Papers by Author: Bong Ki Lee

Abstract: Si and Si/Ni thin film electrodes less than 1
m in total thickness were fabricated on the roughened Cu substrate by rf sputtering. Their surface morphology and crystalline structure were carefully investigated by means of FESEM and XRD. The morphology of films is dependent on the surface feature of substrate, and the grown films were amorphous. The initial capacity and the irreversible capacity loss of a Li/Si film cell were improved with insertion of a Ni buffer layer. The effect of the film morphology on the electrochemical properties of cells was demonstrated based on the observations of film electrodes.

Abstract: Si film electrodes for Li micro-film batteries were fabricated on a Cu substrate and a Ni/Cu film. In the structural properties, Si film had an amorphous structure, while the crystallinity of Ni buffer film was improved after annealing. FE-SEM observation demonstrated differences in surface morphologies of Si films fabricated with different methods. In the electrochemical properties, the Ni-inserted film showed the largest initial charge and discharge capacity, and the cell with annealed Si/Ni/Cu film showed good cycleability. It is believed that the insertion of Ni film as a buffer film improved the charge and discharge capacity owing to the enhancement of adhesion between Si film and Cu substrate.

Abstract: This paper describes the morphology and microstructure of graphitic nanofibers(GNFs) synthesized by the catalytic decomposition of ethylene in the presence of Ni:Cu(70wt%:30wt%) as catalyst at 550°C to 700°C. The catalyst was prepared by the coprecipitation method using aqueous solution of metal nitrates. The catalysts and the graphitic nanofibers(GNFs) were characterized by FE-SEM, HR-TEM and EDXS. The shape, composition and microstructure of the catalyst according to the synthesis temperature of graphitic nanofibers(GNFs)were changed so that it brought about the change of morphology and microstructure of graphitic nanofibers(GNFs). In particular, it should be noted that the composition change of catalysts with different synthesis temperature is one of the key factors in determining the morphology of graphitic nanofibers(GNFs)