Ho-jin Kweon

Modification of LixNi1-yCoyO2 by applying a surface coating of MgO

Mg(OH)2 is coated on the surface of semi-crystalline LixNi1−yCoyO2. By further heating the coated sample, the surface is modified. This lowers the initial discharge capacity and improves the cycle-reversibility of a test lithium-ion cell, which was made with surface-modified LixNi1−yCoyO2 as the cathode material.

Synthesis of LixNi0.85Co0.15O2 by the PVA-precursor method and charge–discharge characteristics of a lithium ion battery using this material as cathode

Abstract Polycrystalline powder of Li x Ni 0.85 Co 0.15 O 2 was synthesized from poly(vinyl alcohol) gel (a PVA-precursor). The crystalline phase of Li x Ni 0.85 Co 0.15 O 2 was developed without any minor phase above 600°C. The crystallization proceeded without any prominent heat event, which indicated homogeneous distribution of constituents and insignificant amount of diffusion barrier. The crystalline powder prepared from the PVA-precursor had relatively smaller particle size, larger surface area, and higher carbon content than the one prepared by the conventional solid state reaction. Charge–discharge property was studied by using a coin-type cell containing Li x Ni 0.85 Co 0.15 O 2 as cathode material, and Li metal as the anode, in a potential range of 2.8–4.3 V. Initial discharge capacity (at a rate of C/10) of the cell was 170 mA h/g. At high rate of 1C, the cycling reversibility for the cell with Li x Ni 0.85 Co 0.15 O 2 prepared from the PVA-precursor was observed to be much better than that with the one prepared by the solid state reaction. After 90 continuous cycles at constant rate of 1C, the decrease of discharge capacity was less than 20 mA h/g in the case of the PVA-precursor method, whereas it was about 80 mA h/g for the solid state reaction.

Microstructured Membrane Electrode Assembly for Direct Methanol Fuel Cell

The concept of microstructured membrane electrode assembly for direct methanol fuel cell featuring a double-catalyst layer and micropatterned interface between the membrane and the catalyst layer was suggested and realized in this work. The doublecatalyst layer, which consists of a dense first layer and a porous second layer, was designed to achieve effective mass transfer in the catalyst layer. The micropatterned interface was generated by forming a micropattern on the membrane surface prior to catalyst coating on the membrane. The introduction of the double-catalyst layer resulted in a power density increase of 18%, and the generation of the micropatterned interface caused an additional power density increase of 23% at 50°C and 0.4 V. The I-V polarization and impedance analysis indicates that mass transfer in the catalyst layer was significantly improved owing to the large pores in the second catalyst layer. The micropatterned interface did not influence the cathode reaction rate; however, it caused a profound increase of the anode reaction rate.