Doctor of Philosophy
Faculty of Engineering
Wang, Guoxiu, Investigations on electrode materials for lithium-ion batteries, Doctor of Philosophy thesis, Faculty of Engineering, University of Wollongong, 2000. http://ro.uow.edu.au/theses/1832
This PH.D project aims to prepare and study the preparations of advanced electrode materials with high capacity and long cycle life for rechargeable lithium batteries. The structural, physical and electrochemical properties of the electrode materials determine the energy density and performance of lithium ion batteries. Therefore, new electrode materials are critical for developing high energy density lithium ion batteries.
A thorough literature review has been made in order to provide a detailed description of the status of current research and development in rechargeable lithium ion battery systems. In particular, many different electrode materials used for lithium ion batteries are described.
A variety of cathode materials have been investigated. Some of them have shown good electrochemical performance when used as electrode materials in lithium ion cells. The LiMxMn2-x04 spinels doped with different metal ions were prepared using either solid state reaction or other chemical methods. The structural characteristics of the doped spinels were determined by neutron diffraction. The best dopant effects were found with Co3+ and Cr3+ ions, in terms of stabilising the spinel structure, improving the cycle life and alleviating the self-discharge when the electrode was charged to the highly charged state. A series of layered LiMgNi-802 compounds were synthesised to improve the cyclability of the LiNi02 electrode. These compounds have many advantages over commercial LiCoO2 cathode material in terms of capacity and cost but they are required to be synthesized in an oxygen atmosphere. An innovative orthorhombic LiMnO2 was also synthesised to explore the feasibility of utilising inexpensive LiMnO2 as cathode material for lithium-ion batteries. In general, dopant effects were found to have positive impact on the improvement of the structural and electrochemical stability as well as rechargeability of the layered electrode materials.
Also, in this project, various different types of anode materials were prepared and their electrochemical properties were tested. Li4Ti5O12 compound demonstrated a very stable cyclability with a voltage plateau at 1.5 V vs. Li/Li+. It can be used as an anode coupled with high potential cathodes such as LiMn204 or LiCoO2 to construct lithium ion cells.
Lithium ions can reversibly insert/extract in the Lao33NbO3 perovskite and LiTi2(PO4)3 with NASICON-type structure. Through the analysis of the structure of these materials, new lithium insertion materials could be identified.
The intermetallic alloys are emerging as new generation anode materials with high lithium storage capacity. Nano-crystalline alloys Cu6Sn5. NiSi, FeSi and NiSn were produced by mechanical ball milling. These alloy anodes delivered large capacities in the range of 800-1400 mAh/g, but their cycle life still needs further improvement.
A series of La(0.57-2x/3) SrLio.3Ti03 solid-state electrolytes have been investigated. The maximum Li-ion conductivity observed at room temperature is about 1.12 x 10-3 Scm-1 for a Sr dopant level of x = 0.08. This Sr doped perovskite could be a candidate material as an electrolyte for solid-state lithium batteries.
The synthesised electrode materials were characterized by x-ray diffraction, SEM, TEM or HREM, through which the phase composition and microstructure were observed. Charge/discharge cycling tests were performed using CR2032 coin cells. The capacity and cycle life of the electrode materials were obtained from these tests. The kinetic characteristics and kinetic parameters of lithium ion insertion and extraction within the electrode materials were determined by a. c. impedance spectroscopy, cyclic voltammograms and galvanostatic intermittent titration technique (GITT).
In summary, the investigations in this project have produced several types of cathode and anode materials with high capacity and long cycle life. The mechanisms of the electrochemical reaction in lithium ion cell were theoretically analyzed and then experimentally determined by various techniques. All of these studies provide a fundamental basis for the development of high energy density lithium ion batteries.