Carbon materials for the electrochemical storage of energy in capacitors

Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation

Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.

Deep eutectic solvents: syntheses, properties and applications

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).

A review of electrolyte materials and compositions for electrochemical supercapacitors

Ionic liquids as electrolytes

Thermal properties of imidazolium ionic liquids

The specific ionic conductivity, dynamic viscosity, and electrochemical stability of several imidazolium salts are reported as neationic liquids and their solutions in several organic solvents. The temperature dependence of conductivity and viscosity are analyzed for 1‐ethyl‐3‐methylimidazolium and 1,2‐dimethyl‐3‐n‐propylimidazolium salts, and the influence of theanions bis(trifluoromethylsulfonyl)imide , bis(perfluoroethylsulfonyl)imide , hexafluoroarsenate , hexafluorophosphate , and tetrafluoroborate on these properties are discussed. These imidazolium salts make possible electrolytes with high concentration (>3 M), high room temperature conductivity (up to 60 mS/cm), and a wide window of stability . Differential scanning calorimetric results confirm a large glass phase for the ionic liquids, with substantial (>80°C) supercooling. Thermal gravimetric results indicate the imidazolium salts with and anions to be thermally more stable than the lithium salt analogs. The Vogel‐Tammann‐Fulcher interpretation accurately describes the conductivity temperature dependence. © 1999 The Electrochemical Society. All rights reserved.

Electrochemical properties of imidazolium salt electrolytes for electrochemical capacitor applications

Electrolytes based on 1-ethyl-3-methylimidazolium cation (EMI{sup +}) and either the hexafluorophosphate (EMIPF{sub 6}) or tetrafluorborate (EMIBF{sub 4}) anion in organic alkyl carbonate solvents have been evaluated for use in electrochemical capacitors. The conductivity, capacitance, limiting oxidation and reduction potentials, and thermal stability were assessed. High conductivity and capacitance values were found regardless of whether cyclic (high viscosity/high dielectric constant) or acyclic (low viscosity/low dielectric constant) alkyl carbonates were used. The best correlation with conductivity for the EMIPF{sub 6} salt was found to be the molecular weight and to a lesser degree the viscosity of the solvent. The high specific capacitance (130 F/g) and excellent stability (>3.5 V, >130 C) make these electrolytes well suited for use in electrochemical double-layer capacitors.

https://iopscience.iop.org/article/10.1149/1.1837561/pdf

Nonaqueous electrolytes for electrochemical capacitors: Imidazolium cations and inorganic fluorides with organic carbonates

Improved electrolytes for application in electrical storage devices, such as batteries and capacitors, electrochromic display and other applications requiring ionically conductive median are disclosed. The electrolytes of the invention contain organic cation salts, also called ionic liquids or molten salts. These improved electrolytes have useful characteristics such as high thermal stability and reduced flammability.

Non-flammable electrolytes

An electrochemical capacitor is disclosed that features two, separated, high surface area carbon cloth electrodes (16, 18) sandwiched between two current collectors (12, 14) fabricated of a conductive polymer having a flow temperature greater than 130 degrees Celsius, with the perimeter of the electrochemical being sealed with a high temperature gasket (20) to form a single cell device. The gasket material is a thermoplastic stable at temperature greater than 100 degrees Celsius, preferably a polyester or a polyurethane, and having a reflow temperature above 130 degrees Celsius but below the softening temperature of the current collector material. The capacitor packaging has good mechanical integrity over a wide temperature range, contributes little to the device equivalent series resistance, and is designed to be easily manufactured by assembly line methods. The individual cells can be stacked in parallel or series configuration to reach the desired device voltage and capacitance.

Alan B. McEwen

Papers

Thermal properties of imidazolium ionic liquids

Electrochemical properties of imidazolium salt electrolytes for electrochemical capacitor applications

Nonaqueous electrolytes for electrochemical capacitors: Imidazolium cations and inorganic fluorides with organic carbonates

Non-flammable electrolytes

Nonaqueous electrical storage device