Showing papers on "Supercapacitor published in 2007"
TL;DR: Graphene oxide paper is reported, a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets that outperforms many other paper-like materials in stiffness and strength.
Abstract: Free-standing paper-like or foil-like materials are an integral part of our technological society. Their uses include protective layers, chemical filters, components of electrical batteries or supercapacitors, adhesive layers, electronic or optoelectronic components, and molecular storage. Inorganic 'paper-like' materials based on nanoscale components such as exfoliated vermiculite or mica platelets have been intensively studied and commercialized as protective coatings, high-temperature binders, dielectric barriers and gas-impermeable membranes. Carbon-based flexible graphite foils composed of stacked platelets of expanded graphite have long been used in packing and gasketing applications because of their chemical resistivity against most media, superior sealability over a wide temperature range, and impermeability to fluids. The discovery of carbon nanotubes brought about bucky paper, which displays excellent mechanical and electrical properties that make it potentially suitable for fuel cell and structural composite applications. Here we report the preparation and characterization of graphene oxide paper, a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets. This new material outperforms many other paper-like materials in stiffness and strength. Its combination of macroscopic flexibility and stiffness is a result of a unique interlocking-tile arrangement of the nanoscale graphene oxide sheets.
5,117 citations
TL;DR: It appears that nanotubes are a perfect conducting additive and/or support for materials with pseudocapacitance properties, e.g. MnO(2), conducting polymers.
Abstract: The most commonly used electrode materials for electrochemical capacitors are activated carbons, because they are commercially available and cheap, and they can be produced with large specific surface area. However, only the electrochemically available surface area is useful for charging the electrical double layer (EDL). The EDL formation is especially efficient in carbon pores of size below 1 nm because of the lack of space charge and a good attraction of ions along the pore walls. The pore size should ideally match the size of the ions. However, for good dynamic charge propagation, some small mesopores are useful. An asymmetric configuration, where the positive and negative electrodes are constructed from different materials, e.g., activated carbon, transition metal oxide or conducting polymer, is of great interest because of an important extension of the operating voltage. In such a case, the energy as well as power is greatly increased. It appears that nanotubes are a perfect conducting additive and/or support for materials with pseudocapacitance properties, e.g. MnO2, conducting polymers. Substitutional heteroatoms in the carbon network (nitrogen, oxygen) are a promising way to enhance the capacitance. Carbons obtained by one-step pyrolysis of organic precursors rich in heteroatoms (nitrogen and/or oxygen) are very interesting, because they are denser than activated carbons. The application of a novel type of electrolyte with a broad voltage window (ionic liquids) is considered, but the stability of this new generation of electrolyte during long term cycling of capacitors is not yet confirmed.
1,762 citations
TL;DR: This work shows that basic components, the electrode, separator, and electrolyte, can all be integrated into single contiguous nanocomposite units that can serve as building blocks for a variety of thin mechanically flexible energy storage devices.
Abstract: There is strong recent interest in ultrathin, flexible, safe energy storage devices to meet the various design and power needs of modern gadgets. To build such fully flexible and robust electrochemical devices, multiple components with specific electrochemical and interfacial properties need to be integrated into single units. Here we show that these basic components, the electrode, separator, and electrolyte, can all be integrated into single contiguous nanocomposite units that can serve as building blocks for a variety of thin mechanically flexible energy storage devices. Nanoporous cellulose paper embedded with aligned carbon nanotube electrode and electrolyte constitutes the basic unit. The units are used to build various flexible supercapacitor, battery, hybrid, and dual-storage battery-in-supercapacitor devices. The thin freestanding nanocomposite paper devices offer complete mechanical flexibility during operation. The supercapacitors operate with electrolytes including aqueous solvents, room temperature ionic liquids, and bioelectrolytes and over record temperature ranges. These easy-to-assemble integrated nanocomposite energy-storage systems could provide unprecedented design ingenuity for a variety of devices operating over a wide range of temperature and environmental conditions.
1,097 citations
30 Apr 2007
TL;DR: In this paper, the authors focused on the use of lithium-ion batteries and carbon/carbon ultracapacitors as the energy storage technologies most likely to be used in future vehicles.
Abstract: The application of batteries and ultracapacitors in electric energy storage units for battery powered (EV) and charge sustaining and plug-in hybrid-electric (HEV and PHEV) vehicles have been studied in detail. The use of IC engines and hydrogen fuel cells as the primary energy converters for the hybrid vehicles was considered. The study focused on the use of lithium-ion batteries and carbon/carbon ultracapacitors as the energy storage technologies most likely to be used in future vehicles. The key findings of the study are as follows. 1) The energy density and power density characteristics of both battery and ultracapacitor technologies are sufficient for the design of attractive EVs, HEVs, and PHEVs. 2) Charge sustaining, engine powered hybrid-electric vehicles (HEVs) can be designed using either batteries or ultracapacitors with fuel economy improvements of 50% and greater. 3) Plug-in hybrids (PHEVs) can be designed with effective all-electric ranges of 30-60 km using lithium-ion batteries that are relatively small. The effective fuel economy of the PHEVs can be very high (greater than 100 mpg) for long daily driving ranges (80-150 km) resulting in a large fraction (greater than 75%) of the energy to power the vehicle being grid electricity. 4) Mild hybrid-electric vehicles (MHEVs) can be designed using ultracapacitors having an energy storage capacity of 75-150 Wh. The fuel economy improvement with the ultracapacitors is 10%-15% higher than with the same weight of batteries due to the higher efficiency of the ultracapacitors and more efficient engine operation. 5) Hybrid-electric vehicles powered by hydrogen fuel cells can use either batteries or ultracapacitors for energy storage. Simulation results indicate the equivalent fuel economy of the fuel cell powered vehicles is 2-3 times higher than that of a gasoline fueled IC vehicle of the same weight and road load. Compared to an engine-powered HEV, the equivalent fuel economy of the hydrogen fuel cell vehicle would be 1.66-2.0 times higher
762 citations
TL;DR: In this article, a coin cell assembled with microporous activated carbon and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ionic liquid as the electrolyte was cycled for 40,000 cycles without any change of cell resistance.
574 citations
TL;DR: In this paper, the performance of carbon materials in a neutral electrolyte for the first time has been studied, and the structural and surface properties of the prepared carbon materials were studied using scanning electron microscopy and N2 adsorption/desorption studies.
Abstract: Carbon materials were synthesized from banana fibers by treating the fibers with pore-forming substances such as ZnCl2 and KOH with an intention to improve the surface area and their electrochemical performance as electrical double-layer capacitor electrodes. The performance of these materials was studied in a neutral electrolyte for the first time. There has been a substantive increase in the specific surface area of the treated carbon material because of the effective pore generations. The structural and surface properties of the prepared carbon materials were studied using scanning electron microscopy and N2 adsorption/desorption studies. The surface area of the 10% ZnCl2 treated sample was found to be 1097 m2/g. The electrochemical properties of untreated and porogen treated carbons were evaluated by using cyclic voltammetry and galvanostatic charge−discharge studies, and the specific capacitance as high as 74 F/g in 1 M Na2SO4 neutral electrolyte was obtained for 10% ZnCl2 treated carbon as determine...
496 citations
TL;DR: In this article, a novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile and propylene as precursors, and Na-Y zeolite as a scaffold.
Abstract: A novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na-Y zeolite as a scaffold. Liquid-phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas-phase impregnation with propylene, enables pore-size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore-size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area (S BET =1680 m 2 g -1 ), the templated carbon material displays a large gravimetric capacitance (340 F g -1 ) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability-beyond 10000 cycles-and is extremely promising for use in the development of high-energy-density supercapacitors.
488 citations
TL;DR: In this paper, the double-layer capacitance of edge-oriented MoS 2 thin films was investigated using electrochemical impedance spectroscopy, and the real and imaginary part of the capacitance was analyzed as a function of frequency, in order to obtain information on the relaxation time constant and frequency dependence of the supercapacitor properties.
Abstract: Edge-oriented MoS 2 films synthesized by single source precursor chemical vapor deposition exhibit a high density of nanowalls, which can potentially exhibit excellent electrochemical charge storage properties. The electrochemical double-layer capacitance of layered, nanowalled MoS 2 film has been investigated in this work using electrochemical impedance spectroscopy. We show that edge-oriented MoS 2 thin films can behave as a supercapacitor at alternating current frequencies up to 100 Hz. The supercapacitor performance is comparable to that of carbon nanotube array electrodes. In addition to double-layer capacitance, diffusion of the ions into the films at slow scan rates gives rise to faradaic capacitance, which enhances the capacitance significantly. The real and imaginary part of the capacitance of the MoS 2 films was analyzed as a function of frequency, in order to obtain information on the relaxation time constant and frequency dependence of the supercapacitor properties.
396 citations
TL;DR: In this article, a simple electrical model has been established to describe supercapacitor behavior as a function of frequency, voltage and temperature for hybrid vehicle applications, which was derived from experimental data using electrochemical impedance spectroscopy (EIS).
383 citations
TL;DR: In this paper, composites of carbon nanotubes with polyaniline (PANI), polypyrrole (PPY) or poly[3,4-ethylenedioxythiophene] (PEDOT) were prepared via electrochemical co-deposition from solutions containing acid treated CNTs and the corresponding monomer.
347 citations
TL;DR: A ternary composite of CNT/polypyrrole/hydrous MnO 2 is prepared by in situ chemical method and its electrochemical performance is evaluated by using cyclic voltammetry (CV), impedance measurement and constant-current charge/discharge cycling techniques as mentioned in this paper.
TL;DR: In this article, a high specific capacitance was obtained for α-Co(OH) 2 potentiostatically deposited onto a stainless-steel electrode in 0.1 M Co(NO 3 ) 2 electrolyte at −1.0 V vs. Ag/AgCl.
TL;DR: In this article, a composite of polyaniline with multi-walled carbon nanotubes (CNTs) is synthesized by in situ chemical polymerization to improve the cycleability of the supercapacitor.
TL;DR: In this article, different types of commercially available double layer capacitors (EDLCs) were analyzed in accelerated ageing tests by impedance spectroscopy and the characteristic change of the impedance parameters was discussed and an ageing model for EDLCs was developed.
TL;DR: In this paper, a kind of mesoporous carbon spheres (MCS) containing in-frame incorporated nitrogen has been prepared by a facile polymerization-induced colloid aggregation method.
TL;DR: In this paper, the XRD analysis was carried out on nanoporous carbon powder samples to investigate the structural changes (graphitisation) in modified carbon that occurred at activation temperatures T ⩾-1150°C.
TL;DR: In this paper, a thermal vapor decomposition method was used to coat a uniform nanothickness graphitized-carbon on the Li 4 Ti 5 O 12 particle surface, which has a 5 nm thick carbon layer and a electrical conductivity of 2.05 S/cm.
Abstract: Li 4 Ti 5 O 12 is a promising electrode material for high power density lithium-ion batteries and hybrid supercapacitors, but has the drawback of low electrical conductivity. We report a thermal vapor decomposition method to coat a uniform nanothickness graphitized-carbon on the Li 4 Ti 5 O 12 particle surface. The resulting product coated at 800°C has a 5 nm thick carbon layer and a electrical conductivity of 2.05 S/cm, which is much higher than that of raw Li 4 Ti 5 O 12 (<10 -13 S/cm). As a result, it shows much better rate capability when used as a negative electrode for electrochemical supercapacitors. AC impedance measurements reveal that the carbon-coated Li 4 Ti 5 O 12 has smaller charge-transfer resistance due to large effective interface reaction area.
TL;DR: In this paper, polyaniline/multi-walled carbon nanotubes composites were synthesized by an in situ chemical oxidative polymerization method and were the new electrode materials used for supercapacitor.
Abstract: Polyaniline/multi-walled carbon nanotubes composites were synthesized by an in situ chemical oxidative polymerization method and were the new electrode materials used for supercapacitor. The composites were characterized physically by transmission electron microscope and X-ray diffraction. The electrochemical capacitance performance of the composites in neutral solution (NaNO 3 ) was investigated by cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy with a three-electrode system. The polyaniline/multi-walled carbon nanotubes composites electrodes showed much higher specific capacitance (328 F g −1 ), better power characteristics and were more promising for application in capacitor than pure polyaniline electrodes. This may be attributed to the introduction of multi-walled carbon nanotubes. The improvement mechanisms of multi-walled carbon nanotubes in the composites electrode were also discussed in detail.
TL;DR: In this article, the electrochemical capacitance properties of composite films prepared from electrically conducting polypyrrole (PPy) and single wall carbon nanotubes (SWNTs) have been investigated for supercapacitor application.
TL;DR: In this paper, double-layer capacitors based on carbon materials were analyzed and the maximum energy density of an imaginary nano-capacitor assembled from single graphene sheets, separated by electrolyte layers (thickness of nanometers) and a capacitor based on porous carbons.
TL;DR: In this paper, Ni/Co molar ratio was investigated for Ni/CNT composite electrode and the highest specific capacitance was obtained at Ni/co molar ratios = 1:1.
TL;DR: In this article, a mesoporous, electrochemical active material, amorphous MnO2 has been synthesized by an improved reduction reaction and using supramolecular as template, which was characterized physically by thermogravimetric analysis, X-ray diffraction, transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET) surface area measurement, respectively.
Abstract: A kind of novel mesoporous, electrochemical active material, amorphous MnO2 has been synthesized by an improved reduction reaction and using supramolecular as template. The synthesized sample was characterized physically by thermogravimetric analysis, X-ray diffraction, transmission electron microscope (TEM), and Brunauer–Emmett–Teller (BET) surface area measurement, respectively. Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in 2 mol/l KOH aqueous solution electrolyte. The results of BET and TEM analysis indicated that supramolecular template plays an important role in the process of big specific surface area mesoporous material forming. After sintering at 200 °C, the sample still remained an amorphous structure, and its specific capacitance reached 298.7 F/g and presented a very stable capacitance after 500 cycles. In addition, the electrochemical process, such as ion transfer and electrical condition, was also investigated with electrochemical impedance spectroscopy.
TL;DR: In this paper, a poly(3,4-ethylenedioxythiophene)/polypyrrole composite (PEDOT/PPy) was performed on Field Emission Scanning Electron Microscope (SEM).
TL;DR: In this article, the authors measured the capacitance of poly[3,4-ethylene-dioxythiophene] (PEDOT) films and showed that they can be potentiostatically grown to very thick films (up to 0.5mm) that were porous at both micro and nanometer scales.
TL;DR: In this paper, a holistic simulation model that combines electrical and thermal simulation of electrochemical double-layer capacitor (EDLC) modules with an ageing model is presented, which allows analysing self-accelerating degradation effects caused by elevated voltages and temperatures.
TL;DR: In this article, a core-shell structure with PANI layers (50-70 nm) was shown to have a high specific capacitance of 322 F/g with a specific energy density of 22 W h/kg, about 12 times that of MWNTs.
TL;DR: LiMn 2 O 4 and manganese oxide (MnO 2 )/carbon nanotube (CNT) nanocomposite as the positive and negative electrode materials, respectively, and 1 M LiClO 4 in propylene carbonate (PC) as the electrolyte has been developed as mentioned in this paper.
TL;DR: In this paper, an ordered mesoporous carbon with a shorter pore length of 200-300 nm was synthesized through a hard-template method and the electrochemical properties as an electrode material for EDLC were investigated in an alkaline solution.
Abstract: The pores of conventional ordered mesoporous carbons (OMCs) are usually over several micrometers in length, making it difficult for electrolyte access and ion diffusion to the deep pores of the carbon grains when they are used as the electrode of electrochemical double layer capacitors (EDLCs). We have synthesized an ordered mesoporous carbon with a much shorter pore length of 200-300 nm through a hard-template method. The electrochemical properties as an electrode material for EDLC were investigated in an alkaline solution in comparison with the conventional OMC. A maximum capacitance of 14 mu F/cm(2) was obtained for this short pore length OMC (SOMC) in 6 M KOH solution compared with 10 mu F/cm(2) of the conventional OMC. SOMC delivered much better capacity retention than the conventional OMC in lower concentration electrolyte solution. The superior performance of SOMCs was attributed to its having more entrances for electrolyte accessibility and a short pathway for rapid ion diffusion. (c) 2007 The Electrochemical Society.
TL;DR: In this paper, the specific capacitance of RuO2·xH2O and VGCF/RuO2 ·xH 2O nanocomposite electrodes at a scan rate of 10mV−s−1 is 410 and 1017 F−g−1, respectively, and at 1000mV −s− 1 are 258 and 824 F −g −1.
TL;DR: Researchers have combined carbon nanotubes and nanoporous cellulose to make lithium-ion batteries and supercapacitors that are both lighter and more flexible than existing devices.
Abstract: Researchers have combined carbon nanotubes and nanoporous cellulose to make lithium-ion batteries and supercapacitors that are both lighter and more flexible than existing devices.