N-Butyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide–PVdF(HFP) gel electrolytes

Ionic liquid–polymer gels were prepared by incorporating N-butyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide (Mor_1,4TFSI) and poly(vinylidene fluoride)–hexafluoropropylene copolymer (PVdF(HFP)) using three different methods in order to observe the variation of ionic conductivities according to the presence of propylene carbonate (PC) and various weight ratios between Mor_1,4TFSI and gel polymer electrolyte (GPE). Ionic conductivities for each gel polymer electrolyte were measured with increasing temperature. Ionic conductivities of the GPEs increased with increasing temperature and weight ratio of Mor_1,4TFSI. In addition, the addition of PC into GPE led to the improvement of ionic conductivities. Thermogravimetric analysis (TGA) showed the suggested gel polymer electrolytes composed of only ionic liquid and polymer were stable up to approximately 400 °C. TGA and infrared spectroscopy data indicated that residual PC remains after evaporating PC in a vacuum oven, which did not affect the ionic conductivities. The GPEs containing PC displayed high conductivity (ca. 10⁻² S cm⁻¹) at 60 °C.     

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.     

High-pressure phase behavior of carbon dioxide in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Phase equilibrium data of carbon dioxide in the ionic liquid 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]) are presented at high pressures up to about 30 MPa and at temperatures between 298.15 K and 343.15 K. The solubilities at a given temperature were determined by measuring the bubble point pressure of the ionic liquid solution with carbon dioxide dissolved using the high-pressure equilibrium apparatus equipped with a variable-volume view cell. Solubility results are reported for carbon dioxide concentrations ranging from 0.21 up to 0.80 mole fraction. Carbon dioxide gave very high solubilities in the ionic liquid at lower pressures, while the equilibrium pressure increased very steeply at higher concentrations of carbon dioxide. The solubility of carbon dioxide in the ionic liquid decreased with an increase in temperature.     

Polymer electrolytes based on poly(ethylene glycol) dimethyl ether and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate: Preparation, physico-chemical characterization, and theoretical study

Polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) and the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) have been prepared and characterized by different techniques. Coordination of the IL by the polymer occurs mainly in the amorphous phase. This finding was correlated with previous theoretical investigations of a similar model for polymer electrolytes based on poly(ethylene oxide), PEO, and IL. It has been obtained ionic conductivity σ ∼ 10⁻³ S cm⁻¹ for the polymer electrolyte with 35 wt% of IL at 100 °C. The same order of magnitude for σ was obtained by molecular dynamics simulation of PEO/IL. This work demonstrates consistency between experimental and theoretical results for polymer electrolytes containing ionic liquids.     

Effect of the alkyl group on the synthesis and the electrochemical properties of N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquids

The effect of the alkyl side group on the synthesis and the electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR_1ATFSI) ionic liquids (ILs) is reported. The investigation was focused on the PYR_1ATFSI ionic liquid family because of the interesting electrochemical properties of the members with propyl and butyl side chains. Side alkyl groups (A = C_nH_2n+1 with n ranging from 1 to 10) of different length and structure were used for the synthesis of PYR_1ATFSI materials. NMR and DSC have shown that the ionic liquids were correctly synthesized with the exception of the compounds with tertiary side chains. Most of the materials exhibited a conductivity higher than 10⁻³ S cm⁻¹ already at 12 °C. In the molten state a moderate conductivity decrease was observed with increasing the length and the branching of the side chain (C₂H_2n+1) group according with the change of viscosity of the ionic liquids. Most of the PYR_1ATFSI samples exhibited an electrochemical stability window exceeding 5 V.     

Studies of a high temperature proton exchange membrane based on incorporating an ionic liquid cation 1-butyl-3-methylimidazolium into a Nafion matrix

High temperature proton exchange membranes based on Nafion were prepared by incorporating the polymer with ionic liquid cation 1-butyl-3-methylimidazolium (BMIm) and doping with phosphoric acid (PA). We found that using the hydroxide form rather than the chloride form of BMIm incorporated more readily the BMIm cation into Nafion film. A mole ratio of about 2 of BMIm cation to Nafion repeat unit, i.e., λ_BMIm/Nafion, was reached with the hydroxide form BMIm. The incorporated BMIm cation enhanced the doping of phosphoric acid into Nafion. A proton conductivity of 10.9 mS cm⁻¹ and a tensile stress at break of 5.3 MPa were achieved, respectively, with a composite membrane of Nafion/2.3BMIm/5.2PA in molar ratio at 160 °C without humidification.     

1-Alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids as highly safe electrolyte for Li/LiFePO4 battery

Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO₄ battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li⁺/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO₄ cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO₄ battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g⁻¹, which the value is near to theoretical specific capacity (170 mAh g⁻¹). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g⁻¹) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g⁻¹ when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future.     

1-丁基-3-甲基咪唑表面活性离子液体的界面膨胀流变行为研究

研究了1-丁基-3-甲基咪唑十二烷基硫酸盐([bmim][DS])和1-丁基-3-甲基咪唑二(2-乙基己基)磺基琥珀酸酯盐([bmin][AOT]两种表面活性离子液体在正庚烷/水界面的动态界面张力和膨胀特性。比较了[bmim][DS]或[bmin][AOT]和传统表面活性剂十二烷基硫酸钠(SDS)或二(2-乙基己基)磺基琥珀酸酯钠(Na[AOT])之间的膨胀弹性,并且考察了1-丁基-3-甲基咪唑阳离子之间静电相互作用对界面膜特性的影响。另外,通过对比[bmim][DS]和[bmim][AOT]在不同浓度下的膨胀弹性,验证了烷基链数量的改变对界面膨胀流变行为的影响。     

Electropolymerization of 1,2-methylenedioxybenzene in 1-butyl-3-methylimidazolium hexafluorophosphate room temperature ionic liquid

The electrochemical polymerization of 1,2-methylenedioxybenzene (MDOB) in a room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆) has been investigated. Its polymer poly(1,2-methylenedioxybenzene) (PMDOB) showed good redox activity and stability even in concentrated sulfuric acid. IR and ¹H NMR spectra confirmed that the polymerization occurred at the C₄ and C₅ positions on the benzene ring of MDOB, resulting in the main backbone of PMDOB similar to polyacetylene. In contrast to acetonitrile containing 0.1 mol/L Bu₄NBF₄, BmimPF₆ serves as both the growth medium and an electrolyte. Hence, enhanced electrochemical stability of PMDOB can be easily obtained on repetitive redox cycling. As-formed PMDOB represented good electrochromic properties from green grass to opalescent between doped and dedoped states. Scanning electron microscopic results demonstrated that smooth and compact PMDOB films composed of ordered nanostructures were obtained, implying their possible utilizations in ion-sieving films, ion-selective, and matrices for catalyst particles.     

Importance of poly(ethylene oxide)-modification and chloride anion for the electron transfer reaction of cytochrome c in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

Horse heart cytochrome c (cyt c) was chemically modified with poly(ethylene oxide) (PEO) to dissolve it in room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim][TFSI]). The redox response of the modified cyt c, hereafter PEO-cyt c, was analyzed in [emim][TFSI]. PEO modification to the surface of cyt c, which exceeded 60% of the total mass of the PEO-cyt c, was an effective method to solubilize the cyt c. In spite of the high ion density and sufficient ionic conductivity of [emim][TFSI], no redox response of pure PEO-cyt c was detected. However, a reversible redox response of PEO-cyt c was observed after adding a simple electrolyte such as KCl to [emim][TFSI]. The redox response of PEO-cyt c was sensitive to the anion radius of the added salt, and the chloride anion was found to be the best anion species to produce a redox response of PEO-cyt c in [emim][TFSI]. However, above a certain salt concentration, the resulting increase in solution viscosity would suppress the redox reaction. The results strongly indicate that the chloride anions, because of their mobility in the polypeptide matrix, compensate the charge change of heme during the electron transfer reaction. Larger anions did not show such an effect due to sterical restrictions on the migration through the protein shell to the heme pocket of cyt c.     

离子液体[Bmim][NTf2]对CO2在碳酸二乙酯中溶解性能的强化

采用恒定容积法在温度范围308.15~328.15 K、压力范围0~3 MPa条件下测定了CO₂在碳酸二乙酯（DEC）、离子液体[Bmim][NTf₂]以及二者不同质量分数配比混合溶剂中的溶解度,并用COSMO-RS模型研究了离子液体的加入对DEC蒸气分压的影响。实验表明,在相同实验条件下CO₂在[Bmim][NTf₂]中的溶解度大于在DEC中的溶解度。[Bmim][NTf₂]的加入可强化CO₂在DEC中的溶解性能,在相同温度下CO₂在混合溶剂中的溶解度随[Bmim][NTf₂]质量分数增加而增大,在相同浓度的混合溶剂中CO₂的溶解度随温度升高而降低。COSMO-RS模型计算表明,DEC的蒸气分压下降的分数随混合溶剂中离子液体质量分数增加而增大,而对于相同质量分数配比的混合溶剂温度对DEC的蒸气分压影响较小。     

Cycling stability of a hybrid activated carbon//poly(3-methylthiophene) supercapacitor with N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid as electrolyte

A long cycle-life, high-voltage supercapacitor featuring an activated carbon//poly(3-methylthiophene) hybrid configuration with N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid, a solvent-free green electrolyte, was developed. The cyclability of a laboratory scale cell with electrode mass loading sized for practical uses was tested at 60 °C over 16,000 galvanostatic charge-discharge cycles at 10 mA cm⁻² in the 1.5 and 3.6 V voltage range. The reported average and maximum specific energy and power, specific capacitance and capacity, equivalent series resistance and coulombic efficiency over cycling demonstrate the long-term viability of this ionic liquid as green electrolyte for high-voltage hybrid supercapacitors.     

Syntheses of high molecular weight aliphatic polyesters in 1-alkyl-3-methylimidazolium ionic liquids

High molecular weight aliphatic polyesters were synthesized, for the first time, in 1-alkyl-3-methylimidazolium ionic liquids via two-step polycondensation. An oligoester with diol/diacid ratio higher than unity was essential for achieving high molecular weight product. Moreover, the molecular weight of the resulting polyesters was found to depend on the activity of the catalyst in the ionic liquids and the miscibility of aliphatic polyester/ionic liquid. The former factor was dominated by the anion of the ionic liquids. The latter factor could readily be tuned by varying the anion and/or the cation of the ionic liquids. A clear correlation was found between the miscibility of aliphatic polyester/ionic liquid and the extent to which their solubility parameters matched.     

Understanding specific effects on the standard potential shifts of electrogenerated species in 1-butyl-3-methylimidazolium ionic liquids

It has been established that the dependence of the E° values in function of the electrochemical media selected for a large amount of reversible redox probes in reduction and also in oxidation. For such a purpose several electroactive substances either in reduction (4-nitrotoluene, 1,3-dinitrobenzene, tetrakis(dimethylamino)ethylene, 1,3,5-trinitrobenzene, and 2,4,6-trinitroanisole) or oxidation (ferrocene, tetrathiofulvalene, tris-4-bromophenylamine, tris-4-tolylamine, and N,N,N′,N′-tetramethyl-para-phenylenediamine) have been studied in aprotic RTILs based on unsymmetrical organic cations (quaternary ammonium cations, such as 1-butyl-3-methyl imidazolium) and a weakly coordinating inorganic anion (anions with low Lewis basicities, e.g., BF₄, PF₆). Ion-pairing effects between imidazolium ions and anions and dianions for the electrochemically generated species, the solvation differences between BF₄⁻/PF₆⁻ cations and dications as well as some different reaction mechanism pathways followed by these electrogenerated species in function of the solvent have also been carefully examined.     

Enhanced high-temperature polymer electrolyte membrane for fuel cells based on polybenzimidazole and ionic liquids

Polybenzimidazole (PBI)/ionic liquid (IL) composite membranes were prepared from an organosoluble, fluorine-containing PBI with ionic liquid, 1-hexyl-3-methylimidazolium tri?uoromethanesulfonate (HMI-Tf). PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The composite membranes achieve high ionic conductivity (1.6 × 10⁻² S/cm) at 250 °C under anhydrous conditions. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes, the PBI/HMI-Tf composite membranes have demonstrated high thermal stability up to 300 °C, which is attractive for high-temperature (>200 °C) polymer electrolyte membrane fuel cells.     

Physical and electrochemical properties of 1-(2-hydroxyethyl)-3-methyl imidazolium and N-(2-hydroxyethyl)-N-methyl morpholinium ionic liquids

Various ionic liquids (ILs) were prepared via metathesis reaction from two kinds of 1-(2-hydroxyethyl)-3-methyl imidazolium ([HEMIm]⁺) and N-(2-hydroxyethyl)-N-methyl morphorinium ([HEMMor]⁺) cations and three kinds of tetrafluoroborate ([BF₄]⁻), bis(trifluoromethanesulfonyl)imide ([TFSI]⁻) and hexafluorophosphate ([PF₆]⁻) anions. All the [HEMIm]⁺ derivatives were in a liquid state at room temperature. In particular, [HEMIm][BF₄] and [HEMIm][TFSI] showed no possible melting point from −150 °C to 200 °C by DSC analysis, and their high thermal stability until 380-400 °C was verified by TGA analysis. Also, their stable electrochemical property (electrochemical window of more than 6.0 V) and high ionic conductivity (0.002-0.004 S cm⁻¹) further confirm that the suggested ILs are potential electrolytes for use in electrochemical devices. Simultaneously, the [HEMMor]⁺ derivatives have practical value in electrolyte applications because of their easy synthesis procedures, cheap morpholinium cation sources and possibilities of high Li⁺ mobility by oxygen group in the morpholinium cation. However, [HEMMor]⁺ derivatives showing high viscosity usually had lower ionic conductivities than [HEMIm]⁺ derivatives.     

Investigation of Ternary Mixtures Containing 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)azanide,Ethylene Carbonate and Lithium Bis(trifluoromethanesulfonyl)azanide

Temperature-dependent viscosity, conductivity and density data of ternary mixtures containing 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)azanide (EMIM-TFSA), ethylene carbonate (EC), and lithium bis(trifluoromethanesulfonyl)azanide (Li-TFSA) were determined at atmospheric pressure in the temperature range of 20 to 80 °C. Differential scanning calorimetry (DSC) measurements were performed to characterize phase conditions of the mixtures in a temperature range of −120 to +100 °C. The viscosity data were fitted according to the Vogel-Fulcher-Tammann-Hesse (VFTH) equation and analyzed with the help of the fractional Walden rule. In this study, fundamental physicochemical data about the mixtures are provided and discussed as a basis for structure-property relationship calculations and for potential use of those mixtures as electrolytes for various applications.     

Anodic behavior of gold in 1-butyl-3-methylimidazolium methanesulfonate ionic liquid with chloride anion

The anodic behavior of gold has been investigated in presence of chloride and/or water in 1-butyl-3-methylimidazolium methanesulfonate (BMI CH₃SO₃) ionic liquid (IL). The cyclic voltammetry (CVs) in presence of chloride ions shows two waves attributed to the oxidation of the gold electrode which occurs under two steps: the first one is attributed to the electrochemical dissolution of gold into to gold(I), while the second one is attributed to an overlap of the chloride oxidation step as well as the oxidation of Au(I) to Au(III). Furthermore the determination of water and chloride content in IL allowed observing that the passive layer induced by water could be removed under chloride. Thanks to those results we were able to clarify the conditions of gold recovering in this kind of electrolyte.     

Poly(oxyethylene) electrolytes based on lithium pentafluorobenzene sulfonate

Lithium pentafluorobenzene sulfonate was synthesized by a protocol whereby pollution by aromatic nucleophilic substitutions on the perfluorinated ring was avoided. Its poly(oxyethylene) complexes, although less conductive than lithium imide complexes, provided cationic transference numbers higher than 0.5. Surprisingly, even at fairly low concentrations, this salt markedly increased the mechanical properties of the polymer electrolyte. This effect was attributed to telechelic interactions of the ion pairs with distinct polyether chains and is in agreement with the high cationic transference numbers.     

Functionalized ionic liquids based on quaternary ammonium cations with three or four ether groups as new electrolytes for lithium battery

New functionalized ILs based on quaternary ammonium cations with three or four ether groups and TFSI⁻ anion were synthesized and characterized. Physical and electrochemical properties, including melting point, thermal stability, viscosity, conductivity and electrochemical stability were investigated for these ILs. Five ILs with lower viscosity in these ILs were applied in lithium battery as new electrolytes. Behavior of lithium redox and charge–discharge characteristics of lithium battery were investigated for these IL electrolytes with 0.6 mol kg⁻¹ LiTFSI. Lithium plating and striping on Ni electrode could be observed in these IL electrolytes. Li/LiFePO₄ cells using these IL electrolytes without additives had good capacity and cycle property at the current rate of 0.1 C, and the N(2o1)₃(2o2)TFSI and N2(2o1)₃TFSI electrolytes owned better rate property.