Solid-State NMR and MRI Studies of Structure-Property Correlations in Fast Li/Na-Ion Conductors

• Other Authors: Chien, Po-Hsiu (author)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Materials science; Chemistry
• Online Access: http://purl.flvc.org/fsu/fd/2019_Spring_Chien_fsu_0071E_14993

This doctoral thesis encompasses wide expanses of studies, which aim to advance the understanding of structure-property relationships in fast ion conductors (FICs) with a variety of characterization tools. In particular, powder X-ray diffraction (PXRD), electrochemical impedance spectroscopy (EIS), solid-state nuclear magnetic resonance (NMR), and magnetic resonance imaging (MRI) are jointly utilized to gain multidimensional knowledge. Two classes of FICs are examined and they are crystalline (Na x Sr 1−x SiO 3−0.5x , Li 7 La 3 Zr 2 O 12 , and Li 10 GeP 2 S 12 ) and glass-ceramic (Na 3−y PS 4−x Cl x and Li 10 P 3 S 12 I) materials. In regard to properties, we focus on ionic conductivity, chemical phase compositions, lithium distribution, and local chemical environments. In this thesis, the structure-property relationships are explored from two aspects: fundamental and practical. Fundamentally, we firstly establish the correlation of chemical phase evolution with ionic conductivity in Na x Sr 1−x SiO 3−0.5x and prove that the origin of conductivity is from Na + motions rather than O 2− . Then, it is found that the ionic conductivity can be improved by careful control of synthesis conditions. The improvement, on one hand, springs from the enhancement of functional defect site, which is associated with the creation of P 4+ in PS 4 3− tetrahedra in Na 3−y PS 4−x Cl x . On the other hand, the promotion of higher ionic conductivity is gained in Li 10 P 3 S 12 I by yielding high content of glassy phase with low activation energy at low temperature. Practically, we are attracted to the development of promising FICs and the chemical stability of FICs against polarizations in solid-state batteries cells. Propelled by the desire, we start with the laser-assisted magic-angle-spinning (LASMAS) probe to monitor phase evolution and ion dynamics in situ during materials synthesis. Model test on Li 7 La 3 Zr 2 O 12 identifies a compositionally similar phase, which also has comparable ion dynamics as verified by sequential T 1 measurements. Lastly, we use MRI to track the Li distribution in the bulk Li 7 La 3 Zr 2 O 12 and Li 10 GeP 2 S 12 , and at the electrolyte−Li interfaces under pristine, cycled, and short-circuit conditions. Different polarizations of Li concentration have witnessed different failing mechanisms in these two materials. Multinuclear ( 6,7 Li, 17 O, 23 Na, 29 Si, 31 P, and 127 I) solid-state NMR and advanced acquisition techniques are adapted to help with the assignment of local chemical environments. === A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Spring Semester 2019. === March 26, 2019. === MRI, Solid electrolyte, Solid-state NMR === Includes bibliographical references. === Yan-Yan Hu, Professor Directing Dissertation; Theo M. Siegrist, University Representative; Michael Shatruk, Committee Member; Susan Latturner, Committee Member; Zhehong Gan, Committee Member.