Poly(ionic liquid)s: Synthesis,properties, and application

The overview of the published data on a new class of polyelectrolytes—the so-called polymeric ionic liquids or poly(ionic liquid)s—is presented. The peculiarities of their synthesis and the factors affecting their molar masses, solubility, ionic conductivity, electrochemical stability, and thermal properties are discussed. The mainstreams in the application of poly(ionic liquid)s and materials formed on their basis are illustrated by specific examples.     

Electrochemical fluorination (Simons process) – A powerful tool for the preparation of new conducting salts, ionic liquids and strong Brønsted acids

Electrochemical fluorination (Simons process) provides a cheap commercial access to a series of tris(perfluoroalkyl)diflurophosphoranes. These substances are convenient starting material for the preparation of various fluoro-chemicals. The synthesis of new conducting salts and ionic liquids with perfluoroalkyl-fluorophosphate (FAP) and perfluoroalkyl-phosphinate anions is described. FAP ionic liquids exhibit excellent hydrolytic stability, low viscosity and high electrochemical and thermal stability. Organic and inorganic salts with FAP anions possess high electrochemical stability and conductivity that makes them attractive for application in several electrochemical devices (Li-ion batteries, super-capacitors, etc.). The possible application of H[(R_F)₃PF₃] (HFAP), (R_F)₂P(O)(OH) and (R_F)P(O)(OH)₂ as components of proton-conducting membranes is discussed.     

Physical and electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquids: PY13FSI and PY14FSI

Two ionic liquids based upon N-alkyl-N-methylpyrrolidinium cations (PY(1R)(+)) (R=3 for propyl or 4 for butyl) and the bis(fluorosulfonyl)imide (FSI(-)), N(SO2F)2(-), anion have been extensively characterized. The ionic conductivity and viscosity of these materials are found to be among the highest and lowest, respectively, reported for aprotic ionic liquids. Both ionic liquids crystallize readily on cooling and undergo several solid-solid phase transitions on heating prior to melting. PY13FSI and PY14FSI are found to melt at -9 and -18 degrees C, respectively. The thermal stability of PY13FSI and PY14FSI is notably lower than for the analogous salts with the bis(trifluoromethanesulfonyl)imide (TFSI(-)), N(SO2CF3)2(-), anion. Both ionic liquids have a relatively wide electrochemical stability window of approximately 5 V.     

Continuous Synthesis of Peralkylated Imidazoles and their Transformation into Ionic Liquids with Improved (Electro)Chemical Stabilities

A versatile and efficient method to synthesize tetrasubstituted imidazoles via a one‐pot modified Debus–Radziszewski reaction and their subsequent transformation into the corresponding imidazolium ionic liquids is reported. The tetrasubstituted imidazoles were also synthesized by means of a continuous flow process. This straightforward synthetic procedure allows for a fast and selective synthesis of tetrasubstituted imidazoles on a large scale. The completely substituted imidazolium dicyanamide and bis(trifluoromethylsulfonyl)imide salts were obtained via a metathesis reaction of the imidazolium iodide salts. The melting points and viscosities are of the same order of magnitude as for their non‐substituted analogues. In addition to the superior chemical stability of these novel ionic liquids, which allows them to be applied in strong alkaline media, the improved thermal and electrochemical stabilities of these compounds compared with conventional imidazolium ionic liquids is also demonstrated by thermogravimetrical analysis (TGA) and cyclic voltammetry (CV). Although increased substitution of the ionic liquids does not further increase thermal stability, a definite increase in cathodic stability is observable.     

Ionic-Liquid-Based Nanofluids and Their Heat-Transfer Applications: A Comprehensive Review

Due to the improved thermophysical characteristics of ionic liquids (ILs), such as their strong ionic conductivity, negligible vapor pressure, and thermal stability at high temperatures, they are being looked at viable contender for future heat transfer fluids. Additionally, the dispersing nanoparticles can further improve the thermophysical characteristics and thermal performance of ionic liquids, which is one of the emerging research interests to increase the heat transfer rates of the thermal devices. The latest investigations about the utilization of ionic liquid nanofluids as a heat transfer fluid is summarized in this work. These summaries are broken down into three types: (a) the thermophysical parameters including thermal conductivity, viscosity, density, and specific heat of ionic liquids (base fluids), (b) the thermophysical properties like thermal conductivity, viscosity, density, and viscosity of ionic liquids based nanofluids (IL nanofluids), and (iii) utilization of IL nanofluids as a heat transfer fluid in the thermal devices. The techniques for measuring the thermophysical characteristics and the synthesis of IL nanofluids are also covered. The suggestions for potential future research directions for IL nanofluids are summarized.     

1-丁腈-3-甲基咪唑双三氟甲基磺酸亚胺的性质

制备了功能化离子液体1-丁腈-3-甲基咪唑双三氟甲基磺酸亚胺。在T为283.15-353.15 K温度范围内,测定了该功能化离子液体的密度、动力粘度、电导率及折光率。讨论了亚甲基的增减对该类功能化离子液体的密度、动力粘度、电导率及折光率等性质的影响,并与传统咪唑类、吡啶类离子液体物理化学性质的变化趋势进行了对比。通过经验方程计算了该功能化离子液体的热膨胀系数、分子体积、标准摩尔熵及晶格能等热力学性质参数。讨论了Vogel-Fulcher-Tamman (VFT)方程和Arrhenius方程的适用性,得出VFT方程适用于该功能化离子液体,而Arrhenius方程并不适用。有关研究对新型离子液体的合成及其工业化的应用具有十分重要的意义。     

Low-viscosity and low-melting point asymmetric trialkylsulfonium based ionic liquids as potential electrolytes

Nine new ionic liquids based on small asymmetric trialkylsulfonium cations with TFSI⁻ anion were prepared and characterized. Physical and electrochemical properties of these ionic liquids, including melting point, thermal stability, viscosity, conductivity and electrochemical window were determined. Reducing symmetry of cations reduces the melting points of these ILs. Some of these hydrophobic ionic liquids showed low-viscosity and low-melting point characteristics. The viscosities of S₂₂₃TFSI, S₂₂₁TFSI and S₁₂₃TFSI were 33, 36 and 39 mPa s at 25 °C, respectively. Electrochemical and thermal stabilities of these ILs permitted them to become promising electrolytes used in electrochemical devices.     

Physicochemical properties of imidazolium-derived ionic liquids with different C-2 substitutions

Five room temperature ionic liquids based on C-2 substituted imidazolium cations and bis(trifluoromethanesulfonyl)imide (TFSI) anions were synthesized and their physicochemical properties: thermal property, density, viscosity, ionic conductivity, self-diffusion coefficients, and electrochemical stability, were systematically investigated. The temperature dependence of both viscosity and ionic conductivities of these ionic liquids can be described by the Vogel-Fulcher-Tamman (VFT) equation. Compared with the reference, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, the introduction of functional groups at the C-2 position generally increased the viscosity and lowered the ionic conductivity. The introduction of an ether group (-CH(2)OCH(2)CH(2)CH(2)CH(3)) at the C-2 position not only enhanced the reduction stability of the ionic liquids but also exhibited the lowest solid electrolyte interfacial resistance (R(SEI)). In contrast, the introduction of a cyano group (-CN) at the C-2 position not only decreased the reduction stability but also adversely increased the SEI resistance. The effect of the C-2 substitution on the reduction stability was explained by the change in the energy level of the lowest unoccupied molecular orbital. The self-diffusion coefficients (D) of each ion were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR). The lithium transference number (t(Li)) of 0.5 M LiTFSI/IL solutions calculated from the self-diffusion coefficients was in the range of 0.04 to 0.09.     

Ionic liquid electrolytes for dye-sensitized solar cells

The potential of room-temperature molten salts (ionic liquids) as solvents for electrolytes for dye-sensitized solar cells has been investigated during the last decade. The non-volatility, good solvent properties and high electrochemical stability of ionic liquids make them attractive solvents in contrast to volatile organic solvents. Despite this, the relatively high viscosity of ionic liquids leads to mass-transport limitations. Here we review recent developments in the application of different ionic liquids as solvents or components of liquid and quasi-solid electrolytes for dye-sensitized solar cells.     

Ionic Liquids as Novel Reaction Media for the Synthesis of Copoly(ester-amide)s Containing 9,10-Anthraquinone Moiety

The use of ionic liquids as novel solvents for the synthesis of aromatic copoly(ester-amide)s, containing a 9,10-anthraquinone moiety in the main chain, from the polycondensation reaction of terephthaloyl chloride and various ratios of p-phenylenediamine and 1,4-dihydroxyanthraquinone is reported. 1,3-Dialkylimidazolium-based ionic liquids are suitable reaction media for the synthesis of copoly(ester-amide)s. These copolymers exhibit color characteristics and thermal stability. The presence of the amide groups in the backbone of these polymers enhances their thermal stabilities. Inherent viscosities of the polymers obtained in 1,3-dialkylimidazolium bromide range from 0.28 to 0.42 dL/g.     

离子液体在分离领域的研究进展

室温离子液体,又称离子液体,是一种在室温及接近室温的环境中完全以离子状态存在的液态物质.由于其具有不可燃、蒸汽压极低、黏度大、导电性和溶解能力好、高温稳定等特点,已被广泛应用于有机合成、催化、电化学、分析化学等领域.本文侧重介绍离子液体在样品预处理、毛细管电泳、高效液相色谱、气相色谱、质谱等分离领域的最新研究进展,并对其发展方向进行了展望.     

Thermal, rheological, and ion-transport properties of phosphonium-based ionic liquids

Phosphonium-based ionic liquids with varying counteranions from commercially available ionic liquid precursors enabled tunable viscosity, ionic conductivity, and thermal stability. Thermogravimetric analysis revealed a relationship between thermal stability and anion composition where anions with lower basicity remained stable to higher temperatures. Determination of glass transition temperatures and melting temperatures using differential scanning calorimetry revealed supercooling, crystallization, and dependence on anion composition. Rheological and ionic conductivity measurements determined the temperature-dependence of the viscosity and ionic conductivity of the phosphonium-based ionic liquids. Arrhenius analyses of conductivity and viscosity provided activation energies, which showed a decrease toward larger, more delocalized anions. An assessment according to the Walden plot displayed their efficacy relative to other ionic liquids.     

离子液体在锂离子电池中的应用研究进展

离子液体具有蒸汽压低、热稳定性好、不易挥发、溶解能力强、环境友好、电化学稳定窗口和液程范围宽等优点,在锂离子电池领域应用前景广泛。本文按照离子液体作为电解质溶剂、与传统电解质复配或与聚合物电解质结合的应用方式,总结其对电池的安全性和热稳定性的影响,并综述了近年来离子液体在锂离子电池电解质中的应用研究进展。     

Towards large-scale, fully ab initio calculations of ionic liquids

Ionic liquids have attracted a substantial amount of interest as replacement of traditional electrolytes in high efficiency electrochemical devices for generation and storage of energy due to their superior physical and chemical properties, especially low volatility and high electrochemical stability. For enhanced performance of the electrochemical devices ionic liquids are required to be highly conductive and low viscous. Long-range Coulomb and short-range dispersion interactions between ions affect physical and chemical properties of ionic liquids in a very complex way, thus preventing direct correlations to the chemical structure. Considering a vast combination of available cations and anions that can be used to synthesize ionic liquids, development of predictive theoretical approaches that allow for accurate tailoring of their physical properties has become crucial to further enhance the performance of electrochemical devices such as lithium batteries, fuel and solar cells. This perspective article gives a thorough overview of current theoretical approaches applied for studying thermodynamic (melting point and enthalpy of vapourisation) and transport (conductivity and viscosity) properties of ionic liquids, emphasizing their reliability and limitations. Strategies for improving predictive power and versatility of existing theoretical approaches are also outlined.     

Synthesis and characterization of new pyrrolidinium based protic ionic liquids. Good and superionic liquids

New pyrrolidinium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reactions between pyrrolidine and Br?nsted acids, HX, where X is NO 3 (-), HSO 4 (-), HCOO (-), CH 3COO (-) or CF 3COO (-) and CH 3(CH 2) 6COO (-). The thermal properties, densities, electrochemical windows, temperature dependency of dynamic viscosity and ionic conductivity were measured for these PILs. All protonated pyrrolidinium salts studied here were liquid at room temperature and possess a high ionic conductivity (up to 56 mS cm (-1)) at room temperature. Pyrrolidinium based PILs have a relatively low cost, a low toxicity and exhibit a large electrochemical window as compared to other protic ionic liquids (up 3 V). Obtained results allow us to classify them according to a classical Walden diagram and to determinate their "Fragility". Pyrrolidinium based PILs are good or superionic liquids and shows extremely fragility. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional inorganic acids.     

Synthesis and Thermophysical Properties of Ether‐Functionalized Sulfonium Ionic Liquids as Potential Electrolytes for Electrochemical Applications

During this work, a novel series of hydrophobic room temperature ionic liquids (ILs) based on five ether functionalized sulfonium cations bearing the bis{(trifluoromethyl)sulfonyl}imide, [NTf₂]^? anion were synthesized and characterized. Their physicochemical properties, such as density, viscosity and ionic conductivity, electrochemical window, along with thermal properties including phase transition behavior and decomposition temperature, have been measured. All of these ILs showed large liquid range temperature, low viscosity, and good conductivity. Additionally, by combining DFT calculations along with electrochemical characterization it appears that these novel ILs show good electrochemical stability windows, suitable for the potential application as electrolyte materials in electrochemical energy storage devices.     

离子液体中聚(3-溴噻吩)的电化学合成和电色效应研究

以1-丁基-3-甲基咪唑六氟磷酸盐离子液体[BMIM]PF₆既作为溶剂又作为支持电介质, 通过恒电流、循环伏安等方法制备聚(3-溴噻吩)(PBrT)膜. 采用红外光谱(FT-IR)和扫描电子显微镜(SEM)对PBrT膜的结构和形貌进行表征, 用热重和差热分析法(TG-DTA)研究聚合膜的热稳定性, 并利用紫外-可见光谱(UV-Vis)、计时电流和计时吸收曲线研究该聚合膜电化学和电致变色的特性. 研究结果表明, 与传统方法比较, 在离子液体[BMIM]PF₆中制备的PBrT膜更致密、光滑, 具有良好的氧化还原可逆性和充放电能力, 电活性高, 热稳定性好. 以该方法制备的PBrT膜颜色变化明显, 响应时间快(0.5 s), 同时由于离子液体具有电位窗宽、导电率高、可循环利用等优点, 因此在电化学聚合等方面具有良好的应用前景.     

Synthesis of Low‐Viscosity Ionic Liquids for Application in Dye‐Sensitized Solar Cells

Two types of ionic liquids (ILs), 1‐(3‐hexenyl)‐3‐methyl imidazolium iodide and 1‐(3‐butenyl)‐3‐methyl imidazolium iodide, are synthesized by introducing an unsaturated bond into the side alkyl chain of the imidazolium cation. These new ionic liquids exhibit high thermal stability and low viscosity (104 cP and 80 cP, respectively). The molecular dynamics simulation shows that the double bond introduced in the alkane chain greatly changes the molecular system space arrangement and diminishes the packing efficiency, leading to low viscosity. The low viscosity of the synthesized ionic liquids would enhance the diffusion of redox couples. This enhancement is detected by fabricating dye‐sensitized solar cells (DSSCs) with electrolytes containing the two ILs and I₂. The highest efficiency of DSSCs is 6.85 % for 1‐(3‐hexenyl)‐3‐methyl imidazolium iodide and 5.93 % for 1‐(3‐butenyl)‐3‐methyl imidazolium iodide electrolyte, which is much higher than that of 5.17 % with the counterpart 1‐hexyl‐3‐methyl imidazolium iodide electrolyte.     

Preparation of single-walled carbon nanotube (SWNT) gel composites using poly(ionic liquids)

This paper reports a new and practical route for synthesizing nanotube-polymeric ionic liquids gel by non-covalent functionalization of oxidized single-walled carbon nanotube (SWNT) surfaces with imidazolium-based poly(ionic liquids) (PILs), using in situ radical polymerization method. A black and homogeneous precipitate SWNTs was obtained as a gel form, which is well dispersed in aqueous solution without any aggregation. The formation of SWNT gels is explained by the electrostatic attractions or π-bonds between the SWNT surface and the PIL matrix. By anion-exchange reaction of PIL bound to SWNTs, hydrophilic anions in PIL were substituted with hydrophobic anions, resulting in an effective transfer of SWNT-PIL hydrogels to organogels. The result also showed that SWNTs can effectively improve the conductivity along with the thermal stability of nanocomposite gels.     

Cyclic quaternary ammonium ionic liquids with perfluoroalkyltrifluoroborates: synthesis, characterization, and properties

New cyclic quaternary ammonium salts, composed of N-alkyl(alkyl ether)-N-methylpyrrolidinium, -oxazolidinium, -piperidinium, or -morpholinium cations (alkyl = nC4H9, alkyl ether = CH3OCH2, CH3OCH2CH2) and a perfluoroalkyltrifluoroborate anion ([R(F)BF3]-, R(F) = CF3, C2F5, nC3F7, nC4F9), were synthesized and characterized. Most of these salts are liquids at room temperature. The key properties of these salts--phase transitions, thermal stability, density, viscosity, conductivity, and electrochemical windows--were measured and compared to those of their corresponding [BF4]- and [(CF3SO2)2N]- salts. The structural effect on all the above properties was intensively studied in terms of the identity of the cation and anion, variation of the side chain in the cation (i.e., alkyl versus alkyl ether), and change in the length of the perfluoroalkyl group (R(F)) in the [R(F)BF3]- ion. The reduction of Li+ ions and reoxidation of Li metal took place in pure N-butyl-N-methylpyrrolidinium pentafluoroethyltrifluoroborate as the supporting electrolyte. Such comprehensive studies enhance the knowledge necessary to design and optimize ionic liquids for many applications, including electrolytes. Some of these new salts show desirable properties, including low melting points, high thermal stabilities, low viscosities, high conductivities, and wide electrochemical windows, and may thus be potential candidates for use as electrolytes in high-energy storage devices. In addition, many salts are ionic plastic crystals.