• Tribology and Lubricants
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• v.35 no.3
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• pp.169-175
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• 2019

In lithium-ion batteries (LIBs), the stress induced by the volume change of an electrode during charge-discharge processes may often cause the mechanical integrity of the electrode to degrade. Polymer binders with enhanced mechanical properties are preferred for improved mechanical integrity and cycling stability of the electrode. In addition, given that sliding and shearing between the polymer binder and components in the electrode may readily occur, frictional and adhesion characteristics of the polymer binder may play a critical role in the mechanical integrity of the electrode. In this study, frictional and adhesion characteristics of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were investigated using a colloidal probe atomic force microscope. Friction loops were obtained under various normal forces ranging from 0 to 159 nN in air and electrolyte and then the interfacial shear strengths of PAN and PVDF in air were calculated to be $1.4{\pm}0.5$ and $1.3{\pm}0.3MPa$, respectively. The results show that in electrolyte, interfacial shear strength of PAN decreased slightly ($1.2{\pm}0.2MPa$), whereas that of PVDF decreased drastically ($0.06{\pm}0.01MPa$). Decreases in mechanical properties and adhesion in electrolyte may be responsible for the decrease in interfacial shear strength in electrolyte. The findings from this study may be helpful in developing polymer binders to improve the mechanical integrity of electrodes in LIBs.

• Journal of the Korean Electrochemical Society
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• v.25 no.1
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• pp.32-41
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• 2022

Various steps in the electrode production process, such as slurry mixing, slurry coating, drying, and calendaring, directly affect the quality and, consequently, mechanical properties and electrochemical performance of electrodes. Herein, a new method of slurry coating is developed: Double-coated electrode. Contrary to single-coated electrode, the cathode is prepared by double coating, wherein each coat is of half the total loading mass of the single-coated electrode. Each coat is dried and calendared. It is found that the double-coated electrode possesses more uniform pore distribution and higher electrode density and allows lesser extent of particle segregation than the single-coated electrode. Consequently, the double-coated electrode exhibits higher adhesion strength (74.7 N m^-1) than the single-coated electrode (57.8 N m^-1). Moreover, the double-coated electrode exhibits lower electric resistance (0.152 Ω cm^-2) than the single-coated electrode (0.177 Ω cm^-2). Compared to the single-coated electrode, the double-coated electrode displays higher electrochemical performance by exhibiting better rate capability, especially at higher C rates, and higher long-term cycling performance. Despite its simplicity, the proposed method allows effective electrode preparation by facilitating high electrochemical performance and is applicable for the large-scale production of high-energy-density electrodes.

• Journal of the Korean Electrochemical Society
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• v.15 no.1
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• pp.27-34
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• 2012

$Li_3V_2(PO_4)_3$/carbon composite materials are synthesized from a sucrose-containing precursor. Amorphous $Li_3V_2(PO_4)_3/C$ (a-LVP/C) and crystalline $Li_3V_2(PO_4)_3/C$ (c-LVP/C) are obtained by calcining at $600^{\circ}C$ and $800^{\circ}C$, respectrively, and electrochemical performance as the negative electrode for lithium secondary batteries is compared for two samples. The a-LVP electrode shows much larger reversible capacity than c-LVP, which is ascribed to the spatial $Li^+$ channels and flexible structure of amorphous material. In addition, this electrode shows an excellent rate capability, which can be accounted for by the facilitated $Li^+$ diffusion through the defect sites. The sloping voltage profile is another advantageous feature for easy SOC (state of charge) estimation.

• Journal of the Korean Electrochemical Society
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• v.16 no.2
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• pp.85-90
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• 2013

Graphite is a commercial anode material to have the specific capacity of 372 mAh/g and the true density of 2.2 g/ml. Many effort had been pouring to find out the better material than graphite. Good candidates are silicon, tin, etc. Zinc is also a plausible candidate to have the specific capacity of 412 mAh/g and the true density of 7.14 g/ml. In this study, the Zn based anode material including indium and nickel as minor additives was synthesised. In order to get the homogeneouly mixed Zn-In-Ni composite material, the sol-gel method was used. The anode prepared by Zn-In-Ni composite material has the $1^{st}$ specific capacity of 910 mAh/g. Through prolonged charge-discharge cycling, the specific capacities were reduced to 365 (at $31^{st}$ cycle) and 378 mAh/g (at $62^{th}$ cycle). The $1^{st}$ Ah efficiency was 45% and Ah efficiencies were exhibited at the prolonged cycle.

• Journal of the Korean Electrochemical Society
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• v.12 no.2
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• pp.189-195
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• 2009

$\beta-Ga_{2}O_{3}$ nanorods were synthesized by chemical vapor deposition method using nickel-oxide nanoparticle as a catalyst and gallium metal powder as a source material. The average diameter of nanorods was around 160 nm and the average length was $4{\mu}m$. Also, we confirmed that the synthesis of nanorods follows the vapor-solid growth mechanism. From the results of X-ray diffraction and HR-TEM observation, it can be found that the synthesized nanorods consisted of a typical core-shell structure with single-crystalline $\beta-Ga_{2}O_{3}$ core with a monoclinic crystal structure and an outer amorphous gallium oxide layer. Li/$\beta-Ga_{2}O_{3}$ nanorods cell delivered capacity of 867 mAh/g-$\beta-Ga_{2}O_{3}$ at first discharge. Although the Li/$\beta-Ga_{2}O_{3}$ nanorods cell showed low coulombic efficiency at first cycle, the cell exhibited stable cycle life property after fifth cycle.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.259-259
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• 2007

층상구조의 전이금속 산화물($LiMO_2$, M=Co, Ni, Mn)은 리튬이차전지용 양극재료로 활발한 연구가 진행되고 있다. 차세대 리튬이차전지 시스템의 개발 및 고성능화를 위해서는 전지의 용량을 결정하는 핵심 부품인 양극재료의 고용량화 및 고안정화는 필수 불가결하다. 따라서 본 연구에서는 상업적으로 큰 장점이 있는 고상반응 공정을 이용하여 리튬이차전지용 양극소재를 제조하고, 소재의 전기화학적, 구조적인 특성을 평가하였으며, 다음과 같은 주제를 가지고 연구를 진행하였다. $LiCoO_2$ 양극재료는 리튬이온전지로 널리 사용되고 있다. 높은 에너지 밀도의 리튬이온전지를 얻기 위해서는 $LiCoO_2$ 양극재료가 고용량화 및 고밀도화를 가져야 한다. 여기서 $LiCoO_2$ 분말이 irregular particle morphology를 가지면 tap density가 $2.2-2.4gcm^{-3}$로 에너지 밀도가 낮으나, 구형 $LiCoO_2$의 정극재료는 tap density가 $2.6-2.8gcm^{-3}$로 상대적으로 energy density가 높아지는 효과가 있다. 구형 $LiCoO_2$ 양극재료를 합성하기 위해서는 chelating agent를 이용한 "controlled crystallization" 침전법을 사용하여 합성한 구형 코발트 수화물을 사용하고 있다. "controlled crystallization" 침전법에서 사용되는 chelating agent로는 주로 ammonia가 이용되고 있다. 본 연구에서는 chelating agent로 ethylene diamine을 사용하여 sodium hydroxides를 precipitation으로 침전 반응하여 구형 코발트 수화물을 합성하였다. 상기 방법으로 합성된 코발트 수화물과 리튬 수화물($LiOH{\cdot}H_2O$-고순도화학(高殉道化學))을 사용하여 고상법을 통하여 $LiCoO_2$를 합성하였다. 제조된 분말의 결정구조와 전기화학적 특성분석은 X-선 회절분석 및 리트벨트 구조정산, 그리고 충/방전 싸이클링을 수행하였으며, 분말의 미세구조 변화를 SEM을 이용하여 분석하였다.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.861-867
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• 2019

$Li_4Ti_5O_{12}$ is a promising next-generation anode material for lithium-ion batteries due to excellent cycle life, low irreversible capacity, and little volume expansion during charge-discharge process. However, it has poor charge capacity at high current density due to its low electrical conductivity. To improve this weakness, porous $Li_4Ti_5O_{12}$ was synthesized by sol-gel method with P123 as chelating agent. The physical characteristics of as-prepared sample was investigated by XRD, SEM, and BET analysis, and electrochemical properties were characterized by cycle performance test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). $Li_4Ti_5O_{12}$ synthesized by 0.01mol ratio of P123/Ti showed most unified particle size, high specific surface area, and relatively high porosity. EIS analysis showed that depressed semicircle size was remarkably reduced, which suggested resistance value in electrode was decreased. Capacity in rate performance showed 178 mAh/g at 0.2C, 170 mAh/g at 0.5C, 110 mA/h at 5C, and 90 mAh/g at 10C. Capacity retention also showed 99% after rate performance.

• Journal of Radiation Protection and Research
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• v.39 no.4
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• pp.199-205
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• 2014

In the field of neutron detections, $^3He$ gas, the so-called "the gold standard," is the most widely used material for neutron detections because of its high efficiency in neutron capturing. However, from variable causes since early 2009, $^3He$ is being depleted, which has maintained an upward pressure on its cost. For this reason, the demands for $^3He$ replacements are rising sharply. Research into neutron converting materials, which has not been used well due to a neutron detection efficiency lower than the efficiency of $^3He$, although it can be chosen for use in a neutron detector, has been highlighted again. $^{10}B$, which is one of the $^3He$ replacements, such as $BF_3$, $^6Li$, $^{10}B$, $Gd_2O_2S$, is being researched by various detector development groups owing to a number of advantages such as easy gamma-ray discrimination, non-toxicity, low cost, etc. One of the possible techniques for the detection is an indirect neutron detection method measuring secondary radiation generated by interactions between neutrons and $^{10}B$. Because of the mean free path of alpha particle from interactions that are very short in a solid material, the thickness of $^{10}B$ should be thin. Therefore, to increase the neutron detection efficiency, it is important to make a $^{10}B$ thin film. In this study, we fabricated a $^{10}B$ thin film that is about 60 um in thickness for neutron detection using well-known technology for the manufacturing of a thin electrode for use in lithium ion batteries. In addition, by performing simple physical tests on the conductivity, dispersion, adhesion, and flexibility, we confirmed that the physical characteristics of the fabricated $^{10}B$ thin film are good. Using the fabricated $^{10}B$ thin film, we made a proportional counter for neutron monitoring and measured the neutron pulse height spectrum at a neutron facility at KAERI. Furthermore, we calculated using the Monte Carlo simulation the change of neutron detection efficiency according to the number of thin film layers. In conclusion, we suggest a fabrication method of a $^{10}B$ thin film using the technology used in making a thin electrode of lithium ion batteries and made the $^{10}B$ thin film for neutron detection using suggested method.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.83-90
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• 2021

In this study, effects of the physical and chemical properties of low temperature heated carbon on electrochemical behavior as a secondary battery anode material were investigated. A heat treatment at 600 ℃ was performed for coking of petroleum based pitch, and the manufactured coke was heat treated with different heat temperatures at 700~1,500 ℃ to prepare low temperature heated anode materials. The physical and chemical properties of carbon anode materials were studied through nitrogen adsorption and desorption, X-ray diffraction (XRD), Raman spectroscopy, elemental analysis. Also the anode properties of low temperature heated carbon were considered through electrochemical properties such as capacity, initial Coulomb efficiency (ICE), rate capability, and cycle performance. The crystal structure of low temperature (≤ 1500 ℃) heated carbon was improved by increasing the crystal size and true density, while the specific surface area decreased. Electrochemical properties of the anode material were changed with respect to the physical and chemical properties of low temperature heated carbon. The capacity and cycle performance were most affected by H/C atomic ratio. Also, the ICE was influenced by the specific surface area, whereas the rate performance was most affected by true density.

• Clean Technology
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• v.24 no.1
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• pp.77-84
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• 2018

In this study, $Li_4Ti_5O_{12}$ anode materials for lithium ion battery were synthesized by dry ball-mill method. Polyvinyl chloride (PVC) as a carbon source was added to improve electrochemical properties. When the PVC was added after $Li_4Ti_5O_{12}$ formation, the spinel structure was well synthesized and it was confirmed by X-ray diffraction (XRD) experiments. When the carbon material was added before the synthesis and the heat treatment was performed, it was confirmed that a material having a different crystal structure was synthesized even when a small amount of carbon material was added. In the case of $Li_4Ti_5O_{12}$ without the carbon material, the electrical conductivity value was about $10{\mu}S\;m^{-1}$, which was very small and similar to that of the nonconductor. As the carbon was added, the electrical conductivity was greatly improved and increased up to 10,000 times. Electrochemical impedance spectroscopy (EIS) analysis showed that the size of semicircle corresponding to the resistance decreased with the carbon addition. This indicates that the resistance inside the electrode is reduced. According to the Cyclic voltammetry (CV) analysis, the potential difference between the oxidation peak and the reduction peak was reduced with carbon addition. This means that the rate of lithium ion insertion and deinsertion was increased. $Li_4Ti_5O_{12}$ with 9.5 wt% PVC added sample showed the best properties in rate capabilities of $180mA\;h\;g^{-1}$ at 0.2 C-rate, $165mA\;h\;g^{-1}$ at 0.5 C-rate, and $95.8mA\;h\;g^{-1}$ at 5 C-rate.