Sung-Ho Jin

Synthesis and electrochemical characteristics of spinel phase LiMn2O4-based cathode materials for lithium polymer batteries

Spinel LiMn 2 O 4 and LiMn 1.95 Ni 0.05 O 4 powders have been synthesized by a sol-gel method using an aqueous solution of metal acetates containing glycine. The dependence of the physicochemical properties of the spinel LiMn 2 O 4 powders on the calcination temperature and glycine quantity have been extensively investigated. The porous LiMn 2 O 4 and LiMn 1.95 N 0.05 O 4 electrodes were electrochemically characterized by using charge/discharge experiments along with ac impedance spectroscopy. The LiMn 1.95 Ni 0.05 O 4 electrode exhibited improved cycling performance in comparison with the stoichiometric LiMn 2 O 4 one in spite of a small reduction in the initial capacity. The good capacity retention of the LiMn 1.95 Ni 0.05 O 4 electrode is attributed to stabilization of the spinel structure by Ni doping for Mn ion sites and higher chemical diffusivity of lithium ions with cycling.

Synthesis and electro-optical properties of electroluminescent polymers containing carbazole unit

Abstract A new series of the processable emissive polymers containing dialkylphenylene vinylene and N -ethylcarbazole units was synthesized by Wittig polymerization. The resulting polymers are soluble in organic solvents and spin-cast to make a thin film. A light emitting diode (LED) was fabricated by sandwiching the emissive polymers between indium-tin oxide and aluminum electrodes. Strong emission at 460 and 490 nm were observed from the devices made by the synthesized polymers. The present polymers have the strong absorption band at around 310 nm, which are due to the π–π∗ transition of the conjugated segments of corresponding polymers. I – V curve shows typical rectifying diode characteristics. The forward bias turn-on voltage for the LEDs are 5 V for poly(dihexylPV-Cvz) and 10 V for poly(MEHPV-Cvz), respectively.

Synthesis and cycling behavior of LiMn2O4 cathode materials prepared by glycine-assisted sol-gel method for lithium secondary batteries

Spinel-type LiMn2O4 powders having submicron, narrow particle-size distribution and excellent phasepure particles have been synthesized at low temperatures from metal acetate aqueous solution containing glycine as a chelating agent by a sol-gel method. The dependence of the physicochemical properties and cycling characteristics of the spinel LiMn2O4 powders on the various calcination temperatures has been extensively studied. It was found that the physicochemical properties of the LiMn2O4 powders could be controlled by simply varying the calcination temperature. Glycine-assisted LiMn2O4 powders have shown excellent rechargeability and delivered discharge capacity of 119 mAh/g for more than 150th cycles in Li/polymer electrolyte/liMn2O4 cells.

POLYMERIZATION OF 4-HYDROXY-N-PROPARGYLPIPERIDINE BY TRANSITION METAL CATALYSTS

The polymerization of 4-hydroxy-N-propargylpiperidine, having 4-hydroxypiperidine moiety, was carried out with various transition metal catalysts. The polymerizations proceeded well to give a relatively high yield of polymer (maximum polymer yield: 93%). Palladium, platinum, and ruthenum chlorides were found to be generally effective for this polymerization. On the other hand, the group 5 and 6 transition metal catalysts such as WCl6, MoCl5, WCl6-organoaluminum compounds etc. fail to polymerize this monomer. The molecular structure of the resulting poly(4-hydroxy-N-propargylpiperidine) was characterized by the various instrumental analysis methods such as NMR (1H-and 13C-)IR, and UV-visible spectroscopies. The IR spectrum of polymer shows neither the acetylenic hydrogen stretching (3197 cm−1) nor the carbon-carbon triple bond stretching (2113 cm−1) frequencies presented in the IR spectrum of monomer. Instead, the carbon-carbon double bond stretching frequency at 1611 cm−1 was newly observed. These polymer...

Surface alignment of ferroelectric liquid crystals using side chain ferroelectric liquid crystal polymer

New surface alignment material for surface stablized ferroelectric liquid crystal displays (SSFLCDs) is investigated. Side chain ferroelectric liquid crystal polymer (SCFLCP) such as Poly{methyl 4-[[[S-(-)-2-methyl-1-butoxy]carbonyl] phenyl ]4′-hexyloxybenzoyl}Siloxane was used as the alignment layer which resulted in good uniform alignment of FLC molecules without zig-zag defects. However, RN-715 polyimide alignment layer showed random alignments with some zig-zag defects in the SSFLC cells. After the field stablization of±20 V AC, the typical stripe-shaped patterns appeared. Good electro-optical performance was observed by using SCFLCP.