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The impact of carbonate solvents on the self-discharge, thermal stability and performance retention of high voltage electrochemical double layer capacitors
Abstract
Advanced electrolytes for supercapacitors with high electrochemical stability are necessary to improve the suitability of supercapacitors for many applications. In this work we investigated electrolytes based on the solvent propylene carbonate (PC) and butylene carbonate (BC). A comparison of different solvent-salt combinations shows that 1 M N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) in BC is superior to conventionally used PC-based electrolytes examined in this work in terms of voltage window and capacitance. In order to gain a better understanding of the influence of the ions and the solvent on the formation of the electrochemical double layer, the self-discharge mechanism and its temperature dependence have been investigated in detail. By coupling thermogravimetry (TGA), infrared spectroscopy (IR), gas chromatography and mass spectrometry (GC-MS), also decomposition and temperature stability have been assessed.
... Fresh 10 mL SGF must be added after each sample was taken. Samples were analyzed at 219 nm using UV1700 (Shimadzu Kyoto, Japan) [30,31]. Percentage dissolution efficiency (DE) was determined using the trapezoidal method: ...
... TGA analysis was performed using a PerkinElmer STA 6000 simultaneous TGA/DSC analyzer. The process was performed by heating at 10 • C per min from 30 • C to 500 • C under a dry nitrogen gas with a flow rate of 20 mL/min [31,33]. ...
The low water solubility of an active pharmaceutical ingredient (aripiprazole) is one of the most critical challenges in pharmaceutical research and development. This antipsychotic drug has an inadequate therapeutic impact because of its minimal and idiosyncratic oral bioavailability to treat schizophrenia. The main objective of this study was to improve the solubility and stability of the antipsychotic drug aripiprazole (ARP) via forming binary as well as ternary inclusion complexes with hydroxypropyl-β-cyclodextrin (HPβCD) and L-Arginine (LA) as solubility enhancers. Physical mixing and lyophilization were used in different molar ratios. The developed formulations were analyzed by saturation solubility analysis, and dissolution studies were performed using the pedal method. The formulations were characterized by FTIR, XRD, DSC, SEM, and TGA. The results showcased that the addition of HPβCD and LA inclusion complexes enhanced the stability, in contrast to the binary formulations and ternary formulations prepared by physical mixing and solvent evaporation. Ternary formulation HLY47 improved dissolution rates by six times in simulated gastric fluid (SGF). However, the effect of LA on the solubility enhancement was concentration-dependent and showed optimal enhancement at the ratio of 1:1:0.27. FTIR spectra showed the bond shifting, which confirmed the formation of new complexes. The surface morphology of complexes in SEM studies showed the rough surface of lyophilization and solvent evaporation products, while physical mixing revealed a comparatively crystalline surface. The exothermic peaks in DSC diffractograms showed diminished peaks previously observed in the diffractogram of pure drug and LA. Lyophilized ternary complexes displayed significantly enhanced thermal stability, as observed from the thermograms of TGA. In conclusion, it was observed that the preparation method and a specific drug-to-polymer and amino acid ratio are critical for achieving high drug solubility and stability. These complexes seem to be promising candidates for novel drug delivery systems development.
... In this approach, charge balancing is a key design route. The charge balancing procedure is much adopted in conventional devices [20][21][22][23][24][25] while not so frequently reported in the field of μSCs [8,26]. In the work of Asbani et al., the charge balancing of a μSCs is carried out by properly balancing the electrode thicknesses of both vanadium nitrate and ruthenium oxide. ...
... Advantages of a mixed solvent of propylene carbonate and acetonitrile with tetraethylammonium tetrafluoroborate as the electrolyte seem to offer low self-discharge and leakage current with an EDLC device [153]. Carbonate-based electrolyte solutions were examined with respect to supercapacitor performance [154], and self-discharge was found to be similar to that observed with common other solvents and solutions. Particular attention was paid to self-discharge of EDLC devices with ionic liquid electrolyte under hightemperature conditions [155]. ...
Self-discharge as an omnipresent and unwelcome feature of electrochemical storage devices driven by fundamental forces is briefly introduced and put into perspective. Causes and observed effects as well as possible consequences and modifications in support of a therapy of these effects are described. Care is taken to consider observed phenomena with respect to different types of supercapacitors and different classes of electrode materials and additives inside a cell. Modeling and further theoretical approaches are presented. Recommendations for reporting and data presentation are provided.
... These devices are relying on a physical charge storage process, in which the ions of the electrolyte form a capacitive double-layer on the surface of the electrodes upon the application of a voltage to the device. This process is extremely efficient, enabling an outstanding lifetimein the order of several million cyclesand especially outstanding when considering short power pulses in which batteries are limited by reaction kinetics enabling the possibility to charge these devices in very short time frames [6][7][8]. The major drawback of EDLCs is their limited energy density (∼ 5-8 Wh kg − 1 ) which is preventing their use in applications where also a relatively high amount of energy is required [9][10][11][12][13][14]. ...
... The densities of the two electrolytes were investigated utilizing a DMA 4100 M (Anton Paar) in the temperature range between 0 and 80°C. The tests have been carried out following a procedure identical to that reported in Ref. [31]. ...
In this work we report about the use of caesium acetate (CsOAc) based electrolytes for Electrical Double Layer Capacitors (EDLCs). We showed that solutions of 6.4 m CsOAc in H 2 O, which is a highly concentrated aqueous electrolyte, and 21 m CsOAc in H 2 O, which is a Water in Salt Electrolyte (WiSE), display very favourable chemical‐physical properties. EDLCs containing 21 m CsOAc in H 2 O as electrolyte display operating voltage of 1.7 V. These devices display good energy density, and are able to retain all their initial capacitance after 400 hours of floating at 1.7V. On the other hand, EDLCs containing 6.4 m CsOAc in H 2 O as electrolyte display operative voltage of 1.6V and are delivering at 10 A g ‐1 very high energy and power density (4 Wh kg ‐1 and 14,1 kW kg ‐1 , respectively). Furthermore, they are able to retain 91% their initial capacitance after 400 hours of floating at 1.6V. This performance, which is among the highest so far reported for aqueous‐based EDLCs, indicates that CsOAc can be considered as a very promising salt for the realization of advanced EDLCs.
... Float tests are widely used to investigate the stability of high power devices, e.g. EDLCs, as they are supplying important information about the aging processes occurring in operating conditions similar to that of many real applications [69][70][71][72][73][74][75][76]. Although LICs are considered high power devices, only a few studies have investigated the stability of these systems during float tests [59,77,78]. ...
Lithium-ion capacitors (LICs) are nowadays considered as one of the most interesting high-power devices, and they are used in an increasing number of applications. In the last years, several efforts have been made to increase the energy of these devices, but only a few studies investigated in detail the degradation processes taking place in LICs. In this contribution, we are reporting on a systematic investigation of the aging processes taking place in LIC containing liquid and gel-polymer electrolytes. We show that the use of both electrolytes enables the realization of LICs that operate at 4.5 V and have very good stability. Furthermore, we report that the aging of LICs involves the deterioration of the solid electrolyte interface (SEI) of the graphite electrode, which leads to a decrease of the concentration of LiC6/LiF and to an increase of phosphide (P/LixP) within the electrode. In the activated carbon electrode, the concentration of phosphide (P/LixP) and fluoride (C-Fx) increases, and trapping of Li-ions on the pores of the carbon occurs. These degradation processes are taking place simultaneously and might affect each other.
... The heating rate for temperature ramp experiments was 10°C min −1 . The tests have been carried out following a procedure identical to the one reported in Ref. 27. ...
In this work, we report a systematic investigation about the chemical-physical properties of mixtures containing glyoxylic solvents (tetramethoxyglyoxal (TMG) and tetraethoxyglyoxal (TEG)) and organic carbonates, and about the use of these blends as electrolytes for lithium-ion batteries (LIBs). We showed that these mixtures display promising conductivities and viscosities as well as high thermal stability. Furthermore, they also display significantly higher flash points (up to 60 °C) than the state-of-the-art LIB electrolytes. These mixtures can be successfully utilized for the realization of lab scale LIBs displaying high stability and good rate capability at high C-rate. Furthermore, LIBs containing this innovative electrolyte display good stability at room temperature as well as at 40 °C and 60 °C. Considering these results, mixtures of glyoxylic acetals and organic carbonates appear as promising electrolytes for advanced LIBs.
... Advanced electrolytes for ultracapacitors with high electrochemical stability are important in enhancing a devices suitability for various usages (Heß, Wittscher, and Balducci 2019). Investigation of electrolytes using propylene carbonate and butylene carbonate solvents were carried out. ...
Electrolyte is one of the key components of ECs and gives the ionic conductivity and enhance charge storage process on electrodes. Currently, most of the existing ultracapacitors employ organic electrolytes that are electrochemically stable for applied voltages ranging from 2.5V to 2.8V. Electrolyte plays cardinal functions like supply of ions, electron conduction and adhesion of electrode particles in determining the performance of ECs, such as solid-state devices. An appropriate ultracapacitor's electrolyte should basically have: broad decomposition potential window, high electrochemical stability, high concentration of ions, low resistivity, low toxicity, etc. It is more effective to improve energy density by increasing the applied voltage window going by the fact that energy and power densities are proportional to voltage squared according to equations of energy and power densities. This is successively achievable by selecting suitable electrolytes that have broader potential window. The formulation or design of novel electrolytes components is taken as one of the significant approaches to achieving the next-generation ultracapacitors with enhanced energy. Advanced electrolytes for ultracapacitors with high electrochemical stability are important in enhancing device suitability for various usages. Investigation of ECs electrolytes that use propylene carbonate (PC) and butylene carbonate (BC) solvents have been carried out. A useful guidelines and requirements for determination of optimum ratios, proper organic electrolytes for optimal performance and the entire blueprint and fabrication of ultracapacitors of enhanced energy and power with a reduction in device mass and volume have been presented. Performances of asymmetric EC can strongly be enhanced with a reduction in cell mass and volume by employing suitable electrode mass and operating potential range ratios employing aqueous electrolytes, and those with suitable electrode mass, operating potential range ratios with organic electrolyte of appropriate operating potential range and specific capacitance. Storable and deliverable energies of the asymmetric EC using suitable electrode mass and operating potential range ratios employing proper organic electrolyte are improved by a factor of 12.9 with 1.73 reduction in cell mass and volume, compared to those of symmetric EDLCs employing aqueous electrolyte. Storable energy, energy density and power density of symmetric EDLCs can be enhanced 5.56 folds with 1.77 folds reduction in cell mass and volume by using suitable electrode mass, operating potential range ratios, and proper organic electrolyte. Also, introduction of an asymmetric electrode and organic electrolyte was very successful in improving the performance of the EC with reduction in cell mass and volume.
These guidelines and requirements aid in development of asymmetric ultracapacitors with optimum battery-type mass ratio, potential range ratio, maximum potential range ratio, and ratio of capacitance of capacitor-type. Also, ECs models that incorporated various self-discharge mechanisms used to determine minimum impurity or redox species concentration and optimum total thickness of separator and anode for self-discharge suppression were presented. Numerous groups have presented Lithium-ion Capacitors (LICs) as the new generation ultracapacitors because they have the capability to give higher energy density compared with the commercial organic ECs. LICs higher energy density is because of Li intercalation/de-intercalation phenomena. The crucial factors in development of new-generation ultracapacitors with high-voltage and outstanding performance are: the design or formulation of electrolytes with enhanced features like high ionic conductivity, viscosity, and electrochemical/chemical stability modified to permit high applied voltages, low equivalent series resistance and long cycling. The mass ratio of anode and cathode are shifted for purpose of balancing charges so as to obtain maximum applied voltage and long life; and the asymmetric arrangements are needed to obtain capacitors with elevated voltage, power and energy densities. Concerning blueprint and optimization of novel electrolyte, choice of electrolytes to enhance the electrochemical stability potential windows, ionic conductivity, thermal stability, reduced viscosity and clearer basic understanding via experiments and theories are essentially needed. Research and development by industries and academia showed that Lithium-ion capacitors could function with applied voltage of 3.7- 4.1V while maintaining high cycle-life and perfect power density, which are regarded as real electrochemical capacitors.
Key words: Aqueous electrolytes; Organic electrolytes; Ionic liquids electrolytes; solid-state electrolytes; ionic conductivity; Electrochemical stability; Energy and power densities; Decomposition potentials; Electrolyte stability potential window and Cell voltage.
High‐performance electrochemical applications have expedited the research in high‐power devices. As such, supercapacitors, including electrical double‐layer capacitors (EDLCs) and pseudocapacitors, have gained significant attention due to their high power density, long cycle life, and fast charging capabilities. Yet, no device lasts forever. It is essential to understand the mechanisms behind performance degradation and aging so that these bottlenecks can be addressed and tailored solutions can be developed. Herein, the factors contributing to the aging and degradation of supercapacitors, including electrode materials, electrolytes, and other aspects of the system, such as pore blocking, electrode compositions, functional groups, and corrosion of current collectors are examined. The monitoring and characterizing of the performance degradation of supercapacitors, including electrochemical methods, in situ, and ex situ techniques are explored. In addition, the degradation mechanisms of different types of electrolytes and electrode materials and the effects of aging from an industrial application standpoint are analyzed. Next, how electrode degradations and electrolyte decompositions can lead to failure, and pore blocking, electrode composition, and other factors that affect the device's lifespan are examined. Finally, the future directions and challenges for reducing supercapacitors' performance degradation, including developing new materials and methods for characterizing and monitoring the devices are summarized.
The thermal processes occurring in electrical double layer capacitors (EDLCs) significantly influence the behavior of these energy storage devices. Their use at high temperature can improve their performance due to a reduction of the internal resistance but, at the same time, can also lead to a higher self-discharge (SD). If the thermal stability of the EDLC is exceeded, accelerated aging (e.g., by electrolyte decomposition, pore blockage) occurs and leads to a premature cell failure showing itself by a decrease in capacitance, an increase in resistance as well as a rise in cell pressure. For this reason, a clear understanding of these processes appears crucial for the development of advanced EDLCs for new applications.
This mini-review provides a critical analysis of the investigations dedicated to the thermal processes occurring in commercial and lab-scale EDLCs, considering in detail the methodologies used for these studies. The aim of this work is to provide the EDLC community with an up-to-date and critical overview of the current knowledge on thermal processes, with a focus on the impact of conventional and alternative electrolytes on them. In addition, the work aims to provide insight into future challenges associated with the investigation of these important processes.
In this work we report the use of a water-in-salt (WiSE) electrolyte based on potassium formate (HCOOK). We showed that a solution of 14 M HCOOK in H2O displays promising transport properties and can be successfully utilized for the realization of electrochemical double layer capacitors (EDLCs) operating at 1.7 V, displaying high energy and power densities and extraordinary cycling stability (90% of capacitance retention after 1700 h of float at 1.7 V). Taking these results into account, and the fact that 14 M HCOOK in H2O is cheap, environmentally friendly and not toxic, this electrolyte can be certainly considered very promising for the realization of a novel generation of cheap and high performance aqueous EDLCs.
Background
Safety and workability under harsh conditions are two of the major challenges for carbon-based electric double layer capacitors (EDLCs).
Methods
Gel polymer electrolytes (GPEs), comprising a graphene oxide (GO)-decorated polymer blend of poly(acrylonitrile-co-methyl acrylate) and poly(ethylene glycol) integrated into a liquid electrolyte (LE), are developed.
Significant findings
Under firing, the polymer entraps solvent molecules and the GO facilitates the charring of the GO-decorated GPE (GPEG), resulting in low flammability. The GO-polymer framework enhances the dissociation of counter-ion pairs and solvent−ion clusters to increase the ionic conductivity (to a value higher than that of the LE) and reduce the dielectric loss. The GPEG–EDLC outperforms EDLCs assembled using the LE and GO-free GPE with respect to capacitance, rate capability, and cycling stability. The high dissociation of the counter-ion pairs and solvent−ion clusters in the GPEG facilitates ion diffusion into the carbon micropores, thus improving the capacitive performance. The GPEG–EDLC presents excellent performance at −20°C due to the solvent−ion cluster dissociation. Its stable performance at 80°C is ascribable to the low dielectric loss, which minimizes the chemical damage to the system. Our study demonstrates the use of a GO-decorated dielectric polymer to address issues of safety and workability at extreme-temperatures.
Suppression of self-discharge is crucial in the development of electrochemical double-layer capacitors (EDLCs). In this study, the rate-controlling element of the self-discharge process in EDLCs was explored without any new additives, and the anion was found to play a critical role in this process. The thickness ratio between the positive and negative electrodes (P/N ratio) was the primary factor used to control the self-discharge rate. As the P/N ratio increased, the anion density in the positive electrode decreased. The P/N ratio was increased to retain the anions for a longer period in the cell, which caused self-discharge suppression and led to a slow change in the positive electrode potential when held at an open-circuit status. Cells with a P/N ratio of 1.37 showed 26% to 32% reduced voltage decay than did those with a P/N ratio of 1.00 after 70 h.
Self‐discharge (SD) of electrical double layer capacitors (EDLCs) has become an important issue that will cause voltage decay and energy loss. Herein, the SD profiles of EDLCs with three‐electrode test cell (Ag/Ag+ as reference electrode) in 1 mol L−1 tetraethyammonium tetrafiuoroborate (TEABF4)/acetonitrile (AN) were examined coupled with the potential record of the positive and negative electrodes. The results show that the negative electrode should be mainly responsible for the SD process in the capacitors regardless of the mass ratio of the electrodes. The hybrid mechanism model, combined with the activation‐controlled faradaic process, diffusion process and ohmic leakage process, can be utilized to explain the SD mechanism of the cell, positive and negative electrodes, showing that the main contribution arises from the effect of activation‐controlled faradaic process. The initial voltage is the driving force of the faradaic process in SD for high energy state, and its contribution decreases with the decrease of initial voltage. The higher temperature will exacerbate the voltage variation from both faradaic and diffusion process, while the contribution proportion from the diffusion process is more significant with temperature. This article is protected by copyright. All rights reserved.
In this manuscript, we report an investigation about the application of 1,1-dimethylpyrrolidinium tetrafluoroborate (Pyr11BF4) as conducting salt for electric double-layer capacitors (EDLCs). Utilizing this non-conventional salt is possible to realize highly conductive acetonitrile (ACN) based electrolytes. We showed that the the use of the electrolyte 2 M Pyr11BF4 in ACN makes possible the realization of high perfomance EDLC operating at 3.4V, and displaying excellent stability (88 % capacitance retention after 500 h floating at 3.4V). Additionally, EDLCs containing this alternative electrolyte outperforms the state-of-the-art devices also at increased temperature (91 % capacitance retention after 500 h floating at 3.0 and 60°C). Taking advantage of the post-mortem GC-MS measuements, we showed that the higher performance possible with this novel electrolyte is associated to the high electrochemical and thermal stability of Pyr11BF4.
In this work we report for the first time about the design and use of a novel in-situ simultaneous thermal analysis (STA) cell, which allows a precise monitoring of the variation of heat flow, mass loss, resistance and capacitance occurring in electrical double layer capacitors (EDLCs) operating in conditions comparable to real applications. Utilizing this in-situ STA cell we investigated the impact of the operating voltage on the stability of EDLCs during float tests, and we showed that the first hours of these tests are the most critical for the stability of the devices. The novel in-situ STA cell proposed in this work can be utilized for the investigation of any kind of electrochemical system, and it can be considered as a novel and powerful tool for the investigation of the heating and mass variations occurring in these systems.
This article is protected by copyright. All rights reserved.
Supercapacitors have rapidly revolutionized energy storage technology since its discovery. The miniaturized, self-sustained, reliable, precise, highly flexible and portable power supply is the urge of futuristic electronics devices which necessitates the development of supercapacitors. The present invincible position of the supercapacitor is the result of a series of evolutions. Nevertheless, there are some hurdles that need to be addressed for making supercapacitors a flawless preference for electrochemical energy storage devices. Herein, a rudimentary analysis of supercapacitors that largely impact the overall performance is discussed. Foremost, investigating the crucial role played by the basic elements of the supercapacitors are demonstrated. Each element of a supercapacitor is given the utmost importance so as not to leave any stone unturned in understanding the primary structure of the device. Subsequently, the principal mechanism of the supercapacitor is largely discussed along with the working procedure of the two different categories of the device. Ultimately, the significance of the key performance factors is scrutinized.
A 3D CNT/few layered graphene construct (CNT−FLG) with mesopore structure was fabricated and applied in supercapacitors. The structure was acquired through a two‐step method. Firstly, commercial multiwalled carbon nanotubes (MCNTs) were oxidized in a mixed solution of concentrated acid and modified with a couple of long‐chain organic ions. Second, the above resultant product was carbonized at a high temperature. The achieved structure offers a 3D interconnected electrically conductive network as well as mesopore structure. It also significantly improves the specific surface area of MCNTs. Result of BET tests showed that the specific surface area of CNT−FLG reached to 2235 m2/g. When acted as electrode materials in a supercapacitor structure, specific capacitance was approximately 531.2 F/g at a current density of 0.8 A/g. At current density of 50 A/g, specific capacitance remained 204.4 F/g. Besides, the capacitance retention was as high as 96.18 % after 10000 cycles at the current density of 5 A/g. The surface of multiwalled carbon nanotubes has been modified by organic oligomer ion pairs, and the resultant product has been carbonized at a high temperature to achieve a novel 3D carbon nanotube‐graphene structure (CNT−FLG). This structure is provided with a large accessible surface area and 3D interconnected electrically conductive networks.
Self-discharge is a spontaneous process taking place in electrochemical double layer capacitors (EDLCs) that might affect their introduction into specific applications. In recent years, several studies investigated the dynamics of the potential decay occurring during the self-discharge of EDLCs, but the impact of diffusion processes on the self-discharge is still not well understood. In order to gain information about this important aspect we carried out a study in which we combined in situ NMR spectroscopy and electrochemical techniques. We found that the diffusion processes taking place at the electrode-electrolyte interphase are not static, as commonly assumed, but dynamically influence the self-discharge of EDLCs. These results suggest that the models describing this spontaneous process should be revised, and the diffusion should not be considered as a static, but as a dynamic process affecting self-discharge of EDLCs.
Ionic liquids (ILs) are promising electrolytes for supercapacitors (SCs) aimed for high-temperature applications, where increased ionic conductivity results in superior capacitive performance compared to room temperature (RT) performance. However, an increased temperature also accelerates the self-discharge rate that adversely affects energy retention and restricts the usage of SCs in standalone applications. In this study, a detailed electrochemical investigation on the self-discharge behaviour of carbon-based SCs containing an IL, 1-Ethyl-3-methylimidazolium acetate (EMIM Ac), has been carried out in the temperature range RT - 60 °C, and the underlying self-discharge mechanisms are identified. The results reveal that at a high voltage of 1.5 V, the self-discharge is characterized by a combination of charge redistribution and diffusion at both RT and 60 °C. At 60 °C, the diffusion-controlled mechanism dominates at lower voltages over the charge redistribution effect, while at RT both mechanisms contribute to a similar extent. The observed difference in the self-discharge mechanism between RT and 60 °C is explained in terms of a decreased RC time constant (τRC) at elevated temperature, and the same conclusions are potentially applicable to other IL-containing SCs as well.
In this work we report a detailed investigation about the self-discharge of lithium-ion capacitors (LICs). To date, this process has been only marginally investigated. However,the understanding of the dynamics of the self-discharge taking place in LICs appear of importance in view of the optimization of their performance. We showed that LIC display a rather high self-discharge, comparable to that of electrochemical capacitor, and that the main responsible for this process is the positive electrode. Furthermore, we demonstrated that the use of repeated float tests is affecting the self-discharge of LICs, and that after 50–100 h at high voltage their self-discharge is significantly reduced.
Reactions of [Me3PrN][(CF3SO2)2N] and [C3mpip][(CF3SO2)2N] (C3mpip = 1-methyl-1-propylpiperidium) in subcritical water were investigated to develop a technique for recycling fluorine element. By adding KMnO4 to the system, quasi-complete mineralization of the ionic liquids was achieved at 300 °C. When [Me3PrN][(CF3SO2)2N] was reacted for 18 h with 186 mM KMnO4, F–, SO42–, and NO3– yields were 98%, 98%, and 91%, respectively, and the amount of total organic carbon (TOC) was below the detection limit. [C3mpip][(CF3SO2)2N] was also almost completely mineralized via the same treatment, affording F–, SO42–, and NO3– yields of 94%, 97%, and 96%, respectively, with no detectable TOC. The rest of the nitrogen atoms were well accounted for by the formation of NO2–. Compared with a previous reported method using FeO, our approach reduces the reaction temperature for complete mineralization by 76 °C and suppresses the formation of environmentally undesirable CHF3.
Over the past decade, interest in electrochemical capacitors as an energy-storage technology has increased enormously, spurring the development and evaluation of a large number of new materials and device configurations. This perspective article aims to propose guidelines by which new materials and devices should be evaluated, and how resulting data should be reported with respect to critical metrics such as capacitance, energy and power.
As members of the redox-flow battery (RFB) family, nonaqueous RFBs can offer a wide range of working temperature, high cell voltage, and potentially high energy density. These key features make nonaqueous RFBs an important complement of aqueous RFBs, broadening the spectrum of RFB applications. The development of nonaqueous RFBs is still at its early research stage and great challenges remain to be addressed before their successful use for practical applications. As such, it is essential to understand the major components in order to advance the nonaqueous RFB technology. In this perspective, three key major components of nonaqueous RFBs: organic solvents, supporting electrolytes, and redox pairs are selectively focused and discussed, with emphasis on providing an overview of those components and on highlighting the relationship between structure and properties. Urgent challenges are also discussed. To advance nonaqueous RFBs, the understanding of both components and systems is critically needed and it calls for inter-disciplinary collaborations across expertise including electrochemistry, organic chemistry, physical chemistry, cell design, and system engineering. In order to demonstrate the key features of nonaqueous RFBs, herein we also present an example of designing a 4.5 V ultrahigh-voltage nonaqueous RFB by combining a BP/BP˙− redox pair and an OFN˙+/OFN redox pair.
Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).
This perspective article outlines some of the key considerations and literature that have been published on self-discharge in electrochemical capacitors. While for some consumer applications self-discharge is not considered to be a significant issue (e.g. energy storage from regenerative breaking) in applications where the electrochemical capacitor is stored in the charged state for significant times (e.g. coupled with a battery in a cell phone), the impact on energy, power and recharging frequency of both the capacitor and battery can be significant. A description is provided here of the common methods of self-discharge study: half cell vs. full cell measurements and open-circuit potential decay versus float currents. A description of some of the models used to evaluate faradaic self-discharge is presented, with a synopsis of the important aspects of the many available charge redistribution models. An overview of the current self-discharge mechanisms for various ECs is provided, highlighting that for many systems there are significant factors of the self-discharge process which remain unknown. Finally, some future directions are anticipated for the field of self-discharge in electrochemical capacitors.
This study compares several electrolytes for application in electrochemical double layer capacitors (EDLCs), as well as their influence on double layer formation on different activated carbon materials. While propylene carbonate (PC) was used as electrolyte solvent in all cases, the applied conductive salt was varied. A change in conductive salt was found to have a great impact on solubility as well as the electrolytes’ ion transport properties. Most importantly the choice of conductive salt strongly influenced the maximum operative potentials of PC based electrolytes, leading to EDLCs exhibiting maximum operative voltages as high as 3.5 V. Furthermore it was found that not only a high operative voltage, but also well adjusted transport properties are needed for an EDLC electrolyte in order to maximize the device’s energy and power capabilities. Finally the electrolytes’ influence on the capacitance of five activated carbon materials was studied, leading to the conclusion that in order to maximize energy storage in EDLCs, electrolyte and carbon material have to be adjusted one to another.
This study analyses and compares the behaviour of 5 commercial porous carbons in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and its mixture with propylene carbonate (PC) as electrolytes. The results of this investigation show that the existence of a distribution of pore sizes and/or constrictions at the entrance of the pores leads to significant changes in the specific capacitance of the investigated materials. The use of PYR14TFSI as an electrolyte has a positive effect on the EDLC energy storage, but its high viscosity limits the power density. The mixture 50 : 50 wt% propylene carbonate-PYR14TFSI provides high operative voltage as well as low viscosity and thus notably enhances EDLC operation.
Rapid storage and efficient delivery of electrical energy in heavy-duty applications are being enabled by electrochemical capacitors.
Dieses praxisnahe Lehrbuch und Nachschlagewerk führt durch die Welt der elektrochemischen Energiewandler und ihren modernen Anwendungen vor dem Hintergrund nachhaltiger Energiekonzepte. Der Fachtext erhellt die Speicherung überschüssiger Wind- und Solarenergie, bis hin zur chemischen Speicherform Wasserstoff aus nicht-fossilen Ressourcen. Jeder Themenbereich behandelt die physikalischen, chemischen, ingenieurtechnischen und materialwissenschaftlichen Grundlagen und erlaubt so eine interdisziplinäre Sicht auf die technischen Anwendungen und den Entwicklungsstand neuartiger Speicherkomponenten. Übungsbeispiele und Rechenaufgaben runden den Text ab und erlauben ein fundiertes Selbststudium, ohne Aspekte der aktuellen Forschung und eine Übersicht der rechtlichen Rahmenbedingungen auszusparen. Für die zweite Auflage wurden zahlreiche Leserzuschriften berücksichtigt und dabei viele Kapitel überarbeitet und erweitert. Die rechtlichen Grundlagen wurden gründlich nach dem Stand der Gesetzgebung im März 2018 aktualisiert.
Der Inhalt
Grundlagen der Energiewandlung - Doppelschichtkondensatoren - Lithiumionen-Batterien - Traktions- und Speicherbatterien: Blei, Nickel, Natrium - Hochenergiebatterien nach Lithium-Ion - Redox-Flow-Batterien - Elektrolyse von Wasser - Wasserstoff als chemischer Speicher - Rechtliche Rahmenbedingungen
Die Zielgruppen
- Studierende der Natur- und Ingenieurwissenschaftler,
- Entwickler und Praktiker
- Entscheider in Firmen und in der Politik
Die Autoren
Professor Dr. Peter Kurzweil lehrt und forscht an der Technischen Hochschule Amberg-Weiden im Fachbereich Maschinenbau/Umwelttechnik. Prof. Dr. jur. Otto K. Dietlmeier hat einen Lehrauftrag für Europarecht und Umweltrecht inkl. Energierecht im gleichen Fachbereich inne.
The solvent 1,2-butylene carbonate (1,2-BC) displays a set of properties and a price comparable with that of propylene carbonate (PC). In this work we investigate the use of 1,2-BC in combination with the salt butyl-1-methylpyrrolidinium tetrafluoroborate (Pyr14BF4). We showed that the electrolyte 1.5 M Pyr14BF4 in BC displays good conductivities and viscosities, and that is use allows the realization of EDLCs with operative cell potential as high as 3.15 V. These high potential devices display good cycling stability at room temperature. At higher temperature their stability appears comparable of that of devices containing standard electrolytes.
Supercapacitors, also known as electrochemical capacitors, have witnessed a fast evolution in the recent years, but challenges remain. This review covers the fundamentals and state-of-the-art developments of supercapacitors. Conventional and novel electrode materials, including high surface area porous carbons for electrical double layer capacitors (EDLCs) and transition metal oxides, carbides, nitrides and their various nanocomposites for pseudocapacitors - are described. Latest characterization techniques help to better understand the charge storage mechanisms in such supercapacitors and recognize their current limitations, while recently proposed synthesis approaches enable various breakthroughs in this field.
This is Part II of a two part series of papers on decomposition of two ionic liquids at lithium metal interfaces. In Part I of this series, ab initio molecular dynamics (AIMD) simulations were used to examine the stability and decomposition of two ionic liquids (ILs), [pyr14][TFSI] and [EMIM][BF4], on Li metal anodes. Here in Part II, density functional calculations of ions and ion pairs in the gas phase are coupled with model electrode surface effects to provide an in-depth analysis of the results obtained from more computationally expensive AIMD simulations of electrolytes on the Li surface in Part I. The gas phase approach is used to examine the cathodic and anodic stability, the electrochemical decomposition thermodynamics, and the kinetic barriers to the electrochemical decomposition of the ions on a Li surface. The states of the ILs are shown to mix with those of the Li surface, which leads to the reduction of the cations by one electron and a partial reduction of the anions. Upon reduction, many ion decomposition reactions are found to be thermodynamically favorable and to have small or moderate kinetic barriers. An examination of reaction transition states for reduced ions and ions in the presence of Li atoms suggests that the reductive decomposition of anions is mediated by chemical association with Li surface atoms, while reductive decomposition of the cations need not involve such chemical interactions. Overall, the gas phase results obtained here corroborate and extend understanding of the stability and decomposition behavior of ILs on Li metal anodes noted from the AIMD simulations in Part I.
This study investigated the anodic dissolution of Al current collectors in unconventional electrolytes for high voltage electrochemical double layer capacitors (EDLC) containing adiponitrile (ADN), 3-cyanopropionic acid methyl ester (CPAME), 2-methyl-glutaronitrile (2-MGN) as solvent, and tetraethylammonium tetrafluroroborate (Et4NBF4) and tetraethylammonium bis(trifluoromethanesulfonyl)imide (Et4NTFSI) as conductive salts. In order to have a comparison with the state-of-the-art electrolytes, the same salts were also used in combination with acetonitrile (ACN). The chemical-physical properties of the electrolytes were investigated. Furthermore, their impact on the anodic dissolution of Al was analysed in detail, as well as the influence of this process on the performance of high voltage EDLCs. The results of this study indicated that in the case of Et4NBF4-based electrolytes the use of alternative solvent is very beneficial for the realization of stable devices. When Et4NTFSI is used, the reduced solubility of the complex Al(TFSI)3 appears to be the key for the realization of advanced electrolytes.
Supercapacitors (SCs) have high power density and exceptional durability. Progress has been made in their materials and chemistries, while extensive research has been carried out to address challenges of SC management. The potential engineering applications of SCs are being continually explored. This paper presents a review of SC modeling, state estimation, and industrial applications reported in the literature, with the overarching goal to summarize recent research progress and stimulate innovative thoughts for SC control /management. For SC modeling, the state-of-the-art models for electrical, self-discharge, and thermal behaviors are systematically reviewed, where electrochemical, equivalent circuit, intelligent, and fractional-order models for electrical behavior simulation are highlighted. For SC state estimation, methods for State-of- Charge (SOC) estimation and State-of-Health (SOH) monitoring are covered, together with an underlying analysis of aging mechanism and its influencing factors. Finally, a wide range of potential SC applications is summarized. Particularly, co-working with high energy-density devices constitutes hybrid energy storage for renewable energy systems and electric vehicles (EVs), sufficiently reaping synergistic benefits of multiple energy-storage units.
In this study we report a systematic investigation of the chemical-physical properties of acetonitrile-based electrolytes, containing the salts tetraethylammonium tetrafluroroborate (Et4NBF4), tetraethylammonium bis(trifluoromethanesulfonyl)imide (Et4NTFSI), 1-butyl-1-methylpyrrolidinium tetrafluoroborate (Pyr14BF4), 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl)imide (Pyr14TFSI)). The ionic conductivity, viscosity, density and electrochemical stability windows (ESW) of these electrolytic solutions are considered in detail. From these results, the electrolyte 1 mol dm-3 Et4NTFSI in ACN appears to display a promising set of properties which allow the realization of ACN-based EDLC able to display a stable behavior at 3.1 V.
abstract
In this manuscript we report about the realization and testing of a high-voltage electrochemical double layer capacitor (EDLC) prototype (IES prototype), which has been assembled using innovative electrode and electrolyte components. The IES prototype displays a nominal capacitance of 4 F, a maximum voltage of 3.2 V and its maximal energy and power are in the order of 37 Wh kg-1 and 65 kW kg-1, respectively. Furthermore, it also displays good cycling stability, high capacitance retention after 80 h float test and acceptable self-discharge. Taking into account substantial improvements of the cell design and assembly procedure, the performance of the IES prototype indicates that the components utilized in this device might be suitable alternatives to the state-of-the-art materials used in high energy EDLCs
The development of innovative electrolyte components is nowadays considered one of the most important aspects for the realization of high energy electrochemical double capacitors (EDLCs). Consequently, in the last years many investigations have been dedicated towards new solvents, new salts and ionic liquids able to replace the current electrolytes.
This perspective article aims to supply a critical analysis about the results obtained so far on the development of new electrolytes for high energy EDLCs and to outline the advantages as well as the limits related to the use of these innovative components. Furthermore, this article aims to give indications about the strategies could be used in the future for a further development of advanced electrolytes.
In this review, the technologies and working principles of different materials used in supercapacitors are explained. The most important supercapacitor active materials are discussed from both research and application perspectives, together with brief explanations of their properties, such as specific surface area and capacitance values. A review of different supercapacitor electrolytes is given and their positive and negative features are discussed. Finally, cell configurations are considered, pointing out the advantages and drawbacks of each configuration.
The stability of 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR13TFSI), 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl) imide (PYR13FSI), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIM TFSI) ionic liquids (ILs) at different temperatures (room temperature and 95 °C) was investigated by ion chromatography (IC) hyphenated to a mass spectrometer. The degradation of the cations can be summarized in the following way: The side chain of the main molecule cleaves and reacts subsequently with the main cation molecule to new decomposition products. In addition, the results show that at elevated temperatures more decomposition products are formed.
The influence of Li+ cation based electrolyte salts, lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and lithium perchlorate (LiClO4), on the decomposition of the ionic liquids was analyzed over a long term stability study at room temperature and 60 °C. It was found out that in the mixtures of ILs and electrolyte salt, the same decomposition products were formed like in the pure ILs at the same temperature. Accordingly, there is no influence of the electrolyte salts on the decomposition behavior of the IL cation. The influence of the counter anion on the decomposition of PYR13+ was analyzed as well. It was observed that different decomposition products were detected for PYR13TFSI and PYR13FSI.
As an important energy storage device for wireless sensor nodes with energy harvesting capabilities, the characteristics of supercapacitors need to be taken into account in developing power management solutions. While supercapacitor self-discharge is usually considered because it causes voltage decay and energy loss, supercapacitor charge redistribution has not been well examined although this process may result in a greater voltage change than self-discharge. This paper studies the supercapacitor voltage change during charge redistribution. The supercapacitor voltage may increase, decrease, or remain almost constant during charge redistribution depending on the initial state. Three approaches are employed to investigate the supercapacitor voltage change during charge redistribution: analytical estimations, numerical simulations, and experimental measurements. Both the supercapacitor voltage change after a charge process and that after a discharge process are examined. Various parameters of the charge or discharge process such as charge current and discharge time that affect the initial state of supercapacitor charge redistribution are swept. The results obtained using different approaches are consistent. These results can be utilized by wireless sensor network application designers to estimate the supercapacitor voltage change during charge redistribution.
In this paper we report on the use of 0.7 M Et4NBF4 in ADN as electrolyte in EDLCs. 0.7 M Et4NBF4 in ADN displays a wide electrochemical stability window and promising values of conductivity and viscosity. Using this electrolyte it is possible to realize EDLCs with an operative voltage as high as 3.75 V. At RT, these high voltage EDLCs display high coulombic efficiencies, low ESRs and high specific capacitances stable for several thousands of cycles. The wide electrochemical stability of ADN contributes to preserve the integrity of the electrolyte at potentials in which other conventional organic electrolytes (e.g. ACN) are normally subject to deterioration and/or decomposition processes. Thanks to this intrinsic stability, EDLCs containing 0.7 M Et4NBF4 ADN as electrolyte display high capacitance retention over 35,000 cycles carried out with cell voltage as high as 3.5 V.
The stability of 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI) and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) ionic liquids at elevated temperatures (60 °C) is investigated by ion chromatography. Additionally, the influence of the electrolyte salts, lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium perchlorate (LiClO4), on the decomposition of both the ionic liquids was analysed over a long term stability study. It has been found out that TFSI has a much higher thermal stability than FSI. The addition of LiTFSI did not show any effect on the aging of both ionic liquid anions. However, PYR13FSI degraded when mixed with the electrolyte salts LiPF6 and LiClO4, while PYR13TFSI did not. Finally, LiPF6 forms the same hydrolysis products in the investigated ionic liquids as in the commonly used electrolytes based on organic solvents in lithium-ion batteries.
It is increasingly recognized that a significant component of apparent
self-discharge in supercapacitors is, in fact, due to charge
redistribution. This charge redistribution is due to the limited
mobility and hence high resistance of ions moving in the smallest pores
of the carbon electrodes. A simple two-branch equivalent circuit has
been used to model this charge redistribution and has been applied to an
ultramicroporous aqueous electrochemical capacitor. The results indicate
that a substantial fraction of the total capacitance is found in the
smallest pores and that the resistance to ionic movement is four orders
of magnitude higher than in the bulk electrolyte. A survey of the
literature indicates that many commercial capacitors with organic
electrolyte have similar electrical properties. These properties mean
that a significant fraction of the overall pore surface and hence
capacitance of the electrode is not accessible during time frames of
practical interest and is therefore wasted. A mechanism for the low
mobility of ions in micropores is proposed.
Electrical energy storage (EES) is one of the most critical areas of technological research around the world. Storing and efficiently using electricity generated by intermittent sources and the transition of our transportation fleet to electric drive depend fundamentally on the development of EES systems with high energy and power densities. Supercapacitors are promising devices for highly efficient energy storage and power management, yet they still suffer from moderate energy densities compared to batteries. To establish a detailed understanding of the science and technology of carbon/carbon supercapacitors, this review discusses the basic principles of the electrical double-layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes. We summarize the key aspects of various carbon materials synthesized for use in supercapacitors. With the objective of improving the energy density, the last two sections are dedicated to strategies to increase the capacitance by either introducing pseudocapacitive materials or by using novel electrolytes that allow to increasing the cell voltage. In particular, advances in ionic liquids, but also in the field of organic electrolytes, are discussed and electrode mass balancing is expanded because of its importance to create higher performance asymmetric electrochemical capacitors.
In this paper we report about the use of N-butyl-N-methylpyrrolidinium tetrafluoroborate (PYR14BF4) as a new conducting salt for propylene carbonate (PC)-based electrochemical double layer capacitors. The electrolyte 2.3 M PYR14BF4 in PC displays conductivity and viscosity values comparable with those of conventional PC-based electrolytes and allows the realization of EDLCs with an operative voltage of 3.2 V. These high voltage EDLCs display higher energy and power compared to conventional EDLCs. Moreover, thanks to the electrochemical stability of the electrolyte, these EDLCs display high cycling stability at 3.2 V as confirmed by charge–discharge experiments as well as float voltage tests.
Owing to recent power- and energy-density advances, higher efficiencies, and almost unlimited lifetimes, electrical double-layer capacitors (EDLCs, also known as supercapacitors) are now used in a wide range of energy harvesting and storage systems, which include portable power and grid applications. Despite offering key performance advantages, many device components pose significant environmental hazards once disposed. They often contain fluorine, sulfur, and cyanide groups, which are harmful if discarded by using conventional landfill or incineration methods, and they are constructed by using multiple metallic parts, which contribute to a high ash content. We explore designs for a fully operational supercapacitor that incorporates materials completely safe to dispose of and easy to incinerate. The components, which include material alternatives for the current collector, electrolyte, separator, particle binder, and packaging, are all mutually compatible, and most of them exhibit better performance than commonly used materials. We selected a graphite foil as current collector, sodium acetate as electrolyte, an ester as porous membrane based on acetate cellulose, and polymers based on polyvinyl alcohol as environmentally benign solutions for device components. The presented materials all originate from simple and inexpensive source compounds, which decreases the environmental impact of their manufacture and renders them more viable for integration into commercial devices for large-scale stationary and transportation energy storage applications.
Molar enthalpies of vaporization of cyclic alkyl carbonates: ethylene carbonate, propylene carbonate, butylene carbonate, and glycerine carbonate were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of the primary experimental results on temperature dependences of vapour pressures have been collected from the literature and have been treated uniformly in order to derive vaporization enthalpies of alkylene carbonates at the reference temperature 298.15 K. This collection together with the new experimental results has been used for the selection of the reliable data sets for each compound under study. Experimental vapour pressure data from various literature sources were reviewed and regressed together with data developed in this work. The resulting correlations for vapour pressure of cyclic alkylene carbonates are recommended for use over a temperature range from ambient to the normal boiling point. Consequently, these correlations were used to derive recommended molar enthalpy of vaporization values at 298.15 K.
In this paper, a study of the supercapacitors’ ageing process is presented. The originality of this paper is that the tests are made under conditions similar to those of an industrial application. A continuous cycling is applied in order to obtain these test conditions. The measurement is done, thanks to a test bench developed in our laboratory. More than 560,000 cycles have already been done, which corresponds to 325 cumulated days of continuous cycling. These tests allow to understand the ageing process of supercapacitors and to follow the evolution of theirs characteristics during their lifetime. The aim of this paper is to study the behavior of the cells, which compose the supercapacitors module (48 V/112 F).
Using a mixture of PC/PYR14TFSI as electrolyte, EDLCs with an operative voltage of 3.5V and ESR comparable with that of conventional electrolyte have been realized. The combination of high operative voltage and low ESR enable the realization of EDLCs with high energy and high power. Moreover, the use of PC/PYR14TFSI mixture also guarantees a remarkable cycling stability, as evidenced by a capacitance loss of only 5% after 100,000 cycles carried out at 3.5V.
Self-discharge is an important performance factor when using supercapacitors. Voltage losses in the range of 5–60% occur over two weeks. Experiments show a dependency of the self-discharge rate on various parameters such as temperature, charge duration and short-term history. In this paper, self-discharge of three commercially available supercapacitors was measured under various conditions. Based on different measurements, the impact of the influence factors is identified. A simple model to explain parts of the voltage decay is presented.
Electrochemical capacitors, based on the double-layer capacitance of high specific-area C materials, are attracting major fundamental and technological interest as highly reversible, electrical charge-storage and delivery devices, capable of being operated at high power-densities. A variety of applications have been described in the literature, e.g. for cold-start vehicle assist, in hybrid load-leveling configurations with batteries, fuel-cells, as well as directly with internal combustion engines. Additionally, high capacitance C electrodes have been usefully employed as anodes coupled with battery-type cathodes, e.g. Pb/PbO2, in so-called “asymmetric” capacitor cells.On account of these perceived various applications, requirements for performance evaluation must be developed in systematic and complementary ways. In the present paper, we examine experimentally the following test procedures as exemplified by application to an high specific-area (ca. 2500m2g−1) woven C-cloth capacitor electrode material: (i) evaluation of the specific capacitances as a function of charge/discharge rates employing cyclic-voltammetry and dc charging curves; (ii) as in (i), examination of reversibility and energy-efficiency as a function of electrolyte (H2SO4) concentration, i.e. conductivity; (iii) interpretation of effects in (i) and (ii) in terms of distributed resistance and capacitance in the porous C matrix according to the de Levie model; (iv) interpretation of data obtained in (i) in terms of Ragone plots which, for capacitor devices, require special treatment owing to the fundamental dependence of electrode- (or device) potential on state of discharge; (v) interpretation of self-discharge (SD) kinetics in terms of porous-electrode structure. Performance data for the C-electrode are given for capacitative charging up to high “C-rates”, extension of operational voltage windows and for SD behaviour.
Pitting corrosion of aluminum as cathode current collector for lithium rechargeable batteries was found to take place at potential positive of 3.5 V in 1 mol dm−3 LiN(SO2CF3)2/EC+DME (1:1) electrolyte. The corrosion mechanism of aluminum in the presence of LiN(SO2CF3)2 was proposed, and three methods were deduced to inhibit the aluminum corrosion based on this mechanism. As a result, an additive of lithium salts based on perfluorinated inorganic anions, especially LiPF6, was found to inhibit the aluminum corrosion to a certain extent by forming a protective film on aluminum surface. The oxidation stability of aluminum in LiN(SO2CF3)2-containing electrolytes depended strongly on the solvent structure. The ether solvents such as tetrahydrofuran (THF) and dimethoxyethane (DME) were effective in preventing aluminum corrosion due to their low dielectric constants. Furthermore, LiN(SO2C2F5)2 salt with a larger anion than that of LiN(SO2CF3)2 was evaluated and good oxidation stability of aluminum was obtained regardless of the kind of solvents.
Organische Carbonate (acylische und cyclische Kohlensäureester) sind schwer flüchtige, polare Lösungsmittel, welche sich durch ihre geringe Toxizität auszeichnen. Durch geschickte Wahl der Alkohole für die Estersynthese können die physikalischen Eigenschaften der resultierenden Carbonate stark beeinflusst werden. Ihr Einsatz ist in der Batterietechnik, Erdgasaufbereitung und Kosmetik weit verbreitet. In verschiedenen übergangsmetallkatalysierten Reaktionen beweist insbesondere Propylencarbonat (PC) hervorragende Lösungsmitteleigenschaften und ermöglicht aufgrund seines polaren Charakters die Reaktionsführung in Zweiphasensystemen unter Verwendung eines unpolaren zweiten Lösungsmittels. Dies ist eine Grundvoraussetzung zum Einsatz in kontinuierlichen Prozessen und zur Verringerung der Katalysatormengen.
Organic carbonates (cyclic and acyclic diesters of carbonic acid) are highly boiling, polar and non-toxic solvents. By selection of suitable mono- and di-alcohols as ester components their physical properties can be influenced dramatically. Their use has been proven in lithium batteries, natural gas purification and in cosmetics. Especially propylene carbonate (PC) owns perfect properties as solvent in biphasic transition metal catalyzed reactions. This is a main issue for the use in continuous processes to minimize the amount of catalysts.
A recent study has shown that the process of self-discharge is determined by a number of parameters such as initial voltage, temperature, and charge duration. Depending on these parameters we observed a voltage decay of 5–15% within 48h after charging. These observations hardly affect dynamic operations for supercapacitors, but have major implications for all static setups. A complex electrical model has been established to account for the redistribution effects of ions occurring in supercapacitors. Intense experimental studies suggest that these redistribution effects are in part responsible for the measured potential decays. Extended charging allows the ions to allocate themselves more homogeneously throughout the pores and therefore the voltage decay during the rest period following the charging is greatly reduced. The introduced model is capable of predicting the effects of charge duration, initial voltage, and temperature on the open circuit voltage decay.
In the porous electrodes typically used for electrochemical capacitors, the self-discharge profile may be affected by charge redistribution in the pores of the electrode and the kinetics of the Faradaic self-discharge. In this paper, the activation-controlled self-discharge of a porous electrode is modelled using a de Levie transmission line hardware circuit to model a pore and an activation-controlled discharge is applied at the mouth of this “pore”. The self-discharge profile exhibits three main regions. The first region is governed purely by the activation-controlled discharge as the charge redistribution has not yet begun. The second region combines both charge redistribution and the activation-controlled discharge, resulting in a shallower slope than expected for a purely activation-controlled discharge. Finally, charge redistribution ends and the profile reverts to the activation-controlled profile. These three regions are mirrored in experimental self-discharge profiles and show that the duration charge redistribution can be determined from the shape of the self-discharge profile.
The effect of charge redistribution on the self-discharge profile of porous carbon (Spectracarb 2225) electrodes is examined. A model pore based on the de Levie transmission line circuit is used to show that self-discharge due purely to charge redistribution results in the same self-discharge profile as that expected for an activation-controlled self-discharge mechanism (the potential falls linearly with logt), thus the linear log time profile is not characteristic of an activation-controlled mechanism. The addition of a hold step reduces the amount of charge redistribution in porous carbon electrodes, although the hold time required to minimize the charge redistribution is much longer than expected, with electrodes which have undergone a 50h hold time still evidencing charge redistribution effects. The time required for the charge redistribution through the porous electrode is also much greater than predicted, likely requiring tens of hours. This highlights the importance of the charge redistribution in self-discharge of systems using porous electrodes, such as electrochemical capacitors.
Solutions of LiTFSI in organic solvents such as carbonates, do not display the ability to prevent the aluminum corrosion and for this reason cannot be conveniently used as electrolytes in LIBs. However, addition of PYR14TFSI to PC-LiTFSI strongly suppresses the aluminum corrosion process, both at 20 degrees C and 60 degrees C. At 60 degrees C, in a mixture PC-PYR14TFSI-LiTFSI containing 50% of IL the charge involved in the corrosion process is one order of magnitude lower than that observed in PC-LiTFSI. The suppression of the corrosion process by PYR14TFSI might be related to the reduced solubility of Al(TFSI)(3) in PYR14TFSI compared to PC. Al(TFSI)(3) is formed on the Al surface in electrolytes containing LiTFSI, and the low solubility of this compound in PYR14TFSI contributes to the formation of a stable protective layer on the Al surface, which in turn reduces the corrosion process. Thanks to their ability to suppress the Al corrosion, PC-PYR14TFSI-LiTFSI mixtures can be conveniently used as electrolytes in LIBs, both at room temperature and 60 degrees C. (c) 2012 Elsevier B.V. All rights reserved.
In this paper we report the physical investigation and the electrochemical performance of the carbon black SC3 from Cabot Corporation. The SC3 carbon black was investigated in terms of BET surface area, pore size distribution, resistivity and morphology. Composite electrodes containing SC3 as active material were prepared and used for the realization of electrochemical double layer capacitor (EDLC) and lithium-ion capacitor (LIC). In EDLC, at 5 mA cm−2 charge–discharge currents, the carbon black displays a specific capacity of 40 mAh g−1 and a specific capacitance of 115 F g−1. It also displays a very good cycling stability for over 50,000 cycles and excellent performance retention at currents up to 50 mA cm−2. The performance retention at high currents outstandingly differentiates this carbon black from a few commercially available EDLC-grade activated carbons. Because of the high specific capacity of SC3, the carbon black electrodes were also used in combination with LiFePO4 electrodes in LIC. The results of this study indicate that SC3 carbon black is an interesting carbonaceous candidate for the realization of LIC.Highlights► Carbon black SC3 is a promising active material for Electrochemical Double Layer capacitors (EDLCs) and Lithium-ion capacitors (LIC). ► Carbon black SC3 displays a specific capacity 40 mAh g−1 and a specific capacitance of 115 F g−1. ► The value of specific capacity and capacitance of SC3 are not strongly affect at high current density. ► EDLC based on SC3 display very good cycling stability.
Water electrolysis and oxygen reduction as possible self-discharge mechanisms for carbon-based, aqueous H2SO4 electrolyte electrochemical capacitors is examined through a comparison of the predicted and actual effects of varying the dissolved oxygen and hydrogen content on self-discharge. Water electrolysis, in the form of oxygen evolution, is not the self-discharge mechanism on the positive electrode, although, the self-discharge profile is consistent with an activation-controlled Faradaic discharge or charge redistribution mechanism. The addition of hydrogen evidences no change in self-discharge from the negative electrode, and the profile is consistent with a diffusion-controlled mechanism, suggesting water electrolysis through hydrogen evolution is not the self-discharge mechanism. Oxygen reduction causes a large increase in self-discharge on the negative electrode which necessitates purging the cell of oxygen. As such, water electrolysis is likely not the cause of self-discharge in carbon-based, aqueous electrolyte electrochemical capacitors but oxygen reduction is a cause of increased self-discharge on the negative electrode.
Due to the stochastic nature of wind, electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems. Energy Storage Systems (ESSs) may play an important role in wind power applications by controlling wind power plant output and providing ancillary services to the power system and therefore, enabling an increased penetration of wind power in the system. This article deals with the review of several energy storage technologies for wind power applications. The main objectives of the article are the introduction of the operating principles, as well as the presentation of the main characteristics of energy storage technologies suitable for stationary applications, and the definition and discussion of potential ESS applications in wind power, according to an extensive literature review.
Several metal oxides were used for synthesis of ethylene carbonate from urea and ethylene glycol. ZnO showed high activity towards the reaction. TPD. FTIR and reaction test indicated that the catalysts with appropriate acid and base properties were favorable to the synthesis of cyclic carbonate. Furthermore, the reaction of urea with various diols revealed that the selectivity of five-membered cyclic carbonates was higher than that of six-membered cyclic carbonates. (c) 2006 Elsevier B.V. All rights reserved.
The self-discharge behaviour of supercapacitors is an important factor when considering their suitability for some applications. In this paper, measurements of the self-discharge rates of carbon-based supercapacitors with organic electrolytes are presented and interpreted in terms of two mechanisms. The first is the diffusion of ions from regions of excess ionic concentration formed during the charging of the capacitor and the second is leakage of charge across the double-layer at the electrolyte–carbon interfaces in the capacitor. The dependence of the self-discharge rate on temperature and on the initial voltage across the capacitor is described. q 2000 Elsevier Science S.A. All rights reserved.
The supercapacitors (SCs), also called ultracapacitors or electrochemical capacitors, are devices with a very high specific power and high capacitance, available for a long period of time with negligible deterioration, that have been historically proposed in small applications (memory back-up in consumer electronics and storage systems for microsolar power generators) and now are proposed for high power/energy applications, such as hybrid and electric vehicles, power quality systems and smart grids. The advancements in new materials and the rapid growth of more demanding storage systems in a variety of applications have created a lack of universally accepted definitions of these devices and, consequently, a real difficulty in describing developments and progress in the SC field.
This paper contains a brief survey of the history of the SC development, which is strongly related to the evolution of the SC technologies, tentatively classified in symmetric, asymmetric and hybrid. A short presentation of key parameters has been given to introduce the description of new applications with large SC devices, covering transport, industrial and electric utility sectors, with some reflections about the foreseen impacts on the future market more than quadrupled in 5 years up to almost $877 million worldwide.
This study reports on new electrolyte systems utilizing linear sulfones. The characteristics of linear sulfones have been evaluated with the primary focus on higher withstand voltage. Investigations have been made on eight different types of linear sulfones with relatively low molecular weights. They were subjected to screening with regard to the melting and boiling point, dielectric constant, viscosity and the solubility of electrolyte salts. The results of the investigations were that Ethyl isopropyl sulfone (EiPS) and Ethyl isobutyl sulfone (EiBS) emerged as solvents with great potential. The EiPS has a relatively low melting point (-8 degrees C) and a high boiling point (265 degrees C), higher than that (242 degrees C) of propylene carbonate (PC). Also, it was possible to dissolve the electrolyte salt in EiPS at 1.5 mol l(-1) or higher. The EiPS system showed a high withstand voltage (3.3-3.7 V), exceeding that of PC (2.5-2.7 V). This high withstand voltage was found to have been caused by the high stability of EiPS at the interface between the activated carbon electrode and the electrolyte. By taking into consideration the degradation mechanisms of the EiPS system, we were able to clarify that one of the reasons for the high stability was the low reactivity between EiPS and H(2)O.
This study describes new electrolyte systems that utilize alkylated cyclic carbonates, with a primary focus on getting a higher withstand voltage for electric double-layer capacitors (EDLCs). We attempted to increase the oxidative durability of carbonate solvents by protecting the 4th and/or 5th positions of the five-membered carbonate ring; protection was achieved by substituting those positions with small alkyl group(s). We investigates six different types of cyclic carbonates, viz., ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), 2,3-butylene carbonate (2,3BC), isobutylene carbonate (iBC), and pentylene carbonate (P1C) have been investigated with regard to the electrochemical stability, as well as the melting point, boiling point, dielectric constant, viscosity, and the solubility of electrolyte salts. As a result, 2,3BC remained as the best potential candidate for an alternative solvent for EDLCs. 2,3BC has a high boiling point (243 degrees C) that is comparable to PC (242 degrees C) and dissolved spirobipyrrolidinium tetrafluoroborate (SBP-BF4). A SBP-BF4/2,3BC system showed a stabilized capacitance within wider voltage windows (Delta V = 3.5 V) that far exceeded that of conventional PC based systems (Delta V = 2.7 V). This high withstand voltage is caused mainly by the outstanding oxidative durability of 2,3BC.
The principle of utilizing the non-Faradaic double-layer capacitance of electrode interfaces as a means of storing electrical energy was suggested and utilized in technologies initiated some 37 years ago. However, only over the last ten years has major interest been manifested in commercial development of this possibility in so-called ‘supercapacitors’ or ‘ultracapacitors’ based on the large double-layer capacitance achievable at high-area, carbon powder electrodes. In parallel with the utilization of double-layer capacitance is the possibility of use of the large pseudocapacitance that is associated with e.g. electrosorption of H or metal adatoms (underpotential deposition) and especially some redox processes. Such pseudocapacitance arises when, for thermodynamic reasons, the charge q required for progression of an electrode process, e.g. electrosorption or conversion of an oxidized species to a corresponding reduced species in liquid or solid solution, is a continuous function of potential, V; then the derivative dq/dV corresponds to a capacitance but one of a Faradaic kind. This behavior is different from that with an ideal battery where, according to the Nernst equation, V is invariant with state-of-charge measured by q Various experimental examples are shown and characterized, especially that for RuO2 and other transition metal oxides. Additionally, electroactive polymers such as polyaniline exhibit analogous pseudocapacitative behavior.
Electrochemical capacitors (EC) also called ‘supercapacitors’ or ‘ultracapacitors’ store the energy in the electric field of the electrochemical double-layer. Use of high surface-area electrodes result in extremely large capacitance. Single cell voltage of ECs is typically limited to 1–3 V depending on the electrolyte used. Small electrochemical capacitors for low-voltage electronic applications have been commercially available for many years. Different applications demanding large ECs with high voltage and improved energy and power density are under discussion. Fundamental principles, performance, characteristics, present and future applications of electrochemical capacitors are presented in this communication.
Dynamics and Control of Electrified Vehicles
- L Zhang
- Zhang
Greener Synthesis of 1, 2-Butylene Carbonate from CO2 Using Graphene-Inorganic Nanocomposite Catalysis
- J Krope
- A G Olabi
- D Goričanec
- S Božičnik
- Krope