Preparation, Characterization and Performance Study of Modified Titanium Dioxide Nanocrystals for the Lithium-Ion Battery
Abstract
The lithium-ion battery is one of the most widely used rechargeable batteries in
today’s life. As an energy storage device, it can convert the stored chemical energy into
electrical energy when it is being used. Titanium dioxide nanocrystals are well-known for
the photocatalytic ability. However, benefited from the nanostructure and the
electrochemical reactivity of lithium-ions, titanium dioxide nanocrystals are also
investigated as a promising anode material used for the lithium-ion battery. It is safer
than graphite as it can prevent the lithium deposition and formation of the solid
electrolyte interphase; additionally, it is an environmentally friendly and economical
material that can also provide good theoretical capacity. These superiorities have
attracted many research interests and make it a target material in this dissertation. However, the battery made by titanium dioxide suffers poor battery performances
that are caused by two major drawbacks of the material. The low electronic conductivity
in the solid phase and the low diffusion coefficient of lithium-ions cause only a thin
surface layer of the titanium dioxide particle to be effectively used for the intercalation
and extraction of lithium-ions at high charge/discharge rates; thus, the actual application
is hindered. In order to improve the battery performances, three modification methods
were discussed: hydrogenation, vacuum treatment, and carbon coating. The structural and
electronic properties of the pure titanium dioxide nanocrystals and the new modified
titanium dioxide nanocrystals were studied with: transmission electron microscopy, x-ray
diffraction patterns, Raman spectroscopy, Fourier transform infrared spectroscopy,
thermal gravimetric analysis, ¹H magic-angle spinning solid state nuclear magnetic
resonance spectroscopy, electron spin resonance spectroscopy, and x-ray photoelectron
spectroscopy. The coin cells used titanium dioxide nanocrystals as electrode materials
and were tested and analyzed in terms of discharge capacity, Coulombic efficiency, and
rate performance. The electrochemical impedance spectroscopy was also studied in order
to understand the electrochemical system. Compared with the pure titanium dioxide
nanocrystals, the hydrogenated titanium dioxide nanocrystals, the vacuum-treated
titanium dioxide nanocrystals, and the carbon-coated titanium dioxide nanocrystals
showed improved battery performances. The structure and battery performances of three
different titanium dioxide nanocrystals were related and discussed systematically.
Table of Contents
Introduction -- Experimental and analytical methods -- Design, preparation and properties of the hydrogenated titanium dioxide nanocrystals -- Design, preparation and properties of the vacuum-treated titanium dioxide nanocrystals -- Design, preparation and properties of the carbon-coated titanium dioxide nanocrystals -- Conclusion
Degree
Ph.D.