Electrochemical Double Layer Capacitor Device Research Articles

LiNO3-poly(vinyl alcohol) polymer electrolytes and its applications in electrochemical capacitors with extended operating temperatures

An ion-conducting neutral pH polymer electrolyte based on LiNO3 and poly(vinyl alcohol) (PVA) was developed for solid electrochemical double layer capacitors (EDLCs). Structural characterizations of LiNO3-PVA electrolytes revealed amorphous structure with well-hydrated ions. The polymer electrolytes are functional over a wide range of temperatures even at −40 °C. Although increasing the concentration of ions can improve the ionic conductivity at and above ambient, it imposes adverse effects at lower temperatures likely due to the freezing of water surrounding the hygroscopic nitrate ions. The optimal electrolyte with relatively high ionic conductivity (ca. 40 mS cm−1 at ambient) and good temperature performance was applied for solid EDLC devices with multi-walled carbon nanotube electrodes. The solid EDLC showed comparable performance to its liquid baseline with excellent rate capability and wide voltage window of 1.6 V. It outperformed the liquid counterpart with lower leakage current and retained capacitive behaviour at −40 °C.

Solid-State EDLC Device Based on Magnesium Ion-Conducting Biopolymer Composite Membrane Electrolytes: Impedance, Circuit Modeling, Dielectric Properties and Electrochemical Characteristics.

The polymer electrolyte based on Dx:Cs:Mg(CH3COO)2:Ni with three different glycerol concentrations have been prepared. The impedance study has verified that the electrolyte with 42 wt.% of glycerol (A3) has the highest ionic conductivity of 7.71 × 10−6 S cm−1 at room temperature. The ionic conductivity is found to be influenced by the transport parameters. From the dielectric analysis, it was shown that the electrolytes in this system obeyed the non-Debye behavior. The A3 electrolyte exhibited a dominancy of ions (tion > te) with a breakdown voltage of 2.08 V. The fabricated electrochemical double layer capacitor (EDLC) achieved the specific capacitance values of 24.46 F/g and 39.68 F/g via the cyclic voltammetry (CV) curve and the charge–discharge profile, respectively. The other significant parameters to evaluate the performance of EDLC have been determined, such as internal resistance (186.80 to 202.27 ) energy density (4.46 Wh/kg), power density (500.58 to 558.57 W/kg) and efficiency (92.88%).

Characteristics of EDLC device fabricated from plasticized chitosan:MgCl2 based polymer electrolyte

Chitosan (CS) based polymer electrolytes are prepared via a simple method called solution casting where the ionic source in this work is magnesium chloride (MgCl2). The plasticization method is implemented using glycerol. Through XRD it appears that amorphous phase enrich with increasing glycerol concentration. The impedance study is carried out to estimate the DC conductivity of the plasticized samples. The highest conducting (1.03 × 10−3 S/cm) plasticized electrolyte is used as electrode separator for electrochemical double-layer capacitor (EDLC) application. Ionic transference number in this work is 0.97 where it concludes that the ion is the main charge carrier. No obvious changes in current are detected as the voltage sweeps from 0 to 1.83 V, meaning that CS:MgCl2: glycerol system is potentially steady up to 1.83 V. The outcome of cyclic voltammetry (CV) indicates that no redox reaction is observed and specific capacitance is influenced by scan rates. The crucial parameters of the EDLC, e.g., specific capacitance, internal resistance, energy density, and power density at the 1st cycle are 117 F/g, 183 Ω, 13.1 Wh/kg and 550 W/kg, respectively.

The study of EDLC device fabricated from plasticized magnesium ion conducting chitosan based polymer electrolyte

Plasticized biopolymer electrolytes based on chitosan (CS) doped with magnesium acetate (Mg(CH3COO)2) and various amounts of glycerol have been prepared for energy storage electrochemical double-layer capacitor (EDLC) application. In this work the dielectric and electrochemical properties have been examined using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). It is confirmed from the frequency changing of the impedance spectra that relatively high dielectric constant has been recorded at low frequency region. From tan δ and M″ spectra, relaxation peaks are clearly seen. It has been found that as the glycerol concentration increased, the DC conductivity increases. In the fabricated system (CS: Mg(CH3COO)2: glycerol.), ions are responsible for charge carrying as the ion transference number is higher than the electron transference number. The electrochemical stability of the system extends to 2.4 V as shown in the LSV. The mechanism of the charge storage has been investigated and indicated that the non-Faradaic dominates where the specific capacitance is significantly affected by scan rate. The fabricated EDLC possessed a constant value of specific capacitance (78.2 F/g), energy density (8.8 Wh/kg), and ESR (78.2 F/g). The EDLC has an tremendous cycleability as high number of Columbic efficiency has accomplished. The value of efficiency of the EDLC has been in the range of 97%–99%.

Electrical, Dielectric Property and Electrochemical Performances of Plasticized Silver Ion-Conducting Chitosan-Based Polymer Nanocomposites.

In the present work, chitosan (CS) as a natural biopolymer was used to prepare nanocomposite polymer electrolytes (NCPEs) in order to reduce plastic waste pollution. The plasticized CS-based NCSPE has been prepared via the solution casting technique. The electrical properties of the films were investigated using AC conductivity, dielectric properties, electric modulus, and electrical impedance spectroscopy (EIS). The obtained results from the dielectric properties and electric modulus study confirm the non-Debye behavior of ion dynamics. The effect of glycerol plasticizer on ionic conductivity of the CS:AgNO3:Al2O3 system was investigated via AC conductivity and impedance studies. The conductivity of the samples was explained based on electrical equivalent circuits and Bode plots. The electrochemical properties such as transfer number measurement (TNM), linear sweep voltammetry (LSV), and cyclic voltammetry (CV) were carried out to inspect the sample suitability for electrochemical double-layer capacitor (EDLC) application. The highest conductivity was 3.7 × 10−4 S cm−1 with the electrochemical stability window up to 2.1 V at room temperature. Through the TNM study, the ionic conductivity of plasticized CS-based NCSPE was confirmed, and ion transport (tion) of the highest conducting sample was found to be 0.985. The activated carbon electrode with the highest conducting sample was employed in the EDLC device fabrication. Accordingly, it can be said that the highest conducting sample had capable performance to be applied in electrochemical device application.

Microporous Carbon Electrodes Derived from Polyacrylonitrile/Poly(Styrene-co-Acrylonitrile) Blends

Current energy demands and technological advancements will require a wide array of energy storage devices such as supercapcitors that can deliver large quantities of energy quickly. Electrochemical double layer capacitors (EDLC) are capable of cycling thousands of times with minimal drop in total capacitance, and when used with an ionic liquid electrolyte they can deliver higher energy densities due to high operating voltages. Surface area, and pore size distribution play a critical role in the performance of EDLC devices due to their relationship to capacitance. Therefore, electrospun carbon nanofibers are a promising EDLC electrode material due to their high surface area, conductivity, and cyclability. Their surface area can be tailored with the inclusion of in-situ porogens in the polymer precursor and activation during carbonization. Polymer derived carbon fibers have been produced from polyacrylonitrile (PAN) using immiscible blends with sacrificial polymers like polystyrene (PS). The resulting carbons have high surface areas (>2,000 m2g-1), but a wide distribution of pore sizes. Altering the miscibility of the sacrificial polymer with the copolymer poly(styrene-co-acrylonitrile) (SAN) affords a unique fiber morphology with a high microporosity. Figure 1

A structural supercapacitor based on activated carbon fabric and a solid electrolyte

ABSTRACTThis paper presents investigations to create a structural supercapacitor with activated carbon fabric electrodes and a solid composite electrolyte, consisting of organic liquid electrolyte 1 M TEABF4 in propylene carbonate and an epoxy matrix where different compositions were considered of 1:2, 1:1 and 2:1 w/w epoxy:liquid electrolyte. Vacuum-assisted resin transfer moulding was used for the impregnation of the electrolyte mixture into the electrochemical double layer capacitor (EDLC) assembly. The best electrochemical performance was exhibited by the 1:2 w/w epoxy: liquid electrolyte ratio, with a cell equivalent-in-series resistance of 160 Ω cm2 and a maximum electrode-specific capacitance of 101.6 mF g−1 while the flexural modulus and strength were 0.3 GPa and 29.1 MPa, respectively, indicating a solid EDLC device.

High Performance Graphene-Based Electrochemical Double Layer Capacitors Using 1-Butyl-1-methylpyrrolidinium tris (pentafluoroethyl) trifluorophosphate Ionic Liquid as an Electrolyte

There are several advantages to developing electrochemical double-layer capacitors (EDLC) or supercapacitors with high specific energy densities, for example, these can be used in applications related to quality power generation, voltage stabilization, and frequency regulation. In this regard, ionic liquids capable of providing a higher voltage window of operations compared to an aqueous and/or polymer electrolyte can significantly enhance the specific energy densities of EDLCs. Here we demonstrate that EDLCs fabricated using ionic liquid 1-butyl-1-methylpyrrolidinium tris (pentafluoroethyl) trifluorophosphate (BMP-FAP) as an electrolyte and few layer liquid-phase exfoliated graphene as electrodes show remarkable performance compared to EDLC devices fabricated with aqueous potassium hydroxide (6M) as well as widely used ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6). We found that graphene EDLC’s with BMP-FAP as an electrolyte possess a high specific energy density of ≈25 Wh/kg along with specific capacitance values as high as 200 F/g and having an operating voltage windows of >5 volts with a rapid charge transfer response. These findings strongly indicate the suitability of BMP-FAP as a good choice of electrolyte for high energy density EDLC devices.

1-Allyl-3-methylimidazolium-based ionic liquids employed as suitable electrolytes for high energy density supercapacitors based on graphene nanosheets electrodes

The preparation of a series of novel low viscosity 1-allyl-3-methylimidazolium ionic liquids (ILs) is performed following dedicated synthetic routes. The physico-chemical properties of resulting molecular solvent-free ILs (true ILs) are investigated and discussed systematically toward the anion constituents. Herein, six electrolytes are studied including one planar structured anion (DCA−) and five anions presenting non-planar structures (PF6−, TFSI−, BF4−, TFA− and OTf−). The as-prepared ILs are employed as green electrolytes for symmetric electrochemical double layer capacitors (EDLCs) based on graphene nanosheets (GNS) electrodes. The EDLC devices deliver specific capacitances ranging from 135 to 228F·g−1, and suitable energy densities, ranging from 41 to 115Wh·kg−1. An electrochemical stability of 94% is reached upon 1000 charge/discharge cycles over a large cell voltage window (3–4V) with a quasi-ideal capacitive behaviour. Among the studied ILs, 1-allyl-3-methylimidazolium dicyanmide (AMIM-DCA) exhibit the highest specific capacitance and the maximum energy density. Such a performance is attributed to the compatibility between the channel-based 2-D graphene network and the planar structure of AMIM-DCA. The resulting AMIM-DCA/GNS interface facilitates the reversible adsorption/desorption process of electrolyte ions during the charge storage. Accordingly, the studied EDLC cells are promising candidates for high-capacity and high-reliability energy-storage applications.

The Influence of Conductive Salt Ion Selection on the Performance of High Voltage Edlcs

In state of the art electrochemical double layer capacitors (EDLCs), solutions of tetraethylammonium tetrafluroroborate (Et4NBF4) in propylene carbonate (PC) or acetonitrile (AN) are used as electrolytes, while activated carbons (AC) are used as electrode active materials. These combinations of materials enable the realization of EDLCs with high power (up to 10 kW kg-1), extraordinary cycle life (>500.000 cycles) and energy in the order of 5Whkg-1. The operative voltages of these devices are of 2.7 to 2.8 V [1]. It is known that an increase of the EDLCs energy would allow the introduction of these high power devices in a larger number of applications [1-2]. Therefore, in the last years many efforts have been made to increase the energy of EDLCs. The energy E stored in an EDLC system is described by the equation E=1/2 CV 2, where C is the capacitance and Vthe operative voltage of the device. Considering this equation, it is evident that to increase the operative voltage in the most convenient strategy to increase the energy of these devices. It has been shown that when the material-electrolyte combination reported above is used, the use of operative voltages higher than 2.8 V results in a significant decrease of the devices’ cycle life [1-2]. Therefore, the development of innovative electrolytes appears therefore a key aspect for the realization of high energy EDLCs: in the future new solvents, new conducting salts as well as new ionic liquids need to be considered [1-2]. Together with the electrode material, the ions of the conducting salts are forming the double layer, effectively influencing charge storage in in EDLCs. The size, electrochemical and chemical stability of these ions have a dramatic impact on the storage process. Nevertheless, it is interesting (and somehow surprising) to notice that in the past only a relatively low number of studies focused on the development of new conducting salt for high voltage EDLCs. In this study we investigated the influence of conductive salts on the physical-chemical as well as electrochemical properties of PC based electrolytes in view of the realization of advanced high voltage EDLCs. We showed that the operative voltage of EDLCs containing PC-based electrolytes can be increased by a mere change in conductive salt. Nevertheless, anions and cations forming the conductive salt have to be carefully selected, as the choice of salt influences both electrochemical properties as well as ion transport properties of EDLC electrolytes, leading to an impact on energy and power storage in EDLC devices. While higher operative voltages are generally desirable, one has to consider and carefully balance the advantages and disadvantages of each electrolyte, as high values for viscosity or decreased ion mobilities can lead to decreased values for energy and power, even if operative voltages are increased [2]. Among the innovative electrolytes we investigated, those based on the salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr14BF4) appear particularly promising. As a matter of fact, the electrolyte containing Pyr14BF4 as salt and in PC as solvent displays good conductivity and low viscosity and, thanks to its anion-cation combination, also allows the achievement of high operative voltages. As a consequence, its application enables the construction of EDLCs with higher energy and power compared to state-of-the-art devices (see Fig. 1) [3]. Furthermore, the use of these electrolytes makes also possible the realization of EDLCs exhibiting a high cycling stability [2-3].

Electrochemical properties of carbon from oil palm kernel shell for high performance supercapacitors

Electrochemical properties of activated carbon (AC) derived from oil palm kernel shell (PKS) are evaluated and compared with other biomass derived AC for fabricating high performance electrochemical double layer capacitors (EDLC). Cleaned PKS are carbonized by pyrolysis and subsequently activated by physical and chemical methods. The chemically AC show a wider pore distribution (1.4–9.3nm) whereas the physically activated one has uniform pores (1.5nm). The electrochemical properties of the two types of AC are evaluated using cyclic voltammetry (CV), charge–discharge cycling (CDC) and electrochemical impedance spectroscopy (EIS) in three-electrode configuration. High specific capacitance (CS) (210Fg−1 in 1M KOH electrolyte at 0.5Ag−1) is obtained for chemically AC whereas the CS for the physically AC is 50% lower (123Fg−1). Galvanostatic CDC tests show that the electrodes maintained ∼95–97% of CS after 1000 cycles. The EIS revealed that the PKS AC has low series resistance (< 0.6Ω) and relaxation time (∼0.69s) which would therefore offers high power density in the EDLC devices.

Increasing Capacitance of Zeolite-Templated Carbons in Electric Double Layer Capacitors

Enhancement of the specific capacitance in electrochemical double layer capacitors (EDLCs) is of high interest due to the ever increasing demand for high power density energy storage devices. Zeolite templated carbon (ZTC) is a promising EDLC electrode material with large specific surface area and straight, ordered well-defined micropores. In this study, ZTC samples were synthesized using a low pressure chemical vapor deposition (LP CVD) of carbon on sacrificial zeolite Y powder using acetylene gas as a precursor. We demonstrate for the first time how various post-treatments of the produced samples can affect the ZTC microstructure and porosity and how such modifications may significantly improve electrochemical performance characteristics of the ZTC-based EDLC electrodes. The effects of CO2 activation, ball milling and high temperature annealing process were systematically studied. The best performing samples achieved very large capacitance of over 240 Fg−1 at 1 mVs−1 in 1 M solution of tetraethylammonium tetrafluoroborate in acetonitrile and stable performance in symmetric EDLC devices with no noticeable degradation for over 20,000 cycles at a very high current density of 20 Ag−1.

Development of an equivalent circuit model for electrochemical double layer capacitors (EDLCs) with distinct electrolytes

An equivalent circuit model for electrochemical double layer capacitors (EDLCs) is proposed through analyzing the electrochemical impedance spectroscopy (EIS) measurements. The model is developed based on the Grahame theory, while these capacitive or resistive behaviors in the presence of charge diffusion and the ion adsorption at the double layer interface and bulk media are investigated. This circuit model, upon its validation against the EIS data, is successfully applied to characterize the practical EDLC devices. Meanwhile, experimental results are obtained from different EDLC cells that consist of the activated carbon-based electrodes and two electrolytes, namely, aqueous (H2SO4) and organic (Et4NBF4/PC). The model predicts the useful parameters (such as resistance and capacitance) which help interpret electrochemical reactions at the electrode/electrolyte interface. The quantitative dependence of impedance on the applied electrode potential is analyzed for two electrolytes during charging/discharging, and its correlation with the internal resistance (referred ESR) is studied.

Steric effects in adsorption of ions from mixed electrolytes into microporous carbon

With the goal to improve the capacitance in electrochemical double-layer capacitors (EDLCs) many studies on pore size/ion size relationship have been undertaken to achieve a better understanding of the charge storage mechanism in the electrochemical double-layer in confinement. A significant capacitance increase was achieved by using carbon electrodes with micropores (< 1 nm), when the carbon pore size was close to the ion size. In this paper, the accessibility of narrow pores is investigated by selecting a carbon with a small pore size (< 0.7 nm) and electrolyte mixtures with different ion sizes. It has been shown that the adsorption capacitance limitation observed for large cations and anions could be overcome by adding ions with a smaller effective size. This result demonstrates that the pores are accessible when their size matches the effective ion size and contradicts the surface saturation assumption; effective ion size which exceeds the pore size leads to current limitation. This work confirms that the steric effect is involved when ions are adsorbed into pores and highlights the importance of controlling ion size/pore size relationship for optimisation of the capacitive performance of EDLC devices.

The Sympathetic and Parasympathetic Nervous Systems of the Fowl: Notes on a Thesis Presented for the Degree of Doctor of Philosophy

An equivalent circuit model for electrochemical double layer capacitors (EDLCs) is proposed through analyzing the electrochemical impedance spectroscopy (EIS) measurements. The model is developed based on the Grahame theory, while these capacitive or resistive behaviors in the presence of charge diffusion and the ion adsorption at the double layer interface and bulk media are investigated. This circuit model, upon its validation against the EIS data, is successfully applied to characterize the practical EDLC devices. Meanwhile, experimental results are obtained from different EDLC cells that consist of the activated carbon-based electrodes and two electrolytes, namely, aqueous (H2SO4) and organic (Et4NBF4/PC). The model predicts the useful parameters (such as resistance and capacitance) which help interpret electrochemical reactions at the electrode/electrolyte interface. The quantitative dependence of impedance on the applied electrode potential is analyzed for two electrolytes during charging/discharging, and its correlation with the internal resistance (referred ESR) is studied.