Electrolytes For Electrochemical Capacitors Research Articles

Anticorrosive performance of green deep eutectic solvent for electrochemical capacitor

Reline Deep Eutectic Solvent (DES) is widely recognized as a novel and green electrolyte for industrial applications due to its low cost and tolerance to moisture. It has received significant attention, however, its application in the energy storage system is still in infancy. Generally, aqueous-based electrochemical capacitors (ECs) present an ideal energy storage technology because of several advantages. Yet, high corrosion of the current collector limits their cyclability. Novel Reline DES electrolyte is studied and its anticorrosive electrochemical performance is evaluated in carbon-based ECs using stainless steel current collector (316L). Our findings show that Reline electrolyte and its water mixture display a strong inhibiting corrosion effect for 316L. Furthermore, a few aqueous electrolytes are studied to confirm the effectiveness of Reline DES as a green and anti-corrosive electrolyte for EC. Floating protocol is applied to monitor the stability of the EC performance in Reline and aqueous electrolytes. The devices using pure Reline and its water mixture exhibit higher electrochemical stability with good capacitive performance compared to 1 M Li2SO4 and 1 M KOH based ECs. The study may pave the way to practical Reline DES-based ECs for sustainable, highly stable, environmentally friendly and cost-effective energy storage systems in the future.

Chitin and chitin-cellulose composite hydrogels prepared by ionic liquid-based process as the novel electrolytes for electrochemical capacitors

This paper reports on the preparation and electrochemical performance of chitin- and chitin-cellulose-based hydrogel electrolytes. The materials were prepared by a casting solution technique using ionic liquid-based solvents. The method of chitin dissolution in ionic liquid with the assistance of dimethyl sulfoxide co-solvent was investigated. The obtained membranes were soaked with 1-M lithium sulfate aqueous solution. The prepared materials were preliminarily characterized in terms of structural and physicochemical properties. Further, the most promising biopolymer membranes were assembled with activated carbon cloth electrodes in symmetric electrochemical capacitor cells. The electrochemical performances of these devices were studied in a 2-electrode system by commonly known electrochemical techniques, such as cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The devices operated at a maximum voltage of 0.8 V. All the investigated materials have shown high efficiency in terms of specific capacitance, power density, and cyclability. The studied capacitors exhibited specific capacitance values in the range of 92–98 F g−1, with excellent capacitance retention (ca. 97–98%) after 20,000 galvanostatic charge and discharge cycles. Taking into account the above information and the eco-friendly nature of the biopolymer, it appears that the prepared chitin- and chitin-cellulose-based hydrogel electrolytes can be promising components for green electrochemical capacitors.

Bis(trifluoromethanesulfonyl)imide Metallic Salts Based Electrolytes for Electrochemical Capacitor Application: Theoretical vs Experimental Performance

In this work we have studied the effect of 1 M bis(trifluoromethanesulfonyl)imide metallic salts in acetonitrile (1 M MeTFSI, where Me = Li, Na, K, Cs or Mg) as an electrolyte for electrochemical capacitors (ECs), using computational quantum mechanical modelling, Raman analysis, cyclic voltammetry, electrochemical impedance spectroscopy and constant power methods. Also, the ionic conductivities of 1 M MeTFSI in AN have been measured and discussed. The ECs based on the 1 M KTFSI in AN electrolyte deliver the higher power density and energy density compared to other MeTFSI based electrolytes and showing excellent characteristics applicable in high energy and power EC devices.

Ionic Liquids as Environmentally Benign Electrolytes for High-Performance Supercapacitors.

Electrochemical capacitors (ECs) are a vital class of electrical energy storage (EES) devices that display the capacity of rapid charging and provide high power density. In the current era, interest in using ionic liquids (ILs) in high‐performance EES devices has grown exponentially, as this novel versatile electrolyte media is associated with high thermal stability, excellent ionic conductivity, and the capability to withstand high voltages without undergoing decomposition. ILs are therefore potentially useful materials for improving the energy/power performances of ECs without compromising on safety, cyclic stability, and power density. The current review article underscores the importance of ILs as sustainable and high‐performance electrolytes for electrochemical capacitors.

Silica-Based Ionogel Electrolyte for Electrical Double Layer Capacitors

Electrochemical Capacitors (ECs), also known as supercapacitors, have now reached the technical maturity for complementing- and sometimes replacing- batteries in a broad range of applications. Conventional electrolytes based on acetonitrile or propylene carbonate solvents have been mainly used in combination with ammonium cations and fluoride anions. Designing solid electrolytes for ECs would be of great interest in the aim of solving packaging issues, corrosion, self-discharge or leaks. Moreover these solid electrolytes could be used for flexible supercapacitors applications. Ionogels are quasi-solid electrolyte obtained from the trapping of an IL into a silica scaffold using a sol-gel process. The first part of our work has been devoted to a better understanding of the non-hydrolytic sol-gel mechanisms occurring during the formation of ionogels, using electrochemical impedance spectroscopy. Change of the conductivity of the sol-gel mixture (a Formic acid and Tetraethyl orthosilicate mixture) shows two different time domains. The mixture conductivity is first decreasing drastically during the first 25 minutes of the sol-gel process, assuming to originate from the in-situ generation of water through esterification reaction. In the second time range (t>25 min), the conductivity tends to level off, associated with a series of chemical reactions. More details about this study will be added during the presentation. In a second part of the talk, we will show the electrochemical performance of an supercapacitors cell assembled with activated carbon as active materials and an ionogel electrolyte containing an ionic liquid mixture (1:1 by weight or molar ratio) of N-methyl-N-propylpiperidinium bis(fluorosulfonyl)imide (PIP13FSI) and N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI). Cyclic voltammetries and electrochemical impedance spectroscopy plots in a large temperature range (-40°C to +60°C) will be presented and discussed. The ionogel exhibits a high ionic conductivity over a wide temperature range (from 0.2 mS.cm−1 at −40 °C up to 10 mS.cm−1 at 60 °C). The ionogel-based supercapacitor using two activated carbon electrodes can be operated over 3 V cell voltage window. Moreover this all solid-supercapacitor shows a capacitance up to 90 F.g−1 at room temperature. These encouraging results show the interest of developing such devices, including non-toxic and safer electrolytes, packaging issues and flexible devices development.

Posibility of using 1-alkoxymethyl-4-(dimethylamine)pyridinium bis(trifluoromethylsulfonyl)imides as Electrolytes for Electrochemical Capacitors

Posibility of using 1-alkoxymethyl-4-(dimethylamine)pyridinium bis(trifluoromethylsulfonyl)imides as Electrolytes for Electrochemical Capacitors

Ionic Liquid Mixtures As Electrolytes for Electrochemical Capacitors

While known for a higher power density than batteries, electrochemical capacitors are limited by their energy density for some energy storage applications. Since the energy density of the device is proportional to the square of operating potential window, an effective way to increase energy density of the device is by increasing this voltage window. Ionic liquid electrolytes are beneficial for this reason since they can theoretically operate at up to 6 V, though experimentally, the value is between 3-4 V, depending on the properties of electrode materials. Electrode materials can be made from high surface area carbons that contain a network of pores (activated carbon, carbide-derived carbon) or lower surface area carbons that consist of an outer surface where charging and discharging takes place. Though they boast a large operating potential window, ionic liquids are known to contain large and bulky ions. This can make it difficult to use an ionic liquid on a porous carbon with a range of pore sizes, some being very small, even though the specific surface area of the electrode material is higher. It has also been shown that the capacitance of porous electrodes is maximized when the ion size and pore size are equal.1 In this case, the ion is small enough to fit inside the pores while still large enough to take advantage of the surface area within the pore walls. While the outer surface materials allow a more accessible surface for adsorbing large ions, their capacitance is limited by their specific surface area. By designing an electrolyte based on mixed ionic liquids, 2 we can match the ions in the mixture to the multiple pore sizes of the electrode material. Imidazolium-based ionic liquids are chosen based on their variable alkyl chain length which alters the cation size and the TFSI is chosen as the anion for all ionic liquids. Different porous carbons with varying pore size distributions are used to illustrate the effect of ionic liquid mixture electrolytes. 1. Lin, R. et al. Solvent effect on the ion adsorption from ionic liquid electrolyte into sub-nanometer carbon pores. Electrochim. Acta 54, 7025–7032 (2009). 2. Van Aken, K. L., Beidaghi, M. & Gogotsi, Y. Formulation of Ionic-Liquid Electrolyte to Expand the Voltage Window of Supercapacitors. Angew. Chemie 127, 4888–4891 (2015).

Silica sol–gel chemistry: creating materials and architectures for energy generation and storage

There is widespread recognition that the use of energy in the twenty-first century must be sustainable. Because of its extraordinary flexibility, silica sol–gel chemistry offers the opportunity to create the novel materials and architectures which can lead to significant advances in renewable energy and energy storage technologies. In this paper, we review some of the significant contributions of silica sol–gel chemistry to these fields with particular emphasis on electrolytes and separators where sol–gel approaches to functionalization and encapsulation have been of central importance. Examples are presented in the areas of dye-sensitized solar cells, biofuel cells, proton exchange membrane fuel cells, redox flow batteries and electrochemical energy storage. Original work is also included for the sol–gel encapsulation of a room temperature ionic liquid to create a solid state electrolyte for electrochemical capacitors. In view of the critical importance of energy and the versatility of the sol–gel process, we expect the sol–gel field to play an increasingly important role in the development of sustainable energy generation and storage technologies.

Tetramethylammonium difluoro(oxalato)borate dissolved in ethylene/propylene carbonates as electrolytes for electrochemical capacitors

Tetramethyl ammonium difluoro(oxalato)borate (TMADFOB) dissolved in the mixed solvents of ethylene and propylene carbonates (EC/PC) instead of neat PC have been proposed as the electrolyte solutions for electrochemical capacitors. The ionic conductivity of 1 M TMADFOB-EC/PC electrolyte solutions has been measured. It climbs up monotonously as EC content increases. Accordingly, the power density of electric double-layer capacitors is enhanced with certain EC addition. The optimum EC content for the power of EDLCs is about 30 volume percentage in the mixed EC/PC solvents. This tendency has been testified by impedance study. The electrochemical behavior of activated carbon/graphite capacitors using these electrolyte solutions has also been studied by galvanostatic charge–discharge test and the charge storage mechanism at the graphite positive electrode has been investigated by in situ XRD and ex situ Raman. The effect of EC addition on DFOB− intercalation into graphite has also been addressed at both room and elevated temperatures.

Alkaline quaternary ammonium hydroxides and their polymer electrolytes for electrochemical capacitors

Tetraethylammonium hydroxide (TEAOH)–poly(vinyl alcohol) (PVA) electrolytes showed superior stability and shelf life to KOH–PVA electrolytes in electrochemical capacitors (ECs).

Ether-Bond-Containing Ionic Liquids as Supercapacitor Electrolytes.

Electrochemical capacitors (ECs) are electrical energy storage devices that have the potential to be very useful in a wide range of applications, especially where there is a large disparity between peak and average power demands. The use of ionic liquids (ILs) as electrolytes in ECs can increase the energy density of devices; however, the viscosity and conductivity of ILs adversely influence the power density of the device. We present experimental results where several ILs containing different cations have been employed as the electrolyte in cells containing mesoporous carbon electrodes. Specifically, the behavior of ILs containing an ether bond in an alkyl side chain are compared with those of a similar structure and size but containing purely alkyl side chains. Using electrochemical impedance spectroscopy and constant current cycling, we show that the presence of the ether bond can dramatically increase the specific capacitance and reduce device resistance. These results have the important implication that such ILs can be used to tailor the physical properties and electrochemical performance of IL-based electrolytes.

Неводные электролиты на основе ониевых ионных жидкостей для электрохимических конденсаторов

The research covers the synthesis of ionic liquids containing anions fluoroboric acid and quaternary ammonium cations with one ether group. The ionic conductivities of 1M solutions of the synthesized ionic liquids in acetonitrile were measured. They range from 27 to 36 mS/cm, which allows to use solutions as working electrolytes in electrochemical capacitors. It was found that the window of electrochemical stability of the investigated ionic liquids constitutes 3.6-6.1 V and depends on cation structure.

Hydrogel membrane electrolyte for electrochemical capacitors

Polymer electrolytes are known to possess excellent physicochemical properties that are very useful for electrochemical energy systems. The mobility in polymer electrolytes is understood to be mainly due to the segmental motion of polymer chains and the ion transport is generally restricted to the amorphous phase of the polymer. Gel polymer electrolytes (GPE) that are formed using plastizicers and polymers along with ionic salts are known to exhibit liquid-like ionic conductivity while maintaining the dimensional stability of a solid matrix. In the present study, the preparation and characterization of poly(vinyl alcohol)-based hydrogel membranes (PHMEs) as electrolytes for electrochemical capacitors have been reported. Varying HClO4 dopant concentration leads to different characteristics of the capacitors. The EC comprising PHME doped with 2 M HClO4 and black pearl carbon (BPC) electrodes has been found to exhibit a maximum specific capacitance value of 97 F g−1, a phase angle value of 78°, and a maximum charge-discharge coulombic efficiency of 88%.

Advanced Polymers as Active Materials and Electrolytes for Electrochemical Capacitors and Hybrid Capacitor Systems

Recent advancements in nanotechnology have resulted in the development of new materials and a greater fundamental understanding of their properties. Those advancements are currently being applied to revolutionary designs of ECs and are enabling new types of hybrid energy-storage devices that exhibit characteristics of batteries and ECs.

Binary Complex Electrolytes Based on LiX [ X = N ( SO2CF3 ) 2 − , CF3SO3 − , ClO4 − ]-Acetamide for Electric Double Layer Capacitors

Binary complex systems have been prepared based on acetamide with lithium bis(trifluoromethane sulfone)imide [, ], lithium triflate , and lithium perchlorate , respectively. Due to their superior physicochemical properties, such as wide liquid-phase range and high ionic conductivity, they can be practically useful electrolytes for electrochemical capacitors. We prepared electric double-layer capacitors (EDLCs) composed of activated carbon electrode and the above three complex systems based on acetamide as the electrolytes and evaluated the electrochemical performances of the EDLCs with cyclic voltammetry (CV), ac impedance spectroscopy, and galvanostatic charge/discharge, etc. The EDLCs with these components show better electrochemical properties in specific capacitance and cycling performances at ambient and elevated temperatures. Considering that the complex electrolytes possess a number of excellent properties such as negligible vapor pressure and high thermal stability, the results demonstrate that these electrolytes are promising electrolyte candidates for the EDLCs and especially for those requiring high safety and stability.

Proton-Conducting Non-Aqueous Gel Electrolyte for a Redox Capacitor System

Novel non-aqueous proton (H+)-conducting polymeric gel systems have bee proposed for utilization as quasi-solid electrolytes in electrochemical capacitors. The gel systems consist of poly(vinylidenedifluoride) (PVdF) or poly(vinylidenedifluoride-co-hexafluoropropylene) (PVdF-HFP) matrix polymer swollen with dimethylformamide (DMF) solutions containing phosphoric acid (H3PO4) or trifluoromethanesulfonic acid (CF3SO3H). High ionic conductivity of 4.5 mS cm−1 was obtained at 60°C for a PVdF-HFP-based polymeric gel containing 85 mass% of 0.5 M CF3SO3H/DMF with sufficient mechanical stability over the temperature range of 20–60°C. Redox process of hydrous ruthenium oxide, RuO2·xH2O, gave high pseudo-capacitance in the PVdF-HFP-based polymeric gel. The pseudo capacitance behavior was somewhat influenced by the composition of electrode/electrolyte interface. The discharge capacitance of ca. 350 F g−1 (with respect to the mass of the oxide) was obtained for PVdF-HFP-based gel using RuO2·xH2O electrode prepared by a “wet process”.