Performance Of Electrochemical Double Layer Capacitors Research Articles

Strain induced electrochemical behaviors of ionic liquid electrolytes in an electrochemical double layer capacitor: Insights from molecular dynamics simulations.

Electrochemical Double Layer Capacitors (EDLCs) with ionic liquid electrolytes outperform conventional ones using aqueous and organic electrolytes in energy density and safety. However, understanding the electrochemical behaviors of ionic liquid electrolytes under compressive/tensile strain is essential for the design of flexible EDLCs as well as normal EDLCs, which are subject to external forces during assembly. Despite many experimental studies, the compression/stretching effects on the performance of ionic liquid EDLCs remain inconclusive and controversial. In addition, there is hardly any evidence of prior theoretical work done in this area, which makes the literature on this topic scarce. Herein, for the first time, we developed an atomistic model to study the processes underlying the electrochemical behaviors of ionic liquids in an EDLC under strain. Constant potential non-equilibrium molecular dynamics simulations are conducted for EMIM BF4 placed between two graphene walls as electrodes. Compared to zero strain, low compression of the EDLC resulted in compromised performance as the electrode charge density dropped by 29%, and the performance reduction deteriorated significantly with a further increase in compression. In contrast, stretching is found to enhance the performance by increasing the charge storage in the electrodes by 7%. The performance changes with compression and stretching are due to changes in the double-layer structure. In addition, an increase in the value of the applied potential during the application of strain leads to capacity retention with compression revealed by the newly performed simulations.

SCOBY-based bacterial cellulose as free standing electrodes for safer, greener and cleaner energy storage technology

Bacterial Cellulose (BC) derived from local market or symbiotic culture of bacteria and yeast (SCOBY) was employed as the polymer matrix for hydroxyl multi-walled carbon nanotube (MWCNT-OH)-based electrochemical double-layer capacitor (EDLC). Chitosan (CS)-sodium iodide (NaI)-glycerol (Gly) electrolyte systems were used as the polymer electrolyte. CS-NaI-Gly electrolyte possesses conductivity, potential stability and ionic transference number of (1.20 ± 0.26) × 10−3 S cm−2, 2.5 V and 0.99, respectively. For the electrodes, MWCNT-OH was observed to be well dispersed in the matrix of BC which was obtained via FESEM analysis. The inclusion of MWCNT-OH reduced the crystallinity of the BC polymeric structure. From EIS measurement, it was verified that the presence of MWCNT-OH decreased the electron transfer resistance of BC-based electrodes. Cyclic voltammetry (CV) showed that the shape of the CV plots changed to a rectangular-like shape plot as more MWCNT were added, thus verifying the capacitive behavior. Various amount of MWCNT-OH was used in the fabrication of the EDLC where it was discovered that more MWCNT-OH leads to a better EDLC performance. The EDLC was tested for 5000 complete charge-discharge cycles. The optimum performance of this low voltage EDLC was obtained with 0.1 g MWCNT where the average specific capacitance was 8.80 F g−1. The maximum power and energy density of the fabricated EDLC were 300 W kg−1 and 1.6 W h kg−1, respectively.

Enhancement of electrical and electrochemical properties of sodium bromide incorporated with poly (ethylene oxide)/poly (vinylidene fluoride-hexafluoropropylene) solid blend polymer electrolytes for electrochemical double layer capacitors

Sodium-ion conducting solid blend polymer electrolytes are prepared with Poly (ethylene oxide) (PEO)/Poly (vinylidene fluoride-hexafluoropropylene) P(VdF-HFP)/Sodium Bromide (NaBr) by solution casting technique. Different analysis such as structural, vibrational, electrical and electrochemical studies reveal promising properties of the prepared solid polymer electrolytes (SPE). The XRD analysis illustrates the increase in amorphous nature of the sample up to 8 wt% NaBr salt concentration. The complexation between polymers and salt has been examined by FTIR analysis. To examine the electrical conductivity, AC impedance analysis was performed in the temperature range of 303–373 K. The higher ionic conductivity (σ) of 1.10 × 10−3 S cm−1 was found for the solid polymer electrolyte (SPE) containing 8 wt% NaBr at room temperature. The temperature dependence of ionic conductivity resembles Arrhenius behavior. The dielectric behavior has been analyzed using dielectric permittivity (ε*) and the relaxation frequency (τ) has been calculated from the loss tangent spectra (tan δ). The modulus spectra indicate the non-Debye nature of the material. Wagner's DC polarization technique was used to compute the transference number. According to the LSV analysis, the solid blend polymer electrolytes have the suitable electrochemical potential window to be used in electrochemical devices. The cyclic voltammetry (CV) and charge-discharge studies (GCD) of the assembled electrochemical double-layer capacitor (EDLC) show specific capacitance (Csp) values of 12.9 F/g and 10.4 F/g respectively. Further the better performance of EDLC is confirmed with its energy density (3.25 to 2.12 Wh/kg), power density (750 to 2623 W/kg) as well as coulombic efficiency (98.2 %) after 1500 cycles.

Amide-based deep eutectic solvents containing LiFSI and NaFSI salts as superionic electrolytes for supercapacitor applications.

This work proposes two deep eutectic solvents (DESs) based on lithium bis(fluorosulfonyl)imide and sodium bis(fluorosulfonyl)imide together with N-methylacetamide and formamide as electrolytes for activated carbon (AC) electrochemical double-layer capacitors (EDLCs) at 25 °C. The formulated DESs exhibit a large electrochemical window (ΔE > 2.5 V), good thermal stability (∼150 °C) and ionic conductivity (3-4 mS cm-1), and moderate viscosity (11.3 mPa s). Through the Vogel-Tamman-Vulcher fitting equation, the evolution of pseudo-energy activation was delineated with respect to the nature of the H-bond donor or alkali salt. These electrolytes present a superionic character gleaned from the Walden classification, and their ionicity exceeds that of standard organic electrolytes based on similar alkali salts. The performance of the AC-based EDLC was assessed by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge, yielding 140 F g-1 with an 8% capacity retention during 200 h of floating. Based on the physicochemical properties and electrochemical performance of these DESs, they represent a promising green-alternative electrolyte for supercapacitor applications.

A Proposed Strategy to Solve the ‎Intermittency Problem in Renewable Energy Systems ‎Using A Hybrid Energy ‎Storage System

Renewable energy resources are a favorable solution for the coming energy. So, a great interest has been paid in the last decades for developing and utilizing renewable energy resources as wind energy. As it has a large energy contents and, particularize with the availability, but the major problems of it are represented in unmatched with load demand because the intermittency and fluctuation of nature conditions. Many studies focused on the new strategy of using Battery Storage System (BSS), and solving some problems that affect the DC bus voltage and the BSS by using Electrochemical Double Layer Capacitor (EDLC). Their capability is to store energy to realize the objective of time shifting of surplus energy with a high efficiency. The article main objective is to model, simulate, design, and study the performance of a Stand-Alone Wind Energy System with Hybrid Energy Storage (SAWS-HES). Thus, a complete model of the proposed system is implemented including a detailed modeling procedure of the HESS components. In addition to the main contribution, a study of the performance of EDLC only as a storage device that has fast response device integrated to the suggested system then it hybridized with the BSS. The HESS has the capability to compensate the DC bus voltage in the transient conditions and gives good stability for the system. The SAWS-HES utilizes one main renewable energy resource as wind turbine and overall model is employed under MATLAB/Simulink including a developed simple logic controller. The SAWS-HES simulation results presented a promising performance and have a satisfied performance in meeting the end load demands at different operation conditions. This ensures the SAWS-HES reliability and the effectiveness with HES and the controller in stand-alone operation formulating an excellent solution for the renewable energy systems

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%).

Effect of conductive polypyrrole in poly(acrylonitrile-co-butyl acrylate) water–based binder on the performance of electrochemical double-layer capacitors

Electrochemical double-layer capacitors (EDLCs) have been widely studied due to their high-power densities, despite their low energy densities compared with those of lithium ion batteries. In particular, there have been numerous studies aiming to developing high surface area carbonic material to increase EDLCs’ capacitance. However, there have been few studies examining water-based polymeric binder as an inactive component of the EDLCs’ electrodes. In this study, we introduce a conductive water-based binder which is synthesized by an in situ two-step polymerization, and use it for EDLC electrodes. Polypyrrole (PPy) is used as an electrically conducting filler for a water-based polyacrylate binder to enhance the electrochemical performance of EDLCs. Consequently, the use of the new poly(pyrrole/acrylonitrile-co-butyl acrylate) (PPyANBA) increases the specific capacitance of the EDLC electrode up to 109.7 F g−1 from the 101.0 F g−1 value of the nonconductive PANBA-containing EDLC electrode at 10,000 cycles. This is mainly attributed to the better dispersion and lower electrical resistance of the PPyANBA binder without losing the thermal, ion transport, and binding characteristics of the PANBA. Graphical abstract

The Study of Electrical and Electrochemical Properties of Magnesium Ion Conducting CS: PVA Based Polymer Blend Electrolytes: Role of Lattice Energy of Magnesium Salts on EDLC Performance.

Plasticized magnesium ion conducting polymer blend electrolytes based on chitosan (CS): polyvinyl alcohol (PVA) was synthesized with a casting technique. The source of ions is magnesium triflate Mg(CF3SO3)2, and glycerol was used as a plasticizer. The electrical and electrochemical characteristics were examined. The outcome from X-ray diffraction (XRD) examination illustrates that the electrolyte with highest conductivity exhibits the minimum degree of crystallinity. The study of the dielectric relaxation has shown that the peak appearance obeys the non-Debye type of relaxation process. An enhancement in conductivity of ions of the electrolyte system was achieved by insertion of glycerol. The total conductivity is essentially ascribed to ions instead of electrons. The maximum DC ionic conductivity was measured to be 1.016 × 10−5 S cm−1 when 42 wt.% of plasticizer was added. Potential stability of the highest conducting electrolyte was found to be 2.4 V. The cyclic voltammetry (CV) response shows the behavior of the capacitor is non-Faradaic where no redox peaks appear. The shape of the CV response and EDLC specific capacitance are influenced by the scan rate. The specific capacitance values were 7.41 F/g and 32.69 F/g at 100 mV/s and 10 mV/s, respectively. Finally, the electrolyte with maximum conductivity value is obtained and used as electrodes separator in the electrochemical double-layer capacitor (EDLC) applications. The role of lattice energy of magnesium salts in energy storage performance is discussed in detail.

Properties of electrochemical double-layer capacitors with carbon-nanotubes-on-carbon-fiber-felt electrodes

Carbon nanotube (CNT) layers deposited on carbon fiber cloth (CFC) materials have been studied as electrodes of electrochemical double layer capacitors (EDLCs), in particular, the electrochemical performance and cycle stability of symmetric EDLCs in an organic electrolyte (tetraethyl-ammonium-fluoroborate in acetonitrile). Due to the large surface area of carbon-fibers, the CNT mass loading can be as high as 18 mg/cm2 which is magnitudes larger than that of what can be deposited on aluminium or nickel metal sheets. The area normalized double layer capacitance of CNT/CFC electrodes in the above organic electrolytes were found to be in the range of 100–400 mF/cm2, and the specific capacitances were 18–48 F/g. These latter values are below the achievable values of single-wall CNT of 80 F/g; the lower values can be attributed to the presence of multi-walled CNTs of some quantities, having lower accessible surface area. The energy density of CNT/CFC supercapacitors is 0.8–1.5 Wh/kg, while the power density varies between 5 and 20 kW/kg calculated on electrode level. Excellent cycling stability of EDLCs built with CNT-on carbon felt electrodes has been demonstrated up to 1 million cycles, which is due to the inert nature of substrate causing the absence of corrosion process and high mass load of CNT.

Influence of Water on the Properties of Protic Ionic Liquids

Protic ionic liquids (PILs) represent an interesting subclass of Ionic Liquids (ILs), with properties suitable for the realization of different kinds of electrochemical energy storage devices. [1-2] PIL have been proposed as electrolytes for electrochemical double layer capacitors (EDLCs) and lithium-ion batteries (LIBs) [ref]. In the case of EDLCs the use of these ILs appears not to be particularly advantageous due to the presence of a proton on their structure, limiting the operative voltage, and their relative high viscosity, limiting the power performance of these devices. In the case of LIBs, to the contrary, the presence of the proton has a positive influence on the lithium coordination and on the performance at high current densities of IL-based LIBs. [3]. The influence of the water content on the chemical-physical properties of PILs have been investigated in the past, and it has been found that even a few hundred ppm of residual water are strongly changing the properties of these ILs, e.g. they might significantly lower the melting point of PILs. Nevertheless, the impact of the water content on the electrochemical performance of electrochemical energy storage devices containing PILs as electrolytes has not been investigated in detail. These important aspects should be investigated because it could supply valuable information about the development of PIL-based devices. In this paper we report about the influence of water on the properties of the PIL butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PyrH4TFSI) containing different amounts of water (0, 1, 2, 3.8 wt%). The viscosity, ionic conductivity, density and electrochemical stability of these PIL have been investigated in detail. Furthermore, the mixtures were utilized as electrolytes for EDLCs containing activated carbon-based electrodes, as well as for LIBs containing graphite anodes and lithium iron phosphate (LFP) cathodes. The results of this study indicate that small amounts of water have a significant impact on the overall transport properties and stability of PyrH4TFSI. Moreover, they also show that the performance of EDLCs and LIBs containing PyrH4TFSI as electrolyte are considerably changing depending on the water content of the PIL. Literature: [1] Menne, Electrochem. Commun. 2013, 31, 39-41.[2] Vogl, Journal of Materials Chemistry A 2016, 4, 10472-10478.[3] Brandt, Electrochim. Acta 2013, 108, 226-231. Figure 1

High temperature solid-state supercapacitor designed with ionogel electrolyte

To date, the design of high temperature electrochemical double layer capacitors (EDLCs) remains a challenge more specifically related to the electrolyte. The electrochemical performance of EDLC can be tuned by the temperature, and a better performance can be achieved at higher temperature if all the components are well suited to this purpose. Subsequently, an all solid-state EDLC operated at high temperature using porous carbon electrodes and a solid-like electrolyte was fabricated. Such an approach opens the route towards safer and flexible devices. An ionogel was used as the solid electrolyte and concomitantly as separator in this all-solid EDLC. The synthetized ionogel exhibits a high ionic conductivity over a wide temperature range, from 4 mS cm−1 at 20 °C up to 26 mS cm−1 cm at 100 °C. The all solid state EDLC thus prepared was able to withstand operating temperature as high as 100 °C, under a 2.5 V cell voltage. Long term galvanostatic charge−discharge cycling over 25 000 cycles were achieved at 100 °C, thus demonstrating very good capacitance retention. The ionogel-based EDLCs therefore appear to be suitable for high temperature environments.

Flexible Graphene/Carbon Nanotube Electrochemical Double-Layer Capacitors with Ultrahigh Areal Performance.

The fabrication of electrochemical double-layer capacitors (EDLCs) with high areal capacitance relies on the use of elevated mass loadings of highly porous active materials. Herein, we demonstrate a high-throughput manufacturing of graphene/carbon nanotubes hybrid EDLCs. The wet-jet milling (WJM) method is exploited to exfoliate the graphite into single-few-layer graphene flakes (WJM-G) in industrial volumes (production rate ca. 0.5 kg/day). Commercial single-/double-walled carbon nanotubes (SDWCNTs) are mixed with graphene flakes in order to act as spacers between the flakes during their film formation. The WJM-G/SDWCNTs films are obtained by one-step vacuum filtration of the material dispersions, resulting in self-standing, metal- and binder-free flexible EDLC electrodes with high active material mass loadings up to around 30 mg cm-2 . The corresponding symmetric WJM-G/SDWCNTs EDLCs exhibit electrode energy densities of 539 μWh cm-2 at 1.3 mW cm-2 and operating power densities up to 532 mW cm-2 (outperforming most of the reported EDLC technologies). The EDCLs show excellent cycling stability and outstanding flexibility even in highly folded states (up to 180°).

An Electrochemical Impedance Spectroscopy Study of Hydroxide Ion Conduction in Polymer Electrolytes

Solid alkaline polymer electrolytes are important enablers for safe, lightweight, electrochemical energy storage devices. Tetraethylammonium hydroxide (TEAOH) is an OH- ion conductor, compatible with various water soluble polymers[1,2]. Polyacrylamide (PAM), a hygroscopic amorphous polymer, was combined with TEAOH to form a solid electrolyte. The resulting TEAOH-PAM electrolyte exhibited good ionic conductivity (> 10 mS cm-1) at room temperature. However, its performance can vary with the environmental relative humidity (RH). It was reported that TEAOH is prone to bond with water, forming different hydrate compounds that may impact OH- ion-conduction[3]. In addition, the role of ion content and ion motion on OH- ion-conduction in a polymer matrix needs to be further clarified by using dielectric analysis[4]. Therefore, it is important to elucidate the influence of these effects on OH- ion-conduction in the solid-state under different environmental conditions (i.e. RH, temperature). In this study, we investigated the ionic conduction mechanism at various temperatures using electrochemical impedance spectroscopy (EIS). The capacitances of the enabled solid cells and conductivities of the electrolytes were correlated to ion content and ion motion by dielectric analyses from the EIS data. The hydration structure of ions in TEAOH-PAM was quantified under three levels of RH[3]. Through analyzing these properties at elevated temperatures, an interplay of conduction mechanisms between ion transport via segmental motion of the polymer chains and OH- ion hopping was discovered (Fig. 1). High temperature studies were performed on 2D solid-state electrochemical double layer capacitors (EDLCs), leveraging the TEAOH-PAM electrolyte with vertically-oriented graphene nanosheet (VOGN). The super high rate performance of the solid-state EDLC was demonstrated at and above 100 °C. While the device operates optimally at 100 °C, it is also capable of withstanding short-term temperature exposure up to 120 °C. The excellent thermal resilience was further evidenced by the repeatable performance after subjecting to thermal cycles. From thermogravimetric analysis and Raman spectroscopy experiments at different temperatures, we found that dehydration of TEAOH-PAM is linked to rearrangement of ion conformations. This change in chemistry with higher thermal energy are key attributes responsible for the device’s temperature dependent performance. These results provide guidelines and strategies to design polymer electrolytes for high performance solid-state energy storage devices.

High‐Voltage Stability of Ionic‐Liquid‐Based Electrochemical Double Layer Capacitors with a Bimodal Porous Carbon Electrode

AbstractMicropores (<2 nm) and small mesopores (width between 2 and 10 nm) in the structure of carbon play an important role in determining both the charge storage properties and voltage stability of ionic‐liquid‐based electrochemical double layer capacitors (EDLCs). We demonstrate that the use of bimodal porous carbon electrodes results in excellent voltage stability and good capacitance retention (>90 %), as determined by using voltage holding tests at 3.5 V over 250 h. Furthermore, a three‐electrode split cell study showed that the voltage stability in bimodal carbon was achieved because of more symmetric potential distribution and similar electrode capacitances between the positive and negative electrodes as compared to purely microporous carbon electrode. The presence of larger mesopores (5–10 nm) in the bimodal carbon facilitates the access and rearrangement of the bulkier cations at the electrode/electrolyte interface, whereas this is severely hindered in purely microporous carbon electrode. By using a lumped transmission line model, we delineated the contribution of both smaller and larger pores in the bimodal carbon towards the impedance performance of EDLCs.

Carbon Capsules of Ionic Liquid for Enhanced Performance of Electrochemical Double-Layer Capacitors.

Ion accessibility, large surface area, and complete wetting of a carbonaceous electrode by the electrolyte are crucial for high-performance electrochemical double-layer capacitors. Herein, we report a facile and scalable method to prepare electrode-electrolyte hybrid materials, where an ionic liquid (IL) electrolyte is encapsulated within a shell of reduced graphene oxide (rGO) nanosheets as the active electrode material (called rGO-IL capsules). These structures were templated using a Pickering emulsion consisting of a dispersed phase of 1-methyl-3-butylimidazolium hexafluorophosphate ([bmim][PF6]) and a continuous water phase; graphene oxide nanosheets were used as the surfactant, and interfacial polymerization yielded polyurea that bound the nanosheets together to form the capsule shell. This method prevents the aggregation and restacking of GO nanosheets and allows wetting of the materials by IL. The chemical composition, thermal properties, morphology, and electrochemical behavior of these new hybrid architectures are fully characterized. Specific capacitances of 80 F g-1 at 18 °C and 127 F g-1 at 60 °C were achieved at a scan rate of 10 mV s-1 for symmetric coin cells of rGO-IL capsules. These architected materials have higher capacitance at low temperature (18 °C) across many scan rates (10-500 mV s-1) compared with analogous cells with the porous carbon YP-50. These results demonstrate a distinct and important methodology to enhance the performance of electrochemical double-layer capacitors by incorporating electrolyte and carbon material together during synthesis.

Perovskite solar cell – electrochemical double layer capacitor interplay

We demonstrate that by a proper design of a system comprising a perovskite solar cell (PSC) coupled to an electrochemical double-layer capacitor (EDLC), it is possible to simultaneously improve both the PSC and EDLC performance and outperform each single unit behavior. Specifically, we propose a parallel connection of PSC and EDLC of different size. The EDLC buffers PSC fluctuations by storing the converted solar energy permitting for very high power output (increased by 1 order of magnitude). At the same time, the PSC improves the capacitive response of the EDLC that can be downsized towards system miniaturization.

On the interaction of carbon electrodes and non conventional electrolytes in high-voltage electrochemical capacitors

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr14BF4) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr14TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et4NBF4/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation.

Anodic Dissolution of Al Current Collectors in Unconventional Solvents for High Voltage Electrochemical Double-Layer Capacitors.

This study investigated the anodic dissolution of Al current collectors in unconventional electrolytes for high voltage electrochemical double-layer capacitors (EDLCs) containing adiponitrile (ADN), 3-cyanopropionic acid methyl ester (CPAME), 2-methyl-glutaronitrile (2-MGN) as solvent, and tetraethylammonium tetrafluoroborate (Et4 NBF4 ) and tetraethylammonium bis(trifluoromethanesulfonyl)imide (Et4 NTFSI) as conductive salts. 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 analyzed 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 Et4 NBF4 -based electrolytes, the use of an alternative solvent is very beneficial for the realization of stable devices. When Et4 NTFSI is used, the reduced solubility of the complex Al(TFSI)3 appears to be the key for the realization of advanced electrolytes.

A study of 3D printed flexible supercapacitors onto silicone rubber substrates

The rapid development of flexible energy storage devices is crucial for various electronics industries. Highly flexible electrochemical double layer capacitors (EDLCs) can be manufactured by 3D printing technology. It was a great challenge to fabricate multiple material layers of the EDLC in one rapid and accurate deposition event. The fabricated structures were composed of twelve electrodes which could be configured in a number of different ways in one block module. This work aims to investigate the performance of the flexible EDLCs manufactured by 3D printing in a honeycomb pattern. The EDLC cells were fabricated using a slurry made from commercial activated carbon (AC) and a gel electrolyte deposited on a transparent silicone substrate. The flexible EDLCs structures can be used in flexible electronics with different patterns and sizes using 3D printer and can be applied to many applications such as wearable technology.

The Influence of Ion-Solvent Interactions on the Performance of Electrochemical Double Layer Capacitors Containing Non-Conventional Solvents

In the state of the art electrochemical double layer capacitors (EDLCs), solutions of tetraethylammonium tetrafluroroborate (Et4NBF4) in propylene carbonate (PC) or acetonitrile (ACN) are used as electrolytes. Using these electrolytes in combination with activated carbons (AC) based electrodes is possible to realize EDLCs with operative voltages of 2.7-2.8 V and energy in the order of 5Whkg-1. The power of these devices is up 10 kW kg-1 and their cycle life higher than 500.000 cycles [1]. Presently the realization of high energy EDLCs is seen as one of the most important goal for an increase of the market of these devices [1]. The most straightforward strategy to increase the EDLC´s energy is to increase their operative voltage. Since such desirable increase is not possible when the state-of-the-art electrolytes are used, the introduction of new electrolytic solution is presently considered of great importance [1] In order to realize advanced electrolytes for EDLC, the introduction of new conducting salts and/or new solvents appears a viable strategy [1,2]. In the past years we showed that using non-conventional salts is possible to realize PC-based EDLCs with operative voltages higher than 3 V [1,2]. More recently, taking advantaged of computational screening [3], we identified cyano esters as new solvent for the realization of high voltage and high energy EDLCs [4,5]. We showed that cyano ester-based EDLCs display operative voltage as high as 3.5 V and good performance in term of specific capacitance and capacitance retention. After 500 h of float tests carried out at 3.2 V EDLCs containing this type of solvent are able to retain almost 80% of their initial capacitance [4]. It is well known that the ion-solvent interaction might have a dramatic effect on the behaviour of EDLCs [1,2]. While these interactions have been considered for conventional salt-solvent combinations, only little information is available on the case of non-conventional electrolyte components [2]. Herein, we report a systematic investigation about the chemical-physical properties of electrolytes containing the salts tetraethylammonium tetrafluroroborate (Et4NBF4), tetraethylammonium bis(trifluoromethanesulfonyl) imide (Et4NTFSI) and N-butyl-1-methylpyrrolidinium tetrafluoroborate (Pyr14BF4), in the state of the art solvent ACN, and in the alternative solvents Adiponitrile (ADN), 2-methylglutaronitril (MGN) and 3-cyanopropionic acid methyl ester (CPAME). The ionic conductivity, viscosity, density and electrochemical stability windows (ESW) of these electrolytic solutions are considered. Furthermore, the electrochemical performance of EDLCs containing these electrolytes are investigate in details. Finally, also the anodic dissolution of the aluminium current collector in these electrolytes is analysed and discussed [6].