• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.157-162
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• 2016

Porous $Co(OH)_2$ nano-flake thin films were prepared by a potential-controlled electro-deposition technique at various deposition voltage (-0.75, -1.0, -1.2, and -1.4 V) on Ti-mesh substrates for supercapacitor application. The potential of electrode was controlled to regulate the film thickness and the amount of $Co(OH)_2$ nano-flake on the titanium substrate. The film thickness was shown to reach the maximum value of $34{\mu}m$ at -1.4 V of electrode potential, where 17.2 g of $Co(OH)_2$ was deposited on the substrate. The specific discharge capacitances were measured to be 226, 370, 720, and $1008mF\;cm^{-2}$ in the 1st cycle corresponding to the films which were formed at -0.75, -1.0, -1.2, and -1.4 V of electrode potentials, respectively. Then the discharge capacities were decreased to be 206, 349, 586 and $866mF/cm^{-2}$, where the persistency rates were 91, 94, 81, and 86%, respectively.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.175-180
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• 2015

A facile soft chemical synthesis route is used to grow nano-buds of copper hydroxide [$Cu(OH)_2$] thin films on stainless steel substrate[SS]. Besides different chemical methods for synthesis of $Cu(OH)_2$ nanostructure, the chemical bath deposition (CBD) is attractive for its simplicity and environment friendly condition. The structural, morphological, and electro-chemical properties of $Cu(OH)_2$ thin films are studied by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) measurement techniques. The results showed that, facile chemical synthesis route allows to form the polycrystalline, granular nano-buds of $Cu(OH)_2$ thin films. The electrochemical properties of $Cu(OH)_2$ thin films are studied in an aqueous 1 M KOH electrolyte using cyclic voltammetry. The sample exhibited supercapacitive behavior with $340Fg^{-1}$ specific capacitance. Moreover, electrochemical capacitive measurements of $Cu(OH)_2/SS$ electrode exhibit a high specific energy and power density about ${\sim}83Wh\;kg^{-1}$ and ${\sim}3.1kW\;kg^{-1}$, respectively, at $1mA\;cm^{-2}$ current density. The superior electrochemical properties of copper hydroxide ($Cu(OH)_2/SS$) electrode with nano-buds like structure mutually improves pseudocapacitive performance. This work evokes scalable chemical synthesis with the enhanced supercapacitive performance of $Cu(OH)_2/SS$ electrode in energy storage devices.

• Applied Chemistry for Engineering
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• v.29 no.6
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• pp.759-764
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• 2018

3D porous carbon electrodes (cNPIM), prepared by solution casting of a polymer of intrinsic microporosity (PIM-1) followed by nonsolvent-induced phase separation (NIPS) and carbonization are presented. In order to effectively control the pore size of 3D porous carbon structures, cNPIM was prepared by varying the THF ratio of mixed solvents. The SEM analysis revealed that cNPIMs have a unique 3D macroporous structure having a gradient pore structure, which is expected to grant a smooth and easy ion transfer capability as an electrode material. In addition, the cNPIMs presented a very large specific surface area ($2,101.1m^2/g$) with a narrow micropore size distribution (0.75 nm). Consequently, the cNPIM exhibits a high specific capacitance (304.8 F/g) and superior rate capability of 77% in an aqueous electrolyte. We believe that our approach can provide a variety of new 3D porous carbon materials for the application to an electrochemical energy storage.

• Korean Chemical Engineering Research
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• v.52 no.5
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• pp.553-557
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• 2014

Sulfonated polypropylene (S-PP) is prepared by sulfuric acid-acetone aldol condensation reaction of polypropylene (PP) separator to yield hydrophilic separator surface with a moderate amount of $-SO_3H$ groups. Activated carbon supercapacitor is also fabricated adopting the S-PP separator coated with potassium polyacrylate (PAAK) hydrogel polymer electrolyte. As a result, the hydrophilic surface of S-PP separator involves better physical and electrochemical properties such as decrease in contact angle, improvements of wettability, electrolyte uptake, and ionic conductivity to give higher specific capacitance and long cycle-life.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2005.09a
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• pp.201-212
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• 2005

[ $Epoxy/BaTiO_3$ ] composite embedded capacitor films (ECFs) were newly designed fur high dielectric constant and low tolerance (less than ${\pm}15\%$) embedded capacitor fabrication for organic substrates. In terms of material formulation, ECFs are composed of specially formulated epoxy resin and latent curing agent, and in terms of coating process, a comma roll coating method is used for uniform film thickness in large area. Dielectric constant of $BaTiO_3\;&\;SrTiO_3$ composite ECF is measured with MIM capacitor at 100 kHz using LCR meter. Dielectric constant of $BaTiO_3$ ECF is bigger than that of $SrTiO_3$ ECF, and it is due to difference of permittivity of $BaTiO_3\;and\;SrTiO_3$ particles. Dielectric constant of $BaTiO_3\;&\;SrTiO_3$ ECF in high frequency range $(0.5\~10GHz)$ is measured using cavity resonance method. In order to estimate dielectric constant, the reflection coefficient is measured with a network analyzer. Dielectric constant is calculated by observing the frequencies of the resonant cavity modes. About both powders, calculated dielectric constants in this frequency range are about 3/4 of the dielectric constants at 1 MHz. This difference is due to the decrease of the dielectric constant of epoxy matrix. For $BaTiO_3$ ECF, there is the dielectric relaxation at $5\~9GHz$. It is due to changing of polarization mode of $BaTiO_3$ powder. In the case of $SrTiO_3$ ECF, there is no relaxation up to 10GHz. Alternative material for embedded capacitor fabrication is $epoxy/BaTiO_3$ composite embedded capacitor paste (ECP). It uses similar materials formulation like ECF and a screen printing method for film coating. The screen printing method has the advantage of forming capacitor partially in desired part. But the screen printing makes surface irregularity during mask peel-off, Surface flatness is significantly improved by adding some additives and by applying pressure during curing. As a result, dielectric layer with improved thickness uniformity is successfully demonstrated. Using $epoxy/BaTiO_3$ composite ECP, dielectric constant of 63 and specific capacitance of 5.1nF/cm2 were achieved.

• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.280-288
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• 2017

Nanocarbon base materials such as, graphene and graphene hybrid with high electrochemical performances have great deal of attention to investigate flexible, stretchable display and wearable electronics in order to develop portable and high efficient energy storage devices. Battery, fuel cell and supercapacitor are able to achieve those properties for flexible, stretchable and wearable electronics, especially the supercapacitor is a promise energy storage device due to their remarkable properties including high power and energy density, environment friendly, fast charge-discharge and high stability. In this study, we have fabricated flexible supercapacitor composed of graphene/conductive polymer composite which could improve its electrochemical performance. As a result, specific capacitance value of the flexible supercapacitor (unbent) was $198.5F\;g^{-1}$ which decreased to $128.3F\;g^{-1}$ (65% retention) after $500^{th}$ bending cycle.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.697-698
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• 2013

최근에 유연한 성질을 갖는 전자기기들의 수요가 증가하면서, 그에 따라서 유연 전자기기를 뒷받침 해줄 수 있는 에너지 저장체의 유연한 성질도 중요성이 점점 부각되고 있으며 많은 연구가 진행되고 있다. 유연한 에너지 저장체의 많은 연구들이 유연한 금속 박막이나 특수 공정처리가 필요한 고분자를 이용하고 있으나, 대부분의 유연 에너지 소자들은 에너지 저장체의 성능에 비해 고온과 산 약품과 같은 환경이 필요하며, 비용과 시간이 많이 소모되고 있다. 그에 반해 섬유는 앞에서와 같이 특수 공정 처리가 따로 필요하지 않으며 상온에서도 손 쉽게 이용 가능하며, 신축성이 뛰어난 장점이 있기 때문에 효율적, 비용적으로 유연한 에너지 저장체에 유리한 소재이다. 몸에 해로운 산과 같은 약품처리의 필요도 없으며, 용매를 흡수하는 능력이 뛰어나기 때문에 용매를 이용한 도포 방법을 사용하면 다양한 물질을 폭넓게 적용 가능하다. 그리고 적용 분야에 맞춰서 섬유의 종류를 조절하면 다양한 성질을 갖는 천 기반의 에너지 저장체가 형성되며, 면 섬유가 수소 결합과 높은 반데르 발스 결합에 의해 탄소나노튜브와 결합하여 높은 에너지 밀도를 갖는 에너지 저장체를 형성하는 것을 분석한 논문들도 보고되고 있다. 면 섬유의 특수한 성질을 이용하여 에너지 저장체를 제작하고 이를 확인하기 위해서 일반 합성 섬유인 polyester와 면 섬유를 비교 제작하였으며, 용매의 형태로 손쉽게 도포 가능한 물질은 탄소 계열의 활물질들이며, 탄소 나노 튜브나 그래핀 등이 분산된 용액을 이용해 천에 도포 가능하다. 탄소 계열의 활물질들은 대표적인 슈퍼캐패시터 물질이며, 천에 도포를 함으로써 천 기반의 슈퍼캐패시터를 제작하였다. 일반 합성 섬유 polyester와 CNT를 결합한 형태의 전극은 최대 에너지 축전 용량(Maximum specific capacitance)이 53.6 F/g으로 나타났으며, 면 섬유와 CNT를 결합한 형태의 전극은 최대 에너지 축전 용량이 122.1 F/g으로 나타났다. 따라서 면 섬유에서 높은 에너지 저장 능력을 보이는 것을 실험적으로 확인하였으며, 에너지 저장 능력이 뛰어난 면 섬유를 다음 전극 디자인에서도 일률적으로 적용하였다. 슈도캐패시터의 대표적 물질인 금속 산화물인 망간 산화물(MnO2)을 3전극 도금 시스템을 이용하여 에너지 축전 용량과 에너지 밀도를 올리는 전극을 제작하였다. 특히 망간 산화물의 형태는 표면적을 극대화하기 위해서 평균 지름은 200~300 nm 정도 되는 나노 입자의 형태로 제작하였다. 그 결과, 확연하게 에너지 축전 용량이 향상되었으며, 최대 에너지 축전 용량은 282.0 F/g, 에너지전력 밀도는 14.2 Wh/kg으로 나타나서 금속 산화물의 형태가 주는 효과를 확인할 수 있었다. 하지만 나노 입자의 형태로 제작된 금속 산화물은 문제점이 발생하였다. 금속 산화물의 전기 전도성이 매우 낮기 때문에, 전기 전도성에 비례해서 전력 밀도의 값이 표현되는데, 전기 전도성이 급격히 감소하기 때문에 전력 밀도도 급격한 감소가 나타난다. 다음과 같이 전기 전도성 물질을 첨가하는 방법은 추가의 공정이 필요한 단점이 있지만 오직 기계적인 인장응력만을 가해서 에너지 밀도와 전력 밀도를 증가시키는 전극을 제작하였다. 인장응력을 섬유 기반의 전극에 가했을 시에 가닥들간의 접촉 증가와 CNT가 정렬되면서 특정 변형률(strain) 이전에서는 전기 전도성이 최대 50% 이상 증가하는 것을 확인할 수 있었으며, 선행 연구에서 보고되었다. 이를 이용해서 전기 전도성과 직결되는 전력 밀도의 양도 증가시키고 에너지 밀도의 증가 여부까지 확인한 결과 인장을 가하기 전 면 섬유의 전력 밀도와 에너지 밀도는 6.4 kW/kg and 6.1 Wh/kg으로 나타났으나 30% 변형 인장 후에는11.4 kW/kg과 7.1 Wh/kg으로 나타났다. 그리고 망간 산화물을 첨가한 전극 역시 4.9 kW/kg과 14.2 Wh/kg으로 나타났었으나 인장 이후 전력 밀도는 14.2 kW/kg, 에너지 밀도는 17.6 Wh/kg으로 확연하게 증가한 것을 확인하였다.

• Journal of the Korean Applied Science and Technology
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• v.37 no.2
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• pp.260-267
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• 2020

In this study, supercapacitor based on the all solid state electrolyte with PVA(polyvinyl alcohol), ionic liquid as a BMIMBF4(1-buthyl-3-methylimidazolium tetrafluoroborate) and activated carbon/Ni-MOF composite was fabricated and characterized its electrochemical properties with function of MOF. In order to analysis and comparison that electrochemical performances [including cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and galvanostatic charge/discharge test] of prepared supercapacitor based on activated carbon/Ni-MOF composite and all solid state electrolyte. As a result, specific capacitance of the supercapacitor without Ni-MOF was 380 F/g which value decreased to 340 F/g after adding Ni-MOF to activated carbon as a electrode material. This result exhibited that decreased electrochemical property of the supercapacitor effected on physical hinderance in the electrode. In further, it needs to optimization of the Ni-MOF amount (wt%) in the electrode composite to maximize its electrochemical performances.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.653-658
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• 2016

In this work, we developed a synthetic method for preparing one-dimensional $MnO_2$ nanowires through a hydrothermal method using a mixture of $KMnO_4$ and $MnSO_4$ precursors. As-prepared $MnO_2$ nanowires had a high surface area and porous structure, which are beneficial to the fast electron and ion transfer during electrochemical reaction. The microstructure and chemical structure of $MnO_2$ nanowires were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller measurements. The electrochemical properties of $MnO_2$ nanowire electrodes were also investigated using cyclic voltammetry and galvanostatic charge-discharge with a three-electrode system. $MnO_2$ nanowire electrodes showed a high specific capacitance of 129 F/g, a high rate capability of 61% retention, and an excellent cycle life of 100% during 1000 cycles.

• Journal of the Korean Electrochemical Society
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• v.6 no.3
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• pp.169-173
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• 2003

Electrochemical capacitor made with metal oxide electrode uses rapid and reversible protonation/deprotonation of metal oxide material under the aqueous acidic solution, generally. Electrochemical stability window of aqueous electrolyte-type capacitor is narrow compared to that of organic electrolyte-type capacitor. Electrochemical characteristics of electrochemical capacitor made with metal oxide electrode and lithium or ammonium cation based organic electrolyte were evaluated. Electrochemical capacitor based on $RuO_2$ electrode material and 1M $LiPF_6$ in mixed solvents of EC, DEC, and EMC has anodic and cathodic specific capacitance of 145 and $142F/g-RuO_2{\cdot}nH_2O$, respectively, by using cyclic voltammetry with scan rate of 2mV/sec $g-RuO_2$ in potential range of $2.0\~4.2V(Li|Li^+))$.