Showing papers on "Supercapacitor published in 2008"
TL;DR: This work has shown that combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries.
Abstract: Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.
14,213 citations
TL;DR: CMG materials are made from 1-atom thick sheets of carbon, functionalized as needed, and here their performance in an ultracapacitor cell is demonstrated, illustrating the exciting potential for high performance, electrical energy storage devices based on this new class of carbon material.
Abstract: The surface area of a single graphene sheet is 2630 m2/g, substantially higher than values derived from BET surface area measurements of activated carbons used in current electrochemical double layer capacitors. Our group has pioneered a new carbon material that we call chemically modified graphene (CMG). CMG materials are made from 1-atom thick sheets of carbon, functionalized as needed, and here we demonstrate in an ultracapacitor cell their performance. Specific capacitances of 135 and 99 F/g in aqueous and organic electrolytes, respectively, have been measured. In addition, high electrical conductivity gives these materials consistently good performance over a wide range of voltage scan rates. These encouraging results illustrate the exciting potential for high performance, electrical energy storage devices based on this new class of carbon material.
7,505 citations
TL;DR: A general approach to EDLC design leading to the maximum energy density is suggested, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes.
Abstract: The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (∼0.7 nm). The capacitance values of TiC−CDC produced at 500 °C are more than 160 F/g and 85 F/cm3 at 60 °C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm3 in ionic liquids. A significant drop in capacitance has been observed in pores that w...
1,913 citations
TL;DR: In this article, a review of the criteria of an ideal polymer electrolyte for electrochemical device applications has been discussed in brief along with presenting an overall glimpse of the progress made in polymer electrolytes materials designing, their broad classification and the recent advancements made in this branch of materials science.
Abstract: Polymer electrolytes are promising materials for electrochemical device applications, namely, high energy density rechargeable batteries, fuel cells, supercapacitors, electrochromic displays, etc. The area of polymer electrolytes has gone through various developmental stages, i.e. from dry solid polymer electrolyte (SPE) systems to plasticized, gels, rubbery to micro/nano-composite polymer electrolytes. The polymer gel electrolytes, incorporating organic solvents, exhibit room temperature conductivity as high as ~10−3 S cm−1, while dry SPEs still suffer from poor ionic conductivity lower than 10−5 S cm−1. Several approaches have been adopted to enhance the room temperature conductivity in the vicinity of 10−4 S cm−1 as well as to improve the mechanical stability and interfacial activity of SPEs. In this review, the criteria of an ideal polymer electrolyte for electrochemical device applications have been discussed in brief along with presenting an overall glimpse of the progress made in polymer electrolyte materials designing, their broad classification and the recent advancements made in this branch of materials science. The characteristic advantages of employing polymer electrolyte membranes in all-solid-state battery applications have also been discussed.
793 citations
TL;DR: The electrochemically co-deposited composites are the most homogeneous and show an unusual interaction between the polymer and nanotubes, giving rise to a strengthened electron delocalisation and conjugation along the polymer chains as mentioned in this paper.
Abstract: Composites of carbon nanotubes and conducting polymers can be prepared via chemical synthesis, electrochemical deposition on preformed carbon nanotube electrodes, or by electrochemical co-deposition. The composites combine the large pseudocapacitance of the conducting polymers with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the carbon nanotubes. The electrochemically co-deposited composites are the most homogeneous and show an unusual interaction between the polymer and nanotubes, giving rise to a strengthened electron delocalisation and conjugation along the polymer chains. As a result they exhibit excellent electrochemical charge storage properties and fast charge/discharge switching, making them promising electrode materials for high power supercapacitors.
641 citations
TL;DR: This work proposes a heuristic model to replace the commonly used model for an electric double-layer capacitor (EDLC) on the basis of anElectric double-cylinder capacitor for mesopores (2 {50 nm pore size), which becomes an electric wire-in-cylinders capacitor (EWCC) for micropores (< 2 nm port size).
Abstract: The unprecedented anomalous increase in capacitance of nanoporous carbon supercapacitors at pore sizes smaller than 1 nm [Science 2006, 313, 1760.] challenges the long-held presumption that pores smaller than the size of solvated electrolyte ions do not contribute to energy storage. We propose a heuristic model to replace the commonly used model for an electric double-layer capacitor (EDLC) on the basis of an electric double-cylinder capacitor (EDCC) for mesopores (2 {50 nm pore size), which becomes an electric wire-in-cylinder capacitor (EWCC) for micropores (< 2 nm pore size). Our analysis of the available experimental data in the micropore regime is confirmed by 1st principles density functional theory calculations and reveals significant curvature effects for carbon capacitance. The EDCC (and/or EWCC) model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size. The new model not only explains the experimental data, but also offers a practical direction for the optimization of the properties of carbon supercapacitors through experiments.
554 citations
TL;DR: A heuristic theoretical model that takes pore curvature into account as a replacement for the EDLC model, which is based on a traditional parallel-plate capacitor, is proposed and may lend support for the systematic optimization of the properties of carbon supercapacitors through experiments.
Abstract: Supercapacitors, commonly called electric double-layer capacitors (EDLCs), are emerging as a novel type of energy-storage device with the potential to substitute batteries in applications that require high power densities. In response to the latest experimental breakthrough in nanoporous carbon supercapacitors, we propose a heuristic theoretical model that takes pore curvature into account as a replacement for the EDLC model, which is based on a traditional parallel-plate capacitor. When the pore size is in the mesopore regime (2-50 nm), counterions enter mesoporous carbon materials and approach the pore wall to form an electric double-cylinder capacitor (EDCC); in the micropore regime ( 50 nm) at which pores are large enough so that pore curvature is no longer significant, the EDCC model can be reduced naturally to the EDLC model. We present density functional theory calculations and detailed analyses of available experimental data in various pore regimes, which show the significant effects of pore curvature on the supercapacitor properties of nanoporous carbon materials. It is shown that the EDCC/EWCC model is universal for carbon supercapacitors with diverse carbon materials, including activated carbon materials, template carbon materials, and novel carbide-derived carbon materials, and with diverse electrolytes, including organic electrolytes, such as tetraethylammonium tetrafluoroborate (TEABF(4)) and tetraethylammonium methylsulfonate (TEAMS) in acetonitrile, aqueous H(2)SO(4) and KOH electrolytes, and even an ionic liquid electrolyte, such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI). The EDCC/EWCC model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size It may lend support for the systematic optimization of the properties of carbon supercapacitors through experiments. On the basis of the insight obtained from the new model, we also discuss the effects of the kinetic solvation/desolvation process, multimodal (versus unimodal) pore size distribution, and exohedral (versus endohedral) capacitors on the electrochemical properties of supercapacitors.
551 citations
TL;DR: In this article, mesoporous carbon with homogeneous boron dopant was prepared by co-impregnation and carbonization of sucrose and boric acid confined in mesopores of SBA-15 silica template.
Abstract: Mesoporous carbon with homogeneous boron dopant was prepared by co-impregnation and carbonization of sucrose and boric acid confined in mesopores of SBA-15 silica template. Low-level boron doping shows catalytic effect on oxygen chemisorption at edge planes and alters electronic structure of space charge layer of doped mesoporous carbon. These characteristics are responsible for substantial improvement of interfacial capacitance by 1.5-1.6 times higher in boron-doped carbon than that in boron-free carbon with alkaline electrolyte (6 M KOH) and/or acid electrolyte (I M H2SO4). This finding should be very useful for developing new doped carbon electrode materials for supercapacitors.
493 citations
TL;DR: Double-tiered capacitive charge shuttling technique is introduced and applied to a battery system in order to balance the battery-cell voltages and MATLAB simulation shows a substantial improvement in charge transport using the new topology.
Abstract: The automobile industry is progressing toward hybrid, plug-in hybrid, and fully electric vehicles in their future car models. The energy storage unit is one of the most important blocks in the power train of future electric-drive vehicles. Batteries and/or ultracapacitors are the most prominent storage systems utilized so far. Hence, their reliability during the lifetime of the vehicle is of great importance. Charge equalization of series-connected batteries or ultracapacitors is essential due to the capacity imbalances stemming from manufacturing, ensuing driving environment, and operational usage. Double-tiered capacitive charge shuttling technique is introduced and applied to a battery system in order to balance the battery-cell voltages. Parameters in the system are varied, and their effects on the performance of the system are determined. Results are compared to a single-tiered approach. MATLAB simulation shows a substantial improvement in charge transport using the new topology. Experimental results verifying simulation are presented.
475 citations
TL;DR: In this paper, the as-prepared MnO 2 nanowire/CNT composite paper (MNCCP) was used as a flexible electrode for electrochemical supercapacitors.
423 citations
TL;DR: In this article, an asymmetric supercapacitor is constructed using hierarchical porous electrode materials of nickel oxide and carbon with the aim to facilitate ion transport, and the capacitance, energy density and power density of the asymmetric SuperCapACitor can be improved by elevating the supercapACitor voltage, and cycling stability decays at high voltage, but the columbic efficiency stays close to 100%.
TL;DR: In this article, a two-electrode cell with a specific capacitance as high as 368 F g−1 was observed, with rectangular cyclic voltammetry curves and stable performance over 10,000 cycles at a cell potential of 1.2 V and current load of 5 A G−1.
TL;DR: In this article, the specific capacitance of supercapacitor electrodes based on activated or porous carbon material, already used in commercial products, was investigated for the investigated experimental super-capacitors.
Abstract: Supercapacitors or electrochemical double-layer capacitors (EDLCs) have capacitance value up to thousands of Farads at the same size as for conventional capacitors. At such capacitance value EDLCs are of interest for electrical energy storage. The specific energy of commercial supercapacitors is limited to 5–6 Wh/kg, whereas for batteries the lower limit is 35–40 Wh/kg. Nonetheless other advantages of supercapacitors make them already useful in conjunction with batteries in power applications. Main results related to supercapacitor performance improvement available in literature are presented. Research efforts have been done to increase the specific capacitance of supercapacitor electrodes based on activated or porous carbon material, already used in commercial products. By using available activated carbon with a specific surface area reaching 3000 m 2 /g, specific capacitance values up to 300 F/g have been reported for the investigated experimental supercapacitors. Nonetheless, further optimization of activated carbon properties and its use in supercapacitor electrodes is required for 300 F/g and higher value. By addition of metallic oxides or conductive polymers in the activated carbon used for EDLC electrodes, specific capacitance enhancement takes place. Carbon nanotubes used in experimental supercapacitor electrodes resulted in specific capacitance as high as 180 F/g but higher electrical conductivity and consequently, specific power than in the case of activated carbon was observed. Addition of a small percent of carbon nanotubes in the activated carbon for electrodes results in performance improvement (higher capacitance and conductivity). Nevertheless, high cost of carbon nanotubes prevents their use in commercial products.
TL;DR: Various topologies of dc/dc converters are presented with effective methodologies of electric power management in the hybrid vehicle to find a better compromise between the dimensions of the embarked devices, the share energy efficiency, the dynamics of the supply, and the electric power storage.
Abstract: In this paper, the authors propose the supercapacitor integration strategy in a hybrid series vehicle. The designed vehicle is an experimental test bench developed at the laboratory of electrical engineering and systems (L2ES) in collaboration with the research in electrical engineering and electronics center of Belfort (CREEBEL). This test bench currently has two diesel motors (each connected to one alternator) and lead-acid batteries with a voltage rating of 540 V and a fluctuation margin between +12% and -20% of the rated voltage. The alternators are connected to the dc link by rectifiers. An original strategy of the supercapacitor integration in this vehicle with their control is presented to find a better compromise between the dimensions of the embarked devices, the share energy efficiency, the dynamics of the supply, and the electric power storage. The supercapacitor packs are made up of two modules of 108 cells each and present a maximum voltage of 270 V. The main objective is to provide a peak power of 216 kW over 20 s from supercapacitors to the dc link. Various topologies of dc/dc converters are presented with effective methodologies of electric power management in the hybrid vehicle.
TL;DR: In this article, a charge storage mechanism in crystallized Mg-doped sodium birnessite-type manganese dioxide used as active supercapacitor electrode material that involves the intercalation/deintercalation of cations between the sheets during electrochemical reduction/oxidation, respectively.
Abstract: This paper provides new insight on the charge storage mechanism in crystallized Mg-doped sodium birnessite-type manganese dioxide used as active supercapacitor electrode material that involves the intercalation/deintercalation of cations between the sheets during electrochemical reduction/oxidation, respectively. An increase of the interlayer spacing from 0.710 to 0.720 nm upon electrochemical oxidation in the presence of Na+ cations in the electrolyte is associated with the deintercalation of Na+ and the intercalation of H2O between the layers. A progressive crystallinity loss of the material is also observed upon potential cycling between the oxidized and reduced states. Despite these structural changes, the birnessite electrode exhibits a stable capacitance of 145 F/g over 1100 cycles.
TL;DR: In this article, the authors explored a room temperature, simple and low cost chemical route for the cobalt oxide film onto copper substrate from cobalt chloride (CoCl 2 ·6H 2 O) precursor and characterization for its structural and electrochemical properties for supercapacitor application.
30 Sep 2008
TL;DR: In this article, the role of the supercapacitor in a PV energy control unit (ECU) is investigated by using Matlab/Simulink models, where the ECU monitors and optimizes the power flow from the PV to the battery-supercapacitors hybrid and the load.
Abstract: Most of the stand-alone photovoltaic (PV) systems require an energy storage buffer to supply continuous energy to the load when there is inadequate solar irradiation. Typically, Valve Regulated Lead Acid (VRLA) batteries are utilized for this application. However, supplying a large burst of current, such as motor startup, from the battery degrades battery plates, resulting in destruction of the battery. An alterative way of supplying large bursts of current is to combine VRLA batteries and supercapacitors to form a hybrid storage system, where the battery can supply continuous energy and the supercapacitor can supply the instant power to the load. In this paper, the role of the supercapacitor in a PV energy control unit (ECU) is investigated by using Matlab/Simulink models. The ECU monitors and optimizes the power flow from the PV to the battery-supercapacitor hybrid and the load. Three different load conditions are studied, including a peak current load, pulsating current load and a constant current load. The simulation results show that the hybrid storage system can achieve higher specific power than the battery storage system.
TL;DR: In this article, a corn grains-based activated carbons (CG-ACs) were prepared and their use as electrodes in the electrical double layer capacitor (EDLC) performed successfully.
TL;DR: In this article, a system integration and power flow management algorithm for a four-wheel-driven series hybrid electric vehicle (HEV) having multiple power sources composed of a diesel-engine-based generator, lead acid battery bank, and super-capacitor bank is presented.
Abstract: In this paper, system integration and power-flow management algorithms for a four-wheel-driven series hybrid electric vehicle (HEV) having multiple power sources composed of a diesel-engine-based generator, lead acid battery bank, and supercapacitor bank are presented The super-capacitor is utilized as a short-term energy storage device to meet the dynamic performance of the vehicle, while the battery is utilized as a mid-term energy storage for the electric vehicle (EV) mode operation due to its higher energy density The generator based on an interior permanent magnet machine (IPMM), run by a diesel engine, provides the average power for the normal operation of the vehicle Thanks to the proposed power-flow management algorithm, each of the energy sources is controlled appropriately and also the dynamic performance of the vehicle has been improved The proposed power-flow management algorithm has been experimentally verified with a full-scale prototype vehicle
TL;DR: In this paper, a well-aligned cone-shaped polypyrrole (WACNP) was successfully grown on Au substrate by using a simple, one-step, reliable, and template-free anodic deposition method.
Abstract: A new well-aligned cone-shaped nanostructure of polypyrrole (WACNP) has been successfully grown on Au substrate by using a simple, one-step, reliable, and template-free anodic deposition method. The formation mechanism of WACNP is proposed, in which the hydrogen bonding introduced from phosphate buffer solution (PBS) promotes the formation of a well-aligned nanostructure of polypyrrole (PPy), while the steric hindrance effect arisen from high concentration of pyrrole (Py) boosts its vertical alignment and further forms a cone-shaped nanostructure. The 3D, arrayed, nanotubular architecture coated with an ultrathin layer of RuO2 by the magnetron sputtering deposition method was tailored to construct a supercapacitor. The unique structure and design not only reduces the diffusion resistance of electrolytes in the electrode material but also enhances its electrochemical performance. The modification of RuO2 on WACNP results in a capacitance higher than that of WACNP by three times. The specific capacitance of...
TL;DR: In this article, the performance of asymmetric double-layer carbon supercapacitors (AEDLCs) and carbon/poly(3-methylthiophene) hybrid supercapACitors operating with different pyrrolidinium-based ionic liquids (ILs) was compared.
TL;DR: Impedance spectroscopy shows that nanotubes have much lower diffusional resistance to charging ions than solid nanowires shielded by an alumina template, providing supporting information for the high charging/discharging efficiency of nanotubular structures.
Abstract: We report the fast charging/discharging capability of poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes during the redox process and their potential application to a high-powered supercapacitor. PEDOT nanotubes were electrochemically synthesized in a porous alumina membrane, and their structures were characterized using electron microscopes. Cyclic voltammetry was used to characterize the specific capacitance of the PEDOT nanotubes at various scan rates. A type I supercapacitor (two symmetric electrodes) based on PEDOT nanotube electrodes was fabricated, and its energy density and power density were evaluated by galvanostatic charge/discharge cycles at various current densities. We show that the PEDOT-nanotube-based supercapacitor can achieve a high power density of 25?kW?kg?1 while maintaining 80% energy density (5.6?W?h?kg?1). This high power capability is attributed to the fast charge/discharge of nanotubular structures: hollow nanotubes allow counter-ions to readily penetrate into the polymer and access their internal surfaces, while the thin wall provides a short diffusion distance to facilitate the ion transport. Impedance spectroscopy shows that nanotubes have much lower diffusional resistance to charging ions than solid nanowires shielded by an alumina template, providing supporting information for the high charging/discharging efficiency of nanotubular structures.
TL;DR: In this paper, the performance of activated carbon (AC) in 0.5-mol/l Li2SO4, NaSO4 and KSO4 aqueous electrolytes was investigated and the cyclic voltammetric results at different scan rates showed that the rate behaviors of AC in the three electrolytes improved in the order of Li 2SO4 Â Â Na2SO 4 Â > KSO 4, which is the main factor influencing the maximum output power.
TL;DR: In this article, a hybrid supercapacitor based on MnO 2 positive electrode and FeOOH negative electrode in Li 2 SO 4 electrolyte solution was designed, which exhibited a good cycling performance and kept 85% of initial capacity over 2000 cycles.
TL;DR: In this paper, the authors used activated carbon fibers (ACFs) with high surface area and highly mesoporous structure for electrochemical double layer capacitors (EDLCs) for high performance EDLCs.
TL;DR: In this paper, the role of amount of hydrates on the electrolyte cations diffusion was investigated with a nanostructured hydrated manganese dioxide, as a supercapacitor electrode.
TL;DR: It is demonstrated that ultra-high power electrochemical double layer capacitors can be engineered using these hybrid nanowires, resulting in very high power densities.
15 Jun 2008
TL;DR: In this article, a flow-battery supercapacitor hybrid energy storage system is proposed to absorb high frequency power surges in a wind farm, which takes advantage of the two complementary technologies to provide large power and energy capacities.
Abstract: An energy storage system (ESS) in a wind farm is required to be able to absorb wind power surges during gusts, and have sufficient energy storage capacity to level wind fluctuations lasting for longer periods. ESS using a single technology, such as batteries, or supercapacitors, will have difficulties providing both large power and energy capacities. This paper proposes a flow-battery supercapacitor hybrid ESS, which takes advantage of the two complementary technologies to provide large power and energy capacities. The flow-battery is directly coupled to the WTG dc bus while the supercapacitor has a dc/dc IGBT converter interface. The dc bus voltage varies within a certain limit determined by the variable battery terminal voltage. With the supercapacitor absorbing high frequency power surges, the battery power rating, degree of discharge, and power losses are all reduced. Therefore the battery in the hybrid ESS has low cost and high longevity; and the system overall efficiency is improved.
TL;DR: In this paper, the ageing process of double-layer capacitors was investigated using infrared, Raman, and photoelectron spectroscopy, and nitrogen porosimetry, and it was shown that oxygen, hydrogen, nitrogen, and fluorine, which originate from trace water and from the electrolyte, can covalently attach to the electrodes and form various chemical groups.
TL;DR: In this paper, a poly(3,4-ethylenedioxythiophene) (PEDOT) was successfully electropolymerized using a purified 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as both the growth medium and the supporting electrolyte.