Young-Ah Jeon

Fabrication and Electrochemical Characterization of LiCoO2 Cathode Powder by Mechanochemical Process

LiCoO 2 cathode powders with a grain size of 1-1.5 μm were synthesized by a mechanochemical process. The Li-Co precursor was prepared by a freeze drying method using a Li and Co acetate as starting raw materials. The surface was modified by lapping the precursor using K 2 SO 4 in a simple ballmill. After the surface modification, the Li-Co precursor was heated at 800°C to form a high-temperature polymorph. The K 2 SO 4 coat on the Li-Co precursor prevented the Li-Co precursors from contacting one another, due to the high decomposition temperature of K 2 SO 4 above 1000°C and constrains grain growth. Because of this, the modified Li-Co precursor is converted to very small crystalline LiCoO 2 particles by phase transformation. The as-synthesized LiCoO 2 powder had well-developed facets and a very uniform grain size distribution. A small capacity fade for high discharge rate was observed in the as-synthesized powder, which can be attributed to the diffusion of Li ions at the grain boundary. Thus, it is possible not only to synthesis LiCoO 2 powder to a desired grain size but also to control the grain size distribution using this method. These results indicated that the synthesis of a high-temperature polymorph of LiCoO 2 with a small grain size is possible by constraining growth during the heat-treatment. The LiCoO 2 powder synthesized here represents a very good candidate for use in fabricating not only of high power bulk batteries but high power slim batteries as well, when a thin and thick film process is used.

Orientation and fatigue improvement of PZT thin films on cubic textured CaRuO3 electrode

ABSTRACT In this study, we report on the (100) cube-textured Pb(Zr0.4,Ti0.6)O3 (PZT) thin films using a conducting perovskite CaRuO3 (CRO) bottom electrode, and which was compared to the (111) textured PZT on Pt electrode. X-ray diffraction (XRD) reveals that the CRO bottom electrode has a pseudo-cubic nature on Si, and the PZT thin films prepared on CRO/Si shows a (100) textured growth. PZT films on CRO electrode have a well-saturated ferroelectricity with a remanent polarization (Pr) and coercive field (Ec) of 25 μ C/cm2 and 75 kV/cm, respectively. These PZT films are more fatigue resistive character than that on Pt bottom electrode.

ELECTRONIC STRUCTURE OF BISMUTH TITANATE-BASE FILMS Bi4-xLnxTi3O12 DEPENDENCE ON SUBSTITUTION ATOM

ABSTRACT Electronic structures and chemical bonding were investigated on Bi4Ti3O12 substituted with lanthanides, such as La, Ce, Pr, and Nd for Bi, using the discrete variational Xα method. Also, we investigated the effect of substitution atom on net charge and overlap population, which is related to the dielectric constant. We found that the net charge and overlap population were dependent on the substitution atom. We concluded that dielectric constant increases as the atomic number of substitution atom increases.