Synthesis and Characterization of Silver Vanadium Oxide as a Cathode for Lithium Ion Batteries

Hal-Bon Gu,Van Hiep Nguyen 한국전기전자재료학회 2016 Transactions on Electrical and Electronic Material Vol.17 No.3

β-AgVO3 nanorods have been successfully synthesized using a soft chemistry route followed by heat treatment. Theywere characterized by X-ray diffraction and field emission scanning electron microscopy, and their electrochemicalproperties were investigated using cyclic voltammetry, impedance spectra, and charge-discharge tests. The resultsshowed that the smooth-surfaced nanorods are very uniform and well dispersed, with diameters of ~100-200 nmand lengths of the order of several macrometers. The nanorods deliver a maximum specific discharge capacity of 275mAh g-1 at 30 mA g-1. They also demonstrated good rate capability with a discharge capacity at the 100th cycle of 51mAh g-1.

Cycling Performance of LiFePO₄ as the Cathode Materials for Lithium Polymer Batteries

Gu, Hal Bon,Jun, Dae Kyoo Trans Tech Publications, Ltd. 2007 Materials science forum Vol.544 No.-

<P>The cycle behavior and rate performance of C-LiFePO4/SPE/Li cell have been investigated at 25 °C. Carbon coated LiFePO4 (C-LiFePO4) was employed as cathode and 25PVDFLiClO4EC10PC10 was used as solid polymer electrolyte (SPE). The C-LiFePO4/SPE/Li cell exhibited above 140 mAh/g of discharge capacity at 0.1 mA/cm2 and excellent reversible cyclability with a stable capacity on cycling. In addition, the discharge capacity of C-LiFePO4/SPE/Li cell was 150 mAh/g at 0.1 C (0.02 mA/cm2) and 130 mAh/g at 1 C (0.2 mA/cm2), respectively.</P>

Electrochemical properties of metal salts polymer electrolyte for DSSC

구할본(Gu, Hal-Bon),Zhao, Xing Guan,Jin, En Mei 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11

Dye-sensitized solar cell(DSSC) have been considered one of the promising alternatives to conventional solar cells, because of their low cost, easy fabrication and relatively high energy conversion efficiency. However, although the cell offers reasonable efficiency at least 11%, the use of a liquid electrolyte placed technological challenges for achieving the desired durability and operational stability of the cell. In order to prevent or reduce electrolyte leakage considerable efforts have been made, such as p-type semiconductor or organic hole-transport material that better mechanical properties and simple fabrication processes. In this work, we synthesized solid-state electrolyte containing LiI and KI metal salt with starting materials of poly ethylene oxide to substitute liquid electrolyte enhance the ionic conductivity and solar conversion efficiency. Li+ leads to faster diffusion and higher efficiency and K+ leading to higher ionic conductivity. The efficiency of poly ethylene oxide/LiI system electrolyte is 1.47% and poly ethylene oxide/potassium electrolyte is 1.21%. An efficiency of 3.24% is achieved using solid-state electrolyte containing LiI and KI concentrations. The increased solar conversion efficiency is attributed to decreased crystallinity in the polymer that leads to enhanced charge transfer.

카본 나노파이버가 도핑된 리튬이온전지의 전기화학적 특성

구할본(Gu, Hal-Bon) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11

올리빈 구조의 LiFePO₄ 정극 활물질은 650?C에서 고상법으로 제조되었다. LiFePO₄의 전자전도도를 향상시키기 위하여 graphite nanofiber(GNF)를 각각 3wt%, 5wt%, 7wt%, 9wt% 첨가하여 LiFePO₄-C를 제조하였다. 제조된 분말의 입자 형태를 확인하기 위하여 X-ray diffraction(XRD)과 File Electronic Scaning Electromicroscopy(FE-SEM)를 측정하였다. XRD결과로부터 제조된 분말은 모두 순수한 결정 구조를 나타내었고 입자의 크기는 약 200nm였다. 5wt% GNF를 첨가한 LiFePO₄-C는 기타 첨가량에 비해 방전용량이 가장 높았다. 첫 사이클의 용량은 151.73mAh/g 나타났고 50 사이클 뒤에도 92% 이상을 유지하고 있었다. 첨가하지 않은 것에 비해 43% 증가하였다. LiFePO₄-C(3wt%), LiFePO₄-C(7wt%), LiFePO₄-C(9wt%)의 첫 사이클 방전용량은 각각 147.94mAh/g, 136.64mAh/g, 121.07mAh/g 나타났다. LiFePO₄-C(5wt%)에 비해 용량은 떨어쪘지만 순수한 LiFePO₄보다 많이 높았다. 임피던스 결과를 보면 기타 첨가량에 비해 LiFePO₄-C(5wt%)의 저항 제일 낮았다. 이는 충방전 결과와 일치하였다. graphite nanofiber의 첨가로 인하여 LiFePO₄ 정극 활물질의 전자전도도가 높아지고, 따라서 전기화학적 특성도 크게 향상되었다.

표면형상 변화에 따른 염료감응 태양전지의 전기화학적 특성

구할본,Gu, Hal-Bon 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.2

We use UV(ultraviolet)-$O_3$ treatment to increase the surface area and porosity of $TiO_2$ films in dye-sensitized solar cells (DSSCs). After the UV-$O_3$ treatment, surface area and porosity of the $TiO_2$ films were increased, the increased porosity lead to amount of dye loading and solar conversion efficiency was improved. Field emission scanning electron microscopy images clearly showed that the nanocrystalline porosity of films were increased by UV-$O_3$ treatment. The Brunauer, Emmett, and Teller surface area of the $TiO_2$ films were increased from $0.71cm^2/g$ to $1.31cm^2/g$ by using UV-$O_3$ treatment for 20 min. Also, UV-$O_3$ treatment of $TiO_2$ films significantly enhanced their solar conversion efficiency. The efficiency of the films without treatment was 4.9%, and was increased to 5.6% by UV-$O_3$ treatment for 20 min. Therefore the process enhanced the solar conversion efficiency of DSSCs, and can be used to develop high sensitivity DSSCs.

Tin Oxide-flyash Composite 전극의 리튬 이온 Intercalation 메카니즘과 임피던스 특성에 관한 연구

구할본,김종욱,Gu, Hal-Bon,Kim, Jong-Uk 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.11

The purpose of this study is to research and develop tin oxide-flyash composite for lithium Ion polymer battery. Tin oxide is one of the promising material as a electrode active material for lithium Ion polymer battery (LIPB). Tin-based oxides have theoretical volumetric and gravimetric capacities that are four and two times that of carbon, respectively. We investigated cyclic voltammetry, AC impedance and charge/discharge cycling of SnO$_2$-flyash/SPE/Li cells. The first discharge capacity of SnO$_2$-flyash composite anode was 639 mAh/g. The discharge capacity of SnO$_2$-flyash composite anode was 563 and 472 mAh/g at 6th and 15th cycle, respectively. The SnO$_2$-flyash composite anode with PVDF-PMMA-PC-EC-LiClO$_4$ electrolyte showed good capacity with cycling.

Structures and Formation Energies of Li_xC_6 (x=1-3) and its Homologues for Lithium Rechargeable Batteries

도칠훈,한병찬,진봉수,Hal-Bon Gu 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.6

Using first principles density functional theory the formation energies of various binary compounds of lithium graphite and its homologues were calculated. Lithium and graphite react to form Li_1C_6 (+141 mV) but not form LiC_4 (.143 mV), LiC_3 (.247 mV) and LiC_2 (.529 mV) because they are less stable than lithium metal itself. Properties of structure and reaction potentials of C_5B, C_5N and B_3N_3 materials as iso-structural graphite were studied. Boron and nitrogen substituted graphite and boron-nitrogen material as a iso-electronic structured graphitic material have longer graphene layer spacing than that of graphite. The layer spacing of Li_xC_6, Li_xC_5B,Li_xC_5N materials increased until to x=1, and then decreased until to x=2 and 3. Nevertheless Li_xB_3N_3 has opposite tendency of layer spacing variation. Among various lithium compositions of Li_xC_5B, Li_xC_5N and Li_xB_3N_3, reaction potentials of Li_xC_5B (x=1-3) and Li_xC_5 (x=1) from total energy analyses have positive values against lithium deposition.

Enhanced Reaction Kinetic of Fe3O4-graphite Nanofiber Composite Electrode for Lithium Ion Batteries

Wan Lin Wang,Hal-Bon Gu,박주영 한국전기전자재료학회 2014 Transactions on Electrical and Electronic Material Vol.15 No.6

A Fe3O4-graphite nanofiber composite for use as an anode material was successfully synthesized by calcining Fe2O3and graphite nanofiber (GNF) together in a N2 atmosphere. Using this Fe3O4-GNF composite in a lithium ion batteryresulted in a higher lithium storage capacity than that obtained using Fe3O4-graphite (Fe3O4-G). The Fe3O4-GNF (10wt%) electrode exhibited a higher lithium ion diffusion coefficient (2.29×10-9 cm2 s-1) than did the Fe3O4-G (10%)(3.17×10-10 cm2 s-1). At a current density of 100 mA g-1, the Fe3O4-GNF (10 wt%) anode showed a higher reversiblecapacity (1,031 mAh g-1) than did the Fe3O4-G (10%) anode (799 mAh g-1). Moreover, the Fe3O4GNF electrodes showedgood cycling performance without the addition of a conductive material.

Synthesis and Characterization of Silver Vanadium Oxide as a Cathode for Lithium Ion Batteries

Nguyen, Van Hiep,Gu, Hal-Bon The Korean Institute of Electrical and Electronic 2016 Transactions on Electrical and Electronic Material Vol.17 No.3

β-AgVO₃ nanorods have been successfully synthesized using a soft chemistry route followed by heat treatment. They were characterized by X-ray diffraction and field emission scanning electron microscopy, and their electrochemical properties were investigated using cyclic voltammetry, impedance spectra, and charge-discharge tests. The results showed that the smooth-surfaced nanorods are very uniform and well dispersed, with diameters of ~100-200 nm and lengths of the order of several macrometers. The nanorods deliver a maximum specific discharge capacity of 275 mAh g^-1 at 30 mA g^-1. They also demonstrated good rate capability with a discharge capacity at the 100^th cycle of 51 mAh g^-1.

Red Organic Light-emitting Diodes utilizing Energy Transfer and Charge Trapping

Kim, Ju-Seung,Gu, Hal-Bon The Korean Institute of Electrical and Electronic 2005 Transactions on Electrical and Electronic Material Vol.6 No.3

We report the efficient red light-emitting diodes based on the fluorescent dye 4-(dicyanomethylene)-2-i-propyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) and 5,6,11,12-tetraphenyl naphthacene (rubrene) codoped in the tris(8-hydroxyquinoline)aluminum $(Alq_3)$. Luminance efficiency of 2.2 cd/A with a Commission International De L'Eclairage (CIE) chromaticity coordinate of x, y = (0.640, 0:350) are achieved at the driving current density of $20\;mA/cm^2$. Adding the rubrene to the DCJTI in tris(8-hydroxyquinoline)aluminum $(Alq_3)$, the red color purity and luminance efficiency improved comparing to the DCJTI only doped devices because the rubrene molecules assist the polarization effect of DCJTI by molecular interaction and enhance the energy transfer from $(Alq_3)$ to DCJTI.