No abstract

No abstract

The structure and the room temperature performances of sulfur cathodes composed of sulfur, carbon, and poly(ethylene oxide) (PEO) binder were studied with varying preparation method and binder content. Two different methods, ball mixing and mechanical stirring, were employed for preparation of slurry to obtain morphologically different cathodes. The cathodes prepared with mechanical stirring (SC cathodes) revealed more porous structure than those with ball mixing (BC cathodes). Scanning electron microscopy observations showed that sulfur particles were covered with dense and thick PEO film in the BC cathodes, whereas sulfur particles were bonded with porous PEO film in the SC cathodes. The SC-based cells exhibited much higher discharge capacity yielding 75% of sulfur utilization than the BC-based cells. The difference of discharge behaviors with different mixing methods indicates that the porosity of the cathode and the morphology of PEO binder are highly important factors for favorable electrochemical performance of lithium sulfur batteries. The cycle life of the SC-based cell was improved with the increase of binder content and with the roll pressing due to the increase of adhesiveness and cohesiveness of the sulfur cathode. © 2002 The Electrochemical Society. All rights reserved.

Al-doped ZnO (AZO) films were deposited onto glass substrates by RF magnetron sputtering for solar cell applications. The effects of the Al 2 O 3 doping concentration on the structural, electrical, and optical properties of the AZO films were investigated. As the Al 2 O 3 doping concentration was increased to 4.0 wt %, X-ray diffraction (XRD) showed a deterioration in the (002) peak intensity and a shift towards a higher angle. The best electrical properties ( ¼ 9:8 Â 10 À4 cm, H ¼ 22 cm 2 V À1 s À1 , and n e ¼ 2:89 Â 10 20 cm À3 ) were obtained in the AZO sample containing 2 wt % Al 2 O 3 . Optical transmission >83% in the visible range was also observed and the optical bandgap was increased to 3.63 eV at an Al 2 O 3 concentration of 4 wt %. For photoluminescence (PL) spectra, one UV emission peak at approximately 3.2 eV and a broad peak in the visible range from 2.3 to 2.7 eV were observed at Al 2 O 3 doping concentrations ranging from 0 -2.0 wt %. Blue emission at 2.67 eV, which indicates a non-stoichiometric structure, was only observed in the 4 wt % doped AZO films.

No abstract

The CO 2 gas sensor, based on the principle of electro-chemistry, was fabricated using the solid-electrolyte Li 3 PO 4 film formed by a thermal evaporator and its sensing performances were studied. Thermal evaporated film was prepared with power of 10A, a working pressure of 10 -6 mTorr and thickness of 1.2 µm. Then, it was annealed at 800 o C for 2h in air. Li 2 TiO 3 +TiO 2 and Li 2 CO 3 film were prepared using a screen printing method as the reference and the sensing electrode, respectively. Li 3 PO 4 film showed a much denser structure than bulk-type Li 3 PO 4in SEM images. The response and recovery characteristics were very good at the higher CO 2 concentration and its value was 280 mV and changed to 260 mV in the higher CO 2 environment. It was also observed that the sensitivity decreased by 98 % when the CO 2 concentration increased from 250 ppm to 5000 ppm. Response time and recovery time were measured to be 5 s and 7 s, respectively. These results showed enough potential for developing a CO 2 gas sensor using Li 3 PO 4 film instead of the bulk-type.

Electro-spun nanofiber web is highly attractive as a separator for lithium ion batteries because of its high electrical properties. In moving toward wider battery applications of the nanofiber separators, a deeper understanding on the structure and property relationship is highly meaningful. In this regard, we prepared electro-spun poly(vinylidene fluoride) (PVdF) webs with various thicknesses (10.5~100 µm) and investigated their structures and electrochemical performances. As the thickness of the web is decreased, a decrease of porosity and an increase of pore size are resulted in. For the 10.5 µm-thick separator, a minor short-circuit was detected, stressing the importance of reducing pore-size on prevention of short-circuit. However, above the thickness of 21 µm, well-connected, submicron-sized pores are generated, and, with lowering the separator thickness, discharge capacity and rate capability are enhanced owing to the lowered area-specific resistance.

No abstract