• Journal of Electrochemical Science and Technology
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• 제11권3호
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• pp.318-321
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• 2020

Here I present a formula which converts a constant phase element (CPE) to its equivalent capacitor. Electrochemical impedance spectroscopy is capable of resolving a complex electrochemical processes into its faradaic and non-faradaic elements, and the non-faradaic process is frequently described as a CPE in place of a capacitor due to the non-ideality. Being described as a capacitor, the non-faradaic element provides information by its capacitance, but a CPE cannot provide a physical meaning. In order to solve the problem, the CPE has been dealt with as an equivalent capacitor of which the capacitance provides practical information. Succeeding the two methods previously suggested, a new conversion method is suggested in this report. While the previous ones manipulate only the CPE, the new method takes both the CPE and its related resistor into account for conversion. By comparing the results obtained by the three methods, we learn that the results are nearly the same within tolerable ranges, and conclude that any of the method choices is acceptable depending on the conditions of the system of interest.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.1125-1128
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• 2002

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 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 142 F/g-$RuO_2{\cdot}nH_2O$, respectively, by using cyclic voltammetry with scan rate of 2 mV/sec g-$RuO_2$ in potential range of 2.0~4.2V(Li|$Li^+$).

• 전기화학회지
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• 제10권2호
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• pp.141-144
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• 2007

Polypyrrole(PPy) was composite with MWNT to attain cycle stable by chemical method. We have been considered PPy is the ideal material for high energy density electrochemical capacitor due to pseudo capacitor reaction. In this study we found that increase in cycle life due to composite MWNT. Also PPy/MWNT composite material have resulted larger capacitance and exhibits better electrochemical behavior. The structural feature was investigated by using SEM and TEM. The PPy/CNT composite is not only a promising ultracapacitor material for energy storages but also has a good possibility because of its great capacitive properties, simple preparation and low cost.

• 전기화학회지
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• 제6권3호
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• pp.169-173
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• 2003

금속산화물 전극을 이용한 전기화학 캐패시터는 일반적으로 산성 수용액 전해질에서 금속산화물에 대한 양성자의 가역적인 전기화학반응을 이용한다. 수계 전해질을. 사용한 수퍼캐패시터는 전위창(electrochemical stability window)이 유기계 전해질을 사용한 수퍼캐패시터에 비해 좁은 문제를 안고 있다. 금속산화물 전극과 리튬 또는 암모늄 이온을 함유한 유기계 전해질을 사용한 전기화학 캐패시터의 특성을 확인하였다. $RuO_2$ 전극을 사용한 전기화학 캐패시터는 1M $LiPF_6$, EC, DEC 및 EMC혼합용매 전해액 중에서 순환전위전류법(주사속도. 2mV/sec, 전위영역: $2.0\~4.2V(Li|Li^+))$으로 산화 및 환원에 대하여 비정전용량을 구한 바, 각각 145 및 $142F/g-RuO_2{\cdot}nH_2O$이었다

• Journal of Electrochemical Science and Technology
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• 제6권2호
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• pp.59-64
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• 2015

Spherical Li₄Ti₅O₁₂ and Li₄Ti₅O₁₂ carbon nanotube (CNT) composites were synthesized using a colloid system. The electrochemical properties of the composites were thoroughly examined to determine their applicability as hybrid capacitor anodes. The electrical conductivity of the spherical Li₄Ti₅O₁₂-CNT composite was improved over that of the spherical Li₄Ti₅O₁₂ composite. The synthesized composites were utilized as the anode of a hybrid capacitor, which was assembled with an activated carbon (AC) positive electrode. The CNTs attached on the spherical Li₄Ti₅O₁₂ particles contributed to a 51% reduction of the equivalent series of resistance of the Li₄Ti₅O₁₂-CNTs/AC hybrid capacitor compared to the Li₄Ti₅O₁₂/AC hybrid capacitor. Moreover, the Li₄Ti₅O₁₂-CNTs/AC hybrid capacitor showed a larger capacitance than the Li₄Ti₅O₁₂/AC hybrid capacitor; specifically, the Li₄Ti₅O₁₂-CNT/AC hybrid capacitor showed 1.6 times greater capacitance at 40 cycles with a 10 mA cm⁻² loading current density.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.681-682
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• 2011

• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.423-428
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• 2010

To reduce polarization of electrochemical capacitor based on carbon nanotube, titanium oxide nanoparticles were deposited by ultrasound. The pore distribution of $TiO_2$/CNT nanoparticle exhibited surface area of $341\;m^2g^{-1}$ when $TiO_2$ content was 4 wt %, which was better than that of pristine CNT with surface area of $188\;m^2g^{-1}$. The analyses indicated that titanium oxide (particle diameter < 20 nm) was deposited on the CNT surface. The electrochemical performance was evaluated by using cyclic voltammetry (CV), impedance measurement, and constant-current charge/discharge cycling techniques. The $TiO_2$/CNT composite electrode showed relatively better electrochemical behaviors than CNT electrode by increasing the specific capacitance from $22\;Fg^{-1}$ to $37\;Fg^{-1}$ in 1 M $H_2SO_4$ solution. A symmetric cell assembled with the composite electrodes showed the specific capacitance value of $11\;Fg^{-1}$ at a current loading of $0.5\;mAcm^{-2}$ during initial cycling.

• Journal of Electrochemical Science and Technology
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• 제4권1호
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• pp.19-26
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• 2013

Graphene/Ni-Al layered double hydroxide (LDH) hybrid materials were synthesized by a hydrothermal reaction. Hexagonal Ni-Al LDH particles nucleated and grew on graphene sheets, thus preventing restacking of the graphene sheets and aggregation of the Ni-Al LDH nanoparticles upon drying. Electrode made from the graphene/Ni-Al LDH hybrid materials showed a substantial improvement in electrochemical capacitance relative to those made with pure Ni-Al LDH nanoparticles. In addition, the graphene/Ni-Al LDH hybrid composite materials showed remarkable stability after 4000 cycles with over 100% capacitance retention. These materials are thus very promising for use in electrochemical capacitor electrodes.

• 한국응용과학기술학회지
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• 제28권3호
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• pp.329-334
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• 2011

The electrochemical performances of an asymmetric hybrid capacitor were investigated using $LiFePO_4$ as the positive electrode and active carbon fibers(ACF) as the negative electrode. The electrochemical behaviors of a nonaqueous hybrid capacitor were characterized by constant current charge/discharge test. The specific capacitance using $LiFePO_4$/ACF electrode turned out to be $0.87F/cm^2$ and the unit cell showed excellent cycling performance. This hybrid capacitor was able to deliver a specific energy as high as 178 Wh/kg at a specific power of 1,068 W/kg.

• 전기화학회지
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• 제6권2호
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• pp.153-157
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• 2003

전기이중층 축전용량(electric double layer capacitance)과 유사축전용량(pseudo-capacitance)을 함께 갖는 하이브리드 전기화학 축전기에 대한 연구를 수행하였다. 양극은 $Ni(OH)_2$ 활성탄소가 복합된 전극을 사용하였으며 음극은 활성탄소를 활물질로 사용하므로써 비대칭 전극 구조를 갖는다. 셀 실험을 위하여 $5\times5cm^2$ 크기인 전극을 제작 사용하였다. Cyclic voltammetry측정 및 교류 임피던스 측정실험을 통하여 각각의 셀들이 갖는 전기화학적 거동을 조사하였고 충 방전 실험을 통하여 양극과 음극의 최적 질량비를 조사하였다.