Abstract
The main objective of this dissertation is to develop a rapid surface modification technique to enhance the electrochemical performance of lithium-ion battery (LIB) anodes. Atmospheric pressure plasma jet was constructed to introduce surface treatment to reduced graphene oxide (RGO) 2D electrodes. Result from x-ray photoelectron microscopy suggests a change in surface chemical bonding with increasing plasma treatment repetitions. Plasma also introduce surface defects creating nitrogen-doping. After 20 times of Ar+N2 plasma treatment, a significant increment in cycling property (~1500 mAh/g) under 0.5 A/g was found. In addition, a specially designed atmospheric dielectric barrier discharge plasma generator that are feasible to modify powders is proposed. The rate capacity of 20 min plasma treated TiO2 anode revealed nearly 20% increment as compared to that of pristine TiO2 at the rates of 0.5, 1, 2, 5, 10 C. As-treated TiO2 was first analyzed by X-ray diffractometer and high resolution transmission electron microscope to confirm that there was no noticeable surface morphology and microstructure change from plasma treatment. In addition, plasma treated TiO2 were reduced before nitrogen-doping were doped with increasing treatment duration. Significant amount of excited argon (Ar*) and excitation of nitrogen second positive system (N2*) was discovered using optical emission spectroscopy. It was believed that Ar* and N2* contributed to formation of surface defects. After forming defects the decomposed N in the plasma can thus be doped onto the surface of RGO and TiO¬2. Plasma surface modification leads to defect formation as well as nitrogen-doping. By integrating plasma diagnosis and surface characterization, dynamic plasma-surface interaction can thus be proposed to provide further guidelines for plasma surface modifications of LIB anodes. These findings help the understanding of the atmospheric plasma treatment on the surface modification of RGO and TiO2 anode material in Li-ion battery.