Performance Of Electric Double-layer Capacitors Research Articles

Influence of the textual properties of activated carbon nanofibers on the performance of electric double-layer capacitors

To investigate the relationship between textural properties and electrochemical properties, activated carbon nanofibers were manufactured using an electrospinning process followed by chemical activation using KOH or NaOH. The specific surface area of the KOH-activated carbon nanofibers was higher than that of NaOH-activated carbon nanofibers; however, the total pore volume and mesopore volume of the NaOH-activated carbon nanofibers were greater than those of the KOH-activated carbon nanofibers when the same number of moles of KOH and NaOH were used. The specific capacitances increased as the specific surface area and pore volume of the activated carbon nanofibers were increased. However, the specific capacitance obtained at a high scan rate (50mV/s) and the retained capacitance of the activated carbon nanofibers increased with increasing total pore and mesopore volume, especially for mesopores with diameters of 2–4nm.

Improved performance of electric double layer capacitor using redox additive (VO2+/VO2+) aqueous electrolyte

Electric double layer capacitors (EDLCs) were fabricated using biomass derived porous activated carbon as electrode material with 1 M H2SO4 and VOSO4 added 1 M H2SO4 as electrolytes. Here, VOSO4 was used as redox additive to improve the overall performance of EDLC. As expected, the VOSO4 electrolyte showed ∼43% of improved specific capacitance of 630.6 F g−1 at 1 mA cm−2 compared to pristine 1 M H2SO4 (440.6 F g−1) due to the contribution of VO2+/VO2+ redox reaction at the electrode–electrolyte interface. Possible redox reaction mechanism of VO2+/VO2+ pair is also briefly illustrated. The good cycling performance of 97.57% capacitance retention was observed even after 4000 cycles. For comparison, the polymer gel electrolyte (PVA/VOSO4/H2SO4) was also prepared and then the performance of the fabricated EDLCs was studied. Overall, these findings could open up a simple and cost effective way to improve the performance of EDLCs significantly.

Electrolytic Characteristics of Fluoroethylene Carbonate for Electric Double-Layer Capacitors at High Concentrations of Electrolyte

The use of partially fluorinated compounds as alternative solvents can increase the solubility of electrolytes and improve the performance of electric double-layer capacitors (EDLCs). The solubility of triethylmethylammonium tetrafluoroborate (TEMABF4) in fluoroethylene carbonate (FEC) was 3.0 M (M = mol dm−3) or more at 25°C. The molar concentration of FEC in 2.5 M TEMABF4 solution was higher than that of propylene carbonate (PC) in 2.0 M TEMABF4 solution. The kinematic viscosity and ionic conductivity of 2.0 M TEMABF4 solution in FEC were slightly lower than those of the counterpart in PC at room temperature. The use of TEMABF4 at the high concentrations in FEC slightly increased the gravimetric capacitance of coin cells.

Synthesis of B-C-N Composite from Melamine-Formaldehyde Resins Containing Boron and Its Electric Double Layer Capacitor Performance

Synthesis of B-C-N Composite from Melamine-Formaldehyde Resins Containing Boron and Its Electric Double Layer Capacitor Performance

Application of Chitosan-based Gel Electrolytes with Ionic Liquids for High-Performance and Safe Electric Double Layer Capacitors

Chitosan-based gel electrolytes with ionic liquids (Chi/IL) were prepared and investigated for use in electric double-layer capacitors (EDLCs). The voltage drop for the test cell with Chi/EMImBF4 (EMImBF4 = 1-ethyl-3-methylimidazolium tetrafluoroborate) or Chi/DEMEBF4 (DEMEBF4 = N,N-diethyl-N-methyl-N-2-methoxyethylammonium tetrafluoroborate) and activated carbon fiber cloth electrodes (ACFCs) was smaller than that with the corresponding ionic liquid electrolyte. To clarify the effect of the presence of Chi in contact with the carbon electrode, we also prepared the Chi-containing ACFC electrode (Chi+ACFC) and evaluated its charge-discharge characteristics in EMImBF4. The results proved that the presence of Chi on the active materials reduces the internal resistances of the cell and plays an important role in the improvement of the EDLC performance. In addition, the high-voltage operation of the test cells with Chi-based gel electrolytes was investigated. These results suggest that the Chi is suitable for use in practical high-performance and safe EDLCs.

An Experimental Investigation of the Ion Storage/Transfer Behavior in an Electrical Double-Layer Capacitor by Using Monodisperse Carbon Spheres with Microporous Structure

Monodisperse carbon spheres with coefficient of variation less than 4% were successfully synthesized through polycondensation of resorcinol with formaldehyde in the presence of ammonia as a catalyst followed by carbonization in an inert atmosphere. The diameters of the carbon spheres can be tuned in the range of 220–1140 nm by adjusting the ammonia concentration in the precursor solutions. Although the particle size decreases with increasing ammonia concentrations, there is no large difference in the internal pore structure between the different-sized carbon spheres. The size-controlled monodisperse carbon spheres were used as a model material to understand the ion storage/transfer behavior in electrical double-layer capacitor (EDLC). The present study clearly indicates that the reducing the particle size and highly monodispersity in both size and shape were effective at reducing mass transport resistance and improving EDLC performance reliability.

전기이중층 커패시터의 성능에 미치는 산소/질소 함유 관능기들의 영향

본 논문에서는 전기이중층 커패시터(EDLC, Electrical Double Layer Capacitor)의 전극소재로 쓰이는 활성탄소의 안정화를 위해 산소함유관능기를 최소화하고 질소함유관능기의 도입을 통해 유기용액계의 전해질을 가지는 EDLC의 축전용량을 개선하는 연구를 하였다. 주사전자현미경(SEM, Scanning Electron Microscopy), 후리에 변환 적외선분광기(FTIR, Fourier Transform Infrared), 자동원소분석기(EA, Elemental Analysis), 보엠(Boehm) 적정법, 충 방전 테스트 등의 분석법을 이용하여 그 결과를 확인하였다. 산 처리를 통하여 산소함유관능기가 도입되고 요소처리를 통하여 질소함유관능기가 도입되었음을 확인하였다. 질소함유관능기 도입을 통하여 EDLC의 g 당 방전용량을 2 mA 상승시켰으며 빠른 속도로 최대 충 방전 성능을 달성하였다. 반면 산소함유관능기는 전해질 속의 전하가 탄소표면에 흡 탈착되는 것을 방해하기 때문에 낮은 방전용량을 보였고, 충 방전 횟수가 늘어남에 따라 방전용량의 큰 감소를 보여주었다. In this study, activated carbons (ACs) were modified as electrode materials for an electric double layer capacitor (EDLC) by controlling oxygen- and nitrogen-containing functional groups. The morphological and chemical properties of ACs were analyzed through scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectrometer, automatic elemental analyzer (EA) and Boehm titration. Also, charge/discharge tests were performed to investigate the EDLC performance. Oxygen- and nitrogen-containing functional groups were introduced on the surface of ACs through acid and urea treatments, respectively. ACs with nitrogen-containing functional groups showed 2 mA increase of gravimetric discharge capacity and quick achievement of maximum charge/discharge performance. However, ACs with oxygen-containing functional groups showed low discharge capacity and its gradual decrease during further cyclic test, since the functional groups interrupted adsorption/desorption of charges in the electrolyte on the surface of ACs.

Influence of separator properties on electrochemical performance of electrical double-layer capacitors

Influence of separator material characteristics on the high and low frequency series and parallel resistance, low and high frequency capacitance, characteristic time constant, energy and power densities of the electrical double-layer capacitors (EDLCs), based on the two identical ideally polarizable microporous titanium carbide-derived carbon electrodes in 1M (C2H5)3CH3NBF4 acetonitrile solution, has been tested by cyclic voltammetry and electrochemical impedance spectroscopy methods. Self-made separator materials have been prepared from 20% or 25% poly(vinylidene fluoride) solutions in N,N-dimethylacetamide or N,N-dimethylformamide and acetone mixture (8:2 mass ratio) by using the electrospinning method at different electric field strengths and polymer solution feed rates. Separator material total porosity, pore size distribution and specific surface area, calculated using mercury porosimetry data, noticeably depend on electrospinning conditions and mercury pressure applied, explained by the compressibility of materials under study. It was established that the separator material structure (total porosity, specific surface area), chemical composition and thickness determines the high frequency series and low frequency parallel resistance, characteristic time constant and power density values of the EDLC. However, the limits of ideal polarizability, low frequency capacitance and the specific energy only weakly depend on the separator material properties used in EDLC cells.

A divalent quaternary alkyl ammonium salt as the electrolyte for high-energy electric double-layer capacitors

A divalent electrolyte salt based on 1,1,4,4-tetramethyl piperazine has been synthesized and applied in electric double-layer capacitors (EDLCs). Traits of the divalent salts have been accessed as well as monovalent quaternary alkyl ammonium salts by the means of galvanostatic charge–discharge tests and ionic conductivity measurements. Compared with monovalent salts, the divalent salts do enlarge the charge storage ability of EDLCs remarkably. However, highly concentrated charge density on the divalent cation has a strong interaction with the organic solvent of propylene carbonate. The adverse effect of this heavy solvation on the performance of EDLCs has been investigated. Moreover, the influence of pore size distribution on the storage ability of these cations at the porous carbon electrode has been addressed.

Activated Mesophase Pitch for High Performance Electric Double Layer Capacitors

not Available.

Electrical double layer capacitor using poly(methyl methacrylate)–C4BO8Li gel polymer electrolyte and carbonaceous material from shells of mata kucing (Dimocarpus longan) fruit

Poly(methyl methacrylate), PMMA based gel polymer electrolytes (GPE) containing immobilized lithium bis(oxalato)borate, C4BO8Li or LiBOB dissolved in a propylene carbonate–ethylene carbonate binary solvent were prepared by heating the cast solution between 70 and 80°C for 20min. The electrolyte composition with 5wt.% PMMA exhibited the highest conductivity of 3.27 and 7.46mScm−1 at 298 and 343K respectively. Cyclic voltammetry studies on the GPE containing 15wt.% PMMA and 85wt.% (0.6M LiBOB) dissolved in equal weight of ethylene and propylene carbonates showed that the electrochemical potential stability window of the electrolyte lies in the range between −1.7 to +1.7V. Linear sweep voltammetry indicates the gel polymer electrolyte is stable up to 1.7V. The electrical double layer capacitor (EDLC) using the highest conducting GPE and activated carbon derived from shells of the mata kucing (Dimocarpus longan) fruit has capacitance of ∼685mFg−1 on the first cycle. The EDLC performance was also characterized using cyclic voltammetry and charge–discharge processes at constant current.

Electrochemical properties of arc-black and carbon nano-balloon as electrochemical capacitor electrodes

In this study, we used two types of carbon nanomaterials, arc-black (AcB) which has an amorphous structure and carbon nano-balloon (CNB) which has a graphitic structure as electrochemical capacitor electrodes. We made a coin electrode from these carbon materials and fabricated an electric double-layer capacitor (EDLC) that sandwiches a separator between the coin electrodes. On the other hand, RuO2 was loaded on these carbon materials, and we fabricated a pseudo-capacitor that has an ion insertion mechanism into RuO2. For comparison with these carbon materials, activated carbon (AC) was also used for a capacitor electrode. The electrochemical properties of all the capacitors were evaluated in 1M H2SO4 aqueous solution. As a result of EDLC performance, AcB electrode had a higher specific capacitance than AC electrode at a high scan rate (≥ 100 mV/s). In the evaluation of pseudo-capacitor performance, RuO2-loaded CNB electrode showed a high specific capacitance of 734 F/g per RuO2 weight.

Pore Size Effect of Carbon Electrodes on the Electrochemical Double-Layer Capacitance in LiTFSI/2-Oxazolidinone Complex Electrolyte

To optimize the performance of electric double-layer capacitors (EDLCs) with ionic liquids (ILs) based on LiTFSI and 2-oxazolidinone as electrolyte, we simulated possible IL structures and ion size...

Physicochemical and Electrochemical Properties of 1-Ethyl-3-Methylimidazolium Tris(pentafluoroethyl)trifluorophosphate and 1-Ethyl-3-Methylimidazolium Tetracyanoborate

The physicochemical (e.g., density, viscosity, ionic conductivity, and self-diffusion coefficient) and electrochemical (e.g., electrochemical window and electric double-layer capacitor performance) properties of two new types of room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMIm-FAP) and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB), were investigated and compared. EMIm-FAP showed a wider electrochemical window with a carbon working electrode compared with EMIm-TCB, in spite of lower viscosity, larger self-diffusion coefficients and higher ionic conductivity. Also, the electric double-layer capacitor using EMIm-FAP shows better cycle reversibility and higher charge/discharge voltage operation (over 3 V) than that using EMIm-TCB.

Local Ordered Structure of Propylene Carbonate in Slit-Shaped Carbon Nanopores by GCMC Simulation

An electric double-layer capacitor (EDLC) has high potential for storing electrical energy at a high power density. It was reported that a narrow nanopore system provides higher performance of EDLCs. In such a system, propylene carbonate (PC) is generally used as a solvent in EDLCs. Hence, the structure of PC in the slit-shaped carbon nanopores should be investigated to reveal the EDLC mechanism. In this paper, grand canonical Monte Carlo simulation of PC adsorbed in nanopores was performed to elucidate molecular-level understanding of the influence of PC on the EDLC performance. PC molecules have a highly ordered structure and longer intermolecular distances in nanopores of a pore width less than 0.7 nm. Thus, the highly ordered and low-density structure formation of the adsorbed PC molecules in narrow nanopores provides a permeation path for electrolytes through nanopores, indicating high-performance EDLCs.

EDLC 전극용 메조기공 활성탄소 섬유의 전기화학적 특성

철 이온 교환방법에 의해 메조기공을 갖는 활성탄소 섬유(ACF)를 제조하고, 이를 사용하여 전기 이중층 커패시터(EDLC)의 전극소재 성능을 조사하였다. 질산처리에 의해 제조된 메조기공 ACF는 비표면적이 1,249, 664 <TEX>$m^2/g$</TEX>이고, 메조 기공 분율이 70.6-81.3%이고, 평균 기공크기는 약 2.78~4.14 nm이다. 질산처리시간이 짧을수록 비표면적이 크고 메조 기공이 적게 발달됨을 알 수 있었다. 전기이중층 커패시터의 성능을 조사하기 위해서, 메조기공 ACF, 도전제, 바인더를 사용하여 단위 셀을 제조하였으며, 유기 전해질을 사용하였다. 2시간 질산으로 처리된 ACF의 비 축전양은 0.47 <TEX>$F/cm^2$</TEX>이고, 20회 충.방전 테스트에서 안정된 실험결과를 얻을 수 있었다. EDLC의 전기화학적 성능은 ACF 전극의 비표면적에 크게 영향을 받으며 메조기공은 전하의 확산저항을 감소시키는 것을 알 수 있었다. The electrode material performances of electric double layer capacitor(EDLC) were investigated using mesopous active carbon fiber(ACF), which was prepared by the iron exchange method. The mesoporous ACF had pore characteristics of specific surface area around 1249, 664 <TEX>$m^2$</TEX>/g, mesoporous fraction around 70.6-81.3% and meanpore size around 2.78-4.14 nm. The results showed that as HNO3 treatment time decreased, the specific surface area increased and mesoporous fraction decreased. To investigate electrochemical performance of EDLC, unit cell was manufactured using mesoporus ACF, conducting material and binder; organic elctrolyte was used on this experiment. The specific capacitance of ACF treated with HNO3 for 2 hours turned out to be 0.47 <TEX>$F/cm^2$</TEX>and the results of the cyclic charge-discharge tests were stable. Thus, the electrochemical performance of EDLC was mainly dependent on specific surface area of ACF electrode and the diffusion resistance of charge decreased as the mesopore increased.

Influence of Particle Size on Rate Performance of Mesoporous Carbon Electric Double-Layer Capacitor (EDLC) Electrodes

Herein, mesoporous carbon materials with different particle sizes were prepared using the direct templating method. To control particle size, the concentration of surfactant/silicate dissolved in aqueous solution was varied. According to a decrease in the concentration, a larger surface area and a smaller particle size were observed, whereas pore size and connectivity remained invariant. From the investigation of electric double-layer capacitor performance, specific capacitance was proportional to surface area. From electrochemical impedance spectroscopy analysis, a resistance relevant to pseudocapacitive faradaic reaction on electrode surface became larger, but a decrease in the total electrolyte resistance in pores was observed as a function of particle size decrease. This contradictory behavior of two resistances resulted in an existence of optimal particle size for the minimum equivalent series resistance , which was comparable with the ordered mesoporous carbon electrode from the MCM-48 template.

Electrical double-layer capacitor performance of nitrogen-doped ordered mesoporous carbon prepared by nanotemplating method

In this work, the electrical double-layer capacitive properties of nitrogen-doped ordered mesoporous carbons (N-OMCs) were investigated. Ordered mesoporous carbons (OMCs) with 3D body-centered Ia3d structure has been prepared by KIT-6 mesoporous silica as a hard template with aniline for N-OMC and sucrose for Su-OMC as a carbon precursor. Using the different carbon precursor, moderate amounts of nitrogen atoms could be doped to the OMC structures. The obtained materials were characterized by powder X-ray diffraction (XRD), nitrogen adsorption isotherms at 77 K, elemental analysis, and X-ray photoelectron spectroscopy (XPS). Prepared OMCs had mesopore properties such as a high surface area with narrow pore-size distribution. From cyclic voltammograms (CVs) test, N-OMC compared to Su-OMC exhibit higher capacitance and fast charge/discharge characteristics, which results from their pseudo-capacitive effect of incorporated nitrogen atoms. It was thought that N-OMC prepared by the nanotemplating method with KIT-6 and aniline were suitable electrode materials for electrical double-layer capacitors.

The effect of pre-carbonization of mesophase pitch-based activated carbons on their electrochemical performance for electric double-layer capacitors

The activated carbons (ACs) are prepared from mesophase pitch which is pre-carbonized by using potassium hydroxide as an activating agent. Nitrogen adsorption at 77 K is used to characterize the surface area and the porous structure of the ACs. By changing the pre-carbonization temperature from 560 to 750 °C, the arrangement of the ACs’ microcrystallines might be controllable, and the pore size could be adjusted between 1.5 and 2.4 nm. The electrochemical performance of the ACs in organic solvent (1 M Et4NBF4 in propylene carbonate) is investigated by voltage sweep cyclic voltammetry and constant current charge–discharge cycling tests. The results show that the ions can transfer rapidly and freely in the pore larger than or equal to 1.85 nm, even when the current density increases to 25 A g−1.

Allyl-functionalized ionic liquids as electrolytes for electric double-layer capacitors

Double-layer capacitor electrolytes employing allyl-functionalized ionic liquids as electrolytes with solvents have been evaluated. Imidazolium cations with allyl groups enabled the high capacitances and low resistances of electric double-layer capacitor (EDLC) cells at a wide range of temperature in spite of the large cation sizes and low ionic conductivities of the electrolytes compared to imidazolium with saturated alkyl groups, 1-ethyl-3-methylimidazolium (EMIm). The improvement of EDLC performance was noted particularly in the case of diallylimidazolium (DAIm) cation and TFSA anion. The substitution of the vinyl group increased the high capacitance only at 298 K and decreased the capacitance at low temperature and direct current resistance (DC-IR) at 243 and 298 K. The butenyl group deteriorated the capacitance and DC-IR at 243 and 298 K. The stability of EDLC cell of DAIm–BF 4/PC was inferior to that of EMIm–BF 4/PC. The addition of DMC to PC improved the stability.