Date of Award

Fall 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Dipankar Ghosh

Committee Member

Tian-Bing Xu

Committee Member

Xiaoyu Zhang

Committee Member

Mileta Tomovic

Abstract

This dissertation focuses on developing a fabrication landscape first time ever for directionally porous lithium titanate (LTO) materials using ice-templating technique. Ice-templating, a promising fabrication technique for porous ceramics, enables the formation of sintered structures with anisotropic pores that are aligned to improve mechanical stability of materials.

The work presented in this dissertation addresses advancements in tuning the porosity, strength, and microstructural characteristics of ice-templated LTO materials through adjustments of intrinsic variables, including sucrose as a water-soluble additive, variations in freezing front velocity, solute concentration, and solid loading. First, this study demonstrated that adding sucrose in LTO suspensions increased the density of lamellar bridges within the resultant microstructure, transforming the pore architecture from lamellar to dendritic. This microstructural refinement substantially enhanced the compressive strength of the LTO materials up to eight-fold. Further microstructural investigations in transition and steady-state regions of LTO materials highlighted how sucrose decreased transition height and promoted early ice-lamella alignment. Resultant LTO materials exhibited fine microstructure in transition region and revealed dendritic branching of ice-lamellae in steady-state region which increased the pore tortuosity.

Next, this dissertation investigated how varying solute concentrations affect the viscosity of the LTO suspensions, the resultant microstructure and compressive strength. By systematically adjusting concentrations of sucrose and a cationic dispersant, the study demonstrated the flexibility to tune LTO microstructures from lamellar to dendritic. This approach yields a broad range of mechanical strengths (23–128 MPa), showing a correlation between solute concentration, morphology, and mechanical strength. Further study expanded the fabrication landscape for ice-templated LTO materials by assessing the lower limit of porosity achievable in these materials while maintaining directional porosity. Solid loading in LTO materials was varied from 30-37 vol.% which decreased the porosity from 50-36 vol.%. LTO materials fabricated with sucrose exhibited well-developed characteristic freeze-cast microstructure. While LTO materials fabricated from sucrose and dispersant exhibited cellular pore morphology irrespective of increasing solid loading.

Finally, the dissertation investigated the effects of electrochemical cycling on microstructure and mechanical stability of ice-templated electrodes, finding that these ice-templated LTO anodes retained their microstructure and mechanical strength over multiple cycles.

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DOI

10.25777/2jns-b858

ISBN

9798302855831

ORCID

0000-0001-5025-5851

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