar and apolar intermolecular interactions to predict the behavior of combinations of common battery materials, specifically the cathode substrate lithium cobalt oxide (LCO) and the polymer separator poly(ethylene oxide). These predictions were first tested qualitatively using hexane and PTFE, which have well-established surface energies, and then by measuring the contact angles of PEO on LCO in hexane and hexadecane, chosen for their immiscibility in PEO. For better comparison, these experiments were repeated using water instead of PEO, for a total of four systems tested. This data allowed an estimate for the experimental surface energy components of LCO to be derived, resulting in 18.3 ± 1 mJ/m2 for [gamma]LW, 0.22 ± 0.02 mJ/m2 for [gamma]+, and 5.8 ± 1.6 mJ/m2 for [gamma]-, compared to the previously reported values of 40.8 mJ/m2 for [gamma]LW, 0.0008 mJ/m2 for [gamma]+, and 0.21 mJ/m2 for [gamma]-. This variation is probably due to a variety of factors, including instrumental uncertainty in the contact angle measurement, a difference in contact angle measurement procedure, and inevitable contamination by water and other materials. Using this new data, self-assembling electrolyte-cathode systems are predicted, like LCO-polyacrylonitrile-chloroform.by Christalee Bieber.S.B
Electrochemically-induced phase transition in olivine type cathode materials
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 159-165).Phase transitions are commonly observed in ion storage compounds when being used in rechargeable batteries and thus, the phase behavior of ion storage compounds as electrode active materials has significant impact on battery performance. This thesis aims to understand the interplay between materials structure, phase behavior and battery performance. The effects of operating conditions, especially overpotential and temperature, on phase behavior and battery performance are also investigated. Using olivine-type phosphates (i.e. phospho-olivines) with varying composition and particle size as model system, strain accommodation mechanism within single nanoparticles (Chapter 2 to 3) and mesoscale kinetics of nanoparticle aggregates (Chapter 4 to 5) during electrochemically-induced phase transition have been systematically investigated. In the first part, phospho-olivines with varying transformation strain, from 0 - 3vol% for LiMnyFe1-yPO4 (LMFP, y<0.5), 5vol% for LiFePO4 (LFP), to 17vol% for NaFePO4 (NFP), have been studied using operando Powder X-ray Diffraction (PXD), among other methods. While small transformation strain as in LMFP is accommodated and even avoided by formation of metastable solid solution, large transformation strain as in NFP is mitigated by formation and dissolution of intermediate amorphous phase. This novel mechanism to accommodate large transformation strain may pave the way of utilizing battery materials that deem not working otherwise. In the second part, potentiostatic studies are conducted and a model modified from Avrami model is developed to quantitatively describe phase transformation progresses. The phase transition of LMFP and LFP nanoparticle aggregates is found to follow a nucleation and growth process while the growth is governed by lithium ion diffusion. Based on analysis using the modified Avrami model, more instantaneous nucleation and facile growth tend to occur when transformation strain is small (intermediate Mn content and/or small particle size), overpotential is high and/or temperature is high. And instantaneous nucleation and facile growth improve the rate capability of batteries. The relationship between phase behavior and material structure as well as operating conditions is attributed to: 1) decreasing transformation strain reduces energy barrier for both nucleation and growth; 2) increasing overpotential and temperature boost the electrochemical driving force for phase transition and promote more instantaneous nucleation and facile growth.by Kai Xiang.Ph. D
Kinetics of phase transformations in lithium-sulfur batteries
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 139-150).Sulfur is a promising positive electrode for lithium batteries with the potential to create the step-change improvement in energy density and cost needed for the widespread adoption of electric vehicles and renewable energy. However, lithium-sulfur batteries suffer from a number of challenges, among them poor rate capability resulting in part from a complex dissolution-precipitation mechanism which produces electronically insulating end members S₈ and Li₂S. Few studies have heretofore been performed on rate-limiting mechanisms in Li-S batteries, which must be elucidated in order to inform rational design of electrodes with high capacity and rate capability. Polysulfide solutions, intermediates in the electrochemical reduction of sulfur, are used for the first time to make an efficient, high energy density flow battery, enabled by a novel flow battery architecture using a percolating network of nanoscale conductive carbon. An extensive experimental study of exchange current density for redox of higher order polysulfide solutions and their ionic conductivity has been conducted. The type and amount of electrolyte solvent has been found to influence both of these. The second portion of this thesis characterizes the kinetics of Li₂S electrodeposition, which is responsible for three-quarters of the theoretical capacity of the sulfur cathode. Kinetics are found to be highly dependent on solvent choice in a manner similar to exchange current density. Furthermore, electrodeposition kinetics are found to slow considerably at the low electrolyte/sulfur ratios which are needed for high energy density and low cost. Materials such as conductive oxides can serve as nucleation promoters and help solve this challenge. The morphology of precipitates is found to be dependent on discharge rate, with large, discrete particles forming at low rates. A model was for describing 3-D electrodeposition of Li₂S under the influence of a soluble redox mediator which enables efficient utilization of conductive surface area and prevents passivation of conductive carbon with insulating Li₂S.by Frank Yongzhen Fan.Ph. D
Building a Better Battery
No full textControlling the charge-induced morphological changes of electrode materials may provide a route to improved battery performance.</jats:p
Phase transformations and microstructural design of lithiated metal anodes for lithium-ion rechargeable batteries
No full textThesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.Includes bibliographical references.There has been great recent interest in lithium storage at the anode of Li-ion rechargeable battery by alloying with metals such as Al, Sn, and Sb, or metalloids such as Si, as an alternative to the intercalation of graphite. This is due to the intrinsically high gravimetric and volumetric energy densities of this type of anodes (can be over an order of magnitude of that of graphite). However, the Achilles' heel of these Li-Me alloys has been the poor cyclability, attributed to mechanical failure resulting from the large volume changes accompanying alloying. Me-oxides, explored as candidates for anode materials because of their higher cyclability relative to pure Me, suffer from the problem of first cycle irreversibility. In both these types of systems, much experimental and empirical data have been provided in the literature on a largely comparative basis (i.e. investigations comparing the anode behavior of some new material with older candidates). It is the belief of the author that, in order to successfully proceed with the development of better anode materials, and the subsequent design and production of batteries with better intrinsic energy densities, a fundamental understanding of the relationship between the science and engineering of anode materials must be achieved, via a systematic and quantitative investigation of a variety of materials under a number of experimental conditions. In this thesis, the effects of composition and processing on microstructure and subsequent electrochemical behavior of anodes for Li-ion rechargeable batteries were investigated, using a number of approaches.(cont.) First, partial reduction of mixed oxides including Sb-V-O, Sb-Mn-O, Ag-V-O, Ag-Mn-O and Sn-Ti-O, was explored as a method to produce anode materials with high cyclability relative to pure metal anodes, and decreased first cycle irreversibility relative to previously produced metal-oxides. The highest cyclability was achieved with anode materials where the more noble metal of the mixed oxide was reduced internally, producing nanoscale active particles which were passivated by an inactive matrix. Second, a systematic study of various metal anode materials, including Si, Sn, Al, Sb and Ag, of different starting particle sizes was undertaken, in order to better understand the micromechanical mechanisms leading to poor cyclability in these pure metals. SEM of these materials revealed fracture in particles of > 1 pm after a single discharge/charge cycle, consistent with literature models which predict such fracture due to volumetric strains upon lithiation. However, TEM of these materials revealed a nanocrystalline structure after one cycle that in some metals was mixed with an amorphous phase. STEM of anode materials after 50 cycles revealed a dissociation of this nanostructure into nanoparticles, suggesting a failure mechanism other than volumetric strains, such as chemical attack. Finally, the appearance of the amorphous phase was investigated in lithiated Si, Sn, Ag and Al metal anode systems. A new mechanism, electrochemically-induced solid-state amorphization was proposed and explored via experiments using calibrated XRD and TEM. Experimental observations of these various Me systems subjected to different degrees of lithiation supported such phenomenon...by Pimpa Limthongkul.Ph.D
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