Degree Type

Thesis

Date of Award

2020

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

Major

Materials Science and Engineering

First Advisor

Steve W Martin

Abstract

With the increasing demand and desire for stronger power and longer life of lithium ion batteries, the lithium ion battery (LIB) system is needed to be developed into next level while it is overcoming the traditional safety issues originated from the use of organic liquid electrolyte. By the physically strong and none volatile feature of solid, one of the simplest and best way to replace the organic liquid electrolyte apply the solid-state electrolyte and establish the all solid-state battery (ASSB). Furthermore, the ASSB system can give an advantage to use Alkali metals to LIB system as electrode that has much huge potential capacity compared to the commercialized current cathode and anode LIB materials.

This research studies two sulfide-based solid-state electrolytes, Li10SiP2S12-xOx (LSiPSO) and Li10[SnySi1-y]P2S12-xOx (LSnSiPSO), a crystalline material based on the Li10GeP2S12 (LGPS) high Li+ ion conductive material. The initial Li+ ion conductivity increase and optimization was observed with the substitution of oxygen into crystal structure of Li10SiPS12, and it is a new phenomenon not confirmed with the LGPS and its oxygen substitution. Further spectroscopy and crystallography analysis reveals that there is a formation of oxy-sulfide phase. The phase purification effect by the added oxygen is also observed that it is consuming impurity phases and coverts them into the high Li+ ion conductive LGPS like phase. However, a high oxygen substitution gives a trade-off between the phase purity and Li+ ion conductivity of material. The high addition of oxygen causes a phase degradation into oxide crystalline phase. The investigation of structure and properties of LSnSiPSO shows the same phase purification by the oxygen substitution but it is much enhanced with the additional substitution of tin. The improved phase purification effect is expected that it was possible to form a much close crystal structure to the parent LGPS by the distribution of large ion sized tin to the LSiPSO structure.

Finally, ASSB assembled with the LSiPSO and LSnSiPSO samples as SE with Li metal electrode. The impedance and cyclic voltammetry (CV) analysis of the LSiPSO and LSnSiPSO exhibit a formation of solid electrolyte interface (SEI) layer which leads a consumption/deformation of the solid-state electrolyte and Li metal. CV analysis reveals chemical reactions such as redox reaction of Si, Sn, S, and P on the interface between the SE and Li metal. The cycled batteries failed with a constant current density of 0.3 mA/cm2. However, the LSnSiPSO samples showed more stable cycling behavior than the LSiPSO sample.

DOI

https://doi.org/10.31274/etd-20200624-221

Copyright Owner

KwangHyun Kim

Language

en

File Format

application/pdf

File Size

181 pages

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