Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Meng, Xiangbo

Committee Member

Zou, Min

Second Committee Member

Tung, Chao-Hung Steve

Keywords

Atomic Layer Deposition; Lithium Ion Battery; Lithium Metal; Molecular Layer Deposition; Silicon Graphite Electrode; Solid State Electrolyte

Abstract

Lithium-ion batteries (LIBs) are promising energy storage devices, which play significant roles in addressing problems related to fossil fuels depletion and environmental pollution. Since the 1990s, LIBs have attracted great attention for many applications. Nowadays, LIBs are dominating portable electronics, having several advantages over their forerunners, such as high voltage (3.3~4.2 V) [1,2], low self-discharge (< 5~10 %/month) [3,4], wide operation temperature (-20~60 °C) [5,6], and fast charge/discharge rate [7,8]. However, LIBs deliver an energy density of 100-220 Wh/kg in practice to date, which is far from their theoretical ones, thus hindering their further applications in electric vehicles. Additionally, LIBs have been plagued by other problems, such as intolerance to overcharge/overdischarge, low heat resistance, lithium dendrites growth, large volume change of the silicon anode, large polarization and even safety problems.

Atomic layer deposition (ALD) and molecular layer deposition (MLD) are two important techniques, both proceeding in self-limiting gas-solid reactions and exhibiting excellent capabilities for ultra-thin films, conformal coatings, and controllable growth. They can be employed to address the problems of LIBs mentioned above by surface coatings, electrode designs, and solid-state electrolyte preparations. In this thesis, ALD is utilized to modify the interface between the electrolyte and Si anode in LIBs and to improve the performance of LIBs. ZnO coating deposited by ALD using precursors of diethylzinc (DEZ) and H2O was found to be effective in accommodating the volume expansion of Si during charging-discharging process and preventing the direct Si-electrolyte contact, thus improving the performance of Li/Si-G battery. Additionally, effects of ALD coatings (Al2O3 and ZnO) on stabilizing lithium metal are investigated.

In chapter 1, the background of LIBs is introduced, as well as ALD and MLD. Chapter 2 investigates the growth properties of different coatings (Al2O3, ZnO, TiO2, AlGL and ZnGL) using quartz crystal microbalance (QCM) method. Chapter 3 reports the modification of Si-electrolyte interface via ALD coatings and the performance of Li/Si-G (silicon-graphite) batteries. Chapter 4 investigates the stabilization of lithium metal using ALD coatings. Conclusions are shown in chapter 5. Future work and promising developments are given in chapter 6.

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