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.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, September 2005. / Includes bibliographical references (leaves 39-40). / Oil is one of the most valuable natural resources in the world. Any technology that could possibly be used to conserve oil is worth studying. Biomass waste to olefin (WTO) technology replaces the use of oil as a feedstock. WTO technology is actually a combination of two different processes: the waste to methanol (WTM) process and the methanol to olefins (MTO) process. However, WTO technology is still not commercially applied. Despite the environmentally beneficial advantages of biomass waste to olefins technology, the economic advantages or disadvantages still need to be explored further. This thesis tries to determine under what operating conditions (production volumes, feedstock prices, etc.) make the biomass waste to olefins technology most competitive. The WTM process is the economical limiting factor in the WTO technology. However, for relatively significant production volumes, the WTO technology is still competitive with a slight decrease in biomass feedstock price. / by Nicholas Chiang. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / First principles density functional theory (DFT) energy calculations combined with the cluster expansion and Monte Carlo techniques are used to understand the cation ordering patterns of multicomponent oxides. Specifically, the lithium ion battery cation material LiNi0.5Mn0.5O2 and the thermoelectric material P2-NaxCoO2 (0.5 =/< x =/< 1) are investigated in the course of this research. It is found that at low temperature the thermodynamically stable state of LiNi0.5Mn0.5O2 has almost no Li/Ni disorder between the Li-rich and transition metal-rich (TM) layer, making it most suitable for battery applications. Heating the material above ~600°C causes an irreversible transformation, which yields a phase with 10~12% Li/Ni disorder and partial disorder of cations in the TM layer. Phase diagrams for the NaxCoO2 system were derived from the results of calculations making use of both the Generalized Gradient Approximation (GGA) to DFT and GGA with Hubbard U correction (GGA+U). This enabled us to study how hole localization, or delocalization, on Co affects the ground states and order-disorder transition temperatures of the system. Comparison of ground states, c lattice parameter and Na1/Na2 ratio with experimental observations suggest that results from the GGA, in which the holes are delocalized, matches the experimental results better for 0.5 =/< x =/< 0.8. We also present several methodological improvements to the cluster expansions. An approach to limit phase space and methods to deal with multicomponent charge balance constrained open systems while including both weak, long-range electrostatic interactions and strong, short-range interactions in a single cluster expansion. / by Yoyo Hinuma. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 152-155). / Solid-state dewetting of thin films is a process through which continuous solid films agglomerate to form islands. This process is driven by capillary forces, often occurring via surface self-diffusion. Solid-state dewetting of single crystal films has the potential to produce a wide range of regular structures because it occurs in ways controlled by crystallographic symmetries in single crystal films. We demonstrate this potential by pursuing two major objectives: understanding the underlying physics of regular morphological evolution during dewetting of single crystal films, and guiding the phenomenon to reproducibly produce regular structures with various morphologies. We used single crystal Ni films grown on single crystal MgO substrates as a model system. Dewetting initiates with the nucleation of holes and proceeds through the retraction of film edges around holes. By analyzing the anisotropy of the edge retraction rate and facet morphologies, we show that the effect of the anisotropy of surface energy and surface diffusion on early-stage dewetting morphologies strongly depends on the initial film orientation and annealing ambient. A series of instabilities increases the complexity of morphological evolution in the latter stages of dewetting. These include inplane faceting of retracting edges, accelerated growth at concave corners, edge drag at convex corners, edge pinch-off, and Rayleigh-like instabilities. Clear identification of these instabilities leads to improved understandings of the kinetic mechanisms that govern the formation of complex dewetting morphologies. We also demonstrate that solid-state dewetting can be used to produce regular structures with specific shapes via dewetting of patches patterned from single crystal films. Initial patches were systematically designed on the basis of the dewetting mechanisms to form a variety of specific morphologies. Morphological evolution of these patches occurs in more deterministic ways because of geometric constraints, and leads to the formation of regular structures with smaller sizes and more complex shapes than the initial patches. / by Jongpil Ye. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 30-31). / Biology has provided us with many organisms that are able to propel themselves through a fluid using cilia or flagella. This provides inspiration to create controllable systems that cannot only propel an organism or device through a fluid but can also create a fluid flow. Research has focused on how to mimic the mechanisms of these organisms for the use in microfluidic devices or drug delivery. This work examines walkers that are created using superparamagnetic beads placed in a rotating external magnetic field. Dipoles align in the beads so they assemble into rotors. These rotors follow the rotating magnetic field and are able to translate across a surface. This work looks at the effect of coating the beads and the surface with a polymer, Polyethylene Glycol(PEG). PEG has been shown to undergo a transition from an expanded state to a collapsed state under certain salt concentrations and temperature ranges. By looking at this transition we can see if the use of a polymer could affect the velocity of the rotors and if PEG could be used to control the velocity of the rotors or to initiate a transition. This transition is only seen by recording the velocity of the rotors, future research using other experimental procedures might be helpful in finalizing the transition of PEG in NaCl. It was unclear from these experiments whether the velocity of the rotors is dependent on the state of the polymer. / by Stephanie E. Moran. / S.B.