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Aging processes occurring in electrical double layer capacitors greatly influence the lifetime of these energy storage devices and an increasing attention has been directed toward their understanding. While most studies approach this topic based on the overall electrochemical performance of the cell (such as enhanced resistance) or the materials degradation, addressing its failure causes at the electrolyte level is of great importance. Doing so, more precise strategies to improve the lifetime and performance can be developed for a wide range of applications. This article provides an overview of the current state of separation tools regarding gas chromatography and detection tools in various combinations with mass spectrometry. The aim of this work is to present the present state of the current knowledge on aging processes, with a focus on gas chromatography and mass spectrometry. Then, an outlook onto the challenges as well as ideas of combining methods is given. Here, the work offers a judgement into future challenges. [ABSTRACT FROM AUTHOR]

Nickel oxide nanoparticles (NiO NPs) are synthesized using olive leaf extract (OLE), which contains a range of polyphenols. These polyphenols serve as both reducing and capping agents, stabilizing the nanoparticles. Aqueous nickel acetate is employed as a precursor. Simultaneously, exfoliated graphene (EG) is obtained via electrochemical exfoliation of graphite in aqueous solutions. These materials were employed as electroactive components in supercapacitor applications. Characterization of NiO and EG involved thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and scanning/transmission electron microscopy (SEM/TEM), alongside Brunauer−Emmett−Teller (BET) analysis, confirming the formation of crystalline NiO NPs with a cubic phase and Fm-3m space group. Micrographs revealed nanoscale dimensions for both NiO and EG with a substantial surface area, as verified by BET analysis. Symmetric (NiO/NiO, EG/EG) and asymmetric (NiO/EG) supercapacitors were fabricated using the doctor blade method. Electrode evaluation, employing field-emission scanning electron microscopy FESEM, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), demonstrated promising morphological and electrochemical characteristics. At low scan rates, both symmetric and asymmetric supercapacitors exhibited a notable gravimetric capacitance (221, 111, and 162 F g–1 at 1 mV s–1). Additionally, they revealed higher power density (173, 137, and 161 W kg–1 at 10 mV s–1), showcasing pseudocapacitive and electric double-layer capacitor (EDLC) behavior for NiO NPs and EG, respectively. This research significantly contributes valuable insights by presenting a sustainable synthesis route for NiO NPs, developing high-performance supercapacitor electrodes, and achieving a comprehensive understanding of the electrochemical behavior of NiO NPs and EG. [ABSTRACT FROM AUTHOR]

An ongoing challenge in the field of supercapacitors revolves around comprehending their failure mechanisms. The aging processes occurring at the electrode/electrolyte interphase of these devices are complex. Thus far, much attention has been directed toward examining the aging of electrodes, while fewer studies have been dedicated to the electrolyte's aging. This study aims to address this point and to gain a deeper understanding of the importance of individual decomposition products on the overall decomposition of the electrolytic solution of electric double‐layer capacitors. Therefore, the decomposition of the state‐of‐the‐art electrolyte 1 m solution of tetraethylammonium‐tetrafluoroborate in acetonitrile and that of the same electrolyte doped with compounds known to form during its aging, such as acetamide, 2,4,6‐trimethyl‐1,3,5‐triazine, and triethylamine has been investigated post‐mortem. The results of this study show that GC‐MS is a useful technique to interpret and understand the degradation processes taking place in the electrolytes of supercapacitors. [ABSTRACT FROM AUTHOR]

The investigated starch biopolymer membrane was found to be a sustainable alternative to currently reported and used separators due to its properties, which were evaluated using physicochemical characterization. The molecular dynamics of the biomembrane were analyzed using low-field nuclear magnetic resonance (LF NMR) as well as Raman and infrared spectroscopy, which proved that the chemical composition of the obtained membrane did not degrade during microwave-assisted polymerization. Easily and cheaply prepared through microwave-assisted polymerization, the starch membrane was successfully used as a biodegradable membrane separating the positive and negative electrodes in electric double-layer capacitors (EDLCs). The obtained results for the electrochemical characterization via cyclic voltammetry (CV), galvanostatic charge with potential limitation (GCPL), and electrochemical impedance spectroscopy (EIS) show a capacitance of 30 F g−1 and a resistance of 2 Ohms; moreover, the longevity of the EDLC during electrochemical floating exceeded more than 200 h or a cyclic ability of 50,000 cycles. Furthermore, due to the flexibility of the membrane, it can be easily used in novel, flexible energy storage systems. This proves that this novel biomembrane can be a significant step toward ecologically friendly energy storage devices and could be considered a cheaper alternative to currently used materials, which cannot easily biodegrade over time in comparison to biopolymers. [ABSTRACT FROM AUTHOR]

The presented work discusses in detail the preparation of a cheap and environmentally friendly biopolymer membrane from isinglass and its physicochemical characterisation. One of the possible uses of the obtained membrane can be as a separator between electrodes in novel green electrochemical devices as in, for example, electric double-layer capacitors (EDLCs). The functionality of the mentioned membrane was investigated and demonstrated by classical electrochemical techniques such as cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), and electrochemical impedance spectroscopy (EIS). The obtained values of capacitance (approximately 30 F g−1) and resistance (approximately. 3 Ohms), as well as the longevity of the EDLC during electrochemical floating at a voltage of 1.6 V (more than 200 h), show that the proposed biopolymer membrane could be an interesting alternative among the more environmentally friendly energy storage devices, while additionally it could be more economically justified. [ABSTRACT FROM AUTHOR]

An ionic liquid (IL) 1-ethyl, 2-methyl imidazolium thiocyanate incorporated biopolymer system is reported in this communication for applications in dual energy devices, i.e., electric double-layer capacitors (EDLCs) and dye-sensitized solar cells (DSSCs). The solution caste method has been used to synthesize ionic-liquid-incorporated biopolymer electrolyte films. The IL mixed biopolymer electrolytes achieve high ionic conductivity up to the order of 10−3 S/cm with good thermal stability above 250 °C. Electrical, structural, and optical studies of these IL-doped biopolymer electrolyte films are presented in detail. The performance of EDLCs was evaluated using low-frequency electrochemical impedance spectroscopy, cyclic voltammetry, and constant current charge–discharge, while that of DSSCs was assessed using J–V characteristics. The EDLC cells exhibited a high specific capacitance of 200 F/gram, while DSSCs delivered 1.53% efficiency under sun conditions. [ABSTRACT FROM AUTHOR]

This study used a physical activation method to prepare asphalt-pitch-derived activated carbon (Pitch AC) for an electric double-layer capacitor (EDLC) electrode. X-ray diffraction analysis and Raman spectroscopy were used to estimate the change in the crystal structure of Pitch AC with activation time. In addition, the textural properties of Pitch AC were studied by Brunauer-Emmett-Teller (BET), Dubinin-Radushkevich (DR) and non-localized density functional theory (NLDFT) equations with N2/77K isotherm adsorption-desorption curves. The electrochemical performance of the Pitch AC was analyzed using a coin-type EDLC with 1 M SBPBF4/PC via galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The specific surface area and total pore volume were 990–2040 m2/g and 0.42–1.51 cm3/g, respectively. The pore characteristics of the Pitch AC varied according to the activation time and changed from a microporous structure to a micro-mesoporous structure as the activation time increased. The electrochemical performance analysis also found that the specific capacity was increased from 43.6 F/g to 84.5 F/g at 0.1 A/g as activation time increased. In particular, Pitch AC-9 exhibited the best electrochemical performance (rectangular CV curve, reversible GCD, lowest ion charge transfer resistance and Warburg impedance). In addition, Pitch AC-9 was confirmed to have a specific capacitance similar to commercial activated carbon for EDLC (YP-50F). Therefore, it was considered that Pitch AC could replace commercial activated carbon for EDLC because it has excellent pore characteristics and electrochemical performance despite being manufactured through a very low-cost precursor and a simple process (physical activation method). [ABSTRACT FROM AUTHOR]

A supercapacitor is a type of electrical component that has larger capacitance, due to asymmetric behavior with better power density, and lower ESR (effective series resistance) than conventional energy-storage components. Supercapacitors can be used with battery technology to create an effective energy storage system due to their qualities and precise characterization. Studies have shown that the use of quantum dots as electrodes in supercapacitors can significantly increase their effectiveness. In this research article, we have used a Drude model based on free electrons (asymmetric nature) to describe the supercapacitor's discharging characteristics. Commercially available Nippon DLA and Green-cap supercapacitors were used to verify the Drude model by discharging them through a constant current source using a simple current mirror circuit. The parameters of both the fractional-order models and our suggested method were estimated using the least-squares regression fitting approach. An intriguing finding from the Drude model is the current-dependent behavior of the leakage-parallel resistance in the constant current discharge process. Instead of using the traditional exponential rule, supercapacitors discharge according to a power law. This work reflects the strong symmetry of different aspects of designing a hybrid supercapacitor with high efficiency and reliability. [ABSTRACT FROM AUTHOR]

In this paper, a facile and rapid aqueous-based electrochemical technique was used for the phase conversion of Ni into Ni(OH)2 thin film. The Ni(OH)2 thin film was directly converted and coated onto the network surface of Ni foam (NF) via the self-hydroxylation process under alkaline conditions using a simple cyclic voltammetry (CV) strategy. The as-formed and coated Ni(OH)2 thin film on the NF was used as the catalyst layer for the direct growth of carbon nanotubes (CNTs). The self-converted Ni(OH)2 thin film is a good catalytic layer for the growth of CNTs due to the fact that the OH− of the Ni(OH)2 can be reduced to H2O to promote the growth of CNTs during the CVD process, and therefore enabling the dense and uniform CNTs growth on the NF substrate. This binder-free CNTs/NF electrode displayed outstanding behavior as an electric double-layer capacitor (EDLC) due to the large surface area of the CNTs, showing excellent specific capacitance values of 737.4 mF cm−2 in the three-electrode configuration and 319.1 mF cm−2 in the two-electrode configuration, at the current density of 1 mA cm−2 in a 6 M KOH electrolyte. The CNTs/NF electrode also displayed good cycling stability, with a capacitance retention of 96.41% after 10,000 cycles, and this the excellent cycling performance can be attributed to the stable structure of the direct growth of CNTs with a strong attachment to the NF current collector, ensuring a good mechanical and electrical connection between the NF collector and the CNTs. [ABSTRACT FROM AUTHOR]

Carbon soot derived from Sinapis alba (yellow mustard oil), referred to as mustard oil carbon soot (MoCS), shows particles with a distinct layered (3D onion-like) spherical structure and demonstrates competitive electrochemical characteristics to graphene, carbon nanotubes and other carbonaceous materials. MoCS has the potential to be a competent material for fabricating electrodes for energy storage devices. In synthesis, effortless burning of Sinapis alba (yellow mustard) oil with braided cellulose fibers (cotton wick), utilizing the flame synthesis method, produces a nanopowder containing the layered structure of spherical soot particles. X-ray diffraction studies reveal enhanced spacing between the layered graphitic planes from 3.50 Å to 3.75 Å due to activation of MoCS. The electric double-layer capacitor (EDLC) utilizing the activated MoCS electrode displays capacitance of 57.78 F g−1 along with a good energy density of 2 Wh kg−1 and power density of 278 W kg−1. The easy process involved in the preparation and the attractive electrochemical properties prove the worth of MoCS as an electrode material for EDLCs and its availability for large-scale production. [ABSTRACT FROM AUTHOR]

This paper investigates the characterization of an electric double-layer capacitor (EDLC). In this study, the 300 F and 400 F EDLC supercapacitors are connected in a circuit in a laboratory experiment to produce their charge/discharge profiles at a constant current. The acquired charge/discharge profiles were used to determine the mathematical parameters of the EDLCs using the "Faranda model", or "two-branch model", of the EDLC. The parameters extracted from the equivalent circuit model were then used as inputs to a designed Python/MATLAB/Simulink (PMS)-hybrid model of an EDLC. This was simulated to obtain charge/discharge profiles. The resulting experimental- and simulated-charge/discharge profiles of the EDLCs were compared with each other, by superimposing their profiles to determine the accuracy of the PMS model. The PMS model was found to be very accurate. The innovation of this work lies in modeling a supercapacitor, mostly in the Python programming language in combination with a MATLAB/Simulink model. The experimental-charge/discharge profiles obtained were used to calculate the equivalent circuit resistance (ESR) and the capacitance of the EDLCs, which were compared with the existing datasheet values of the EDLCs. The characterization of the EDLC supercapacitor was done to derive a flexible PMS model of the EDLC, which can be used in a microgrid hybrid energy-storage system (HESS) to show the potential of the EDLC in improving battery lifespan. [ABSTRACT FROM AUTHOR]

Electrical storage devices as lithium-ion battery (LIB) and electric double layer capacitor (EDLC) have greatly contributed to downsizing and weight reduction of electronics. In the future, these devices are expected to be used for powertrains and electricity storage applications. With the increasing requirement to high energy density of electrical storage devices, safety and power density of the devices are becoming more important, and the boundaries between capacitors and rechargeable batteries are disappearing in both of technologies and applications. In this article, Pseudo-capacitor, hybrid capacitor and bipolar structure by using PANI electrodes that have a great impact on capacitor and battery technologies have been studied. [ABSTRACT FROM AUTHOR]

Most of commercialized electrical double layer capacitors (EDLCs) with liquid electrolyte are bulky, non-flexible and unsafe which require solid polymer electrolyte (SPE) as the replacement. Herein, SPE containing tetraglyme as the ionic conductivity booster was prepared in which polyvinyl alcohol (PVA), magnesium trifluoromethane sulfonate (Mg (Tf)2) and tetraglyme (TEDGME) have been utilized as the host polymer, salt and additive, respectively. After the addition of TEDGME, the SPE exhibited a significant boost in ionic conductivity from 1.43 × 10−9 to 3.10 × 10−5 S cm−1. This is attributed to the presence of multiple ether oxygen atom functional group from TEDGME that provides more charge carriers. Fourier transform infrared spectroscopy authenticates the formation of complex within the SPE systems which indicates the formation of good interaction between the host polymer and the salts. X-ray diffraction analysis demonstrates the reduction in crystallinity of the SPE after the addition of TEDGME which is beneficial for the ion diffusion. The maximum specific capacitance achieved by the EDLC employing the SPE incorporated with TEDGME is 6.34 F/g at 0.04 A/g, with the rate capability of 74.1%. [ABSTRACT FROM AUTHOR]

Abstract In this work, a lithium ion capacitor (LIC) based on carbon electrodes prepared from furfuryl alcohol-derived polymers is presented. While furfuryl alcohol is not a new carbon precursor, it has been evaluated in the past mainly for negative electrodes with Li-ion insertion. Here we describe both an activated carbon (AC) and a hard carbon (HC) made from the same furfuryl alcohol-derived polymers, for both electrodes of the LIC. The polymerization technique used to make carbon from the furfuryl alcohol precursor is different from all the methods described earlier, and is flexible enough to make soft, high surface area AC, as well as a denser, low surface area HC. The HC and the HC-based negative electrode used in this study are targeted at a high-energy and high-power LIC application by specifically reducing the carbon particle size to sub-micrometric levels, using a HC with a specific surface area of ∼300 m2 g−1 and keeping the electrode mass loading to <2 mg cm−2. The HC delivers a stable capacity of ∼400 mAh g−1 vs. Li+/Li at C/10, with excellent capacity retention of 50% at 10C (>200 mAh g−1) and 25% at 50C (∼100 mAh g−1). The AC used for the capacitor-type positive electrode was activated to a specific surface area of ∼1670 m2 g−1. For comparison purposes, a symmetric electric double layer capacitor (EDLC) using the same AC, in a 1.5 M Et 4 NBF 4 (acetonitrile) electrolyte, was also fabricated. Overall, the LIC showed considerably higher energy density over its EDLC counterpart, delivering a maximum energy density (based on the total electrode active mass weight) of 150 Wh kg−1 AM at a power density of 150 W kg−1 AM , with a 66% retention of the initial energy at the highly demanding 10,000 W kg−1 AM power peak point. Additionally, long cycle life was measured, with 83% capacitance retention after 10,000 cycles. Graphical abstract Image 1 Highlights • Synthesis of Hard Carbon and Activated Carbon from furfuryl alcohol. • Development of ultrafast performing Hard Carbon (<100 mAh g−1 at 50C). • Fabrication of Lithium Ion Capacitor with mass balance 1:2 (HC:AC). • Fabrication of Lithium Ion Capacitor exceeding 100 Wh Kg−1 AM at 10 KW Kg−1 AM. • Lithium Ion Capacitor with 83% capacity retention after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Highlights • Electrochemical capacitors provide highly-reversible energy storage. • Specialized meetings held to advance electrochemical capacitor technology. • Perspective view presented on electrochemical capacitor technology. Abstract Electrochemical capacitors, a type of capacitor also known by the product names Supercapacitor or Ultracapacitor, can provide short-term energy storage in a wide range of applications. These capacitors are powerful, have extremely high cycle life, store energy efficiently, and operate with unexcelled reliability. This article discusses highly-reversible energy storage, presents electrochemical capacitor basics, and identifies several resources that may be useful to a researcher who wishes to participate in this technology arena. A perspective on the future of electrochemical capacitor technology is offered. [ABSTRACT FROM AUTHOR]

Abstract Development of biomass based activated carbon materials for electrical double layer capacitor (EDLC) usage has gained attention as a result of requesting efficient and low cost energy storage device production. In this study, pine cone based activated carbons were produced with a combined chemical and physical activation route. ZnCl 2 and CO 2 were used for chemical and physical activation of the material, respectively. Activation parameters are adjusted to give different chemical and textural characteristics. FTIR and Raman spectroscopies were used for functional group identification and structural order characterization, respectively. As a result, efficient active materials for EDLC usage were obtained, with as high as 87 F/g specific capacitance in organic electrolytes. Highlights • Activated carbons were produced using combined chemical and physical activation. • Impregnation ratio was the most important parameter regarding the porosity. • Heat treatment temperature altered the structural evolution of activated carbon. • Resistivity of the active material has a pronounced effect on electrochemical behavior. • CO 2 treated activated carbons showed as high as 87 F/g specific capacitance. [ABSTRACT FROM AUTHOR]

A room temperature ionic liquid is immobilized on the surfaces of layered double hydroxides to form a solvent-free fluid via a silylation reaction. A series of solid polymer electrolyte membranes based on quaternized polysulfone and the solvent-free fluid are fabricated by solution casting method, which are tough and flexible and display moderate KOH aqueous solution uptakes. A symmetric electrical double-layer capacitor is assembled by using an optimized quaternized polysulfone-based solid polymer electrolyte membrane with KOH solution and two activated carbon electrodes. The single carbon electrode delivers a specific capacitance of 114.0 F g −1 at a current density of 1 A g −1 and outstanding cycling stability, indicating that this novel solid polymer electrolyte membrane may be appropriate for electrical double-layer capacitors. [ABSTRACT FROM AUTHOR]

Carbonization and post-activation of polysaccharides (utilized as food residue) created new bio-nanocarbons for the electrode of electric double layer capacitors (EDLC). Large specific capacitance (46.1 F/g, 26.4 F/cm 3 ) and high rate performance was confirmed under optimized conditions of carbonization temperature (600 °C) and supplied amount of sodium hydroxide in NaOH-activation process (250 wt %). The capacitance and rate performance were larger than the reported values, 42.9 F/g, 19.7 F/cm 3 of currently used activated carbon MSP-20. The feature that NaOH is usable as the activation agent, instead of KOH, is advantageous for reducing the cost of EDLC. [ABSTRACT FROM AUTHOR]

The operation of electrochemical double layer capacitors at high currents and viscosities and at low temperatures is difficult. Under these conditions, ion transport is limited, and some of the electrode area is unavailable for adsorption, which results in a low capacitance. Increasing the temperature helps to increase the ionic movement, leading to enhanced adsorption and increased capacitance. In contrast, ion desorption (self-discharge) surpasses the capacitance improvement when ions gain a high amount of energy with increasing temperature. For example, temperatures as high as 70 °C cause a very high rate of ionic desorption in acetonitrile solutions in which the individual properties of the two electrolytes—tetraethylammonium tetrafluoroborate (TEA BF 4 ) and ethylmethylimidazolium tetrafluoroborate (EMI BF 4 )—are not distinguishable. The capacitance improvement and self-discharge are balanced, resulting in a capacitance peak at mid-range temperatures, i.e., 35–45 °C, in the more viscous electrolyte, i.e., TEA BF 4 . The less viscous electrolyte, i.e., EMI BF 4 has a wider capacitance peak from 25 to 45 °C and higher capacitance than that of TEA BF 4 . Because the maximum power is obtained in the mid-temperature range (35–45 °C), it is necessary to control the viscosity and temperature to obtain the maximum power in a given device. [ABSTRACT FROM AUTHOR]

In this work, we are presenting both lithium and sodium ion capacitors (LIC and NIC) entirely based on electrodes designed from recycled olive pit bio-waste derived carbon materials. On the one hand, olive pits were pyrolized to obtain a low specific surface area semigraphitic hard carbon to be used as the ion intercalation (battery-type) negative electrode. On the other hand, the same hard carbon was chemically activated with KOH to obtain a high specific surface area activated carbon that was further used as the ion-adsorption (capacitor-type) positive electrode. Both electrodes were custom-made to be assembled in a hybrid cell to either build a LIC or NIC in the corresponding Li- and Na-based electrolytes. For comparison purposes, a symmetric EDLC supercapacitor cell using the same activated carbon in 1.5 M Et 4 NBF 4 /acetonitrile electrolyte was also built. Both LIC and NIC systems demonstrate remarkable energy and power density enhancement over its EDLC counterpart while showing good cycle life. This breakthrough offers the possibility to easily fabricate versatile hybrid ion capacitors, covering a wide variety of applications where different requirements are demanded. [ABSTRACT FROM AUTHOR]

In this work, the impact of temperature and voltage on aging of electrical double-layer capacitors (EDLCs) made with a model silica-templated carbon has been investigated by using an in-situ simultaneous thermal analysis (STA) cell. We show that the use of such a cell allows the electrochemical performance of EDLCs and the heat generation occurring within these devices to be simultaneously measured. In EDLCs containing adiponitrile (ADN) based electrolytes, the combination of high voltage (≥ 3.5 V) and elevated temperature of 60 °C leads not only to a fast decrease in capacitance retention, but also to important degradation processes causing a significant increase of heat flow within the system. For a temperature of 60 °C, the heat flow at 3.75 V is about 6.5 times higher than in an EDLC operating at 3.0 V. The correlation of the heat flow and electrochemical properties provides a helpful insight into the stability of EDLCs, and thus the in-situ STA cell appears as an interesting and novel tool for the investigation of these systems. [ABSTRACT FROM AUTHOR]

In this manuscript are reported the synthesis and physicochemical characterization of low viscosity pyrrolidinium dicyanamide (DCA − ) ionic liquids (ILs). Due to their high ionic conductivity, these fluorine-free, molecular solvent-free ILs are excellent candidates to be employed as electrolytes in electrochemical double layer capacitors (EDLCs). Tests of lab-scale prototypes reported herein show that DCA − -based EDLCs display high power at room temperature as well as high cycling stability. [ABSTRACT FROM AUTHOR]

Lithium oxalyldifluoroborate (LiODFB) has several unique characteristics, such as high ionic conductivity over a wide temperature range and the ability to form and stabilize solid electrolyte interface films on graphite surfaces. A series of binary, room-temperature, molten electrolytes composed of LiODFB and organic compounds with acylamino groups (acetamide, oxazolidinone or OZO) have been synthesized. Fourier-transform infrared (FT-IR) spectroscopy indicates that C O and N–H functional groups undergo blue or red shifts upon addition of LiODFB. The electrolytes have excellent thermal stabilities and electrochemical characteristics that allow them to be promising electrolytes for electrochemical double layer capacitors (EDLCs). Here, we examine 1:5 molar ratio LiODFB and acetamide/OZO ionic liquid (IL) electrolytes in EDLCs. IL compatibility with two types of carbon-based electrodes is investigated theoretically and experimentally. We simulate possible structures and ion diameters for the ILs, which must be compatible with pore sizes of the carbon electrodes. Mesoporous activated carbon AC2, with a pore size similar to the ionic diameter of LiODFB–acetamide, has a specific capacitance of 154.2 Fg −1 at 20 m Ag −1 . Additionally, typical capacitive and reversibility behaviors can be seen in the charge–discharge curves over 0–2 V. Finally, the EDLCs exhibit good charging/discharging performances. [ABSTRACT FROM AUTHOR]

In this paper, the general design of a battery buffer system (BBS) consisting of a dc/dc converter and electric double layer capacitors for an electric vehicle is presented. This is intended to save the regenerative braking energy and to support the battery during acceleration. The design of a multiphase converter in interleaved operation with nonideal coupled inductors is stated to minimize volume and power losses while maintaining given current ripple limitations. A reduced sensor current-sharing control method is developed and its correct choice of the sensor position is explained. The peak efficiency of the designed and built converter can be measured to nearly 99%. The corresponding BBS is implemented in a lead-acid battery powered electric lift truck propulsion system. The system operation with and without the BBS is compared to examine the behavior and the overall efficiency. It can be shown that the traction battery stress can be strictly reduced as well as the temperature rise in the battery. Furthermore, the efficiency can be increased in the range of 5-6%. The battery's lifetime improvement is estimated by means of the difference in the temperature rise to approximately 20%. [ABSTRACT FROM AUTHOR]

Symmetric EDLCs made using high purity carbon electrodes derived from coconut char were tested using 1 M Tetraethylammonium hexafluorophosphate dissolved in two different solvents namely acetonitrile and propylene carbonate. The cell voltage of the capacitor made using propylene carbonate can be extended to 3.5 V and it exhibited good cycling and thermal stability upto 70 °C while the voltage was limited to below 3.0 V in acetonitrile. XPS analysis of the positive and negative electrodes of EDLCs post cycling showed that the primary degradation products were related to ring opening reactions in propylene carbonate based electrolytes while water played a key role in degradation of acetonitrile based EDLCs. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical double layer capacitors (EDLCs) are inherently high power devices when compared to rechargeable batteries. While capacitance and energy storage ability are mainly increased by optimizing the electrode active material or the electrolyte, the power capability could be improved by including conductive additives in the electrode formulations. This publication deals with the use of four different carbon additives – two carbon blacks and two graphites – in standard activated carbon based EDLC electrodes. The investigations include: (i) physical characterization of carbon powder mixtures such as surface area, press density, and electrical resistivity measurements, and (ii), electrochemical characterization via impedance spectroscopy and cyclic voltammetry of full cells made with electrodes containing 5 wt.% of carbon additive and compared to cells made with pure activated carbon electrodes in organic electrolyte. Improved cell performance was observed in both impedance and cyclic voltammetry responses. The results are discussed considering the main characteristics of the different carbon additives, and important considerations about electrode structure and processability are drawn. [Copyright &y& Elsevier]

Abstract: Carbon aerogel (CA) was prepared by a carbonization of resorcinol–formaldehyde (RF) polymer gels, and it was chemically activated with KOH to obtain activated carbon aerogel (ACA) for electrode material for EDLC in organic electrolyte. Coin-type EDLC cells with two symmetrical carbon electrode were assembled using the prepared carbon materials. Electrochemical performance of the carbon electrodes was measured by galvanostatic charge/discharge and cyclic voltammetry methods. Activated carbon aerogel (20.9 F/g) showed much higher specific capacitance than carbon aerogel (7.9 F/g) and commercial activated carbon (8.5 F/g) at a scan rate of 100 mV/s. This indicates that chemical activation with KOH served as an efficient method to improve electrochemical performance of carbon aerogel for EDLC electrode in organic electrolyte. The enhanced electrochemical performance of activated carbon aerogel was attributed to the high effective surface area and the well-developed pore structure with appropriate pore size obtained from activation with KOH. [Copyright &y& Elsevier]

Highlights: [•] The HyperCoal based ACs for EDLCs were prepared by single step direct KOH-activation. [•] The capacitance of ACs not only depends on surface area, but also on pore size distribution. [•] AC-500 shows the capacitance of 46.0Fg−1 and BET surface area of 2540m2 g−1. [•] HyperCoal is an excellent and low-cost candidate for manufacturing ACs for EDLC. [ABSTRACT FROM AUTHOR]

We previously reported some findings on the applicability of porous Ni materials to the electrodes of electric double layer capacitors (EDLCs) [1]. It was found that the porous Ni material prepared via alkali-leaching of Ni–Al alloys and dry process without heating and air-contact provides pseudocapacitance as well as electric double-layer (EDL) capacitance in organic electrolyte solution, TEA·BF4/PC. The pseudocapacitance is ascribed to the electrochemically active surface and bulk state of the porous Ni with low crystallinity. In TEA·BF4/PC, porous Ni materials were found to provide lower volumetric total capacitance than the values of the commercial activated carbons, due to the large difference of specific surface areas (i.e., porous Ni: 43m2/g, the activated carbons examined: 1508–2164m2/g). However, a significant point was the high value of EDL capacitance normalized by the surface areas (C SA), i.e., 10.2μF/cm2, which was beyond 3.6–6.6μF/cm2 of the activated carbons. In this study, the volumetric total capacitance and C SA of porous Ni materials have been further enhanced by using ionic liquids as electrolytes. The volumetric total capacitance has reached 67.4F/cm3 (three-electrode evaluation) in EMIm·BF4 ionic liquid, which approaches 79.3F/cm3 of a high-capacitance-type activated carbon, MSP-20. The total capacitance is affected by the class of ionic liquids due to the difference of the viscosity and conductivity, whereas the pure EDL capacitance is dependent on the ion sizes rather than the physical properties of ionic liquids. Furthermore, the difference of either anions or cations affects the capacitive behaviors in both positive and negative electrodes. Significantly, the C SA value of porous Ni electrodes has increased from 10.2μF/cm2 in TEA·BF4/PC to 16.6μF/cm2 in EMIm·BF4, which is much higher than 7.0μF/cm2 of MSP-20. Furthermore, the electrochemical stabilization of porous Ni materials has been achieved by heat treatment under vacuum, resulting in an excellent cycle performance caused by the exclusion of pseudocapacitance. More noteworthy is that the high C SA can be retained even after the stabilization. The results of this study further emphasize the potential of porous Ni materials as EDLC electrodes. [ABSTRACT FROM AUTHOR]

In this work, graphene nanosheets were prepared using the Hummers-Offeman method. We prepared the resultant graphene electrode with kneading type. The prepared graphene nanosheets were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, Fourier transform infrared spectroscopy instrument and Raman spectra. Finally, the electrochemical performances of graphene nanosheets in an electrolyte solution of tetraethylammonium tetrafluoroborate ((C2H5)4NBF4, TEABF4) in propylene carbonate (C4H6O3, PC) were examined. [ABSTRACT FROM PUBLISHER]

Abstract: An electric double-layer capacitor (EDLC) was tested using load tests involving charging/discharging at 60°C for 17h using an electrolyte consisting of a solution of 1moll−1 of tetraethylammonium tetrafluoroborate (TEA·BF4) in sulfolane (SL) in order to examine the deterioration of the properties of the EDLC, including its capacitance. The interactions between the molecules of the electrolyte and the surface of the activated-carbon electrode were investigated by solid-state 13C-MAS-NMR spectroscopy. The molecules (ions) adsorbed on the surfaces of the positive and negative electrodes and the free molecules (ions) in liquid phase were clearly detectable by solid-sate 13C-MAS-NMR. In the blank spectrum, corresponding to the electrode prior to the load test, four pairs of sharp and broad peaks could be observed. Two sharp peaks from the liquid-phase SL appeared at about 24ppm and 52ppm, respectively, and those for the adsorbed molecules on the electrode surface appeared at about 17ppm and 45ppm, respectively, both being shifted to a higher magnetic field by about 7ppm. The peak shapes of the latter two adsorbed molecules were much broader than those in liquid phase, suggesting stronger interaction with the electrode surface and restriction of molecular movement. Two pairs of such sharp and broad peaks could also be observed for the TEA molecule, which contained two types of carbon atoms. The chemical shifts of the peaks of the adsorbed molecules gradually shifted to a lower magnetic field after the load test at higher voltages ranging from 0.7V to 1.3V. Such changes in the chemical shift of adsorbed molecules were intimately related to the weaker adsorption forces acting on the adsorbed molecules, indicating that the electrode surface had been deteriorated by the load test at higher voltages. On the basis of these solid-state 13C-MAS-NMR spectra, the deterioration mechanism of the EDLC electrode at higher temperatures was discussed. [Copyright &y& Elsevier]

Mesoporous carbons were synthesized using thermoplastic phenolic resin (PF) as carbonaceous precursor and magnesium citrate as template precursor. Pore structure was determined as ink-bottle-like geometry through TEM, N2 adsorption analysis combined with TG curves. The porous carbons prepared were then applied as electrode material for electric double-layer capacitors. The capacitor performance was examined in 30 wt% KOH aqueous solution by cyclic voltammetry and galvanostatic charge/discharge measurements. The carbon prepared with MgO/PF mass ratio of 8/2 had a BET surface area of 1920 m g and exhibited a capacitance of 220 F g at a current density of 50 mA g. Besides, the carbon with the ratio of 4/6 had the optimize proportion of mesopores, which ensures its good rate performance that up to 98.3%, expressed as the ratio of the capacitance measured at 1000 mA g against that at 50 mA g. [ABSTRACT FROM AUTHOR]

Abstract: The present study aims at assessing the applicability of porous metals to the electrodes of electric double layer capacitors (EDLC). Porous Ni materials for test electrodes were prepared from commercially available Ni–Al alloys through an alkali-leaching process and the subsequent dry and surface-treatment processes. The surface area and pore structure (mesoporous structure) have been found to depend on the class of the alloys. Furthermore, the porous Ni materials prepared via the dry processes with heating and with exposure to air have shown high electrochemical stability but quite low capacitance. In contrast, the dry process without heating and in no contact with air has made the surface and bulk sate electrochemically more active, which induces pseudocapacitance as well as double-layer capacitance. The pseudocapacitive reaction is responsible for the gradual modification of the active electrode to a high-resistance material with charge/discharge cycles. The volumetric total capacitance has reached as high as 31.9F/cm3 (in a three-electrode system) irrespective of not so high specific surface areas (SSA) of 43m2/g. At present, the capacitance is lower than the values, i.e., 40.3–78.0F/cm3, of the commercial microporous active carbons with the high SSAs of 1508–2164m2/g. However, the capacitance normalized by the surface areas has reached 10.2μF/cm2, which is beyond 3.6–6.6μF/cm2 of the active carbons. In addition, the mesoporous Ni electrodes have shown more favorable rate performance than the microporous active carbons due to the low ion-transfer resistance. [Copyright &y& Elsevier]

Abstract: 1M NaClO4 and 1M NaPF6 electrolyte solutions in ethylene carbonate–dimethyl carbonate solvent mixture (1:1 by volume) were studied for the possible application in electrical double layer capacitors (EDLCs) with carbide-derived carbon electrodes (synthesized from Mo2C). Two- and three-electrode test cells were electrochemically characterized by using cyclic voltammetry, constant current charge/discharge and electrochemical impedance spectroscopy methods. Region of ideal polarizability, values of series capacitance, high-frequency resistance, time constants, etc. have been established. Based on the specific energy and power calculations, and other characteristics, it was found that the Na-salts based EDLC test cells have similar electrochemical behavior compared to LiPF6 and LiClO4 based systems that have been studied earlier. The studied Na-salts based electrolytes are potential candidates for EDLCs, however, future improvement of the cyclability is inevitable to achieve long-lasting high performance. [Copyright &y& Elsevier]

PHEVs and BEVs make use of battery cells optimized for high energy rather than for high power. This means that the power abilities of these batteries are limited. In order to enhance their performance, a hybrid Rechargeable Energy Storage System (RESS) architecture can be used combining batteries with electrical-double layer capacitors (EDLCs). Such a hybridized architecture can be accomplished using passive or active systems. In this paper, the characteristics of these topologies have been analyzed and compared based on a newly developed hybridization simulation tool for association of lithium-ion batteries and EDLCs. The analysis shows that the beneficial impact of the EDLCs brings about enhanced battery performances in terms of energy efficiency and voltage drops, rather than extension of vehicle range. These issues have been particularly studied for the passive and active hybrid topologies. The classical passive and active topologies being expensive and less beneficial in term of cost, volume and weight, a new hybrid configuration based on the parallel combination of lithium-ion and EDLCs on cell level has been proposed in this article. This topology allows reducing cost, volume, and weight and system complexity in a significant way. Furthermore, a number of experimental setups have illustrated the power of the novel topology in terms of battery capacity increase and power capabilities during charging and discharging. Finally, a unique cycle life test campaign demonstrated that the lifetime of highly optimized lithium-ion batteries can be extended up to 30%-40%. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The fascinating properties of graphene are attracting considerable attention in engineering fields such as electronics, optics, and energy engineering. These properties can be controlled by controlling graphene''s structure, e.g., the number of layers and the sheet size. In this study, we synthesized nanosized graphene from a platelet-type carbon nanofiber. The thickness and size of nanographene oxide are around 1nm and 60nm and we obtained nanographene by hydrazine reduction of nanographene oxide. We applied the nanographene to an ionic-liquid electric double-layer capacitor (EDLC), which exhibited a much larger capacitance per specific surface area than an EDLC using conventional activated carbon. Furthermore, the capacitance increased significantly with increasing cycle time. After 30th cycle, the capacitance was achieved 130Fg−1, though the surface area was only 240m2 g−1. These results suggest that nanographene structure induce the capacitance enhancement. [Copyright &y& Elsevier]

Abstract: This work describes the preparation and characterization of poly (methyl methacrylate) (PMMA) based gel polymer electrolytes with magnesium triflate (Mg(CF3SO3)2) as the ion providing salt. Liquid electrolytes containing 0.4M Mg(CF3SO3)2 in solvents comprising different ratios of ethylene carbonate (EC) and diethyl carbonate (DEC) have been prepared at room temperature. The highest conducting electrolyte contains EC and DEC in the weight ratio of 2:1. To the highest conducting liquid electrolyte, 25–50wt.% PMMA has been added and the mixtures were heated at 80°C for 2min to form gel polymer electrolytes. The gel electrolyte with composition 40wt.% PMMA and 60wt.% of 0.4M Mg(CF3SO3)2 in EC:DEC (2:1, w/w) has the highest conductivity of 5.58×10−5 Scm−1 and activation energy 0.11eV. The gel polymer electrolyte with highest conductivity at room temperature has Mg2+ ion transference number of 0.37 and electrochemical stability window 2.42V. The highest conducting gel polymer electrolyte has been used to fabricate an electric double layer capacitor (EDLC) which exhibits a nearly rectangular voltammogram even after the 50th discharge cycle. The capacitance of the EDLC is about 27Fg−1 after the 1st cycle and 23Fg−1 after the 50th cycles. [Copyright &y& Elsevier]

Abstract: We have demonstrated, for the first time, efficient 120Hz filtering by an electric double layer capacitor (EDLC). The key to this ultra-high-power performance is electrodes made from vertically oriented graphene nanosheets grown directly on metal current collectors. This design minimized both electronic and ionic resistance and produced capacitors having RC time-constants of less than 200μs. Significantly, graphene nanosheets have a preponderance of exposed edge planes that greatly increase stored charge over designs relying on basal plane surfaces. Collectively these factors make vertically oriented graphene nanosheet electrodes ideally suited for producing high-frequency EDLCs. Capacitors constructed with these electrodes are predicted to be significantly smaller than aluminum electrolyte capacitors that they could functionally replace plus be manufactured using standard semiconductor process equipment, creating interesting commercial opportunities. [Copyright &y& Elsevier]

Abstract: This paper presents a method to deal with the fluctuation problems caused by large-scale wind power integration to a distribution power system. Two types of energy storage devices which have different response characteristics and costs - EDLC (Electrical Double Layer Capacitor) with extremely high response, long life cycle but costly and Secondary Electrical Battery with relatively low response and low cost, are considered for the purpose of mitigation of fast wind power fluctuation and power leveling, respectively. Digital simulations with a typical wind farm distribution power system model are conducted in this study, and these simulation results have illustrated the validity of the combined use of these energy storage systems. [Copyright &y& Elsevier]

An energy management strategy is proposed to save both the loss in the hybrid powered traction system and the capacitance of the electric double-layer capacitors (EDLCs). The authors aim at providing a method to design appropriate capacitance of EDLCs under the proposed energy management strategy. The energy versus power plain is proposed to be used for designing the appropriate capacitance of the EDLCs, considering the requirement for the power and the energy of the EDLCs, the traction performance, and the limit of the current due to dc/dc chopper for charging and discharging the EDLCs. The proposed methods are verified by numerical simulations, assuming different load cases such as a local train and an express train in a nonelectrified line. The results in this paper can be extended to designing a method on how to manage the energy and decide the capacitance of EDLCs for the general hybrid powered systems to drive motors with inertial loads. [ABSTRACT FROM AUTHOR]

Abstract: Six electrodes with a varying amount (5, 10, and 15wt.%) of conducting carbon nanotubes (CNT) and carbon nanofibers (CNF) were fabricated and their performance evaluated against a control sample that was devoid of any conducting material. The goal of this work was to determine the correlation between electrode conductivity and capacitance in 1M tetraethyl ammonium tetrafluoroborate (TEABF4) in propylene carbonate (PC) electrolyte. CNT electrodes exhibit the lowest electrical resistance, while CNF electrodes had the highest capacitance. The specific capacitance (120–140F/g) increased monotonically up to 2.5V. An inverse correlation between electrical resistance and capacitance was observed for various concentrations. The electrodes were characterized using CV, EIS, SEM, and BET analysis. [ABSTRACT FROM AUTHOR]

Abstract: 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 298K and decreased the capacitance at low temperature and direct current resistance (DC-IR) at 243 and 298K. The butenyl group deteriorated the capacitance and DC-IR at 243 and 298K. The stability of EDLC cell of DAIm–BF4/PC was inferior to that of EMIm–BF4/PC. The addition of DMC to PC improved the stability. [Copyright &y& Elsevier]

Abstract: The performance of a battery–EDLC hybrid power source under pulse-operated power systems is theoretically and experimentally analyzed. Electrical double layer capacitors (or EDLC) enhance the power of lead-acid battery as it acts as a buffer in charging and discharging. Consequently, this hybrid technology is able to provide and absorb charge rapidly during vehicle acceleration and braking. The experimental results show considerable extension of runtime and reducing of internal losses. Using this association, the battery current draw is reduced and the EDLC source supplies the majority of transient current. As a result the battery stress is reduced up to 58%. Other laboratory tests showed a substantial improvement over stand-alone lead-acid battery pack and the lifetime of the battery is increased with 30%. This article proposes a new approach to perform accelerated life cycle analysis of lead-acid batteries with/without EDLC based on Dynamic Endurance Test according to standard IEC 61982-2. At least the power capabilities and internal resistance characteristics during charge/discharge of this technology have been evaluated by hybrid pulse power characterization test (HPPC). This paper introduces further new definition of the battery stress in terms of battery current and depth of discharge. [Copyright &y& Elsevier]

Farad-size capacitors were first introduced 32 years ago for memory backup. Today million farad-size systems are used in advanced transportation and power quality applications. [ABSTRACT FROM AUTHOR]

The electric double-layer capacitor (EDLC) has attracted attention by using activated carbon (AC) as an active electrode material with a high power density and high cost-efficiency in industrial applications. The EDLC has been actively developed over the past decade to improve the power density and capacitance. Extensive studies on EDLCs have been conducted to investigate the relation of EDLC capacitance to the physical properties of AC, such as the specific surface area, pore type and size, and electrical conductivity. In this study, EDLC was fabricated with AC, and its capacitance was evaluated with the physical properties of AC. The AC was prepared using petroleum-based pitch synthesized using pyrolysis fuel oil (PFO) with polyethylene terephthalate (PET). The AC based on PFO and PET (PPAC) exhibited high specific surface area and low micropore fraction compared to the PFO-based AC without PET addition (PAC). Furthermore, the reduction of the EDLC capacitance of PPAC was smaller than that of PAC, as the scan rate was increased from 5 to 100 mV s−1. It was determined that the minor reduction of capacitance with an increase in the scan rate resulted from the development of 4 nm-sized mesopores in PPAC. In addition, a comprehensive correlation of EDLC capacitance with various physical properties of ACs, such as specific surface area, pore characteristics, and electrical conductivity, was established. Finally, the optimal properties of AC were thereupon derived to improve the EDLC capacitance. [ABSTRACT FROM AUTHOR]

Abstract: Morphology and porous structure of the pitch-based carbon aerogels (CAs) were characterized by scanning electron microscopy (SEM) and N2 adsorption–desorption measurement. Their electrochemical performances as electric double-layer capacitor (EDLC) electrodes were studied by cyclic voltammetry and galvanostatic charge–discharge measurements. It was found that the particle size of the CAs decreased with the increase of the volume ratio of toluene to acetic acid (T/A ratio). The BET surface areas of the obtained CAs were in the range of 290–450m2 g−1. CA electrodes had good electrochemical performance and appropriate specific capacitance. Moreover, the electrochemical performance of the CAs was enhanced by the existence of extensive mesoporous networks of the CAs. CA with 2.23 of T/A ratio had the highest specific capacitance, i.e., 131.9Fg−1 for cyclic voltammetry. Thus, it was thought that the pitch-based CAs were suitable electrode materials for EDLCs. [Copyright &y& Elsevier]

In our previous work, we proposed the current-source energy capacitor system (CS-ECS), which consists of an electric double-layer capacitor, current-source inverter, and bi-directional four-quadrant DC-DC (FQ DC-DC) converter to control active/reactive power that can achieve the output leveling of wind energy system. However, this system had low conversion efficiency due to hard-switching losses. The improvement of conversion efficiency and performance are indispensable to implement the CS-ECS. This article proposes the soft-switched FQ DC-DC converter with a simple L-C resonant circuit for the CS-ECS. Since the insulated gate bipolar transistors of the converter softly turns on and off by using current-mode resonance, the conversion efficiency for the proposed system improves. In order to illustrate the operating principle of the proposed system, we analyze the transition of conversion efficiency with charge and discharge operation in detail through a theoretical approach and computer simulations with MATLAB/SIMULINK and SimPowerSystems Toolbox. [ABSTRACT FROM AUTHOR]