Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Prof. Xueliang (Andy) Sun

Abstract

Electrochemical energy storage is one of the important strategies to address the strong demand for clean energy. Rechargeable lithium ion batteries (LIBs) are one of the typical electrochemical devices and have been used in a great number of areas. Now, the challenge for the LIB research is to make the batteries carry higher energy density so as to fulfill the demand of the emerging markets, particularly, electric vehicles and portable smart electronics. In this regard, the present commercial anode material can not meet this requirement. Much effort is being made toward either exploring new morphologies of carbon materials or searching for new materials that possess high theoretical lithium ion storage capacities. Among these, graphene and silicon have been receiving rapidly increasing interest.

As such, this Ph D research focused on two topics: (1) developing graphene-based freestanding materials used as anodes for LIBs, which will find potential applications in flexible LIBs; (2) developing cost-effective processes for mass production of low-dimensional nanostructured silicon with controlled morphologies from low-cost materials.

The freestanding anodes include graphene papers, graphene-carbon nanotubes papers, graphene-MoS2 papers and graphene-Si nanowires papers. They exhibited very high mechanical strength. Their battery performances were highly dependent on the composites of the papers and the ratios of graphene to the guest component (e.g., Si), and graphene-Si nanowires papers exhibited the highest lithium-storage capacities of >1000 mA h g-1. The materials have high potential for use as freestanding anodes for LIBs. The related results are organized in Chapter 3-6 in this thesis.

A catalyst-free etching process was developed to produce 1D silicon nanostructures (nanobelts and nanowires) from low-cost and metallurgical ferrosilicon alloys with relatively high yields. When used as an anode material, the 1D nanostructured silicon demonstrated reversible lithium storage capacity of 2600 mA h g-1, high rate capability and relatively stable cyclic performances in lab made Li-ion cells. This invention offers a method that is highly potential for low cost, mass production of 1D nanostructured silicon. The related results are organized in Chapter 7 in this thesis.

Challenges and future research opportunities in the two areas were suggested.

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