Degree Type

Thesis

Date of Award

2018

Degree Name

Master of Science

Department

Materials Science and Engineering

Major

Materials Science and Engineering

First Advisor

Steve W. Martin

Abstract

An increasing demand for renewable energy has catalyzed investigations into improving battery technology. High energy density, longer cycling life, and safer battery materials are highly desirable. Research must go into developing advanced battery materials with properties designed for fast ionic conductivity, good chemical stability with the anode, and facile and low cost formability. Studying the short-range and intermediate-range atomic structures of materials will give insight into relationships between the atomic level structures of battery materials and their properties. In this research, the focus was upon developing new lithium ion conducting amorphous solid electrolytes in the compositional series 0.6 Li2S + 0.4[xSiS2+1.5(1-x)PS5/2] prepared via mechanochemical synthesis. These new amorphous solid electrolytes hold promise in improving the overall lithium battery performance by increasing the lithium ion conductivity and being electrochemically stable in contact with metallic lithium. In this work, these new lithium thiosilicophosphate amorphous solid electrolytes were characterized using Far/Mid Infrared (IR), Raman, and Nuclear Magnetic Resonance (NMR) spectroscopies, as well as X-Ray Diffraction (XRD) to determine their atomic level structures. Differential Scanning Calorimetry (DSC) was used to determine whether these planetary milled materials were in fact glassy in nature, which is having a thermal history consistent with one being formed from cooling a liquid, or whether they were just simply amorphous materials that would rapidly crystallize upon heating. The DSC measurements showed that these amorphous materials are in fact glasses as they all exhibited a proper glass transition temperature, Tg, which indicates that these materials have sufficient internal thermal stability to access the supercooled liquid state above the Tg however below the crystallization temperature, Tc of the liquid. As a general trend, it was observed that the Tg increased as the phosphorous was replaced by silicon, that is with increasing x. The short range order (SRO) structures of these glasses, as determined by IR, Raman, and NMR spectroscopies, showed that the general trend for the compositional change of the SRO structural units was the expected P1 structures which were formed at x = 0, where the superscript 1 defines the number of bridging sulfurs (BS) on the P center, and upon addition of expected Si units, x > 0, the P1 units were extracted away to form ESi2 units and P0 SRO with no BS structures. In turn and required for charge compensation, the P1 SRO units upon losing this Li+ charge, were converted to edge sharing ESi2 possessing an additional BS structure. At the end of the compositional series as the P content decreases to zero, the Si SRO units necessarily convert back to Si0 units as required by the stoichiometry of the composition.

Copyright Owner

Mark Anthony Paul Aguilar

Language

en

File Format

application/pdf

File Size

59 pages

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