Li1.3Al0.3Ti1.7(PO4)3 as a solid state Li-Ion conductor: Issues with microcracking and stability in aqueous solutions

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Title Li1.3Al0.3Ti1.7(PO4)3 as a solid state Li-Ion conductor: Issues with microcracking and stability in aqueous solutions
Publication Type thesis
School or College College of Engineering
Department Materials Science & Engineering
Author Jackman, Spencer D.
Date 2012-12
Description Lithium aluminum titanium phosphate (LATP) with formula Li1.3Al0.3Ti1.7(PO4)3 was analyzed and tested to better understand its applicability as a solid state ion conducting ceramic material for electrochemical applications. Sintered samples were obtained from Ceramatec, Inc. in Salt Lake City and characterized in terms of density, phase-purity, fracture toughness, Young‟s modulus, thermal expansion behavior, mechanical strength, a.c. and d.c. ionic conductivity, and susceptibility to static and electrochemical corrosion in aqueous Li salt solutions. It was shown that LATP is prone to microcrack generation because of high thermal expansion anisotropy. A.c. impedance spectra of high-purity LATP of varying grain sizes showed that microcracking had a negative impact on the ionic conduction of Li along grain boundaries, with fine-grained (1.7±0.7 μm) LATP having twice the ionic conductivity of the same purity of coarse-grained (4.8±1.9 μm) LATP at 50°C. LATP with detectible secondary phases had lower ionic conductivity for similar grain sizes, as would be expected. The Young‟s modulus of fine-grained LATP was measured to be 115 GPa, and the highest biaxial strength was 191±11 MPa when tested in mineral oil, 144±13 MPa as measured in air, and 26±7 MPa after exposure to deionized water, suggesting that LATP undergoes stress-corrosion cracking. After exposure to LiOH, the strength was 76±19 MPa. This decrease in strength was observed despite there being no measureable change iv in a.c. impedance spectra, X-ray diffraction, or sample mass, suggesting phosphate glasses at grain boundaries. The chemical and electrochemical stability of high-purity LATP in aqueous electrochemical cells was evaluated using LiOH, LiCl, LiNO3, and LiCOOCH3 salts as the Li source. LATP was found to be most stable between pH 8-9, with the longest cell operating continuously at 25 mA cm-2 for 625 hours at 40°C in LiCOOCH3. At pH values outside of the 7-10 range, eventual membrane degradation was observed in all aqueous systems under electrochemical conditions. While LATP was surprisingly resistant to static corrosion in a hot, aqueous LiOH solution, electrochemical degradation was observed at the cathode due to subsurface pitting. Strength measurements were more instructive than impedance measurements in detecting this degradation.
Type Text
Publisher University of Utah
Subject Corrosion; Ionic conductivity; Microcracking; Stability; Strength
Dissertation Institution University of Utah
Dissertation Name Master of Science
Language eng
Rights Management Copyright © Spencer D. Jackman 2012
Format application/pdf
Format Medium application/pdf
Format Extent 3,035,896 bytes
ARK ark:/87278/s6f76tc3
Setname ir_etd
ID 195724
Reference URL https://collections.lib.utah.edu/ark:/87278/s6f76tc3
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