The catalytic performance study of polymerized ionic liquid synthesized in different conditions on alkylation of o‐Xylene with styrene

In this work, a series of novel acidic polymerized ionic liquids were used as heterogeneous catalyst for alkylation of o‐Xylene with styrene. And the effect of the amount of initiator and the type of acid used for ion exchange on catalyst structure and the catalytic performance of catalysts for alkylation were studied thoroughly. The experiment results show: when the percentage of the amount of initiator in the total material is 3%, the polymerized ionic liquid catalyst MPM‐SO₃H‐[C₃V][SO₃CF₃] has the most uniform with a specific surface area of 97.30 m²/g and a pore volume of 0.35 cm³/g. Benefiting from the unique structure features, MPM‐SO₃H‐[C₃V][SO₃CF₃] manifested an excellent catalytic performance for alkylation of o‐Xylene with styrene, along with the conversion of styrene was 96.8% and the yield of 1‐Phenyl‐1‐ortho‐xylene ethane was 94.7%. Therefore, this work provides a novel reference to the synthesis of polymerized ionic liquids and clearly explains the advantage of novel acidic polymerized ionic liquids on alkylation.     

The thermochemistry of solvation of imidazolium-based ionic liquids in benzene

ABSTRACT

The present work is devoted to the thermochemical study of solvation of ionic liquids (IL) in benzene. The solution enthalpies of 1-ethyl-3-methylimidazolium tricyanomethanide [EMIM][C(CN)₃], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄], 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF₆], 1-octyl-3-methylimidazolium tetrafluoroborate [OMIM][BF₄], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][NTf₂], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTf₂] and 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][TfO] in benzene were measured. The solvation enthalpies of imidazolium-based IL were calculated. Molar refractions of imidazolium-based IL form literature data on density and refractive indexes of IL were also calculated. The linear correlation between solvation enthalpy and molar refraction of IL was observed. This correlation can be used to calculate the vaporization enthalpy of imidazolium-based IL from solution calorimetry data.     

Synthesis of Carbonyl Compounds from Alcohols Using Electrochemically Generated Superoxide Ions in RTILs

Abstract

We show that the superoxide ion (O₂ ^??) generated electrochemically from oxygen dissolved in room-temperature ionic liquids (RTILs) reacts with primary and secondary alcohols to form the corresponding ketones and carboxylic acids, respectively. Specifically, we study the conversion of benzhydrol to benzophenone and benzyl alcohol to benzaldehyde/benzoic acid. The kinetics (e.g., rate, selectivity, and yield) for these reactions are also determined as functions of the variations in the structure of the ionic liquids. The RTILs used here are imidazolium-based cations where the functional groups on the imidazolium ring are modified. Specifically, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆], 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][PF₆], and 1-hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF₆] are used as the reaction medium. These results are compared to an ammonium-based RTIL (N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide). The results show that the nucleophilic attack by the O₂ ^?? of both the RTIL and the alcohol, especially that of the H atom at the R2 position of the [bmim][PF₆] and [hmim][PF₆], greatly affects the yields. No RTIL degradation products were detected for the reactions in [bdmim][PF₆] and N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide ionic liquids. For the benzyl alcohol oxidation reaction in the RTIL, N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide, benzaldehyde formed did not undergo further oxidation to form benzoic acid, which may be due to the greater hydrophobicity of this RTIL. The competitive reaction kinetics between the alcohol and RTIL component must be considered in the selection of the RTIL solvent system.     

Ideal and non-ideal behaviour of {1-butyl-1-methylpyrrolydinium bis(trifluoromethylsulfonyl)imide + γ-butyrolactone} binary mixtures

Density, electrical conductivity and viscosity of binary liquid mixtures of 1-butyl-1-methylpyrrolydinium bis(trifluoromethylsulfonyl)imide, [bmpyrr][NTf₂], with γ-butyrolactone (GBL) were measured at temperatures from (293.15 to 323.15) K and at atmospheric pressure over the whole composition range. Excess molar volumes have been calculated from the experimental densities and fitted with the Redlich–Kister polynomial equation. These values are positive over the whole range of ionic liquid mole fraction and at all temperatures. In the range between 0.55 and 0.6 [bmpyrr][NTf₂] mole fraction, an ideal behaviour of the ionic liquid mixture with molecular solvent was observed for the first time. Other volumetric properties, such as isobaric thermal expansion coefficients, partial molar volumes and partial molar volumes at infinite dilution have been also calculated, in order to obtain information about interactions between GBL and selected ionic liquid. Positive values of these properties for both components also indicate weaker interactions between GBL and IL compared to the pure components. From the viscosity results, the Angell strength parameter was calculated and found to be 3.24 indicating that [bmpyrr][NTf₂] is a “fragile” liquid. From the volumetric and transport properties obtained, formation of the [bmpyrr]⁺ micellar structures was also discussed. All the results are compared to those obtained for imidazolium-based ionic liquid with GBL.     

Model Studies on the Ozone-Mediated Synthesis of Cobalt Oxide Nanoparticles from Dicobalt Octacarbonyl in Ionic Liquids

Low-temperature synthesis in ionic liquids (ILs) offers an efficient route for the preparation of metal oxide nanomaterials with tailor-made properties in a water-free environment. In this work, we investigated the role of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C₄C₁Pyr][NTf₂] in the synthesis of cobalt oxide nanoparticles from the molecular precursor Co₂(CO)₈ with ozone. We performed a model study in ultra-clean, ultrahigh vacuum (UHV) conditions by infrared reflection absorption spectroscopy (IRAS) using Au(111) as a substrate. Exposure of the pure precursor to ozone at low temperatures results in the oxidation of the first layers, leading to the formation of a disordered Co_xO_y passivation layer. Similar protection to ozone is also achieved by deposition of an IL layer onto a precursor film prior to ozone exposure. With increasing temperature, the IL gets permeable for ozone and a cobalt oxide film forms at the IL/precursor interface. We show that the interaction with the IL mediates the oxidation and leads to a more densely packed Co_xO_y film compared to a direct oxidation of the precursor.     

On-Surface Metathesis of an Ionic Liquid on Ag(111)

We investigated the adsorption, surface enrichment, ion exchange, and on-surface metathesis of ultrathin mixed IL films on Ag(111). We stepwise deposited 0.5 ML of the protic IL diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) and 1.0 ML of the aprotic IL 1-methyl-3-octylimidazolium hexafluorophosphate ([C₈C₁Im][PF₆]) at around 90 K. Thereafter, the resulting layered frozen film was heated to 550 K, and the thermally induced phenomena were monitored in situ by angle-resolved X-ray photoelectron spectroscopy. Between 135 and 200 K, [TfO]⁻ anions at the Ag(111) surface are exchanged by [PF₆]⁻ anions and enriched together with [C₈C₁Im]⁺ cations at the IL/vacuum interface. Upon further heating, [dema][PF₆] and [OMIm][PF₆] desorb selectively at ∼235 and ∼380 K, respectively. Hereby, a wetting layer of pure [C₈C₁Im][TfO] is formed by on-surface metathesis at the IL/metal interface, which completely desorbs at ∼480 K. For comparison, ion enrichment at the vacuum/IL interface was also studied in macroscopic IL mixtures, where no influence of the solid support is expected.     

Ionic Association of the Ionic Liquids [C4mim][BF4], [C4mim][PF6], and [Cnmim]Br in Molecular Solvents

Considering the ionic nature of ionic liquids (ILs), ionic association is expected to be essential in solutions of ILs and to have an important influence on their applications. Although numerous studies have been reported for the ionic association behavior of ILs in solution, quantitative results are quite scarce. Herein, the conductivities of the ILs [C_nmim]Br (n=4, 6, 8, 10, 12), [C₄mim][BF₄], and [C₄mim][PF₆] in various molecular solvents (water, methanol, 1‐propanol, 1‐pentanol, acetonitrile, and acetone) are determined at 298.15 K as a function of IL concentration. The conductance data are analyzed by the Lee–Wheaton conductivity equation in terms of the ionic association constant (K_A) and the limiting molar conductance (Λ_m⁰). Combined with the values for the Br^? anion reported in the literature, the limiting molar conductivities and the transference numbers of the cations and [BF₄]^? and [PF₆]^? anions are calculated in the molecular solvents. It is shown that the alkyl chain length of the cations and type of anion affect the ionic association constants and limiting molar conductivities of the ILs. For a given anion (Br^?), the Λ_m⁰ values decrease with increasing alkyl chain length of the cations in all the molecular solvents, whereas the K_A values of the ILs decrease in organic solvents but increase in water as the alkyl chain length of the cations increases. For the [C₄mim]⁺ cation, the limiting molar conductivities of the ILs decrease in the order Br^?>[BF₄]^?>[PF₆]^?, and their ionic association constants follow the order [BF₄]^?>[PF₆]^?>Br^? in water, acetone, and acetonitrile. Furthermore, and similar to the classical electrolytes, a linear relationship is observed between ln K_A of the ILs and the reciprocal of the dielectric constants of the molecular solvents. The ILs are solvated to a different extent by the molecular solvents, and ionic association is affected significantly by ionic solvation. This information is expected to be useful for the modulation of the IL conductance by the alkyl chain length of the cations, type of anion, and physical properties of the molecular solvents.     

Application of novel room temperature ionic liquids in flexible supercapacitors

This paper studied application of different types of room temperature ionic liquids (RTILs) into flexible supercapacitors. Typical RTILs including 1-buthyl-3-methyl-imidazolium [BMIM][Cl], trioctylmethylammonium bis(trifluoromethylsulfonyl)imide [OMA][TFSI] and triethylsulfonium bis(trifluoromethylsulfonyl)imide ([SET₃][TFSI]) were studied. [SET₃][TFSI] shows the best result as electrolyte in electrochemical double-layer (EDLC) supercapacitors with very high specific capacitance of 244 F/g at room temperature, overceiling the performance of conventional carbonate electrolyte such as dimethyl carbonate (DMC) with more stable performance and much larger electrochemical window.     

Physical Vapor Deposition of [EMIM][Tf2N]: A New Approach to the Modification of Surface Properties with Ultrathin Ionic Liquid Films

Ultrathin films of the ionic liquid (IL) 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][Tf₂N], are prepared on a glass substrate by means of an in situ thermal‐evaporation/condensation process under ultrahigh‐vacuum conditions. By using X‐ray photoelectron spectroscopy (XPS), it is demonstrated that the first layer of the IL film grows two dimensionally, followed by the three‐dimensional growth of successive layers. The first molecular layer consists of a bilayer, with the [EMIM]⁺ cations in contact to the surface and the [Tf₂N]^? anions at the vacuum side. The ultrathin IL films are found to be stable under ambient conditions.     

Effect of water on the interfacial structures of room-temperature ionic liquids

The interfacial structures of cyano-based room-temperature ionic liquids play a very important role in reducing friction. However, the presence of water impairs their tribological performance. The interfacial structures and friction forces of 1-ethyl-3-methylimidazolium dicyanamide, [EMIM][DCN], and the effect of water on these structures and forces were investigated using atomic force microscopy. In addition, the interaction of water and [EMIM][DCN] was evaluated using Fourier-transform infrared (FT-IR) spectroscopy. Multiple repulsive layers were observed in the [EMIM][DCN] solution. This solution showed low friction force because these repulsive layers worked as protective layers against friction. On the other hand, the specific repulsive layer characteristics of [EMIM][DCN] could not be observed in a [EMIM][DCN] + 2 wt% H₂O solution. FT-IR results indicated that the layer structure of [EMIM][DCN] was disturbed by the addition of H₂O. Therefore, the solution containing water exhibited a high friction force.     

Conductivity and Redox Potentials of Ionic Liquid Trihalogen Monoanions [X3]−, [XY2]−, and [BrF4]− (X=Cl,Br, I and Y=Cl,Br)

The ionic liquid (IL) trihalogen monoanions [N₂₂₂₁][X₃]⁻ and [N₂₂₂₁][XY₂]⁻ ([N₂₂₂₁]⁺=triethylmethylammonium, X=Cl, Br, I, Y=Cl, Br) were investigated electrochemically via temperature dependent conductance and cyclic voltammetry (CV) measurements. The polyhalogen monoanions were measured both as neat salts and as double salts in 1-butyl-1-methyl-pyrrolidinium trifluoromethane-sulfonate ([BMP][OTf], [X₃]⁻/[XY₂]⁻ 0.5 M). Lighter IL trihalogen monoanions displayed higher conductivities than their heavier homologues, with [Cl₃]⁻ being 1.1 and 3.7 times greater than [Br₃]⁻ and [I₃]⁻, respectively. The addition of [BMP][OTf] reduced the conductivity significantly. Within the group of polyhalogen monoanions, the oxidation potential develops in the series [Cl₃]⁻>[BrCl₂]⁻>[Br₃]⁻>[IBr₂]⁻>[ICl₂]⁻>[I₃]⁻. The redox potential of the interhalogen monoanions was found to be primarily determined by the central halogen, I in [ICl₂]⁻ and [IBr₂]⁻_, and Br in [BrCl₂]⁻. Additionally, tetrafluorobromate(III) ([N₂₂₂₁]⁺[BrF₄]⁻) was analyzed via CV in MeCN at 0 °C, yielding a single reversible redox process ([BrF₂]⁻/[BrF₄]⁻).     

Temperature-Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non-Fluorinated Ionic Liquids

Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at different temperatures in the liquid state. The mixtures consist of ILs with the same [PF₆]⁻ anion but two different cations, namely 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF₆], and 1-butyl-3-methylimidazolium hexafluorophosphate, [C₄C₁Im][PF₆], with 10, 25, 50 and 75 mol % content of [PFBMIm][PF₆]. We observe a preferential enrichment of the fluorinated chain in the topmost layer, relative to the bulk composition, which is most pronounced for the lowest content of [PFBMIm][PF₆]. Upon cooling the mixtures stepwise from 95 °C until surface charging effects in XPS indicate solidification, we observe a pronounced increase in surface enrichment of the fluorinated chain with decreasing temperature in the liquid state. In contrast to the mixtures with lower [PFBMIm][PF₆] contents, cooling the 75 mol % mixture additionally shows an abrupt decrease of the fluorinated chain signal before complete solidification occurs, which is assigned to partial precipitation effects.     

Conductive polymeric ionic liquids for electroanalysis and solid-phase microextraction

Three novel electropolymerizable thiophene-based ionic liquids (ILs) were synthesized and characterized as potential candidates for developing selective extraction media for chemical analysis. Electropolymerization of the bis[(trifluoromethyl)sulfonyl]imide ([NTf₂]^-) analogs successfully produced uniform polymeric thin-films on macro- and microelectrode substrates from both vinyl and methylimidazolium IL monomer derivatives. The resultant conducting polymer IL (CPIL) films were characterized by electrochemical methods and found to exhibit attractive behavior towards anionic species while simultaneously providing an exclusion barrier toward cationic species. Thermogravimetric analysis of the thiophene-based IL monomers established a high thermal stability, particularly for the methylimidazolium IL, which was stable until temperatures above 350 °C. Subsequently, the methylimidazolium IL was polymerized on 125 μm platinum wires and utilized for the first time as a sorbent coating for headspace solid-phase microextraction (HS-SPME). The sorbent coating was easily prepared in a reproducible manner, provided high thermal stability, and allowed for the gas chromatographic analysis of polar analytes. The normalized response of the poly[thioph-C₆MIm][NTf₂]-based sorbent coating exhibited higher extraction efficiency compared to an 85 μm polyacrylate fiber and excellent fiber-to-fiber reproducibility. Therefore, the electropolymerizable thiophene-based ILs were found to be viable new materials for the preparation of sorbent coatings for HS-SPME.     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

The physicochemical properties of some imidazolium-based ionic liquids and their binary mixtures

The density, viscosity and conductivity of ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]), 1-octyl-3-methylimidazolium chloride ([omim][Cl]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim] BF4]), 1-hexyl- 3-methylimidazolium chloride ([hmim][Cl]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), and the [omim][BF4] + [omim][Cl], [hmim][BF4] + [hmim][Cl], and [hmim][PF6] + [hmim][Cl] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes (VE) of [hmim][BF4] + [hmim][Cl] and [hmim][PF6] + [hmim][Cl] mixtures are positive in the whole composition range. For [omim][BF4] + [omim][Cl], the VE is also positive in the [omim][Cl]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher (VTF) equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.     

Physicochemical properties of (1-butyl-1-methylpyrrolydinium dicyanamide + γ-butyrolactone) binary mixtures

Experimental densities, electrical conductivities and dynamic viscosities of the pure 1-butyl-1-methylpyrrolydinium dicyanamide ionic liquid, [bmpyrr][DCA], and its binary liquid mixtures with γ-butyrolactone (GBL) were measured at temperatures from (273.15 to 323.15) K and at pressure of 0.1 MPa over the whole composition range. From the experimental density data the related excess molar volumes were calculated and fitted using Redlich–Kister’s polynomial equation. Obtained values are negative in the whole range of ionic liquid mole fraction and at all temperatures. Other volumetric properties, such as isobaric thermal expansion coefficients, partial molar volumes and partial molar volumes at infinite dilution were also calculated, in order to obtain information about the interactions between GBL and the selected ionic liquid. Negative values of these properties for both components indicate stronger interactions between GBL and IL compared to the pure components and better packing due to the differences in size and shape of the studied molecules. From the viscosity results, the Angell strength parameter was calculated and found to be 5.47 indicating that [bmpyrr][DCA] is a “fragile” liquid. All the results are compared with those obtained for binary mixtures of 1-butyl-1-methylpyrrolydinium bis(trifluoromethylsulfonyl)imide, [bmpyrr][NTf₂], with GBL.     

Stable poly (ionic liquids) with unique cross‐linked mesoporous‐macroporous structure as efficient catalyst for alkylation of o‐xylene and styrene

In this work, using divinylbenzene (D), 1‐vinylimidazole (V) and 1‐vinyl‐3‐butylimidazolium bromide ([VBIM][Br]) as monomers, the binary‐monomer poly (ionic liquids) (PILs) and ternary‐monomer PILs were successfully synthesized, via hydrothermal polymerization and anion exchange, sequentially. Compared with each other, the ternary polymeric acidic IL catalyst has a clear spongy porous structure, while having a more stable macroporous structure, a larger specific surface area, more acidic groups and more active sites. Catalytic performance of catalyst was investigated through the alkylation of o‐xylene and styrene. The effect of the amount of IL added and the length of the cation chain on the ternary polymerization of acidic IL was systematically investigated. Under optimal reaction conditions (molar ratio of monomers was D:V:[VBIM][Br] = 2:1:1, the most suitable cation chain length was C₄), the synthesized MPD‐[C₄V]‐[VBIM][SO₃CF₃] has a larger specific surface area (89.47 m²/g), large pore volume (0.29 cm³/g), and abundant mesopores and macropores, which help to improve the contact between the active site and reactants. Moreover, the catalyst could maintain a relatively high conversion of styrene (99.0%), 1,2‐diphenylethane yield (98.7%) and high thermostability under reaction and be easily be divided from the solution, which is critical for heterogeneous solid catalysts.     

Supramolecular Ionic‐Liquid Gels with High Ionic Conductivity

Supramolecular ionogels were prepared by the gelation of room‐temperature ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIm][BF₄]) with (S,S)‐bis(leucinol)oxalamide. Remarkably, the ionic conductivity of solutions and ionogels with low gelator concentrations is higher than that of neat [BMIm][BF₄]. On the basis of molecular dynamics simulations and quantum mechanical calculations, the origin of this phenomenon is attributed to the higher affinity of gelator molecules towards [BF₄]^? ions, which reduces the electrostatic attraction between [BMIm]⁺ and [BF₄]^? and thus increases their mobility. With increasing gelator concentration, the ionic conductivity decreases due to the formation of a denser gelator matrix, which hinders the pathways for ionic transport. However, even for very dense ionogels, this decrease is less than one order of magnitude relative to neat [BMIm][BF₄], and thus they can be classified as highly conductive materials with strong potential for application as functional electrolytes.     

Efficient Extractive Desulfurization of Fuel Oils Using N‐Pyrrolidone/Alkylphosphate‐Based Ionic Liquids

Four BrØsted acid ionic liquids (ILS) [MMP][DMP], [MEP][DEP], [HMP][DMP] and [HEP][DEP] were synthesized and used as extractants for desulfurization of aromatic sulfur compounds in model oil. The mutual solubility of four ILs were investigated. The extraction equilibrium of four ILs could be reached in as soon as 5 min and the extraction capability followed the order [MMP][DMP]>[MEP][DEP]>[HEP][DEP]>[HMP][DMP]. The S extraction showed the highest efficiency under the conditions of 30°C, 30 min and 1:1 (V/V) IL:oil. Under the optimal condition, 70.9% of thiophene (TS), 76.9% of benzothiophene (BT) and 87.5% of dibenzothiophene (DBT) in n‐octane could be efficiently removed by [MMP][DMP]. The multiple extraction and regeneration performance of [MMP][DMP] for TS was also investigated and the results were satisfying. These results suggest that [MMP][DMP] has the best extraction capability and can serve as a promising solvent for extractive desulfurization of fuel oils.     

Vinyl-functionalized imidazolium ionic liquids as new electrolyte additives for high-voltage Li-ion batteries

Four functionalized ionic liquids based on imidazolium cations with vinyl or alllyl group and TFSI^? anion were synthesized as electrolyte additives for high-voltage Li-ion battery to stabilize carbonate-based electrolytes on the surface of 5 V class cathode materials. The electrochemical behaviors and surface morphology of LiNi_0.5Mn_1.5O₄ cathode had been investigated by cyclic voltammetry, charge–discharge test, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. Cycle life and rate performance of the Li/LiNi_0.5Mn_1.5O₄ cells containing 1.2 M LiPF₆ in ethylene carbonate/ethyl methyl carbonate can be improved by adding 1-allyl-3-vinyl imidazolium bis(trifluoromethanesulphonyl)imide ([AVIm][TFSI]). The addition of 3 wt.% [AVIm][TFSI] results in high discharge capacity of above 130 mAh g^?1. Surface analysis of the cathode material (XPS and SEM) suggested that a stable and compact polymer film was formed on the LiNi_0.5Mn_1.5O₄ cathode by electroinitiated polymerization of imidazolium cation with vinyl and allyl group.