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dc.contributor.advisorLi, Xin
dc.contributor.authorFitzhugh, William
dc.date.accessioned2020-09-15T10:41:58Z
dash.embargo.terms2021-03-01
dc.date.created2020-03
dc.date.issued2020-01-22
dc.date.submitted2020
dc.identifier.citationFitzhugh, William. 2020. Mechanical Effects on the Phase Stability of Ceramic-Sulfide Solid-Electrolytes. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
dc.identifier.urihttps://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37365154*
dc.description.abstractThis dissertation presents the theoretical, computational and experimental results of studies on the voltage widening of ceramic-sulfide solid-electrolytes. In particular, we demonstrate the use of mechanically-induced metastability as a method to expand the operating voltage windows of all-solid-state lithium ion batteries based on $Li_{10}GeP_{2}S_{12}$ and/or $Li_{10}SiP_{2}S_{12}$. In short, mechanical constriction is seen to improve the bulk and interfacial stability by introducing energy barriers that oppose structural decay. The impact of mechanical constriction on both the bulk stability of these ceramic-sulfides as well as the interfaces with common electrode materials are considered. A theory of mechanically induced metastability is first formulated and introduced with experimental and computational evidence for the case of core-shell $Li_{10}SiP_{2}S_{12}$. Here we show that the electrochemical stability window of sulfide electrolytes can be improved by controlling synthesis parameters and the consequent core-shell microstructural compositions. This results in a stability window of 0.7-3.1V and quasi-stability window of up to 5V for Li-Si-P-S sulfide electrolytes with high Si composition in the shell, a window much larger than the intrinsic 1.7-2.1V. Theoretical and computational work explains this improved voltage window in terms of volume constriction, which resists the expansion of the solid electrolyte that accompanies decomposition. It is shown that in the limiting case of a core-shell morphology that imposes a constant volume constraint on the electrolyte, the stability window can be further expanded. Next, a framework is introduced to generalize the above theory for the case of arbitrary decay morphologies. Two limiting cases, hydrostatic decay and spherically nucleated decay, are explored to better understand the impact of decay morphology on the stability window. $Li_{10}GeP_{2}S_{12}$ is experimentally seen to decay in a nucleated form, which is predicted to generate higher local stress and hence a larger energy barrier for decomposition. This allows the use of thinner stabilizing shell structures than would be required if the material was to decay homogeneously. In addition to a limited intrinsic electrochemical window of roughly 1.7-2.1V, the ceramic-sulfides are known to [electro-]chemically react when in contact with typical commercial electrode materials such as $LiCoO_2$. Thus coating materials that form physical separation layers between the electrolyte and the electrode materials are required. High-throughput calculations are performed to search over 67,000 material phases to find the best coating materials for use in $Li_{10}SiP_{2}S_{12}$ based batteries. Over 2,000 materials are found to be suitable for the case of cathode voltage ranges and over 1,000 materials are found to be suitable for the case of anode voltage ranges. New computational methods are developed to enable this rapid high-throughput searching. Six phases ranging in predicted stability from stable to highly unstable are experimentally evaluated to confirm computational predictions. Finally, evidence is presented that battery cell level mechanical constriction can provide even greater capability than core-shell morphologies for voltage widening. We show that ceramic-sulfides in cell level constriction mechanisms can achieve kinetically stable operation up to nearly 10V. This is in stark contrast with current commercial liquid electrolytes which begin to decay at approximately 4.5V. This behavior is attributed to rate-limited kinetic processes that occur in pressurized electrolytes.
dc.description.sponsorshipEngineering and Applied Sciences - Applied Physics
dc.format.mimetypeapplication/pdf
dc.language.isoen
dash.licenseLAA
dc.subjectSolid-state batteries, ceramic-sulfides, solid-electrolytes
dc.titleMechanical Effects on the Phase Stability of Ceramic-Sulfide Solid-Electrolytes
dc.typeThesis or Dissertation
dash.depositing.authorFitzhugh, William
dash.embargo.until2021-03-01
dc.date.available2020-09-15T10:41:58Z
thesis.degree.date2020
thesis.degree.grantorGraduate School of Arts & Sciences
thesis.degree.grantorGraduate School of Arts & Sciences
thesis.degree.levelDoctoral
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy
thesis.degree.nameDoctor of Philosophy
dc.contributor.committeeMemberSpaepen, Frans
dc.contributor.committeeMemberAziz, Michael
dc.type.materialtext
thesis.degree.departmentEngineering and Applied Sciences - Applied Physics
thesis.degree.departmentEngineering and Applied Sciences - Applied Physics
dash.identifier.vireo
dash.author.emailfitzhugh@outlook.com


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