Imide Room Temperature Ionic Liquid Research Articles

Investigation of the Electrochemical Behaviour of Al Current Collector Material Polarised Highly Anodically and Located in Butyltrimethylammonium Bis(trifluoromethylsulfonyl)imide Room-Temperature Ionic Liquid

The electrochemical behaviour of Al, used as a current collector in supercapacitors and in Li-ion and Na-ion electrochemical power sources, was investigated for the first time using the in situ soft X-ray photoelectron spectroscopy (XPS) method, collecting the information directly at the electrolyte-covered Al current collector polarised electrochemically at high anodic potentials. Cyclic voltammetry, electrochemical impedance spectroscopy, and synchrotron in situ soft XPS methods were applied to collect physical and electrochemical information characterising the electrochemically polarised Al-current-collector RTIL interface soaked into the butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N4111(TFSI)) room-temperature ionic liquid. The obtained data show the start of intensive oxidation processes, including aluminium oxidation and the formation of an insoluble Al(TFSI)3 surface layer in N4111(TFSI) at E ≥ 3.0 V (vs. Ag-QRE). Very intensive electro-oxidation of TFSI− anions at E ≥ 6.5 V (vs. Ag-QRE) has been observed. CV data indicate that the electrochemical oxidation of once-activated Al is possible in N4111(TFSI) at 1.1 V < E < 1.6 V (vs. Ag-QRE). Therefore, the oxidation of Al starts at E ≥ 2.05 V (vs. Ag-QRE) if the Al surface is modified with electro-oxidation products of TFSI− anions.

On the Influence of the Menthol Moiety on the Transport Properties of a Homologue Series of Functionalized Bis(trifluoromethylsulfonyl)imide Room-Temperature Ionic Liquids: A Quest for the Structure-Property Relationship.

This study explores the transport properties of bis(trifluoromethylsulfonyl)imide-based ionic liquids with a naturally derived (1R,2S,5R)-(−)-menthol moiety in the cationic part. In particular, we investigated the dependence of the dynamic viscosity and electrical conductivity as functions of the alkyl chain length. An important finding of this study is that both properties show nonmonotonic behavior with respect to the alkyl chain length. The nonmonotonic dependency is an obstacle for establishing the relationships between the structure and transport properties of homologues. To overcome this difficulty, we recommend fast property screening using a theoretical model that we developed, which allows for efficient viscosity prediction by means of the group contribution method. As demonstrated in this study, the model allows for reliable predictions of viscosity in the studied series with an overall relative deviation of less than 8%.

Silver(I) chlorides speciation and its relationship to the design, construction and evaluation of true Ag(s)/[AgCln]1−n reference electrodes for their use in bis(trifluoromethylsulfonyl)imide room temperature ionic liquids

This study describes a methodology for the design of true reference electrodes of the second kind based on the chemical speciation of the system AgCl(s)/[AgCln]1−n in both homogeneous and heterogeneous systems in bis(trifluoromethylsulfonyl)imide room temperature ionic liquids (RTIL), based on measurements of the open circuit potential (OCP) of Ag(s) or Ag(s)|AgCl(s) indicator electrodes immersed in solutions of Ag [NTf2] and [C2mim]Cl in RTIL, as well as on representative potentiometric titrations of Ag(I) or of chloride ions in the same media. The found values of the apparent equilibrium constants of the chemical equilibrium processes associated to the electrode potential at the metal|RTIL interface, lay the foundation for the design of true reference electrode systems. To test the usefulness of the information collected during the chemical speciation of these systems, four true reference electrodes were built for their use in four imidazolium-based bis(trifluoromethylsulfonyl) RTIL, and their electrode potentials were determined over time using the [Co(Cp)2]+/0 or [Fe(Cp)2]+/0 redox couples as internal redox references. The aim of this work is to provide a simple method for the development and characterization of true reference electrodes for their use in RTIL, thus averting the use of QRE and enabling the construction of comparable potential scales in RTIL.

High Voltage LiNi0.5Mn1.5O4/Li4Ti5O12 Lithium Ion Cells at Elevated Temperatures: Carbonate- versus Ionic Liquid-Based Electrolytes.

Thanks to its high operating voltage, the LiNi0.5Mn1.5O4 (LNMO) spinel represents a promising next-generation cathode material candidate for Lithium ion batteries. However, LNMO-based full-cells with organic carbonate solvent electrolytes suffer from severe capacity fading issues, associated with electrolyte decomposition and concurrent degradative reactions at the electrode/electrolyte interface, especially at elevated temperatures. As promising alternatives, two selected LiTFSI/pyrrolidinium bis(trifluoromethane-sulfonyl)imide room temperature ionic liquid (RTIL) based electrolytes with inherent thermal stability were investigated in this work. Linear sweep voltammetry (LSV) profiles of the investigated LiTFSI/RTIL electrolytes display much higher oxidative stability compared to the state-of-the-art LiPF6/organic carbonate based electrolyte at elevated temperatures. Cycling performance of the LNMO/Li4Ti5O12 (LTO) full-cells with LiTFSI/RTIL electrolytes reveals remarkable improvements with respect to capacity retention and Coulombic efficiency. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns indicate maintained pristine morphology and structure of LNMO particles after 50 cycles at 0.5C. The investigated LiTFSI/RTIL based electrolytes outperform the LiPF6/organic carbonate-based electrolyte in terms of cycling performance in LNMO/LTO full-cells at elevated temperatures.

Alkyl Chain Length Dependence of the Dynamics and Structure in the Ionic Regions of Room-Temperature Ionic Liquids.

The dynamics of four 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquids (RTILs) with carbon chain lengths of 2, 4, 6, and 10 were studied by measuring the orientational and spectral diffusion dynamics of the vibrational probe SeCN(-). Vibrational absorption spectra, two-dimensional infrared (2D IR), and polarization-selective pump-probe (PSPP) experiments were performed on the CN stretch. In addition, optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments were performed on the bulk liquids. The PSPP experiments yielded triexponential anisotropy decays, which were analyzed with the wobbling-in-a-cone model. The slowest decay, the complete orientational randomization, slows with increasing chain length in a hydrodynamic trend consistent with the increasing viscosity. The shortest time scale wobbling motions are insensitive to chain length, while the intermediate time scale wobbling slows mildly as the chain length increases. The 2D IR spectra measured in parallel (⟨XXXX⟩) and perpendicular (⟨XXYY⟩) polarization configurations gave different decays, showing that reorientation-induced spectral diffusion (RISD) contributes to the dynamics. The spectral diffusion caused by the RTIL structural fluctuations was obtained by removing the RISD contributions. The faster structural fluctuations are relatively insensitive to chain length. The slowest structural fluctuations slow substantially when going from Emim (2 carbon chain) to Bmim (4 carbon chain) and slow further, but more gradually, as the chain length is increased. It was shown previously that K(+) causes local ion clustering in the Emim RTIL. The K(+) effect increases with increasing chain length. The OHD-OKE measured complete structural randomization times slow substantially with increasing chain length and are much slower than the dynamics experienced by the SeCN(-) located in the ionic regions of the RTILs.

Stabilizing lithium metal using ionic liquids for long-lived batteries

Suppressing dendrite formation at lithium metal anodes during cycling is critical for the implementation of future lithium metal-based battery technology. Here we report that it can be achieved via the facile process of immersing the electrodes in ionic liquid electrolytes for a period of time before battery assembly. This creates a durable and lithium ion-permeable solid–electrolyte interphase that allows safe charge–discharge cycling of commercially applicable Li|electrolyte|LiFePO4 batteries for 1,000 cycles with Coulombic efficiencies >99.5%. The tailored solid–electrolyte interphase is prepared using a variety of electrolytes based on the N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide room temperature ionic liquid containing lithium salts. The formation is both time- and lithium salt-dependant, showing dynamic morphology changes, which when optimized prevent dendrite formation and consumption of electrolyte during cycling. This work illustrates that a simple, effective and industrially applicable lithium metal pretreatment process results in a commercially viable cycle life for a lithium metal battery.

Analysis of tribochemical decomposition of two imidazolium ionic liquids on Ti–6Al–4V through Mechanically Stimulated Gas Emission Spectrometry

Mechanochemical degradation of imidazolium bis(trifluoromethanesulfonyl)imide room-temperature ionic liquids (RTIL) with alkyl and mPEG side groups on Ti–6Al–4V substrate was studied through analysis of gas triboemission and Raman spectroscopy. In vacuum the RTIL with longer mPEG chain had better lubricity due to its higher capacity for tribochemical passivation. Raman spectroscopy showed possible bonding of fluorine to the substrate. Mechanical stimulus caused degradation of both anionic and the cationic moieties that further reacted with the substrate and with each other. The relevant decrement of water content during rubbing was found attributable to the proper RTIL and not only to the absorption on the substrate. No volatile sulphur compounds were found supporting the hypothesis of their bonding to Ti substrate.

Cathodic electrochemical deposition of CuI from room temperature ionic liquid-based electrolytes

Abstract An innovative electrochemical route is proposed to obtain CuI films. The approach is based on the electrochemical reduction of I 2 in a solution of copper bis(trifluoromethanesulfonyl)imide salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide room temperature ionic liquid. The mechanisms involved in the deposition process are analyzed by cyclic voltammetry, pointing out that the CuI formation occurs from the chemical reaction between the Cu 2 + and I - generated from the I 2 reduction. Homogenous films constituted of open-packed primary CuI nanocrystals (~ 100 nm) are obtained. The electrodeposition from organic solvent-based media is also investigated, finding that the solvent nature affects strongly to the nanocrystal packing density. Compact CuI thin films are electrodeposited from the isopropanol-based electrolytes. The electrodeposition of ZnO/CuI heterostructures, with high transmittance in the visible range (i.e. > 75%), is also reported. The current density-voltage characteristic of the resulting device exhibits clear rectifying behavior, with a rectification of ~ 2x10 3 at V = ± 1.5 V. This result anticipates a significant potential of the present electrochemical route to obtain CuI films with competitive optoelectronic functionalities.

Importance of weak interactions and conformational equilibrium in N-butyl-N-methylpiperidinium bis(trifluromethanesulfonyl) imide room temperature ionic liquids: Vibrational and theoretical studies

Piperidinium cation-based room temperature ionic liquids (RTILs) constitute an important class of ILs because of their unique electrochemical properties as well as non-aromatic nature of the cation. However, detailed structural studies are yet to be done. In this paper, we discuss the molecular structure and vibrational spectra of N-butyl-N-methylpiperidinium bis(trifluromethanesulfonyl) imide, (PIP14NTf2; where, PIP14 is N-butyl-N-methylpiperidinium and NTf2 is bis(trifluromethanesulfonyl) imide), obtained with a combined approach of infrared (IR) and Raman spectroscopies in the liquid state and density functional theory (DFT) and Hartree–Fock (H–F) based theoretical calculations. DFT calculations, which are found to produce the most stable geometry compared to other two methods (MP2 and H–F), reproduce the experimental IR and Raman spectra reasonably well. Our findings reveal structural properties that profoundly influence intermolecular interactions and melting point. There exists a large variation in the melting point of the ILs studied. While the bromide salt of the piperidinium derivative (PIP14Br) is solid with very high melting point (241°C), the corresponding NTf2 salt is low viscous liquid at room temperature (mp: −25°C). bmimBr (bmim=1-butyl-1-methylimidazolium) exhibits a substantially lower melting point of 79°C than PIP14Br, suggesting that more number of strong classical hydrogen bonding interactions in the latter is primarily responsible for the much higher melting point. In addition, involvement of the alkyl group in PIP14 in H-bonding interaction provides additional rigidity in n-butyl chain which is otherwise absent in bmimBr. Interaction energy for PIP14Br is found to be higher than PIP14NTf2, showing a positive correlation between interaction energy and melting point. A blue shift in CH stretching wavenumber as evident from IR and Raman spectra of PIP14Br IL is a clear indication of the stronger hydrogen bonding as compared to PIP14NTf2 IL. Furthermore, we experimentally observe the existence of cisoid–transoid conformational equilibrium of NTf2− anion in the Raman spectrum of PIP14NTf2 for the first time and determined that transoid NTf2− anion to be more stable than the corresponding cisoid conformer by 1.04kcal/mol using DFT. Examination of various conformational possibilities of the cation shows that the butyl group preferentially exists in gauche conformation.

The role of cations in the reduction of 9-fluorenone in bis(trifluoromethylsulfonyl)imide room temperature ionic liquids

A comprehensive study of the electrochemical reduction of 9-fluorenone in various room temperature ionic liquids using the silver electrode as a cathode material.

Acoustics as a Tool for Better Characterization of Ionic Liquids: A Comparative Study of 1-Alkyl-3-methylimidazolium Bis[(trifluoromethyl)sulfonyl]imide Room-Temperature Ionic Liquids

Acoustic properties of three (1-ethyl-, 1-butyl-, and 1-octyl-) 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide room-temperature ionic liquids are reported and discussed. The speeds of sound in RTILs were measured as a function of temperature in the range 288-323 K by means of a sing around method. The densities and isobaric heat capacities were determined from 288.15 to 363.15 K and from 293.15 to 323.15 K, respectively. The related properties, like isentropic and isothermal compressibilities, isobaric coefficients of thermal expansion, molar isochoric heat capacities, and internal pressures, were calculated. It was found that for some ionic liquids, temperature dependence of isobaric coefficients of thermal expansion is small and negative. All investigations were completed by the ultrasound absorption coefficient measurements in 1-ethyl- and 1-octyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide as a function of frequency from 10 to 300 MHz at temperatures 293.15-298.15 K. The ultrasound absorption spectra indicate relaxation frequencies in the megahertz range.

NiO cathodic electrochemical deposition from an aprotic ionic liquid: Building metal oxide n–p heterojunctions

NiO thin films have been successfully deposited by cathodic electrochemical deposition in N-butyl-N-methylpyrrolidinium bis(trifloromethanesulfonyl)imide room temperature ionic liquid (IL), giving an unambiguous proof of concept of the metal oxide electrodeposition in aprotic ILs without metal hydroxide formation as an intermediate phase. The electrochemical phenomena involved in the deposition process have been analyzed by cyclic voltammetry, pointing out that the electrochemical reduction of Ni2+ may be quenched in oxygenated IL electrolytes. The physico-chemical properties of the obtained NiO thin films have been characterized by electron scanning and atomic force microscopies, X-ray diffraction and Fourier transform infrared X-ray photo-electron spectroscopies. By taking advantage of the present electrodeposition route, ZnO/NiO heterostructures have been built. The current density-voltage characteristic of the resulting device exhibits clear rectifying behavior, with a rectification factor of 3×103 at V=±1V. This result anticipates a significant potential of the present electrochemical route in the metal oxide electronics.

Kinetics of Li+ reduction in 1-methyl-3-propylpiperidinium bis(trifluoromethylsulfonyl) imide room temperature ionic liquid

Separation of the total Li/LiTFSI+MPPipTFSI/Li cell impedance into single contributions was performed with the use of electrochemical impedance spectroscopy (EIS). The structure of the electrode was observed by scanning electron microscopy (SEM). The charge transfer process occurs at a solid|solid Li+(SEI)→Li(metal) interphase (SEI is the solid electrolyte interphase). SEM images show that the structure of the electrode surface (and of the interphase) is grain-like. The kinetics of Li+ reduction in ionic liquids is interesting as the Li+ desolvation step (which takes place in classical solutions) does not take place which leads to a simpler process. Deconvolution of the EIS spectra indicates three resistances and corresponding three lnR=f(T−1) straight lines of different slopes, associated with the resistance of liquid electrolyte, SEI and the charge transfer process, respectively. Activation energy for the Li+ conduction process in the liquid electrolyte and solid SEI is 23 and 32kJmol−1, respectively. Activation energy for the charge transfer process Li+(SEI)→Li is 62kJmol−1 and the corresponding exchange current density at T=298K is 1.92×10−5Acm−2. As the process occurs at the SEI|Li interphase, the concentration independent rate constant cannot be calculated.

Lithium redox behavior in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulphonyl)imide room temperature ionic liquid

The lithium metal–Li+ interface was investigated in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulphonyl)imide room temperature ionic liquid, using impedance simulation, experimental electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The electrolyte contained vinylene carbonate as the solid electrolyte interphase (SEI) forming additive. The Warburg coefficient value obtained from impedance plot deconvolution (AW>10Ωs−1/2) and SEM lithium surface image suggest the SEI layer formation. Therefore, the charge transfer process on lithium reduction and oxidation takes place at the solid Li|SEI interface. Simulation studies show that the typical shape of impedance plots for the Li|Li+ system (reported in the literature) suggests the exchange current density below 10−2Acm−2. The exchange current density of Li|SEI|Li+ in the ionic liquid electrolyte, obtained from impedance spectra and Tafel plot is between 4.5×10−4Acm−2 and 3.0×10−4Acm−2 (Li+ concentration of 0.7moldm−3).

Changes of the near-surface chemical composition of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide room temperature ionic liquid under the influence of irradiation

Radiation induced degradation effects are studied for a model ionic liquid (IL)--[EMIm]Tf(2)N--in order to distinguish in which way the results of X-ray based material analysis methods can be falsified by the radiation supplied by typical X-ray sources itself. Photoelectron spectroscopy is commonly used for determining the electronic structure of ionic liquids. Degradation effects, which often occur e.g. in organic materials during X-ray or electron irradiation, are potentially critical for the interpretation of data obtained from ionic liquids. The changes of the chemical composition as well as the radiation-induced desorption of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm]Tf(2)N) fragments are analysed by X-ray photoelectron spectroscopy (XPS) as well as quadrupole mass spectroscopy (QMS) upon exposure to monochromated or non-monochromated AlKα X-rays from typical laboratory sources. During the irradiation of [EMIm]Tf(2)N, an increasing carbon concentration is observed in both cases and especially the [Tf(2)N](-) ion is strongly altered. This observation is supported by the results from the QMS analysis which revealed a variety of different IL fragments that are desorbed during X-ray irradiation. It is shown that the decomposition rate is directly linked to the photon flux on the sample and hence has to be considered when planning an XPS experiment. However, for typical experiments on this particular IL the measurements suggest that the changes are on a larger time scale as typically required for spectra acquisition, in particular if monochromated X-ray sources are used.

Electrochemical deposition of ZnO in a room temperature ionic liquid: 1-Butyl-1-methylpyrrolidinium bis(trifluoromethane sulfonyl)imide

An innovative electrochemical route is proposed to deposit nanocrystalline ZnO films. The approach is based on the electrochemical reduction of O 2 in a solution of zinc bis(trifluoromethanesulfonyl)imide salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide room temperature ionic liquid. The mechanisms involved in the deposition process are analyzed by cyclic voltammetry, pointing out that the ZnO formation occurs from the chemical reaction between the Zn 2+ and O 2 - generated from the O 2 reduction. Homogenous films constituted of primary ZnO nanocrystals (15–25 nm) assembled in close-packed desert rose-like and open-packed round-top shape agglomerates are obtained at 100 and 150 °C, respectively. The differences with respect to the electrochemical routes based on aqueous and organic media are discussed.

Excitation-Wavelength Dependence of Fluorescence Intermittency in CdSe Nanorods

The influence of excitation wavelength and embedding media on fluorescence blinking statistics of 4 nm x 20 nm cadmium selenide (CdSe) nanorods is investigated. Photon antibunching (PAB) experiments confirm nonclassical emission from single CdSe nanorods that exhibit a radiative lifetime of 26 +/- 13 ns. The blinking data show behaviors that can be categorized into two classes: excitation near the energy of the band gap and at energies exceeding 240 meV above the band gap. Excitation at the band gap energy (lambda >or= 560 nm) results in more pronounced "on" time probabilities in the distribution of "on" and "off" events, while those resulting from excitation exceeding the band gap by 240 meV or more (lambda <or= 560 nm) are 200 times less likely to display continuous "on" fluorescence persisting beyond 4 s. The "off" time statistics are also sensitive to the excitation wavelength, showing a similar, but inversely correlated, effect. To understand better the excitation-wavelength dependence, fluorescence measurements are obtained for single nanorods deposited both on a bare microscope coverslip and embedded in 1-ethyl-3-methylimidizolium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquid (RTIL). The embedding RTIL medium has a significant influence on the resultant fluorescence statistics only when the excitation energy exceeds the 240 meV threshold. The results are explained by a threshold to access nonemissive trap states, attributed to self-trapping of hot charge carriers at the higher photon excitation energies.

Electrochemical Behavior of the Li+/Li Couple and Stability of Lithium Deposits in Tri‐1‐Butylmethylammonium Bis((Trifluoromethyl)Sulfonyl)Imide Room Temperature Ionic Liquid

AbstractThe electrochemical behavior of the Li+/Li couple was studied at polycrystalline tungsten, platinum, copper and aluminum electrodes in tri‐1‐butylmethylammonium bis((trifluoromethyl)sulfonyl)imide ionic liquid mixed with a little propylene carbonate at 30 °C. Lithium cations were introduced into the ionic liquid by dissolution of lithium bis((trifluoromethyl)sulfonyl)imide which is highly soluble in ionic liquid. Propylene carbonate was used to reduce the viscosity of this ionic liquid in order to enhance the mass transfer and to additionally improve the stability of lithium deposits. At the tungsten and copper electrodes, the cyclic voltammetric behavior of a Li+/Li couple is a quasi‐reversible reaction. At the platinum electrode, the behavior becomes very complicated because of the alloy formation. Coulombic efficiency was used to evaluate the stability of lithium deposits at each electrode. The aluminum electrode showed the best efficiency due to the formation of Li‐Al alloy. However, lowest efficiency was obtained at the platinum electrode because of the low redox reversibility of the lithium in the Li‐Pt alloy. The diffusion coefficient of lithium cation in this solution was 1.0 ± 0.1 × 10−;7 cm2 s−;1 as determined by chronopotentiometry. The best coulombic efficiency obtained at the Al electrode is 97% but dropped to about 90% after 12 hours. The self‐discharge current of the lithium deposits at the Al electrode was 0.4 μA/cm2 during the experimental period.

Electrodeposition of Pure Mn and Zn-Mn Alloys from the Tri-1-butylmethylammonium Bis((trifluoromethyl)sulfonyl)imide Room Temperature Ionic Liquid

not Available.

1-Alkyl-3-methylimidazolium Bis(perfluoroalkylsulfonyl)imide Water-Immiscible Ionic Liquids : The Effect of Water on Electrochemical and Physical Properties

The electrochemical and physical properties of a class of 1-n-alkyl-3-methylimidazolium bis(perfluoroalkylsulfonyl)imide room-temperature ionic liquids (RTILs) is reported. By varying the chain length on the cation 8, and 10) and the perfluorinated carbon chains of the imide anions, (BMSI) to (BETI), the effect on water content, viscosity, conductivity, and potential window has been examined. The water content of the RTILs, both ambient and water-equilibrated, varies linearly with the imidazolium alkyl chain length. The viscosities of the water-equilibrated BMSI- and BETI-based RTILs were accurately calculated using a linear combination of the viscosity of water and the ambient RTILs. The conductivities for this series ranges from 2.9 mS/cm to 0.92 mS/cm and were accurately estimated based on the viscosity, density, and molecular weight. The potential windows of the ambient RTILs are 4.3 and 4.9 V for the BMSI and BETI salts, respectively. The window is reduced to 3.9 and 4.3 V upon equilibration with water. The reversible electrochemistry of ferrocene and decamethylferrocene has been measured in water-equilibrated imide-based RTILs with as much as 23 mol% © 2004 The Electrochemical Society. All rights reserved.