Capacitance Of Electric Double Layer Capacitors Research Articles

A quantitative evaluation of the large pore-size effect on the electric double-layer capacitance for high voltage by 19F-NMR

Electric double-layer capacitors (EDLCs) afford long cycle life and high-power density by dielectric ion adsorption and desorption on the surface of porous materials. However, high potential charges/discharges lower the capacitance of EDLCs. In this study, we quantitatively evaluated the large pore-size effect of activated carbons (ACs) on the electric double layer capacitances at various voltages based on a hierarchical domain model from a structural point of view. ACs with highly developed microporous and mesoporous (2–4 nm) structures were prepared using KOH activation. The AC with small amount of mesopores showed a specific capacitance of 30.35 F/g at a voltage of 2.7 V, where it significantly lowered to 20.93 F/g at a high voltage of 3.3 V. Meanwhile, the highly microporous AC with abundant mesopores had a higher specific capacitance (40.77 F/g at 2.7 V to 38.22 F/g at 3.3 V). 19F-NMR results indicate that the amounts of solvated ions in the mesopores significantly increased in all the ACs after charging at a higher voltage. The mitigation of the high-voltage capacitance drop might occur because of the mesopore structure that functions as a buffer space for the electric double layer.

Coherent construction of recovered γ-Al2O3 embedded N-doped activated carbon by supercritical-CO2 pathway: Robust hybrid electrode material for energy storage device

Electrochemical energy storage application is one of the most impressive solutions to the problem of fossil fuel depletion. However, the lower capacitance in electric double-layer capacitors and poor stability in pseudocapacitors remain significant challenges. State of an art, we demonstrated the fabrication of hybrid electrode material with aluminium oxide nanoparticles (Al2O3 NPs) embedded in N-doped activated carbon (AC) by supercritical-CO2 approach. The N-doped activated carbon and Al2O3 NPs were prepared by Dracaena trifasciata biomass and the strategic recovery of domestic aluminium waste. The prepared materials were inspected through microscopic and various spectroscopic techniques. The morphological observation of Al2O3@DT-AC manifested well impregnation of Al2O3 NPs to DT-AC surface, resulting in a higher capacitance of 1031.6 F/g at 0.5 A/g than Al2O3 (258.5 F/g). Further, the respectable capacitance retention signifies that Al2O3@DT-AC are promising electrode materials for supercapacitors. The material preparation and processing techniques are eco-friendly and considered to be green processing.

Structurally integrated 3D carbon tube grid-based high-performance filter capacitor.

Filter capacitors play a critical role in ensuring the quality and reliability of electrical and electronic equipment. Aluminum electrolytic capacitors are the most commonly used but are the largest filtering components, limiting device miniaturization. The high areal and volumetric capacitance of electric double-layer capacitors should make them ideal miniaturized filter capacitors, but they are hindered by their slow frequency responses. We report the development of interconnected and structurally integrated carbon tube grid-based electric double-layer capacitors with high areal capacitance and rapid frequency response. These capacitors exhibit excellent line filtering of 120-hertz voltage signal and volumetric advantages under low-voltage operations for digital circuits, portable electronics, and electrical appliances. These findings provide a sound technological basis for developing electric double-layer capacitors for miniaturizing filter and power devices.

Characteristics of graphite oxide membranes with different thickness by low temperature thermal reduction for aqueous EDLC electrodes and hot activation phenomenon

Reduced graphite oxide membrane (RGOM) with different thickness were prepared and used as electric double layer capacitor (EDLC) electrodes with aqueous electrolyte. According to quantum and molecular dynamic simulations, it was difficult for K+ and OH− to diffuse into graphene sheets due to dense structure, which made the RGOM electrodes show poor EDLC behaviors. Electrochemical tests showed that controlling the thickness of electrodes and modifying the dense structure could improve the specific capacitance of EDLC. Further studies indicated that during galvanostatic charge/discharge processes, if the EDLC were heated at 70 °C for one cycle and then cooled down to room temperature, the specific capacitance could be increased further. Additionally, according to 10,000 times cycling tests at 5000 mA g−1, the improved capacitance could be maintained for long time (154–167 F g−1 during test process), indicating that the hot activation could make RGOM electrodes obtain good and stable EDLC performances.

Computing the Capacitance of Electric Double-Layer Capacitors from Time-Domain and Frequency-Domain Measurements

In this study we show the relationship between capacitances of electric double-layer ca- pacitors (EDLC) computed from time-domain and frequency-domain measurements. EDLC are assumed to be linear time-invariant (LTI), causal and stable systems that map an input time-domain voltage signal v = [v0, v1, . , vN ] to an output time-domain charge q = [q0, q1, ..., qN ] = [f(v0), f(v1), ..., f(vN)]. When a voltage v0 is applied on an uncharged EDLC, the corresponding measured charge is q0 = c0v0 , where c0 is the value of the system impulse response at that instant. Subsequently, by considering the superposition principle in causal LTI systems, the input voltage v1 applied after a lapse of time ∆t with the impulse response of the device c0 results in a certain amount of charge c0v1 , but the preceding value of voltage v0 contributes also with another amount of charge c1v0 that depends on the current response of the device c1 at the instant ∆t. Thus the charge q1 accumulated on the device after ∆t is the sum c0v1 + c1v0 . Repeating this procedure for all discrete times tk = k∆t until N∆t (time duration of the applied signal) corresponds to the (discrete) convolution sum of the input voltage by the systems impulse response which results in the output charge: qτ = c ∗ v =Σj cτ− j vj . In continuous-time form, one can write: q(t) = ∫ c(t − τ )v(τ )dτ. The function c(t) can be viewed as the system-level, macroscopic capacitance of the device that takes into account (in a lumped form) all microscopic events of charge transport taking place inside the device. The convolution operation is carried out here in the time domain, but in the frequency domain, by virtue of the convolution theorem, it turns out to be the point-by-point multiplication Q = CV , where Q, C and V are the Fourier transforms of q, c and v respectively [1–3]. Thus, one cannot compute the capacitance of EDLCs by dividing charge-by-voltage both in the time-domain and frequency-domain as commonly done in the literature [3]. We will show examples using linear voltage ramp and constant current excitations [1,2].REFERENCES A. Allagui and M. E. Fouda, “Inverse problem of reconstructing the capacitance of electric double-layer capacitors,” Electrochim. Acta , 138848 (2021).A. Allagui, A. S. Elwakil, and M. E. Fouda, “Revisiting the time-domain and frequency-domain definitions of capacitance,” IEEE Trans. Electron Devices 68 (2021).A. Allagui, A. S. Elwakil, and H. Eleuch, “Highlighting a common confusion in the computation of capacitance of electrochemical energy storage devices,” J. Phys. Chem. C 125, 9591–9592 (2021).

MOF-derived hierarchical carbon network as an extremely-high-performance supercapacitor electrode

Electric double-layer capacitor (EDLC), as one type of supercapacitor, holds great promises for fast-charging energy storage devices but suffers from limited specific capacitance. The design and development of high performance EDLC-type carbon materials with the effective synergistic effect of high conductivity, tailored porous structure, and high surface area still remain challenging. Here, we report a novel hierarchical porous carbon with a combination of highly conductive electronic pathways and rich ionic storage units in three-dimensional network morphology, leading to high specific capacitance of EDLC. Specifically, by facile hydrothermal synthesis and carbonization, the carbon electrode derived from metal-organic framework and polymer fibers, exhibits extremely high specific capacitance of ∼ 385 F g−1 at 0.1 A g−1 and can still maintain capacitance of 303 F g−1 at 10 A g−1. The high electrochemical performance can be attributed to the rich network of micro and mesoporous structures for electrolyte transport and ion adsorption as well as highly conductive electronic pathways inside the electrodes. The assembled EDLC thus delivers a high energy density of 10.51 Wh kg−1 and a power density of 5.454 kW kg−1 at the current density of 10 A g−1 in the aqueous electrolyte. Hence, the present study is expected to open a promising route to developing porous materials for high-performance energy devices.

Inverse problem of reconstructing the capacitance of electric double-layer capacitors

The capacitance is a characteristic function of a capacitive energy storage device that is inaccessible to direct measurements, but can be estimated from input and output signals. Knowing that electric double-layer capacitors (EDLC) exhibit non-ideal capacitive behavior, their capacitance is commonly estimated from the time-domain definition of capacitance times voltage giving charge (using cyclic voltammetry and galvanostatic charge/discharge data), and in the same time from the same multiplicative relationship but in the frequency-domain (using impedance spectroscopy data), as if the capacitance is constant. The purpose of this study is to provide the recommended procedure to compute the capacitance of such types of devices from time-domain data starting from the definition of capacitance being the ratio of charge by voltage both defined in the frequency domain, which is consistent with the definition of conventional impedance. This turns the situation in the time domain to be an ill-posed inverse problem of convolution, wherein the to-be-deconvolved or reconstructed capacitance can be very sensitive to experimental errors. We show results of the procedure using (i) synthetic data generated using a fractional-order capacitor model of impedance Z(jω)=1/[(jω)αCα] and (ii) experimental data of a commercial aluminium electrolytic capacitor and an EDLC for the two cases of linear voltage ramp and constant-current step excitations.

(Invited) Theoretical Study on the Energy Storage Mechanism of Transition-Metal-Carbide MXene By Quantum-Classical Hybrid Simulation

Two-dimensional transition-metal carbide MXenes has been known as a promising material of high-performance electrode for energy storage applications with both non-aqueous and aqueous electrolytes because it has electronic conductivity, ion capability in interlayer nanospace, and the redox activity of Ti. Especially, as an electrode of electrochemical capacitors, MXenes have a unique dependence of capacitance on intercalated cation species and a distinctive behavior that is both capacitive and pseudocapacitive depending on the electrolyte. To better understand electrochemical mechanism of these behaviors, we performed a microscopic theoretical analysis of the electric-double layer (EDL) in the interlayer nanospace of the MXene electrode by combining first-principles calculations based on density functional theory (DFT) and classical implicit solvation theory named three dimensional reference-site interaction model (3D-RISM) method [1]. By using the quantum-classical hybrid simulation, solvation effect at the interlayer nanospace of MXene electrode was taken into consideration appropriately with low computational cost comparable with conventional DFT simulation.For the unique dependence of capacitance on intercalated cation species, our simulation results showed that the capacitance of EDL capacitors can be enhanced by a factor of 1.8, when the water molecules are strongly confined into the two-dimensional nanoslits of titanium carbide MXene electrode. This is because that dipolar polarization of strongly confined water overscreens an external electric field applied on the EDL and enhances capacitance with a characteristically negative dielectric constant of a water molecule [2, 3]. Another investigated feature is the distinctive behavior that is both capacitive and pseudocapacitive depending on the electrolyte. As a result of their electronic states simulated via the quantum-classical hybrid simulation, it was found that the hydration shell of intercalated ions prevents orbital coupling between MXene and the intercalated ions, which leads to the formation of an EDL and capacitive behavior. However, once the cations are partially dehydrated and adsorbed onto the MXene surface directly, because of orbital coupling of the cation states with the MXene states, particularly for surface-termination groups, charge transfer occurs and results in a pseudocapacitive behavior [4].

Negative dielectric constant of water confined in nanosheets

Electric double-layer capacitors are efficient energy storage devices that have the potential to account for uneven power demand in sustainable energy systems. Earlier attempts to improve an unsatisfactory capacitance of electric double-layer capacitors have focused on meso- or nanostructuring to increase the accessible surface area and minimize the distance between the adsorbed ions and the electrode. However, the dielectric constant of the electrolyte solvent embedded between adsorbed ions and the electrode surface, which also governs the capacitance, has not been previously exploited to manipulate the capacitance. Here we show that the capacitance of electric double-layer capacitor electrodes can be enlarged when the water molecules are strongly confined into the two-dimensional slits of titanium carbide MXene nanosheets. Using electrochemical methods and theoretical modeling, we find that dipolar polarization of strongly confined water resonantly overscreens an external electric field and enhances capacitance with a characteristically negative dielectric constant of a water molecule.

The effect in the film thickness reducing mechanism of functional groups in porous carbon sulfuric acid supercapacitor

In this paper, the different types and number of functional groups in porous carbon–carbon pore channels are discussed in the thinning mechanism of ionic solvent thin films, which has a significant impact on the absorption of H2SO4 electrolyte based Electric Double Layer Capacitors (EDLC). By exploring the binding energy of –OH, –COOH, –SO3H, –NO2 and other four functional groups with sulfuric acid and hexahydrate sulfuric acid of porous carbon channel and hexahydrate sulfuric acid, it was found that –OH had no repulsive effect on the cathode of the battery, and –COOH, –SO3H, –NO2 and other functional groups had obvious repulsive effect on the cathode of EDLC with the increase of the functional groups number, that is, there was an effect of increasing the capacitance of EDLC by increasing the number of sulfide molecular. This will excavate the potential electrode material in the practical application.

Investigation of hydroxide ion-conduction in solid polymer electrolytes via electrochemical impedance spectroscopy

This study explores the conduction of hydroxide (OH−) ions in solid alkaline polymer electrolytes, and their contribution to the performance of solid-state electric double layer capacitors (EDLCs). The conductivity of tetraethylammonium hydroxide (TEAOH) polyacrylamide (PAM) and the capacitance of a solid-state EDLC based on this solid polymer electrolyte were investigated under three controlled relative humidity (RH) conditions (15, 45, and 75% RH). These properties are found to be highly dependent on the hydration structure of OH− ions that evolved in the different environments. To identify the role of hydration and ion structure in solid alkaline polymer electrolytes on device performance, dielectric analyses on the impedance spectra of TEAOH-PAM were utilized and revealed an interesting connection between the frequency dependent capacitive behaviour of the device and the ion response in the polymer electrolyte. The capacitance of EDLCs is closely related to the accumulation of ions at electrode/electrolyte interface, while the high frequency time constant for EDLCs corresponds to the transition of ion motion from vibration (energy dissipating) to translation (energy storing). Based on dielectric analysis and correlating the hydration of TEAOH-PAM with the activation energies of ionic conductivity in the three environments, we propose a framework to explain the changes of OH− ion transport in the solid-state. Under 15% RH, the segmental motion of the polymer chains facilitates the transport of TEAOH ions bound as 4:1 H2O:TEAOH crystal hydrates in the solid phase. As hydration rises under 45% RH, the segmental motion coordinates the conduction of 7.5:1 H2O:TEAOH crystal hydrates in the liquid phase. Under 75% RH, TEAOH-PAM is well hydrated and the conduction mechanism is dominated by liquid-like OH− ion-hopping of fully dissociated ions (hydration number 16.6:1). These results demonstrate the interplay of segmental motion and OH− ion-hopping in solid alkaline polymer electrolytes. The methods and findings of this study can be used to design solid aqueous polymer electrolytes with predictable long-term behaviour for inherently safe, thin, and lightweight electrochemical devices.

Modeling electrokinetics in ionic liquids.

Using direct numerical simulations, we provide a thorough study regarding the electrokinetics of ionic liquids. In particular, modified Poisson-Nernst-Planck equations are solved to capture the crowding and overscreening effects characteristic of an ionic liquid. For modeling electrokinetic flows in an ionic liquid, the modified Poisson-Nernst-Planck equations are coupled with Navier-Stokes equations to study the coupling of ion transport, hydrodynamics, and electrostatic forces. Specifically, we consider the ion transport between two parallel charged surfaces, charging dynamics in a nanopore, capacitance of electric double-layer capacitors, electroosmotic flow in a nanochannel, electroconvective instability on a plane ion-selective surface, and electroconvective flow on a curved ion-selective surface. We also discuss how crowding and overscreening and their interplay affect the electrokinetic behaviors of ionic liquids in these application problems.

Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors.

Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC’s specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes— Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)—and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost.

Enhancing the Electrochemical Performance of Electric Double-Layer Capacitors by Applying Mesoporous Carbon Gel RFCX to the Electrode

Electric double-layer capacitor (EDLC) has been required high capacitance and high-rate performance. The capacitance of EDLC comes from the electrostatic charge accumulation at the interface between electrode and electrolyte. So the capacitance is highly dependent on the surface area of elecrode material. For this reason, microporous activated carbon had been used for many years as EDLC electrode materials. However, recent research use organic electrolyte to enhance the energy density of EDLC. In this case, microporous electrode materials are not good at ion transport and reduce rate perfermance because of the large ion diameter of organic electrolyte. Therefore, an optimal electrode material must provide an appropriate pore size for ion transport. Recently, mesoporous materials have been reported to be more effective in increasing capacitance at high charge/discharge rates. Based on the recent reports, we focused on the study of novel mesoporous materials. We prepared several kinds of mesoporous materials carbon gel RFCX (resorcinol formaldehyde carbon xerogel) with different pore size distribution. RFCX is a kind of mesoporous carbon material with a 3D interconnected network structure and under the control of the pore structure by varying certain conditions of the sol-gel process. We controled the concentration of catalyst and developed three types of mesoporous materials carbon gel RFCX with a large number of mesopores around 10 nm, 25 nm and 40 nm. For comparison, we used two kinds of commercial activated carbon products M (surface area 900 m2g-1) and Y (surface area 1500 m2g-1). Both of them are high-surface-area microporous activated carbon. And we examined each sample’s electrochemical behavior as the electrode for electric double-layer capacitors in organic electrolyte of tetra ethyl ammonium tetra fluoroborate in propylene carbonate (TEABF4/PC). Ion diameter of electrolyte ion TEA+ in solvation is 1.96 nm. And ion diameter of electrolyte ion BF4 - in solvation is 1.71 nm. Diameter was caculated by Car-Parrinello method. Carbon gel RFCX enhanced the electrolyte ion transport by the large pore diameter (2 ~ 50 nm). RFCXs showed higher surface areal capacitance of 4.0 ~ 6.2 μF cm−2 than the commercial product M (0.5 ~1.5 μF cm−2) in organic electrolyte. Though they are the similar surface area (about 800 m2g-1 and 900 m2g-1). Moreover, the RFCXs also showed higher surface areal capacitance than the commercial product Y (2.2 ~ 3.5 μF cm−2). Though surface area of RFCX is only a half of Y (1500 m2g-1). And RFCXs showed high-rate performance of 70% owing to the large mesopore volume. These results indicated that capacitance of EDLC in organic electrolyte indepandent of surface area of electrode material. Thus, we considered that the volume rate of mesopore of electrode material is one of the most important determinant of rate performance. In summary, EDLC based on the mesoporous carbon RFCX exhibited better electrochemical performance than microporous activated carbon in organic electrolyte. It is considered that RFCX has potential for high performance energy-related applications.

Investigation of Dielectric Decrement and Correlation Effects on Electric Double-Layer Capacitance by Self-Consistent Field Model

AbstractThe differential capacitance of electric double-layer capacitors is studied by developing a generalized model of the self-consistent Gaussian field theory. This model includes many-body effects of particles near the interface such as ionic sizes, the order of water alignment and electrostatic correlations, and thus can present more accurate predictions of the electric double-layer structure and hence the capacitance than traditional continuum theories. Analytical simplification of the model and efficient numerical method are introduced, in particular, the approximation of the self-Green's function which describes the self energy of a mobile ion. We show that, when the applied voltage on interfaces is small the dielectric effect of the electrode materials plays an important role. For large voltage, this effect is screened, but the dielectric saturation due to the alignment of the nearby water is shown to be essential. For 2:1 electrolytes, abnormal enhancement on the capacitance due to the dielectric electrode is observed, which is due to the interplay of the image charge effect and Born solvation energy in the self energy of ions.

Enhanced capacitance of EDLCs (electrical double layer capacitors) based on ionic liquid-added polymer electrolytes

Ionic liquid added PVA (poly (vinyl alcohol))-based ion conductors are investigated for EDLCs (Electric Double Layer Capacitors) using electrochemical measurements. Polymer electrolytes incorporated with ammonium acetate (CH3COONH4) as salt and 1-butyl-3-methylimidazolium iodide (BmImI) as the ionic liquid exhibit VTF (Vogel–Tamman–Fulcher) relationship, which is associated with free volume theory. ATR–FTIR (Attenuated Total Reflectance–Fourier transform infrared) confirms the occurrence of complexation between PVA, CH3COONH4 and BmImI. Thermal stability of the polymer electrolytes is studied using TGA (thermogravimetry analysis). The electrochemical potential window of ionic liquid-added polymer electrolyte is extended from 3.3 V to 3.8 V. CV (Cyclic voltammetry) proves the improvement in specific capacitance of the EDLC containing ionic liquid-added polymer electrolyte. The specific capacitance is found to decrease as the scan rate increases. The specific capacitance of EDLCs obtained in CV is in good agreement with low frequency-EIS (electrochemical impedance spectroscopy) and GCD (galvanostatic charge–discharge) curve. This system is suitable for EDLC owing to its high energy and power densities.

열처리 온도에 의한 피치계 활성탄소섬유의 기공구조 변화가 전기화학적 특성에 미치는 영향

In this study, electrochemical properties of pitch-based activated carbon fibers (ACFs) were investigated by different heat-treatment temperature of the pitch-based ACFs in order to improve the specific capacitance of electric double-layer capacitor (EDLC). The ACFs were prepared by different heat-treatment temperatures of 1050 and , after activation with 4 M KOH at using stabilized pitch fiber. The specific surface area of prepared ACFs increased from to , also the micropore and mesopore volumes of prepared ACFs were increased. These results because pore was produced by desorbing oxygen and hydrogen elements within the ACFs, and pore size was increased by contraction ACFs by heat-treatment process. Because of the porous properties, the specific capacitance was increased from 73 F/g to 119 F/g using cyclic voltammetry with 1 M at scan rates of 5 mV/s.

Electrical, structural, thermal and electrochemical properties of corn starch-based biopolymer electrolytes

Biopolymer electrolytes containing corn starch, lithium hexafluorophosphate (LiPF6) and ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF6) are prepared by solution casting technique. Temperature dependence-ionic conductivity studies reveal Vogel–Tamman–Fulcher (VTF) relationship which is associated with free volume theory. Ionic liquid-based biopolymer electrolytes show lower glass transition temperature (Tg) than ionic liquid-free biopolymer electrolyte. X-ray diffraction (XRD) studies demonstrate higher amorphous region of ionic liquid-added biopolymer electrolytes. In addition, the potential stability window of the biopolymer electrolyte becomes wider and stable up to 2.9V. Conclusively, the fabricated electric double layer capacitor (EDLC) shows improved electrochemical performance upon addition of ionic liquid into the biopolymer electrolyte. The specific capacitance of EDLC based on ionic liquid-added polymer electrolyte is relatively higher than that of ionic liquid-free polymer electrolyte as depicted in cyclic voltammogram.

Poly(ε-caprolactone)-based polymer electrolyte for electrical double-layer capacitors

The potential of electrical double-layer capacitors (EDLCs) fabricated from symmetry activated carbon electrodes and poly(ε-caprolactone) (PCL)-based polymer electrolytes (PE) have been studied. PEs that consisted of PCL, ammonium thiocyanate, and ethylene carbonate (EC) were prepared by solution casting. In this system, EC was added as a plasticizing solvent to improve the conductivity. The room temperature ionic conductivity of PE increased from 3.94 × 10−7 S cm−1 to 3.8 × 10−5 S cm−1 at 50 wt% EC. In the structural studies carried out by X-ray diffraction, it was found that addition of EC reduces the degree of crystallinity of the entire system. Temperature-dependent conductivity studies showed that Vogel–Tamman–Fulcher model fits very well with regression value close to unity. This observation demonstrates a close coupling between the ionic motion and the polymer segment mobility. The preliminary result of EDLC cell was evaluated by cyclic voltammetry. The single-electrode specific capacitance of EDLC is obtained to be 42.4 F g−1.

Improving the characteristic of electric double layer capacitors using oxidized carbon nanoballoon

Carbon nanomaterials are used as an electrode of electric double layer capacitors (EDLCs). In this research, we used arc black (AcB) and carbon nanoballoon (CNB) as the electrode material. AcB was produced by an arc discharge of graphite in N2 atmosphere, and CNB was formed by a heat treatment of AcB. CNB is graphitic, and the particle shape is hollow. CNB has a higher specific capacitance than AcB at a high scan rate. In order to increase the specific capacitance of EDLC, CNB was oxidized at 625°C in the air. By oxidization, the outer shell of CNB forms wrinkle. We call this material oxidized CNB (Ox-CNB). AcB, CNB, and Ox-CNB were used for the EDLC electrodes and were compared with commercially available activated carbon (AC). Cyclic voltammetry and electrochemical impedance spectroscopy of the EDLC electrodes were measured by an electrochemical measurement system. The specific capacitance of Ox-CNB (29 F/g) was larger than that of AC (16 F/g) at a scan rate of 500mV/s. Furthermore, Ox-CNB had a high conductivity as a result of impedance measurement. Ox-CNB is an excellent electrode material of EDLC when using at a high charge/discharge rate.