Materials Science Forum Vols. 486-487

Abstract: Induction melting was attempted to prepare the undoped and Nb-doped CoSb3 compounds, and their thermoelectric properties were investigated. Single phase d-CoSb3 was successfully obtained by induction melting and subsequent annealing at 400°C for 2 hours in vacuum. The positive signs of Seebeck coefficients for all the specimens revealed that Nb atoms acted as p-type dopants by substituting Co atoms. Electrical conductivity decreased and then increased withincreasing temperature, indicating mixed behaviors of metallic and semiconducting conductions. Electrical conductivity increased by Nb doping, and it was saturated at high temperature. Maximum value of the thermoelectric power factor was shifted to higher temperature with the increasing amount of Nb doping, mainly originated from the Seebeck coefficient variation.

Abstract: The purpose of this research is to develop tin oxide electrode for lithium ion polymer battery. We have investigated cyclic voltammetry and charge/discharge cycling of SnO2/SPE/Li cells. The first discharge capacity of SnO2 anode was 612mAh/g. The discharge capacity of SnO2 anode was 560 and 376mAh/g at 2nd and 15th cycle at room temperature, respectively. The SnO2 composite anode with PVDF-PC-EC-LiClO4 electrolyte showed good cycling performance.

Abstract: The effect of mixed electrolytes and organic additives on the electrochemical performance of rechargeable lithium/sulfur battery is investigated. The mixture of organic electrolytes, DME, DIG, TEGDME, and DIOX, was prepared to have appropriate composition, and to the electrolyte were added various organic additives, such as toluene, γ-butyrolactone, and MA. They showed an improved cyclic efficiency of lithium/sulfur battery and made utilization of active material, sulfur, more effective.

Abstract: In this work, a simple way was contrived to enhance the rate capability and cycle life of LiNixMnyCo(1-x-y)O2 by doping Zr into the material. Zr-doped LiNixMnyCo(1-x-y)O2 was synthesized by solution-based synthetic route, and its electrochemical performance was investigated as 2016 coin-type half cell. With doping, some impurity peaks appeared in the XRD pattern, which seems to be related to Zr containing oxides. The enhanced characteristics in the rate capability and cycle life might be the result of the protective effect of Zr oxide against the decomposition of electrolyte and a faster Li diffusion rate.

Abstract: Surface sulfide layers were formed on the surface of Ti-50.0(at%)Ni alloys by isothermal annealing at 873 K for 3.6 ks under the sulfur pressure of 80 kPa, and then transformation behavior and mechanical properties were investigated by means of differential scanning calorimetery(DSC), thermal cycling tests under constant load, and tensile tests. The DSC peaks were broadened and martensitic transformation start temperature(Ms) increased from 281 K to 289 K by sulfurization. An equiatomic Ti-Ni alloy with surface sulfide layers showed good shape memory characteristics and partial superelasticity.

Abstract: Ti and Ni sulfides were formed on the surface of Ti-Ni alloys by isothermal annealing at various sulfur pressures, and then microstructures of the surface sulfide layers were investigated by means of scanning electron microscopy and X-ray diffractions. Morphology of sulfurized surface changed from granular shape to porous shape at the sulfur pressure of 80 kPa, which is related to the change in sulfide from NiS1.97 to NiS. Two-layered sulfide was observed in which the inner layer was mainly Ti8.2S11 , and the outer layer was a mixture of NiS1.97 and NiS. The discharge curve of the Ti and Ni sulfides cathode formed on the Ti-Ni current collector at the first cycle showed a plateau voltage of 1.6 V, and the discharge capacity was found to be about 530 mAh/g-NiS1.97.

Abstract: The MFS and MFIS structures were prepared on the Si and PbO/Si substrate by the r.f. magnetron sputtering method. When the PbO buffer layer was inserted between the PZT thin film and Si substrate, the crystallization of the PZT thin films was considerably improved, and the processing temperature was lowered. Compared with the MFS structure, memory window values of the MFIS structure with the buffer layer were considerably improved. In particular, in the MFIS structure, the maximum value of the memory window is 2.0 V under the applied voltage of 9V for Pt/PZT (200 nm, 400ı)/PbO (80 nm)/Si structures with the PbO buffer layer deposited at the substrate temperature of 300ı.

Abstract: We investigated the self discharge behavior of lithium/sulfur cell using an alumium current collector. The discharge capacity decreased by 14% for oriniginal one after 30 days’ storage at room temperature. The open circuit voltage(OCV) of Li/S battery gradually decreased from 2.45V to 2.38V during the 30 days. The self discharge behavior was related to the decrease of elemental sulfur in the sulfur electrode.

Abstract: The sulfur electrodes were prepared from sulfur, carbon, and PEO as a binder. Poly(ethylene-oxide) with LiCF3SO3 was used as a solid polymer electrolyte for Li/S cell. Sulfur content of the sulfur electrode was 70wt%, and the carbon content was varied from 10wt% to 25wt%. The weight ratio of PEO and LiCF3SO3 in the polymer electrolyte was 9:1. The lithium/PEO/sulfur cell showed two plateau potential regions (2.4V, 2.1V) and high discharge capacity, i.e., 1068mAh/g(63.7% utilization of sulfur). The discharge capacity decreased drastically during charge-discharge cycling. The capacity fade depended on the composition of sulfur electrode regardless of similar initial discharge capacity. The sulfur electrode with high carbon content retained high capacity after repeated cycling. The optimum composition of 70wt% sulfur electrode was composed of 20wt% carbon and 10% PEO.

Abstract: To find out the proper sodium ion conducting electrolyte at room temperature, we investigated the ac impedance measurement of PVdF gel polymer electrolyte and liquid tetraglyme(TEGDME) with various concentrations of sodium trifluoromethane sulfonate(NaCF3SO3). The concentration of NaCF3SO3 did not severely affect the ionic conductivity. The sodium ionic conductivity using TEGDME with NaCF3SO3 was about 3.3×10-4 S㎝-1 which was lower than that of the PVdF gel polymer electrolyte, 5.0×10-4 S㎝-1. From the viewpoint of ionic conductivity, PVdF gel polymer electrolyte was proper electrolyte for sodium battery.