Electrochemical Characteristics of LiFePO4 with Conductivity Materials for Lithium Polymer Batteries

( En Mei Kim ),( Kyung Hee Park ),( Hal Bod Gu ) 조선대학교 공학기술연구원 2008 공학기술논문지 Vol.1 No.1

Phospho-olivine LiFePO4 cathode materials were prepared by hydrothermal reaction. In this study, Multi-walled carbon nanotube (MWCNT) and Carbon black was added to enhance the electrical conductivity of LiFePO4. LiFePO4, LiFePO4-MWCNT and LiFePO4-C particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) transmission electron microscope (TEM). LiFePO4/SPF/Li, LiFePO4-MWCMT/SPF/Li and LiFePO4-C/SPE/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm(-2) in a range between 2.5 and 4.3 V vs. Li/Li(+) and cyclic voltammetry (CV). The results showed that initial discharge capacity of LiFePO4 was 103 mA h g(-1). The discharge capacity of LiFePO4-MWCNT/SPF/Li cell with 5 wt % MWCNT was 124 mAh g(-), LiFePO4-C/SPE/Li cell with 5 wt % carbon black was 128 mAh g(-1) at the first cycle.

MnO₂-HCS 복합체를 이용한 슈퍼커패시터의 전기화학적 특성

김은미(En Mei Jin),정상문(Sang Mun Jeong) 한국청정기술학회 2018 청정기술 Vol.24 No.3

중공형 구형 탄소(hollow carbon spheres, HCS) 또는 구형 탄소(carbon spheres, CS)는 수열합성법에 의해 제조되었고 MnO₂를 증착하기 위한 탄소 지지체로 사용하였다. MnO₂는 화학적 레독스 증착법에 의해 HCS 또는 CS 표면에 증착하였다. 화학적 산화환원 증착법은 미립자 지지체의 표면에 다른 산화물 합성에 특히 효과적이다. MnO₂는 HCS 또는 CS의 표면에 일정한 슬릿 모양의 분포를 보였고 HCS 표면에서 보다 엉성한 슬릿 모양의 MnO₂ 입자가 생성되었다. MnO₂-HCS는 20 mv s<SUP>-1</SUP>의 스캔 속도에서 초기 사이클에서 약 164.1 F g<SUP>-1</SUP>의 정전용량을 나타내었고 1000 사이클 후에는 약 141.3 F g<SUP>-1</SUP>의 정전용량을 나타내었다. 1000 사이클 기준으로 MnO₂-HCS와 MnO₂-CS는 각각 86%와 78%의 용량유지율을 나타내었다. 이것은 HCS 표면에서 엉성한 슬릿모양의 MnO₂의 성장이 전해질의 흐름 및 전해질 내의 Na⁺ 이온의 흡탈착이 보다 용이하여 나타난 결과로 생각된다. Hollow carbon spheres (HCS) and carbon spheres (CS) were prepared by a hydrothermal reaction and they were introduced as a substrate for the deposition of MnO₂ nanoparticles. The MnO₂ nanoparticles were deposited on the carbon surface by a chemical redox deposition method. After deposition, the MnO₂ nanoparticles were uniformally distributed on the carbon surface in a slit-shape, and sparse MnO₂ slits appeared on the HCS surface. The MnO₂-HCS showed an initial specific capacitance of 164.1 F g<SUP>-1</SUP> at scan rate of 20 mv s<SUP>-1</SUP>, and after 1,000 cycles, the specific capacitance was maintained to 141.3 F g<SUP>-1</SUP>. The capacity retention of MnO₂-HCS and MnO₂-CS were calculated to 86% and 78% in the cycle performance test up to 1,000 cycles, respectively. MnO₂-HCS showed a good cycle stability due to the mesoporous hollow structure which can cause a faster diffusion of the electrolyte and can easily adsorb and desorb Na+ ions on the surface of the electrode.

상용 고용량 리튬이온이차전지용 NCA 양극활물질의 전기화학적 특성

김은미 ( En Mei Jin ),이가을 ( Ga-eul Lee ),나병기 ( Byuong-ki Na ),정상문 ( Sang Mun Jeong ) 한국화학공학회 2017 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.55 No.2

LiNi_1-x-yCo_xAl_yO₂(x=0.15, y=0.045 혹은 0.05, NCA) 양극소재의 전기화학적 특성 및 양극소재의 입자 크기 분포에 대한 리튬이온이차전지의 수명특성에 대한 영향을 살피기 위해 두 종의 상업용 NCA (NCA#1, NCA#2) 양극소재를 리튬이온이차전지의 양극으로 사용하였다. NCA#1은 약 5 μm의 균일한 구형의 입자로 구성되어 있고 NCA#2는 약 5 μm와 11 μm 정도의 입자들이 혼합되어 있는 분말이다. 충방전 측정 결과 NCA#2는 초기 방전용량은 197.0 mAh/g으로 NCA#1에 비해 높게 나타났다. NCA#1과 NCA#2의 용량 유지율(30사이클 기준)은 각각 92%와 94%로 나타났다. In order to investigate the electrochemical properties and the particle size effect of LiNi_1-x-yCo_xAl_yO₂ (x=0.15, y=0.045 or 0.05, NCA) for lithium ion batteries (LIBs), two commercial NCA cathode materials (NCA#1, NCA#2) were used as cathode materials for LIB. The average particle size of the NCA#1 which consisted of uniform spherical particles was found to be approximately 5 μm. NCA#2 consisted of particles with bimodal size distribution of approximately 5 μm and 11 μm. From the results of charge-discharge performance test, a high initial discharge capacity of 197.0 mAh/g was obtained with NCA#2, which is a higher value than that with NCA#1. The cycle retentions of NCA#1 and NCA#2 up to 30 cycles were 92% and 94%, respectively.

Biotemplated hybrid TiO₂ nanoparticle and TiO₂–SiO₂ composites for dye-sensitized solar cells

Jin, En Mei,Park, Ju-Young,Hwang, Kyung-Jun,Gu, Hal-Bon,Jeong, Sang Mun Elsevier 2014 Materials letters Vol.131 No.-

<P><B>Abstract</B></P> <P>Hybrid TiO<SUB>2</SUB>-nanoparticle (NP)/TiO<SUB>2</SUB>–SiO<SUB>2</SUB> (TS) composites, prepared using rice straw biotemplates were used as photoelectrodes in dye-sensitized solar cells. The hybrid TiO<SUB>2</SUB>-NP/TS composite showed increased dye loading due to a faster electron diffusion pathway. This could effectively improve the photoelectrode properties of this nanocomposite material, which would improve its solar conversion efficiency. TiO<SUB>2</SUB>-NP/TS (10wt%) based DSSC demonstrated a <I>τ</I> <SUB>t</SUB> of 1.17ms, <I>τ</I> <SUB>r</SUB> of 37.14ms, and showed a maximum power conversion efficiency of 5.81%. <I>V</I> <SUB>oc</SUB>, <I>J</I> <SUB>sc</SUB>, and fill factor values of TiO<SUB>2</SUB>-NP/TS were found to be 0.69V, 14.01mAcm<SUP>−2</SUP>, and 60.11%, respectively under AM 1.5 simulated sunlight illumination (100mWcm<SUP>−2</SUP>).</P> <P><B>Highlights</B></P> <P> <UL> <LI> TiO<SUB>2</SUB>–SiO<SUB>2</SUB> composite was fabricated by using rice straw as a biotemplate. </LI> <LI> Biotemplated TiO<SUB>2</SUB>–SiO<SUB>2</SUB> composites provide a faster electron diffusion pathway. </LI> <LI> Hybrid TiO<SUB>2</SUB>-NP/TiO<SUB>2</SUB>–SiO<SUB>2</SUB> composite increased the dye adsorption ability. </LI> <LI> Photovoltaic properties of hybrid TiO<SUB>2</SUB>-NP/TiO<SUB>2</SUB>–SiO<SUB>2</SUB> composite were enhanced. </LI> </UL> </P>

TiO2 광전극의 광산란 특성을 이용한 염료감응형 태양전지

김은미 ( En Mei Jin ),박경희 ( Kyung Hee Park ),구할본 ( Hal Bon Gu ) 조선대학교 공학기술연구원 2010 공학기술논문지 Vol.3 No.2

In this study, we increase the solar conversion efficiency of DSSC (dye-sensitized solar cell) using nanocrystalline TiO2 semiconductor. We preparation of TiO2 photoelectrode, assembly the DSSC and put a focus in analyses electrochemical properties of DSSC by using quartz glass powder in TiO2 photoelectrode to increase light scattering effect and improved conversion efficiency. Morphology of the photoelectrode was investigate using field emission scanning electron microscopy (FE-SEM) and photovoltaic properties was examined under illumination with AM 1.5 simulated sunlight. The results showed 146% power conversion efficiency when the optimal content of quartz glass powder was 5 wt.% than another content.

Photosensitization of nanoporous TiO₂ films with natural dye

Jin, En Mei,Park, Kyung-Hee,Jin, Bo,Yun, Je-Jung,Gu, Hal-Bon Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139

<P>Dye-sensitized solar cells were assembled by using natural dyes extracted from wormwood, bamboo leaves and red maple leaves as photosensitizers. The <I>V</I><SUB>oc</SUB> values of natural dyes from wormwood, bamboo leaves and maple leaves were 0.67, 0.66 and 0.59, respectively. The <I>I</I><SUB>SC</SUB> values were varied from 2.56 to 5.95 mA cm<SUP>−2</SUP> and the fill factors from 56 to 66%. Based on investigations into the structure and properties of dye molecules, wormwood revealed the best photosensitized effects among several kinds of natural dyes, which is due to the interaction between the carbonyl and hydroxyl groups of anthocyanin and the surface of TiO<SUB>2</SUB>; these wormwood extracts act as efficient sensitizers.</P>

수열합성한 TiO2을 이용한 염료감응형 태양전지의 전기화학적 특성

김은미 ( En Mei Jin ),왕만림 ( Wan Lin Wang ),구할본 ( Hal Bon Gu ) 조선대학교 공학기술연구원 2013 공학기술논문지 Vol.6 No.1

In this study, the TiO2 was prepared by hydrothermal reactions; and 0.5 M, 1.0 M and 2.0 M TTIP were added. The different contents of TTIP added TiO2 are studied by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and photocurrent density-voltage test. The photovoltaic properties under illumination with AM 1.5 simulated under sunlight. In the results, the XRD patterns index to single-phase material having an anatage structure and the particle size of 1.0 M TTIP added TiO2 is 7.61 nm. Using the 1.0 M TTIP added TiO2 demonstrates a higher solar conversion efficiency than the other samples. We got 114% and 131% enhanced power conversion efficiency when the optimal content of TTIP.

염료감응 태양전지의 염료 흡착 특성 향상에 관한 연구

김은미 ( En Mei Jin ),구할본 ( Hal Bon Gu ) 조선대학교 공학기술연구원 2011 공학기술논문지 Vol.4 No.2

The acid treatment have been used for nanocrystalline TiO2 particles. It ha been observed that nitric acid treatment can enhance transparency of thin films a well as higher level of dispersion of nanoparticles. HNO3 treated surfaces has showed higher surface area and increase in hydroxy functional groups at TiO2 photoelectrode film surfaces was observed. This process has allowed to increase the conversion efficiency of solar cell which is possibly due to higher amount of dye adsorption. These process have significantly enhanced the efficiency of DSCs for developing high sensitivity. The efficiency increased upto 11 8% and this is observed at non nitric acid treatment of TiO2 photoelectrode.

Hydrothermal Carbon Nanosphere (CNS) Based CNS/S Composite as a Cathode Material for Lithium-Sulfur Batteries

Jin, En Mei,Jeong, Hee-Young,Jeong, Sang Mun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10

<P>Hydrothermal carbon nanospheres (CNSs) were incorporated into S/CNS composites as the cathode materials for rechargeable lithium-sulfur (Li-S) batteries. The particle sizes of the CNS ranged from 160 similar to 230 nm. The S/CNS composite was prepared by the solution-based processing technique. Homogenous mixing generated S/CNS composites in which the carbon materials successfully enfolded the sulfur particles; thus, the electrical conductivity of sulfur was improved. An electrical conductivity of 6.8 S m(-1) at 129 MPa and the highest discharge capacity of 672.6 mAh g(-1) for the initial cycle were achieved with S/CNS composite prepared with 0.5 M glucose followed by carbonization at 800 degrees C.</P>

Photovoltaic Effect of Metal-Doped TiO₂ Nanoparticles for Dye-Sensitized Solar Cells

Jin, En Mei,Jeong, Sang Mun,Kang, Hee-Cheol,Gu, Hal-Bon The Electrochemical Society 2016 ECS journal of solid state science and technology Vol.5 No.5

<P>Crystalline anatase TiO2 nanoparticles (NPs) synthesized by a sol-gel method were used as photoelectrodes in dye-sensitized solar cells (DSSCs). In order to improve the electrochemical properties such as the open circuit voltage (V-oc) and the rate of electron transfer, various amounts of Al and Zn were doped into TiO2 NPs. Al doping of TiO2 NPs successfully improved the photovoltaic performance of the DSSCs as seen in the V-oc of 0.79 V for these electrodes. The Zn-doped TiO2 NPs exhibited faster electron transport than pure TiO2 or Al-doped TiO2 NPs. The photovoltaic efficiency (eta) of pure TiO2 NPs, 4 mmol Al-doped TiO2 NPs, and 3 mmol Zn-doped TiO2 NPs-based DSSCs are 3.90, 5.86, and 5.58%, respectively. In order to improve the V-oc, J(sc), and electron transfer rates simultaneously, the 4 mmol Al-doped TiO2 NP and 3 mmol Zn-doped TiO2 NP powders were mixed together and used for the preparation of photoelectrodes. The eta of the mixed Al/Zn-doped TiO2 NPs-based DSSC was 7.12%, while the V-oc, J(sc), and electron transport times were 0.75 V, 14.38 mA cm(-2) and 3.112 x 10(-4) s, respectively. (C) 2016 The Electrochemical Society. All rights reserved.</P>