Papers by Author: Joong Kee Lee

Abstract: Lithium-ion capacitors (LIC) is believed to be an ideal option in certain application as energy storage device due to its properties either possessing high energy density (four times higher than electrical double-layer capacitor) or having as much power density as a supercapacitor. In this study, a biomass-based activated carbon (WHAC) was prepared by using the water hyacinth plant through the activation process utilizing a chemical activating agent, KOH. The water hyacinth was carbonized at 500 °C for a 1 h holding time with a ramping temperature of 10 °C/min. Then, the LICs electrode is constructed by two different types of electrode, WHAC as the main active material of cathode and lithium titanate oxide (LTO) for the anode. The biomass-derived activated carbon exhibits a high specific surface area of 791.8 m²/g and a high pore volume of 1.13 m^3/g. The assembled LiCs shows a reasonable electrochemical performance with a maximum specific capacitance of 1.12 F/g with the highest specific energy of 4.48 Wh/kg and specific power of 34.14 W/kg. This LIC cell is one of the promising candidates for future applications due to its low-cost materials and owns more advantages than typical Lithium-ion Batteries (LIBs).

Abstract: Carbon nanospheres (CNSs) were synthesized from commercial activated carbons and cooking oil as carbon precursors using simple pyrolytic process and then were used as anode materials of lithium secondary batteries Prior to the synthesis of CNSs, a series of Fe catalysts supported on commercial activated carbons were prepared by two different methods, namely impregnations and adsorptions. The effect of preparation method on the characteristics of CNSs were then studied by scanning electron microscopy (SEM) , transmission electron microscope (TEM) and BET surface area measurements. Preliminary electrochemical measurements of as-synthesized CNTs were carried out using cyclic voltammetry instruments at constant scan rate to see the mechanism of Li-ion insertion and extraction into/from CNSs structures during cycle tests.

Abstract: Carbon Nanospheres (CNSs) have been synthesized by thermal pyrolysis method. A mixture of Fe-catalyst supported activated carbons and palm oil was used in the furnace to produce CNSs. Prior to the synthesis of CNSs, Fe-catalyst was deposited onto the surface of activated carbons by wet incipient impregnation method. The ratio of carbon support and palm oil was varied (1:1, 1: 2 and 1:3) to obtain CNSs. The characteristics of produced CNSs were then evaluated with BET surface area analysis, pore size distribution analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that some impurities were still found in the CNSs in the forms of iron oxide and amorphous carbons.

Abstract: Activated carbons were prepared from coconut shell by chemical activation method and utilized as electrode materials for electrochemical double layer capacitor (EDLC). A preliminary characteristic of activated carbon from coconut shell includes the Brunnaeur Emmett Teller (BET) analysis and cyclic voltammetry measurements. The BET surface area is not affected by the variation of activation temperature as both of the samples showed BET surface area of about 850-870 m2g-1. The N2 adsorption–desorption isotherms showed that the sample exhibited type I characteristics according to IUPAC classification, which confirms its micro-porosity. Compared with the un-activated carbon samples, the activated ones exhibited the better electrochemical properties with a specific capacitance of 150 F g−1 at a scan rate of 2 mV s−1. The good performance of activated carbon is attributed to the enhancement of surface area due to the KOH pretreatment which can open new pores accessible for the ionic transport

Abstract: In this work, activated carbon was prepared from Indonesian local orange peel using ZnCl₂ activation method at various chemical ratios. The structural and morphological characteristics of orange peel based activated carbons were investigated using scanning electron microscope (SEM), Brunaeuer-Emmett-Teller surface analyzer. The highest surface area was estimated as 1200 m²g^-1, obtained by the mass ratio of 1:2 (biomass : ZnCl₂). The obtained carbon samples were then tested as cathodes in Lithium Ion Capacitors. Electrochemical measurement was examined by half cell configuration, using 1 M LiPF₆ in EC/EMC/DMC solution (1:1:1 v/v) as electrolyte and Li metal as reference electrode. From cyclic voltammetry (CV) test, it was shown that orange peel based activated carbon demonstrated a stable electrochemical characteristics, with specific capacitance of 56 Fg^-1 measured at scan rate of 1 mVs^-1 under cut-off voltages between 2.5 and 4 V.

Abstract: Silicon would seem to be a possible candidate to replace graphite or carbon as anode materials for lithium ion batteries based on its potential high capacity of 4200 mAhg-1. The main problem that must be solved for commercial application of silicon as anode material was the poor cyclic performance due to severe volume expansion during repeated charged-discharged cycles and its low electrical conductivity. In this work, we proposed Phosphorus doped (P-doped) Si films as anodes in lithium ion batteries. The electrochemical properties of the silicon based electrodes were examined by means of charge-discharge and impedance test. In comparison with the bare silicon electrode, the P type silicon electrode exhibited higher specific capacity of 2585 mAhg-1 until the 50th cycle. It was attributed to the improved electrical conductivity of Si film and reduced charge transfer resistance

Abstract: C₆₀ coated Si thin films were prepared sequentially by a plasma enhanced chemical vapor deposition and a plasma assisted thermal evaporation technique. The films were then utilized as anode materials for lithium ion batteries. The diffusion coefficients of Li-ions in the film electrodes were then estimated by typical electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. The diffusion coefficients determined by both methods were found to be consistent each other. The diffusion coefficient of coated samples was obviously higher than that of bare silicon thin films, indicated that the kinetic properties of lithium ion transport in silicon film electrodes were enhanced by the C₆₀ film coating on its surface.

Abstract: A feasibility study on the use of a thermal plasma process for the destruction of HFC-23 is carried out in comparison with an incineration process. The material and energy balances for both processes are calculated using the commercial simulator, Pro/II (ver. 8.0). Based on the computational analysis, the volume of the plasma process and NOx and CO2 emissions in the plasma process are 25, 10 and 40% of those in the incineration process, respectively. Therefore, more compact units can be employed in the plasma process. However, the operating cost of the plasma process would be higher than that of the incineration process using LNG as a fuel.

Abstract: The porous TiO2 layer on the silicon surface not only acts as a buffer layer to relieve the strain associated with the volume expansion but also prevents the aggregation of the particles upon normal cycles of charging and discharging. The control of the optimum amount of catalyst has led to enhance the cycle performance of TiO2 coated silicon anode.

Abstract: Zinc oxide and tin oxide (ZnSnOx) films on PET (Polyethylene Terephthalate) substrate were prepared by the electron cyclotron resonance-metal organic chemical vapor deposition (ECR-MOCVD) under an hydrogen, oxygen and argon atmosphere. The used tin and zinc precursor are TMT (tetramethyltin) and DEZn(diethylzinc), respectively. The metal (Zinc and Tin) oxidation content plays an important role to control the optical and electrical characteristics of the films. Therefore the optimum DEZn/TMT content can be determined by the counter stability effect between oxidation and zinc-tin deposition. The obtained ZnSnOx (or SnOx-ZnO) of high mobility films exhibited c.a. 7.0×10-3 ohm ·cm of electrical resistivity.