Chang Sam Kim

Electrochemical Performance of Spherical LiCoO₂ Powders Synthesized Using Ultrasonic Spray Pyrolysis Method (I) : Effect of Pyrolysis Conditions on Powder Characteristics

Process parameters were studied in synthesis of LiCoO₂ powder by ultrasonic spray pyrolysis. Concentration of the mixed solution influenced the size, shape, and yield of the synthesized powder. The yield was affected primarily by the height of the solution, and then by the flow rate of a carrier gas. The temperature of the reactor governed the crystallinity and morphology of the powder. LiCoO₂ powders were synthesized as a layered high temperature phase above 800℃. The synthesized powders were sphere and secondary particles consisted of primary particles of 55-70 nm. The secondary particles became bigger from 0.28 to 1.43 ㎛ as the concentration of the solution was increased from 0.05 to 2.0 M. The 2.0 M solution provided the higher production rate.

Electrochemical Properties of LiFePO4/C Composite Improved by High Energy Milling

The electrochemical properties of LiFePO4 as a cathode of lithium ion batteries considerably depend on a particle size of LiFePO4 and a condition of carbon coating. In this study, LiFePO4 powders were prepared using ultrasonic spray pyrolysis method, and then LiFePO4/C composites were made by infiltrating sucrose solution into LiFePO4 powders, drying, high-energy milling and annealing. The effects of high-energy milling were analyzed by comparing with electrochemical properties of powders synthesized without high-energy milling. It was found that the milling process drastically reduced the particle size of synthesized powders and electrical conductivity, and improved discharge capacity, cycle stability and rate performance.

Electrochemical properties of Al doped Li (Ni1/3Co1/3Mn1/3 )O2

Al doped Li(Ni1/3Co1/3Mn1/3-xAlx)O2 (x=0.005, 0.01, 0.05) and Li(Ni1/3-x/2Co1/3Mn1/3-x/2Alx)O2 (x=0.01, 0.05) cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis and heat treatment. The substitution with Al reduced the content of Mn3+, promoted grain growth, and broadened the particle size distribution of synthesized powders. The initial discharge capacity of cells made with 0.5 mol% Al doped Li(Ni1/3Co1/3Mn1/3-0.005Al0.005)O2 powder was as high as that of the undoped (~180 mAhg-1, 3.04.5 V), and showed an excellent cycle stability. The improvement of the cycle stability was considered to be due to the decrease of Mn3+ in Li(Co1/3Ni1/3Mn1/3-xAlx)O2 by Al doping.

Oxidation State of Manganese in LiMn2O4 Powders and Its Effect on Electrochemical Properties

Lithium manganese oxide (LiMn2O4) powders for lithium ion batteries were synthesized from two separate raw material pairs, LiOH/MnO and LiOH/MnO2. The prepared powders and their electrochemical properties were investigated. Powders calcined at 780°C were composed of a single-phase spinel structure but those treated at 850°C showed a higher intensity ratio of I400 to I311, a slightly larger lattice parameter, and an increased discharge capacity by 10% under 3.0~4.3V voltage range. The XPS study on the oxidation states of manganese repealed that powders made from LiOH/MnO had less Mn3+ ion and gave better battery performances than those from LiOH/MnO2.

Synthesis and Sintering of La0.8Sr0.2CrO3 for the Separator of SOFC

The ultrasonic spray pyrolysis method and proper heat treatments were applied in order to synthesize La0.8Sr0.2CrO3 (LSC) which is one of promising materials for separator in soild oxide fuel cell in this study. LSC powders that were sprayed at 800oC, heat-treated at 900oC for 5 hrs, ball-milled and finally heat-treated again at 1200oC for 20 hrs showed the average diameter of 0.3 *m and narrow size distribution to find particles above 0.5 *m hardly. In addition, the synthesizing temperature of LSC powders in ultrasonic spray pyrolysis method was 100 lower than conventional ball milling and drying method. Therefore the proper combination of heat treatment and milling process after spray pyrolysis was found to be very critical in synthesizing fine and uniform LSC powders. Finally, the sintering properties of these LSC powders were analyzed and compared with those of conventional ones.

Surface Modification of Li (Co1/3Mn1/3Ni1/ 3)O2 Fine Powders Using Aqueous Al2O3 Sol

The surface of Li(Ni1/3Co1/3Mn1/3)O2 was modified with Al2O3 using aqueous alumina sol and the electrochemical properties of the coated oxide were measured and compared with both uncoated and Al-doped one. The alumina coated powder showed 185 mAh/g at first cycle, and 139 mAh/g after 50 cycles in the voltage range of 3.0~4.6 V at 1C rate. The initial discharge capacity of the coated powder was slightly lower than that of the alumina doped one, but the cycle stability of the coated was better than that of the doped.

Cu/GDC cermet anodes by sintering via surface modification with MgO sol

CuO/GDC composite powder with 50 wt% of CuO was prepared by surface modification of ~60 nm GDC powder with Cu precursors. Since copper oxide melts at lower temperature than GDC sintering temperature, fabrication procedure was modified by inducing infiltration of molten copper oxide via capillary force and then followed by heat treatment at ~1000. Surface modification was carried out with a MgO sol to suppress agglomeration of GDC. Such prepared Cu/GDC cermets showed uniform microstructure and excellent electronic conductivity of ~8500 S/cm for the Cu/GDC cermet and ~10200 S/cm for the modified one at 800.

Combinational Effects of Ni Precursors on Ni/YSZ Cermet Anode

NiO/YSZ composite powder with 70 wt% of NiO was prepared by surface modification of ~30 nm YSZ with Ni precursors. As Ni precursors, acidic nickel nitrate and basic nickel carbonate were employed. By varying the ratio of Ni precursors, substantially different particle sizes were obtained. Their Ni/YSZ cermets also showed substantially different microstructures and porosities. Effects of combination of Ni precursors on Ni/YSZ cermets were studied by using XRD, zetapotential, and SEM.

Microstructure and electrochemical properties of post heat-treated Li(Ni1/3Co1/3Mn1/3)O2 cathode materials for lithium ion battery

Li(Ni1/3Co1/3Mn1/3)O2 powders were synthesized by using an ultrasonic spray pyrolysis method, and then heat-treated at 900 or 1000°C for 20 h. The morphology of the as-synthesized powder was spherical. The post heat-treatment changed the particle size and morphology of the synthesized powders. Structural characteristics of the heat-treated powders were analyzed using XRD and SEM, and their electrochemical properties were compared. Higher first discharge capacity was obtained from the powder heat-treated at 1000°C, but its rough and rugged surface might cause a rapid decrease of the capacity retention.

Preparation of Cu/GDC Cermet Anode by Sintering via Surface Modification with MgO Sol

CuO/GDC composite powder with 50 wt% of CuO was prepared by surface modification of ~60 nm GDC powder with Cu precursors. Since copper oxide melts at lower temperature than GDC sintering temperature, fabrication procedure was modified by inducing infiltration of molten copper oxide via capillary force and then followed by heat treatment at ~1000 °C . Surface modification was carried out with a MgO sol to suppress agglomeration of GDC. Such prepared Cu/GDC cermets showed uniform microstructure and excellent electric conductivity of ~6000 S/cm for the Cu/GDC cermet and ~10000 S/cm for the modified one at 800°C.