Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (p. 85-89). / An investigation was completed to assess the viability of a group of metallic microfabrication techniques aimed at the production of microelectromechanical systems (MEMS) This undertaking was done to show which methods hold the most promise for the near future. The methods investigated include LIGA, micromilling, jet molding, three dimensional printing, microcasting, micro-injection molding, metal injection molding, Microforming, and microextrusion. This study presents a technique overview, assembly issues, an applications survey, basic cost modeling and a survey of the relevant intellectual property. / by Abel Z. Hastings. / M.Eng.

Thesis: 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.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Vita. / Includes bibliographical references (leaves 126-128). / by Linda K. Molnar. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references. / by Elliot M. Schwartz. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 111-115). / by Yong-Gang Frank Ren. / Ph.D.

Thesis (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.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 145-153). / In order to accelerate the electrification of the automotive fleet, the energy density and power density limitations of commercial Li-ion battery cathodes (layered LiMO2) must be overcome. In this thesis, we use ab initio methods to gain critical insights on two important classes of alternative Li-ion battery cathodes, namely high-capacity Li-excess cation-disordered rocksalts and high-rate LiFePO4 In the first part of this thesis (Chapters 3 and 4), we provide the first voltage-based design rules for high-capacity cation-disordered rocksalts. We demonstrate that, depending on the transition metal species, cation disorder can increase or decrease the average voltage of lithium transition metal oxides, and hence increase or decrease the total energy density of these compounds In particular, the disordered Ni3+/4+ voltage is found to be high (~4.4V), value at which it is likely to be preceded by oxygen activity. We further investigate the effect of cation-disorder on the voltage slope of lithium transition metal oxides, which controls the total capacity accessible below the stability limit of the electrolyte. We demonstrate that cation-disorder increases the voltage slope by increasing the Li site energy distribution and by enabling Li occupation of high-voltage tetrahedral sites. We further demonstrate that the voltage slope increase upon disorder is smaller for high-voltage transition metals, and that short-range ordering and Liexcess contribute in reducing the inaccessible capacity at high voltage upon disorder. In the second part of this thesis (Chapter 5), we resolve the apparent paradox between the high Li diffusivity in phase-separating LiFePO 4 and the persistence of thermodynamically unstable solid-solution states during (dis)charge at low to moderate C-rates. We demonstrate that, even under rate conditions such that relaxation to a two-phase state is kinetically possible, the thermodynamically favorable state in a single particle is not a sharp interface but rather a diffuse interface with an intermediate solid-solution region that occupies a significant fraction of the particle volume. Our results not only explain the persistence of solid-solution regions at low to moderate C-rates in nano-LiFePO4, but also explain the observations of stable intermediate solid-solution states at an ac interface in particles quenched from a solid solution. / by Aziz Abdellahi. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 148-158). / Many neurological disorders are now classified as circuit disorders, in which the underlying pathology arises from a failure in dynamic communication between anatomically distinct regions of the brain. Systemic therapies are often not effective due to their untargeted nature. The injectrode is a multifunctional probe designed to treat neurological disorders through targeted chemical and electrical stimulation directly to a focal point within the implicated neural circuit. This thesis details the characterization and biocompatibility of the injectrode for the treatment of neurological disorders on chronic timescales. In vitro and in vivo infusion tests were conducted to validate the ability to deliver nanoliter scale volumes (10-1000 n1) of drug to targeted brain structures over the course of an eight week implantation period. Muscimol was delivered to deep brain structures to demonstrate effective modulation of neural activity and behavior. These findings highlight the utility of a local chemical delivery approach to treat circuit diseases of the brain. Glial scar is a major barrier to neural probe function. A main objective of this thesis is focused on understanding the process of glial scar formation from a materials perspective. Micromotion and mechanical mismatch are thought to be key drivers of scar formation. This hypothesis was investigated using a novel 3D in vitro glial scar model, which replicates the magnitude and frequency of micromotions that are observed in vivo. Astrocytes were found to have a significant increase in cellular area and perimeter in response to micromotion compared to static control wells. These findings were applied to improve the biocompatibility of the injectrode. Hydrogel coatings, with moduli matched to brain tissue, were formed to mitigate the effects of micromotion. These coatings were found to reduce local strain by up to 70%. In vivo studies were conducted to explore the impact that implant diameter and modulus have on scar formation. Hydrogel coated implants (E=1 1.6 kPa) were found to significantly reduce scarring at 8 weeks post implantation, compared to uncoated implants (E=70 GPa). Size effects from increasing the overall implant diameter were also observed, highlighting the importance of considering both mechanical and geometric factors when designing chronic neural implants. / by Kevin C. Spencer. / Ph. D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2001. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 35-36). / The DLVO theory of colloids is used to consider the stability of clay colloid particles. An approach to colloid physics using classical electrostatic methods is presented. Specifically, the electrical double layer is examined using computational methods. To this end, the Poisson-Boltzman equation is solved numerically for geometries corresponding to interacting clay particles. The interaction energies of double layers is calculated for several particle configurations. / by Mark Jhon. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Steven Anthony Gedeon. / M.S.