Ho Suk Ryu

High capacity cathode materials for Li–S batteries

To enhance the stability of sulfur cathode for a high energy lithium–sulfur battery, sulfur–activated carbon (S–AC) composite was prepared by encapsulating sulfur into micropores of activated carbon using a solution-based processing technique. In the analysis using the prepared specimen of S–AC composite by the focused ion beam (FIB) technique, the elemental sulfur exists in a highly dispersed state inside the micropores of activated carbon, which has a large surface area and a narrow pore distribution. The S–AC composite was characterized through X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method, selected area electron diffraction (SAED), energy dispersive X-ray spectrometry (EDX), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA), and field emission scanning electron microscopy (FESEM). A lithium–sulfur cell using the S–AC composite has a high first discharge capacity over 800 mA h g−1 S even at a high current density such as 2C (3200 mA g−1 S) and has good cycleability around 500 mA h g−1 S discharge capacity at the 50th cycle at the same current density.

The Electrochemical Properties of Poly(acrylonitrile) Polymer Electrolyte for Li/S Battery

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.

Self-Discharge Behavior of Lithium/Sulfur Battery Using Aluminum Current Collector

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.

Electrochemical properties of Fe2O3 thin film fabricated by electrostatic spray deposition for lithium-ion batteries

Fe2O3 thin films are important for the fabrication of rechargeable lithium microbatteries. Thin films of Fe2O3 were prepared by the electrostatic spray deposition (ESD) technique by using iron chloride as the precursor. The thin film electrodes, without inert additives such as polymer binder and conducting material, can deliver a first discharge capacity of 912?mA?h?g?1 and retain a discharge capacity of 537?mA?h?g?1 at a current density of 200?mA?g?1 to the 100th cycle. The coulombic efficiency of the Fe2O3 thin-film electrode was over 96% after several cycles.

The Characteristics of Sulfur Electrode with Carbon Nanotube

We investigated on the additive effect of carbon nanotube in the sulfur electrode on the first discharge curve and cycling property of lithium/sulfur cell. The sulfur electrode with carbon nanotube had two discharge plateau potentials and the first discharge capacity about 1200 mAh/g sulfur. The addition carbon nanotube into the sulfur electrode did not affect the first discharge behavior, but improved the cycling property of lithium/sulfur cell. The optimum content of carbon nanotube was 6 wt% of sulfur electrode.

The Discharge Properties of Nickel Sulfide Thin Film Prepared from Sulfidation of Nickel Foil

The nickel sulfide (Ni3S2) thin film could be prepared from Ni/S double layer, which was deposited on nickel foil using evaporation and sputtering. The nickel sulfide electrode was discharged and charged between 0.6V and 2.6V versus Li/Li+ at room temperature. The nickel sulfide film had the first discharge capacity of 270mAh/g, and two plateaus at 1.3V and 1.8V.

Ionic Conductivity of Sodium Ion with NaCF3SO3 Salts in Electrolyte for Sodium Batteries

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.

Discharge-charge property of lithium/PEO/sulfur battery with high sulfur content

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.

Charge/Discharge and Electrochemical Characteristics of Secondary Lithium/Pyrite Battery

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.