Gyeong-Ok Kim

Synthesis and control of the shell thickness of polyaniline and polypyrrole half hollow spheres using the polystyrene cores

Polyaniline (Pani) and polypyrrole (Ppy) half hollow spheres with different shell thicknesses were successfully synthesized by three steps process using polystyrene (PS) as the core. The PS core was synthesized by emulsion polymerization. Aniline and pyrrole monomers were polymerized on the surface of the PS core. The shells of Pani and Ppy were fabricated by adding different amounts of aniline and pyrrole monomers. PS cores were dissolved and removed from the core shell structure by solvent extraction. The thicknesses of the Pani and Ppy half hollow spheres were observed by FE-SEM and FE-TEM. The chemical structures of the Pani and Ppy half hollow spheres were characterized by FT-IR spectroscopy and UV-Vis spectroscopy. The shell thicknesses of the Pani half hollow spheres were 30.2, 38.0, 42.2, 48.2, and 52.4 nm, while the shell thicknesses of the Ppy half hollow spheres were 16.0, 22.0, 27.0, and 34.0 nm. The shell thicknesses of Pani and Ppy half hollow spheres linearly increased as the amount of themonomer increased. Therefore, the shell thickness of the Pani and Ppy half hollow spheres can be controlled in these ranges.

X-ray absorption spectroscopy studies of the Ni ion of Li(Ni{sub 0.8}Co{sub 0.15}Al{sub 0.05}){sub 0.8}(Ni{sub 0.5}Mn{sub 0.5}){sub 0.2}O{sub 2} with a core–shell structure and LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} as cathode materials

Core–shell materials have attracted a great deal of interest since core–shell particles have superior physical and chemical properties compared to their single-component counterparts. The cathode material Li(Ni{sub 0.8}Co{sub 0.15}Al{sub 0.05}){sub 0.8}(Ni{sub 0.5}Mn{sub 0.5}){sub 0.2}O{sub 2} (LNCANMO) with a core–shell structure was synthesized via a co-precipitation method and investigated as the cathode material for lithium ion batteries. The core–shell particle consisted of LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} (LNCAO) as the core and LiNi{sub 0.5}Mn{sub 0.5}O{sub 2} as the shell. The cycling behavior between 2.8 and 4.3 V at a current of 0.1 C-rate showed a reversible capacity of ∼195 mAh g{sup −1} with little capacity loss after 50 cycles. Extensive assessment of the electronic structures of the LNCAO and LNCANMO cathode materials was carried out using X-ray absorption spectroscopy (XAS). XAS has been used for structure refinement on the transition metal ion of the cathode. In particular, XAS studies of electrochemical reactions have been done from the viewpoint of the transition metal ion. In this study, Ni K-edge XAS spectra of the charge and discharge processes of LNCAO and LNCANMO were investigated.