Papers by Author: Jae Won Choi

Abstract: The effect of lithium salts such as LiPF6, LiBF4, LiCF3SO3 and LiN(CF3SO2)2 (LiTFSI) in tetra(ethylene glycol) dimethyl ether (TEGDME) electrolyte on the ionic conductivity, interfacial resistance and discharge properties of Li/pyrite cell at room temperature was studied. The electrolytes had good ionic conductivity at room temperature in the range 0.61 to 1.86 × 10-3 S/
. The discharge capacities of Li/pyrite cells with 1M LiPF6 and LiBF4 in TEGDME were lower compared to those of the other two non-HF containing salts. The best cycle performance was exhibited by LiTFSI in TEGDME electrolyte, with a discharge capacity of 438 mAhg-1 after 20 cycles, which is ~49% of FeS2 theoretical capacity (894 mAhg-1). The good performance of LiTFSI-TEGDME electrolyte resulted mainly from its low interfacial resistance in Li/FeS2 cells, which showed a decreasing trend with cycling.

Abstract: Iron, sulfur and transition metal powders were used as the starting materials to prepare iron disulfide (FeS2) cathode material at room temperature by high energy mechanical alloying. Modified FeS2 were also prepared by incorporation of transition metals like Co and Ni. Li/FeS2 cells with the prepared iron disulfides as cathodes were studied for discharge properties at room temperature using the 0.5M LiTFSI in tetra(ethylene glycol) dimethyl ether (TEGDME). The first discharge capacities of Li/composite FeS2 cell with 5 wt.% Co and 3 wt.% Ni were 571 and 844 mAh/g, respectively, compared to 389 mAh/g for the cell without any additive. The enhanced properties resulted from the better electronic conductivity of the material containing the metallic additive. The initial capacity and cyclic performance were improved when nickel and cobalt were added to prepare the modified iron disulfide.

Abstract: Iron disulfide (FeS2) is attractive as a positive electrode material in lithium batteries because of its low material cost, environmental non-toxicity, and high specific energy density. Furthermore, natural pyrite is a secondary product of the mining extraction of coal. For these reasons, natural and synthetic pyrites have been proposed as active cathode materials in secondary lithium batteries. We investigated the effect of various solvents on the electrochemical properties of lithium-FeS2 batteries. The specific discharge capacity of Li/FeS2 cells varied from 500 to 780mAh/g based on FeS2.

Abstract: The lithium ionic conductivity of Poly (acrylonitrile) (PAN) gel polymer electrolyte with PC/EC was found to be about 1.3 x 10-3S/cm at room temperature. The discharge curve of Li/ PAN (PC+EC)/S battery showed only one plateau region, which is different from that using PVdF(TEGDME) gel polymer electrolyte. Also, the first discharge capacity was 556mAh/g-sulfur in Li/S battery using PAN (PC+EC) gel electrolyte at room temperature.

Abstract: Iron disulfide (FeS2) is attractive as a positive electrode material in lithium batteries because of its low material cost, environmental non-toxicity, and high specific energy density. Furthermore, natural pyrite is a secondary product of the mining extraction of coal. For such reasons, natural and synthetic pyrites have been proposed as active cathode materials in primary lithium batteries. We investigated the effect of temperature and current density on the electrochemical properties of lithium-FeS2 batteries. The specific discharge capacity of Li/FeS2 cells varied from 700 to 900mAh/g based on FeS2.

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: 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.