Ion transport properties of lithium ionic liquids and their ion gels

A new series of lithium ionic liquids were prepared by introducing of two electron-withdrawing trifluoroacetyl groups in borate salts containing two methoxy-oligo(ethylene oxide) groups in the structures. Successive substitution reactions of oligo-ethylene glycol monomethyl ether and trifluroacetic acid from LiBH₄ yielded the lithium salts, which were clear and colorless liquids at room temperature. The fundamental physicochemical properties, such as density, thermal property, viscosity, ionic conductivity, self-diffusion coefficients, and electrochemical stability, were measured. The lithium ionic liquids had self-dissociation ability and conducted ions even in the absence of organic solvents. New polymer electrolytes, named ‘ion gels’, were prepared by radical cross-linking reactions of a poly(ethylene oxide-co-propylene oxide)tri-acrylate macromonomer in the presence the lithium ionic liquid. An increase in the glass transition temperatures (T_g) of the ion gels was very small even with increasing lithium ionic liquid concentration, and the T_g's were lower than that of the ionic liquid itself. The ionic conductivity of the ion gels surpassed that of the lithium ionic liquid in the bulk at certain compositions.     

Poly(ionic liquid)s: Polymers expanding classical property profiles

In recent years, polymeric/polymerized ionic liquids or poly(ionic liquid)s (PILs) were found to take an enabling role in some fields of polymer chemistry and material science. PILs combine the unique properties of ionic liquids with the flexibility and properties of macromolecular architectures and provide novel properties and functions that are of huge potential in a multitude of applications, including solid ionic conductor, powerful dispersant and stabilizer, absorbent, precursor for carbon materials, porous polymers, etc. So far, the preparation of PILs with various forms in cations and anions has mostly focused on the conventional free radical polymerization of IL monomers. Recent progress in the preparation of PILs via controlled/“living” radical polymerizations points out an unprecedented opportunity to precisely design and control macromolecular architecture of IL species on a meso-/nanoscale within a polymer matrix. There are also newly emerging polymerization techniques that have appeared for the preparation of PILs which have further pushed the limit of the design of PILs. In this review, we try to summarize the current preparative strategies of PILs, providing a systematic and actual view on the polymer chemistry behind. A discussion of the properties and applications of PILs constitutes the second part of this review.     

Polymeric ionic liquids based on ether functionalized ammoniums and perfluorinated sulfonimides

A new family of polymeric ionic liquids (PILs) based on alkyl and alkyl ether substituted ammoniums and perfluorinated sulfonimides (i.e., bis(fluorosulfonyl)imide (FSI⁻), and bis(trifluoromethanesulfonyl)imide (TFSI⁻)) have been synthesized by polymerization of the corresponding ionic liquid monomers (ILMs). Their structures and compositions have been characterized by ¹H and ¹⁹F NMR, FTIR and viscosity-average molecular weight (M_v). The physicochemical properties of both the ILMs and the PILs have been studied in terms of thermal stability, phase transition, and ionic conductivity. All the prepared ILMs and PILs reveal excellent thermal stabilities to greater than 250 °C. The PILs containing alkyl ether side unit show significant decrease in glass transition temperature (T_g), the values of T_g of the alkyl ether based-PILs are all significantly lower by 10–77 °C in magnitude than those of the corresponding alkyl based ones. The ionic conductivity of alkyl ether based-PILs in the best case increases up to 4.0 × 10⁻⁶ S cm⁻¹ at 30 °C, and reaches 7.6 × 10⁻⁵ S cm⁻¹ at 60 °C, and outperform their ammonium counterparts with alkyl side chain that were synthesized as references.     

Ionic Liquids and their Polymers in Lithium‐Sulfur Batteries

Future optimized lithium‐sulfur batteries may promise higher energy densities than the current standard. However, there are many barriers which hinder their commercialization. In this review we describe how ionic liquids (ILs) and their polymers are utilized in different components of the battery to address some of these issues. For example, IL‐based electrolytes have the potential to reduce the solubility of polysulfides compared to conventional organic electrolytes. Polymerizing ILs directly on the surface of the Li‐metal anode is suggested as an approach to protect the surface of this electrode. Finally, using poly(ionic liquids) (PILs) as binders for the cathode active material may increase the performance of the cathode as compared to polyvinylidene difluoride (PVdF) and could inhibit swelling‐induced degradation. These results demonstrate the advantages of ILs and their polymers for improving the performance of Li?S batteries.     

Anion exchanged polymerized ionic liquids: High free volume single ion conductors

In this study, we investigate the isolated effect of anion type on the chemical, thermal, and conductive properties of imidazolium-based polymerized ionic liquids (PILs). PILs with various anions at constant average chain length were prepared by ion exchange with a water-soluble PIL precursor, (poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bromide) (poly(MEBIm-Br)). NMR, IR, and elemental analysis confirm that anion exchange of ploy(MEBIm-Br) with bis(trifluoromethanesulfonyl) imide (TFSI), tetrafluoroborate (BF₄), trifluoromethanesulfonate (Tf), and hexafluorophosphate (PF₆) in water resulted in nearly fully exchanged PILs. As a function of anion type, the glass transition temperature plays a dominant role, but not the sole role in determining ion conductivity. Other factors affecting ionic conductivity include the size and symmetry of the anion and dissociation energy of the ion pair. Both the Vogel-Fulcher-Tammann (VFT) and Williams-Landel-Ferry (WLF) equations were employed to investigate the temperature dependent ionic conductivities. The (9.03) and (168 K) values obtained from the WLF regression of these PILs greatly deviate from the classical WLF values originally obtained from the mechanical relaxation of uncharged polymers ( = 17.44,  = 51.6 K) and the WLF values obtained from the conductive properties of other polymer electrolytes. This suggests that the fractional free volume (f (T_g) = B/(2.303)) and Vogel temperature (T₀ = T_g − ) are strong functions of ion concentration, where high free volume allows for ion mobility at temperatures farther below the glass transition temperature of the polymer.     

Protic ionic liquids for the selective absorption of H2S from CO2: Thermodynamic analysis

The solubilities of H₂S and CO₂ in four protic ionic liquids (PILs)—methyldiethanolammonium acetate, methyldiethanolammonium formate, dimethylethanolammonium acetate, and dimethylethanolammonium formate were determined at 303.2–333.2 K and 0–1.2 bar. It is shown PILs have higher absorption capacity for H₂S than normal ionic liquids (ILs) and the Henry's law constants of H₂S in PILs (3.5–11.5 bar at 303.2 K) are much lower than those in normal ILs. In contrast, the solubility of CO₂ in PILs is found to be a magnitude lower than that of H₂S, implying these PILs have both higher absorption capacity for H₂S and higher ideal selectivity of H₂S/CO₂ (8.9–19.5 at 303.2 K) in comparison with normal ILs. The behavior of H₂S and CO₂ absorption in PILs is further demonstrated based on thermodynamic analysis. The results illustrate that PILs are a kind of promising absorbents for the selective separation of H₂S/CO₂ and believed to have potential use in gas sweetening. © 2014 American Institute of Chemical Engineers AIChE J 60: 4232–4240, 2014     

Voltammetric and physicochemical characterization of hydroxyl- and ether-functionalized onium bis(trifluoromethanesulfonyl)imide ionic liquids

Several hydroxyl- and ether-functionalized binary task specific ionic liquids (ILs) are prepared, ether-functionalized ILs exhibit higher conductivity and lower viscosity than those of hydroxyl-functionalized ILs, whereas hydroxyl-functionalized ILs show wider potential window than those of ether-functionalized ILs. The correlation between ionic conductivity and viscosity is based on the classical Walden rule; a relatively large deviation of the plots from the ideal Walden line is observed for the ILs without considering the ion size, whereas the deviation decreases significantly when the adjusted Walden plot is adopted. The α values of ILs calculated from the slopes of the Walden plots are compared to those calculated from the ratio of activation energies for viscosity and molar conductivity (E_a,Λ/E_a,η). There are very few reports where electrochemically derived activation energy from conductivity and voltammetric characterization are available for comparison, so a key concept of activation energy in electrochemistry could be developed in this paper.     

A Review on Ionic Liquids-Based Membranes for Middle and High Temperature Polymer Electrolyte Membrane Fuel Cells (PEM FCs)

Today, the use of polymer electrolyte membranes (PEMs) possessing ionic liquids (ILs) in middle and high temperature polymer electrolyte membrane fuel cells (MT-PEMFCs and HT-PEMFCs) have been increased. ILs are the organic salts, and they are typically liquid at the temperature lower than 100 °C with high conductivity and thermal stability. The membranes containing ILs can conduct protons through the PEMs at elevated temperatures (more than 80 °C), unlike the Nafion-based membranes. A wide range of ILs have been identified, including chiral ILs, bio-ILs, basic ILs, energetic ILs, metallic ILs, and neutral ILs, that, from among them, functionalized ionic liquids (FILs) include a lot of ion exchange groups in their structure that improve and accelerate proton conduction through the polymeric membrane. In spite of positive features of using ILs, the leaching of ILs from the membranes during the operation of fuel cell is the main downside of these organic salts, which leads to reducing the performance of the membranes; however, there are some ways to diminish leaching from the membranes. The aim of this review is to provide an overview of these issues by evaluating key studies that have been undertaken in the last years in order to present objective and comprehensive updated information that presents the progress that has been made in this field. Significant information regarding the utilization of ILs in MT-PEMFCs and HT-PEMFCs, ILs structure, properties, and synthesis is given. Moreover, leaching of ILs as a challenging demerit and the possible methods to tackle this problem are approached in this paper. The present review will be of interest to chemists, electrochemists, environmentalists, and any other researchers working on sustainable energy production field.     

Ionic liquids containing an alkyl sulfate group as potential electrolytes

Various types of ionic liquid (IL) containing an alkyl sulfate group are synthesized and their physical and electrochemical properties are investigated. The temperature dependency of dynamic viscosity and ionic conductivity are measured for these ILs. The low temperature phase behaviour of the ethylsulfate salts is investigated using differential scanning calorimetry. Three ethylsulfate-containing ionic liquids exhibit wide electrochemical windows of about 5.0 V, and one pyrrolidinium-containing ionic liquid shows a conductivity of 3.8 mS cm⁻¹. The various cations of alkylsulfate-containing ionic liquids are shown to greatly influence viscosity, density, and conductivity. Absorbance solvatochromic probe, Nile Red is used to investigate the relative polarity of alkylsulfate base ionic liquids compared with several organic solvents. The electrochemical and thermal stabilities of these ILs make them promising electrolytes for use in electrochemical devices.     

Protic ionic liquid-based deep eutectic solvents with multiple hydrogen bonding sites for efficient absorption of NH3

The emerging of ionic liquids (ILs) provides an efficient and sustainable way to separate and recover NH₃ due to their unique properties. However, the solid or highly viscous ILs are not suitable for traditional scrubbing. Therefore, an effective strategy was proposed by combining the protic ILs (PILs) with acidic H and low viscous ethylene glycol (EG) to form IL-based deep eutectic solvents (DESs) for NH₃ absorption. The results indicated that these PIL-based DESs not only have fast absorption rate, but also exhibit exceptional NH₃ capacity and excellent recyclability. The highest mass capacity of 211 mg NH₃/g DES was achieved by [Im][NO₃]/EG with molar ratio of 1:3, and was higher than all the reported ILs and IL-based DESs, which was originated from multiple hydrogen bonding between acidic H and hydroxyl groups of the DESs and NH₃. This work will provide useful idea for designing IL-based solvents for NH₃ separation applications.     

Synthesis of Bipyridine‐Stabilized Rhodium Nanoparticles in Non‐Aqueous Ionic Liquids: A New Efficient Approach for Arene Hydrogenation with Nanocatalysts

A new approach to stabilize metal nanoparticles with polynitrogen ligands in ionic liquids (ILs) is described. Zerovalent metal nanospecies in the size range of 2.0 nm were easily prepared in various ionic liquids by chemical reduction of a rhodium salt with an excess amount of sodium borohydride (NaBH₄) and efficiently stabilized by 2,2′‐bipyridine. The influence of the bipyridine ratio in various ILs according to the nature of the cation‐anion association was investigated. These nanocatalysts were evaluated in the hydrogenation of aromatic compounds in ILs under various catalytic conditions (P=1–40 bar, T=20–80 °C).     

Ionic liquids as active pharmaceutical ingredients

Ionic liquids (ILs) are ionic compounds that possess a melting temperature below 100 °C. Their physical and chemical properties are attractive for various applications. Several organic materials that are now classified as ionic liquids were described as far back as the mid-19th century. The search for new and different ILs has led to the progressive development and application of three generations of ILs: 1) The focus of the first generation was mainly on their unique intrinsic physical and chemical properties, such as density, viscosity, conductivity, solubility, and high thermal and chemical stability. 2) The second generation of ILs offered the potential to tune some of these physical and chemical properties, allowing the formation of "task-specific ionic liquids" which can have application as lubricants, energetic materials (in the case of selective separation and extraction processes), and as more environmentally friendly (greener) reaction solvents, among others. 3) The third and most recent generation of ILs involve active pharmaceutical ingredients (API), which are being used to produce ILs with biological activity. Herein we summarize recent developments in the area of third-generation ionic liquids that are being used as APIs, with a particular focus on efforts to overcome current hurdles encountered by APIs. We also offer some innovative solutions in new medical treatment and delivery options.     

Truly solid state electrochromic devices constructed from polymeric ionic liquids as solid electrolytes and electrodes formulated by vapor phase polymerization of 3,4-ethylenedioxythiophene

Using polymeric ionic liquids, namely poly[1-(2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl)-3-methylimidazolium]bis(trifluoromethylsulfonyl)imide or tetracyanoborate, and poly(3,4-ethylenedioxythiophene) (PEDOT) as an ion conductor and electrodes, respectively, the all-polymer-based thin-film symmetrical electrochromic devices (ECDs) have been constructed and tested. The proposed architecture serves as a prove of concept that polymeric ionic liquids (PILs) can be themselves used as solid electrolytes thus avoiding any electrolyte leakage since the ionic liquid species are grafted on the polymer backbone. Three different methods for the synthesis of PEDOT electrode films, including two new approaches consisted in vapor phase polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of ionic monomer and poly(ethylene glycol)(di)methacrylates, have been investigated. Two oxidants, Fe[(CF₃SO₂)₂N]₃ and Fe[(CN)₄B]₃, bearing the same anions as PILs were prepared for the first time and utilized in the vapor phase polymerization of EDOT. It was found that the more compact structure and the highest conductivity are achieved for PEDOT electrodes prepared by vapor phase polymerization of EDOT in the presence of ionic monomer and poly(ethylene glycol)(di)methacrylates, followed by radical polymerization of the latters. The simplicity of ECDs assembly, their fast switching times (3–5 s), high coloration efficiency (up to 430 cm²/C), satisfactory optical contrast (up to 28.5%), absence of any liquids and good performance in air and in vacuum were found among the advantages of the proposed technology.     

Effects of ionicity and chain structure on the physicochemical properties of protic ionic liquids

The physicochemical properties of protic ionic liquids (PILs) determine their industrial applications. In this study, six PILs based on 1-vinylimidazole were synthesized, and their ionicities were determined by ¹H NMR method. The thermodynamic properties, viscosities, densities, and conductivities of these PILs were correlated with the ionicities and the chain lengths of the anions. The ionicity was found to depend on the acidity of the alkyl carboxylic acid. Since HAc has the strongest acidity among these acid precursors, Vim·HAc has the highest ionicity and thus the strongest Coulombic interactions among the six PILs. The other five PILs have similar ionicities but different chain lengths in their anions. So, we can separately identify the effects of Coulombic interactions and van der Waals forces on the physicochemical properties of PILs. From these trends, the viscosity and conductivity of PILs may be tuned by varying the acidity and alkyl chain length of the precursors.     

Antimicrobial polyurethane coatings based on ionic liquid quaternary ammonium compounds

The antimicrobial effect of ionic liquids (ILs) as comonomers in polyurethane surface coatings was investigated. Ionic liquid-containing coatings were prepared from a hydroxyl end-capped liquid oligoester and a triisocyanate crosslinker. Three different commercially available hydroxyl end-capped ionic liquids were covalently incorporated into the coatings in order to end up with antimicrobial polyurethane films. The ionic liquids used in this study were chosen because of their structural similarities to other antimicrobial quaternary ammonium compounds (QACs). Prepared films have been examined against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli type bacteria, and showed strong antimicrobial activity.     

手性功能化离子液体的合成进展

手性离子液体作为功能化离子液体的一种,综合了离子液体与手性物质两方面的特性。不仅具有手性特征,而且几乎无蒸气压,无可燃性,具有很高的热力学和化学稳定性,电导率高,可以循环使用,对无机和有机物有良好的溶解性、稳定性等。手性离子液体可以作为手性溶剂,催化剂载体或手性诱导剂,应用于手性合成、手性分离和手性催化等领域。本文综述了近些年来手性离子液体合成的最新进展,结构上按阴、阳离子分类,同一离子类型中按物质种类分类。同时介绍了一些新的合成技术。最后对手性离子液体可能的发展趋势和以后的研究方向进行了展望。     

Electrochemical studies and self diffusion coefficients in cyclic ammonium based ionic liquids with allyl substituents

Several cyclic ammonium-based ionic liquids (ILs) with allyl substituent are synthesized, these allyl substituent ILs have high ionic conductivity (up to 4.72 mS cm⁻¹ at 30 °C) and wide electrochemical window of 5 V. The electrochemical behaviors of two organometallic redox couples Fc/Fc⁺ (ferrocene/ferrocenium) and Cc/Cc⁺ (cobaltocene/cobaltocenium) have been studied in these ILs, the calculated Stokes–Einstein product (Dη T⁻¹) of ferrocene in ILs is larger than that of cobaltocenium in ILs. The self-diffusion coefficients of cation and anion in these ILs are studied using pulsed gradient spin-echo NMR technique. There are very few reports where electrochemically derived diffusion coefficients and self diffusion coefficients are available for comparison, so a new key concept in electrochemistry could be developed in this paper.     

Ionic Liquids as Extraction Solvents: Where do We Stand?

Abstract

The unique physicochemical properties of ionic liquids (ILs) and the relative ease with which these properties can be fine‐tuned by altering the cationic or anionic moieties comprising the IL have led to intense interest in their use as alternatives to conventional organic solvents in a wide range of synthetic, catalytic, and electrochemical applications. Recent work by a number of investigators has been directed at the application of ionic liquids in various separation processes, among them the liquid‐liquid extraction of metal ions. Although certain IL‐extractant combinations have been shown to yield metal ion extraction efficiencies far greater than those obtained with molecular organic solvents, other work suggests that the utility of ILs may be limited by solubilization losses and difficulty in recovering extracted metal ions. In this report, recent efforts to overcome these limitations are described, and progress both in achieving an improved understanding of the fundamental aspects of metal ion transfer into ILs and in devising viable IL‐based systems for metal ion separation is detailed. In addition, areas upon which future research efforts might profitably be focused are identified.     

Synthesis and characterization of two ionic liquids with emphasis on their chemical stability towards metallic lithium

Two room temperature ionic liquids (RTILs) without acidic protons, based on different cationic species (1-n-butyl-2,3-dimethylimidazolium) (BMMI) and N-n-butyl-N-methylpiperidinium (BMP) using (CF₃SO₂)₂N⁻ (TFSI) as anion, were prepared by quaternization of their respective amines with an appropriate alkyl halide, followed by ion exchange reaction. All relevant properties of these ionic liquids, such as, thermal stability, density, viscosity, electrochemical behavior, ionic conductivity and self-diffusion coefficients for both ionic species, were determined at different temperatures. In spite of their ionic conductivity being lower than 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (BMITFSI), the absence of an acidic proton in both compounds is crucial to maintain their chemical stability towards metallic lithium and, thereby, to make possible the safe assembly of lithium ion batteries. Both ionic liquids without acidic protons do not react with metallic lithium; on the other hand, the formation of carbene species when BMITFSI was exposed to Li was confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS).     

A new series of cross-linked (meth)acrylate polymer electrolytes for energy storage

A series of methacrylate-crosslinked polymers were investigated as potential polymer electrolytes for energy storage application. Methacrylate ester crosslinkers (25–50 mol.%) with different spacer lengths and MMA as comonomer were polymerised into thin films. Mixtures of ethylene carbonate and propylene carbonate (EC/PC) or alternatively the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI), both doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI), fulfilled the role of electrolyte and porogen simultaneously. Ionic conductivity increased with increasing porogen content, Li ion concentration, and decreasing amounts of crosslinker (maximum values: 0.5 mS/cm (EC/PC) and 4.5 mS/cm (EMIM TFSI)). Thin films with permanent porosity were obtained for both electrolyte systems. The flexibility of the films increased with a lower concentration of crosslinker or the choice of a crosslinker with a longer spacer. The relationship between pore size, pore morphology, glass transition temperature and ionic conductivity on the other hand was complex and did not exhibit distinct trends. High thermal stability, ionic conductivity and tunable mechanical properties make these polymer thin films attractive candidates as in situ filled Li ion battery separator films either preformed or directly printed.