Organosilicon functionalized quaternary ammonium ionic liquids as electrolytes for lithium-ion batteries

Organosilicon-functionalized quaternary ammonium ionic liquids (ILs) with oligo(ethylene oxide) substituent are designed and synthesized. Such properties as viscosity, conductivity, and thermal/electrochemical stability of these ILs are characterized. These ILs are miscible with the commercial carbonate electrolyte (EC: DEC?=?1:1(w/w), 1 M LiPF₆) and are used as cosolvents to form hybrid electrolytes in proportions up to 30 vol%. By using such hybrid electrolytes, the LiFePO₄/Li half cells exhibit no deterioration in specific capacity and cyclability, and the graphite/Li half cells show improved compatibility in the presence of lithium oxalyldifluoroborate. These hybrid electrolytes exhibit less flammability compared with the commercial baseline electrolyte, and thus improved safety for use in lithium-ion batteries.     

Physicochemical properties of ionic liquids based on imidazolium/pyrrolidinium cations and maleate/phthalate anions

Ionic liquids (ILs) based on imidazolium/pyrrolidinium cations and maleate/phthalate anions can be used as excellent electrolyte materials for electrolytic capacitors. In this study, we synthesized four ILs of this family and investigated their thermal behaviors, ionic conductivities and sparking voltages. The four ILs have high thermal stability for capacitor requirements. The conductivities of imidazolium ILs are slightly higher than those of pyrrolidinium analogs and the conductivities of maleate anion-based ILs are higher than those of corresponding phthalate anion-based ILs. Besides, the long-term thermal stability of imidazolium ILs in conductivity is superior to that of pyrrolidinium analogs. Whereas the long-term thermal stability of phthalate anion-based ILs is better than that of corresponding maleate anion-based ILs. The influence of cationic structure of the ILs on conductivity was analyzed. The temperature dependence of conductivity was also discussed in this work. The Vogel–Tammann–Fulcher (VTF) equation accurately describes the temperature dependence of conductivity for the ILs. In addition, the result of sparking voltage measurement shows that neither Ikonopisov nor Albella model is valid for the ILs.     

Temperature effect on the molecular interactions between two ammonium ionic liquids and dimethylsulfoxide

To understand the molecular interactions between newly synthesized ammonium ionic liquids (ILs) and highly polar solvent dimethylsulfoxide (DMSO), precise measurements such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been performed over the whole composition range at temperature ranging from 298.15 to 308.15 K and at atmospheric pressure. The ILs investigated in the present study included diethyl ammonium acetate ([Et₂NH][CH₃COO], DEAA) and triethyl ammonium acetate ([Et₃NH][CH₃COO], TEAA). Further, to gain some insight into the nature of molecular interactions in these mixed solvents, we predicted the excess molar volume (V^E), the deviation in isentropic compressibilities (ΔK_s) and deviation in viscosity (Δη) as a function of the concentration of IL using the measured properties of ρ, u and η, respectively. Redlich-Kister polynomial was used to correlate the results. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and DMSO molecules and their structural factors.     

Electrochemical performance of lead acid battery using ammonium hydrogen sulphate with different alkyl groups

In this work, the application of ionic liquids (ILs)??mono-, bicycyclohexyl, monohexyl and tetrahexyl ammonium hydrogen sulphate??as electrolyte additives on the electrochemical performance of lead acid batteries is proposed. The electrochemical behaviour of Pb?C1.66% Sb?C0.24% Sn alloy in sulphuric acid solution is investigated in the presence of the mentioned ILs with different numbers of alkyl or cycloalkyl chains. Particularly, the hydrogen and oxygen evolution potential and anodic layer characteristics were studied using cyclic and linear sweep voltammetric methods. The obtained results indicate that hydrogen evolution overpotential of Pb/Sb/Sn alloy in the presence of ILs increases. This overpotential mainly depends on the concentration of ILs and the number of alkyl and cycloalkyl chains on the cations. Also, the difference between the oxygen oxidation potential in anodic and cathodic scans (?E) decreases using different ILs.     

A piperidinium-based ester-functionalized ionic liquid as electrolytes in Li/LiFePO<Subscript>4</Subscript> batteries

A new functionalized ionic liquid (IL) based on cyclic quaternary ammonium cations with ester group and bis(trifluoromethanesulfonyl)imide ([TFSI]^?) anion, namely, N-methyl-N-methoxycarbonylpiperidinium bis(trifluoromethanesulfonyl)imide ([MMOCPip][TFSI]), was synthesized and characterized. Physical and electrochemical properties, including Li-ion transference number, ionic conductivity, and electrochemical stability, were investigated. The electrochemical window of [MMOCPip][TFSI] was 6 V, which was wide enough to be used as a common electrolyte material. The Li-ion transference number of this IL electrolyte containing 0.1 M LiTFSI was 0.56. The half-cell tests indicated that the [MMOCPip][TFSI] obviously improved the cyclability of a Li/LiFePO₄ cell. For the Li/LiFePO₄ half-cells, after 20 cycles at room temperature at 0.1 C, the discharge capacity was 109.7 mAh g^?1 with 98.7% capacity retention in the [MMOCPip][TFSI]/0.1 M LiTFSI electrolyte. The good electrochemical performance demonstrated that the [MMOCPip][TFSI] could be used as electrolyte for lithium-ion batteries.     

Modified equation of state extended to imidazolium-, phosphonium-, pyridinium-, pyrrolidinium- and ammonium-based ionic liquids

An analytical equation of state (EoS) has been previously employed by Hosseini and Sharafi (Ionics 17:511, 2011) for modelling of PVT data of some ionic liquids (ILs). In this work, we have extended the mentioned model to five classes of ILs by the use of alternative scaling constants for corresponding states correlation procedure. For this purpose, ILs involving imidazolium, phosphonium, pyridinium, pyrrolidinium and ammonium cations have been taken into account. From these, 1,294 experimental data points examined to show the reliability of the modified EoS. The comparison of predicted densities with the measured values over a broad range of temperature 293?C452 K and pressures up to 150 MPa led to the encouraging results. The average absolute deviation of calculated densities from literature values was found to be 0.73%. Moreover, to establish the predictive power of proposed model, the reproduced densities have been compared with those obtained by another literature work. Moreover, we have demonstrated the density behaviour of studied ILs in terms of alkyl chain length of imidazolium cation via proposed model.     

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10^?4 S cm^?1), lithium ion conductivity (1.40?×?10^?4 S cm^?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li⁺ at 30 °C). Furthermore, the surface of LiFePO₄ cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO₄ cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO₄. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g^?1 for graphene oxide-coated LiFePO₄ and without coated LiFePO₄ at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO₄ cathode after coating with graphene oxide.     

A novel and shortcut method to prepare ionic liquid gel polymer electrolyte membranes for lithium-ion battery

The ionic liquid polymer electrolyte (IL-PE) membrane is prepared by ultraviolet (UV) cross-linking technology with polyurethane acrylate (PUA), methyl methacrylate (MMA), ionic liquid (Py₁₃TFSI), lithium salt (LiTFSI), ethylene glycol dimethacrylate (EGDMA), and benzoyl peroxide (BPO). N-methyl-N-propyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py₁₃TFSI) ionic liquid is synthesized by mixing N-methyl-N-propyl pyrrolidinium bromide (Py₁₃Br) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The addition of Py₁₃TFSI to polymer electrolyte membranes leads to network structures by the chain cross-linking. The resultant electrolyte membranes display the room temperature ionic conductivity of 1.37 × 10^?3 S cm^?1 and the lithium ions transference number of 0.22. The electrochemical stability window of IL-PE is about 4.8 V (vs. Li⁺/Li), indicating sufficient electrochemical stability. The interfacial resistances between the IL-PE and the electrodes have the less change after 10 cycles than before 10 cycles. IL-PE has better compatibility with the LiFePO₄ electrode and the Li electrode after 10 cycles. The first discharge performance of Li/IL-PE/LiFePO₄ half-cell shows a capacity of 151.9 mAh g^?1 and coulombic efficiency of 87.9%. The discharge capacity is 131.9 mAh g^?1 with 95.5% coulombic efficiency after 80 cycles. Therefore, the battery using the IL-PE exhibits a good cycle and rate performance.     

Synergic effects of ultrasound and ionic liquids on fluconazole emulsion

The aim of this work was to evaluate the influence of US on the properties of the fluconazole emulsions prepared using imidazolium-based ILs ([C_n C₁im]Br). The effects of the preparation method (mechanical stirring or US), US amplitude, alkyl chain length (of [C₁₂C₁im]Br or [C₁₆C₁im]Br), and IL concentration on the physicochemical properties were evaluated. Properties such as droplet size, span index, morphology, viscosity encapsulation efficiency, and drug release profile were determined. The results showed that US-prepared emulsions had a smaller droplet size and smaller polydispersity (Span) than those prepared by mechanical stirring. Additionally, the results showed that emulsions prepared with [C₁₆C₁im]Br and US had spherical shapes and increased stability compared to emulsions prepared by MS, and also depended on the IL concentration. The emulsion prepared by US at 40% amplitude had increased encapsulation efficiency. US provided a decrease in the viscosity of emulsions containing [C₁₂C₁im]Br; however, in general, all emulsions had viscosity close to that of water. Emulsions containing [C₁₆C₁im]Br had the lowest viscosities of all the emulsions. The emulsions containing the IL [C₁₆C₁im]Br had more controlled release and a lower cumulative percentage of drug release. The IL concentration required to prepare these emulsions was lower than the amount of conventional surfactant required, which highlights the potential synergic effects of ILs and US in preparing emulsions of hydrophobic drugs.     

Physicochemical characterization of paramagnetic ionic liquids 1‐vinyl‐3‐alkylimidazolium tetrahalogenidoferrate(III) [VRIM][FeClmBr4 − m]

Using microwave‐assisted synthesis method, a series of paramagnetic ionic liquids comprising 1‐vinyl‐3‐alkylimidazolium VRIM⁺ cation and tetrahalogenidoferrate (III) FeCl_mBr_{4 ? m}^? anion were designed and synthesized. The structure was analyzed using ¹H NMR and Raman spectroscopy. Ultraviolet–visible absorption spectra, thermal stability, magnetic susceptibility, viscosity, ionic conductivity, and solubility were characterized. Results show that elongation of the alkyl chain leads to replacement of bromides with a small amount of chlorides in the anion, shifting of UV maximum absorption peaks to shorter wavelengths, reduction of ionic conductivity, and solubility in polar solvents, as well as increase in fluidity, magnetic susceptibility, and solubility in nonpolar solvents. Copyright © 2014 John Wiley & Sons, Ltd.     

Volumetric and transport properties of <Emphasis Type="Italic">N</Emphasis>-Butyl-<Emphasis Type="Italic">N</Emphasis>-methylpyrrolidinium bis(Trifluoromethanesulfonyl)imide–methanol binary mixtures

Densities, viscosities, and ionic conductivities were measured for the binary mixtures containing the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and methanol over the entire range of compositions at the temperature varying from 253.15 to 318.15 K. The densities and viscosities decrease monotonously with temperature and the content of ionic liquids (ILs). Furthermore, excess isobaric expansion coefficient has been calculated from the experimental densities. The dependence of temperature on the viscosity has been fitted to the Arrhenius law with high precision. The dependence of temperature on the ionic conductivity has also been gauged by both of the Arrhenius and Vogel–Tamman–Fulcher (VTF) equations. In fact, the shape of the curves shows that the temperature dependence of the conductivity does not follow a simple Arrhenius law, but a better fitting of experimental results is achieved using the VTF model. Additionally, the effects of ILs concentration on the viscosity and the conductivity have been examined using the Walden rule, which shows that the variation of conductivity is inversely proportional to viscosity. Excess molar volumes and viscosity deviations for all mixtures are evaluated and well fitted to the Redlich–Kister polynomial expansions. Physicochemical properties show two clearly distinguished behaviors corresponding to ILs-rich and methanol-rich regions, with distinct transport and volumetric properties. The obtained results are discussed in terms of dipolar interactions and hydrogen bonding establishment between ions of ILs and the methanol molecules.     

Mesophilic alcohol dehydrogenase behavior in imidazolium based ionic liquids

The use of ionic liquids to replace organic solvents in biocatalytic processes has recently gained much attention. Despite the wide applications of oxidoreductases, there are few reports of their catalyzed reaction in ionic liquid. We have investigated the influence of four water miscible ionic liquids on the activity, stability and structure of the mesophilic alcohol dehydrogenase from yeast. Upon changes in ionic liquids concentration, both activity and stability of the enzyme were affected. As the concentration of ionic liquids increased, K_m increased while k_cat decreased. Associated conformational changes caused by ILs (150 mM) were monitored using fluorescence technique. Finally, the effects of ILs cations and anions on the enzyme activity and stability in aqueous IL mixtures were discussed.     

Ultrasound and ionic-liquid-assisted synthesis and characterization of polyaniline/Y2O3 nanocomposite with controlled conductivity

A sonochemical method has been employed to prepare polyaniline-Y₂O₃ nanocomposite with controlled conductivity with the assistance of an ionic liquid (IL). Ultrasound energy and the IL replace conventional oxidants and metal complexes in promoting the polymerization of aniline monomer for the first time. Structural characterization has revealed that the resulting nanocomposite consists of microspheres of average diameter 3–5 μm. The products were found to consist of regular solid microspheres covered with some 40 nm nanoparticles. Under certain polymerization conditions, polyaniline nanofibers and nanosheet were obtained. The method may open a new pathway for the preparation of nanoscale conducting polymer nanocomposites with the aid of ILs. The conductivity of the product varies with the mass ratio of aniline monomer to Y₂O₃ and IL. TG curves of the products suggest that the thermal degradation process of the PANI/Y₂O₃ composites proceeds in two steps and that the composites are more thermally stable than pure PANI. The reaction conditions have been optimized by varying parameters such as the aniline/Y₂O₃ ratio and the type and amount of IL used. The effect of the ultrasonic irritation time and frequency on the morphology, conductivity and yield were discussed.     

Revisited vibrational assignments of imidazolium‐based ionic liquids

Imidazolium‐based ionic liquids (ILs) involving anions of variable coordinating strength have been investigated using infrared (IR) and Raman spectroscopies, density functional theory (DFT) calculations and selective deuteration of the imidazolium CH groups. Particular emphasis has been placed on the vibrational assignments of the anion and cation internal vibrations, a prerequisite before any interpretation of spectral changes due to ion–ion interactions in these unconventional liquids. The vibrations of highly symmetric and weakly coordinating anions, such as PF₆⁻, have unperturbed wavenumbers, but unexpected IR or Raman activity for some modes, showing that the anion is subjected to an anisotropic electric field. The stretching as well as the in‐plane and out‐of‐plane bending modes of the imidazolium CH groups are anharmonic. They give broad bands that reflect a large distribution of interactions with the surrounding anions. All the bending modes are mixed with ring vibrations and the stretching modes are complicated by Fermi resonance interactions with overtones and combination of in‐plane ring modes. However, the stretching vibration of the quasi‐diatomic C₍₂₎ D bond appears to be a good spectroscopic probe of the increasing cation–anion interactions when the coordinating strength of the anion increases. The broad absorption observed in the far IR with weakly coordinating anions remains practically unchanged when the acidic C₍₂₎ H imidazolium bond is methylated and even when the imidazolium cation is substituted by tetra‐alkyl ammonium or pyrrolidinium cations. It is concluded that this absorption is a general feature of any IL, coming from the relative translational and librational motions of the ions without needing to invoke C₍₂₎ H anion hydrogen bonds. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling phase equilibria of pure ionic liquids from a new equation of state

A perturbed hard-trimer (PHT) equation of state (EOS) has been employed to model densities and some derived thermodynamic properties of 39 ionic liquids (ILs) considering a trimer expression obtained from the statistical associating fluid theory as the reference physical model. The van der Waals dispersion forces were applied as perturbation term. The proposed model was tested using ILs containing imidazolium, pyrrolidinium, pyridinium, phosphonium and piperidinium cations. Two parameters appeared in the PHT EOS which are temperature-dependent, reflecting the dispersive energy parameters among trimers, ε and the hard-core diameter, σ, were determined based on the molecular scaling parameters. The performance of the proposed PHT EOS has been evaluated by predicting the volumetric and first and second derivatives thermodynamic properties in the pressure and temperature ranges within 0.1–200 MPa and 273–472.6 K, respectively. From 6331 data points examined, the average absolute deviation (AAD) of the correlated (at 0.1 MPa) and predicted (at high pressures) densities from the experimental ones was found to be 0.18 %. Furthermore, the isothermal compressibilities and thermal expansion coefficients as well as the heat capacities were estimated through the PHT EOS with uncertainties of the order of ±11.09, ±11.76 and ±3.34 %, respectively. Further, the vapour pressures of ILs are also predicted by the proposed model. The trend of the predicted vapour pressure is in accord with those reported in literature.

     

Bromide ion conductivities of eutectic mixtures of quaternary ammonium bromides possessing long alkyl chains

Several quaternary ammonium bromides possessing long alkyl chains and their mixtures were found to be bromide ion conductors. The ionic conductivities of quaternary ammonium bromides themselves were lower than 10^?9 S cm^?1 at a room temperature. On the other hand, the eutectic mixtures of the quaternary ammonium bromides showed large increase of ionic conductivity. The best bromide ion conductors were found for the eutectic of Q₅, Q₇, Q₈, and Q₁₂: 4×10^?8 S cm^?1 at 30°C, and 6.3×10^?6 S cm^?1 at 50°C. Addition of asymmetric quarternary ammonium bromides had a negative effect on the ionic conductivity. These results were explained by a space filling factor in the solid.     

Influence of nano-sized fumed silica on physicochemical and electrochemical properties of cellulose derivatives-ionic liquid biopolymer electrolytes

Nanocomposite biopolymer electrolyte was prepared by solution-casting technique. Carboxymethyl cellulose from kenaf bast fibre, ammonium acetate, (1-butyl)trimethyl ammonium bis(trifluoromethylsulfonyl)imide ionic liquid and silica nanofiller was used to prepare the biopolymer electrolyte samples. The films were characterized by Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, scanning electron microscopy, transference number measurement and linear sweep voltammetry. The interactions of doping salt, ionic liquid and inorganic nanofiller with the host biopolymer were confirmed by FTIR study. The highest conductivity achieved was 8.63 × 10^?3 S cm^?1 by the incorporation of 1 wt% of SiO₂ at ambient temperature. The electrochemical stability of the highest conducting sample was stable up to 3.4 V, and the ion transference number in the film was 0.99.     

Effect of monocationic ionic liquids as electrolyte additives on the electrochemical and thermal properties of Li-ion batteries

The conventional electrolyte system has been compared with the ionic liquid (IL) additive containing electrolyte system at room temperature as well as elevated temperature. In this work, two types of monocationic ILs such as 1-butyl-3-methylpyrrolidinium hexafluorophosphate (Pyr IL) and 1-ethyl-3-methylimidazolium hexafluorophosphate (IMI IL) are added as an additive at two different weight ratios in 1.15 M LiPF₆ (EC/EMC = 3/7 v/v) electrolyte solution, the structural, electrochemical and thermal characteristics of LiNi_0.80Co_0.15Al_0.05O₂ (NCA)/carbon full-cell in different electrolyte formulations have been reconnoitered. X-ray diffraction (XRD) studies have proved that IL as an electrolyte additive does not alter the structural stability of cathode materials after cycling. Under room temperature, Pyr IL additives at 1 wt% and 3 wt% deliver better cycleability than others, with the retention ratios of 93.62% and 92.8%, respectively. At elevated temperature, only 1 wt% Pyr IL additive is giving stable capacity retention ratio of 80.74%. Ionic conductivity and self-extinguishing time (SET) values are increasing with respect to the amount of additive added to the electrolyte. Thermal studies reveal that 3 wt% Pyr IL is favorable regarding the safety of the battery as it shows shifting of peak to higher temperature of 272.10 °C. Among the IL additives evaluated in this study, addition of 1 wt% Pyr IL is the most desirable additive for achieving the best cycling performance as well as thermal behavior of Li-ion batteries.     

Unexpected acceleration of Ultrasonic-Assisted iodide dosimetry in the catalytic presence of ionic liquids

This study investigates the potential of using small amounts of ionic liquids (IL) to enhance ultrasound-assisted extraction of lipids content from green microalgae. Three imidazolium-based ILs (butyl, octyl and dodecyl), each of them with two anions (bromide and acetate) were tested as additives. Viscosity and surface tension of the ILs aqueous mixtures were analyzed to determine the influence of ILs’ anions and alkyl chain length, whereas KI dosimetry experiments were used as an indicator of radicals formation. A key finding suggests that the small addition of ILs improves the ultrasonication either by enhancing the viscosity and reducing the water surface tension, leading to a more powerful acoustic cavitation process or by increasing HO° production likely to oxidize the microalgae cells membranes, and consequently disrupting them on a more efficient manner. KI dosimetry also revealed that long ILs alkyl chain is detrimental. This experimental observation is confirmed thus strengthened as the yield of extracted lipids from green microalgae has shown an incremental trend when the IL concentration also increased. These hypotheses are currently under investigation to spot detailed impact of ILs on cavitation process.     

Ionothermal Synthesis of Hollow Aluminophosphate Molecular Sieves

Hollow AlPO₄‐5 spheres (E‐AP and B‐AP) are synthesized ionothermally in tri‐substituted imidazolium bromide ionic liquids (ILs), that is, 1‐ethyl‐2,3‐dimethylimidazolium bromide and 1‐butyl‐2,3‐dimethylimidazolium bromide, respectively. Moreover, the morphologies of the hollow AlPO₄‐5 particles vary with the type of ILs and the amounts of ILs, phosphoric acid, amine, and hydrofluoric acid. The thicknesses of the shells of the hollow spheres are substantially affected by the length of the alkyl chain on the imidazole ring of the ILs. The shell thicknesses significantly increase from 300–500 nm to 4–5 µm as the alkyl chain length increases, and solid AlPO₄‐5 spheres (H‐AP) are generated in 1‐hexyl‐2,3‐dimethylimidazolium bromide IL. Furthermore, the experimental results suggest that the formation of hollow AlPO₄‐5 spheres in an IL is consistent with Ostwald ripening theory. In addition, compared with ordinary solid AlPO₄‐5 (S‐AP) prepared by hydrothermal methods, the hollow E‐AP particles are small and spherical. Moreover, the Co‐loaded hollow AlPO₄‐5 (Co/E‐AP) catalyst exhibits excellent catalytic activities in the selective oxidation of tetralin. The reaction conversions are 73.5 and 5.7% over the Co/E‐AP catalyst and Co‐loaded solid AlPO₄‐5 (Co/S‐AP) catalyst, respectively, which means that the hollow structure facilitates the mass transfer of the reactants and products in the catalytic reaction.