Trifluoromethanesulfonyl Imide Research Articles

Ionic Liquids with the Bis(fluorosulfonyl)imide Anion: Electrochemical Properties and Applications in Battery Technology

Room temperature ionic liquids (RTILs) with the bis(fluorosulfonyl)imide (FSI) anion exhibit higher conductivities than the corresponding bis(trifluoromethanesulfonyl)imide (TFSI) compounds, thereby generating interest as novel electrolytes for lithium batteries. The electrochemical properties of a series of FSI RTILs, at inert metal and lithium electrodes, have been investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Addition of , , or LiTFSI extends cathodic limits to significantly more negative values and allows reversible lithium electrodeposition. Variable-current cycling of symmetrical coin cells reveals significant changes in electrode–electrolyte interphasial impedance, which depends on the identity of the lithium salt anion, the concentration of the salt, and the RTIL cation. For most cells, voltage–time curves become unsteady early in duty, which is consistent with the formation of dendrites on the lithium surface. A stable voltage behavior returns within around 20 cycles, at notably a lower current density presumably because detachment/reattachment of dendrites eventually re-establishes a contiguous lithium electrode with a higher surface area. Importantly, the combination of the kinetics of lithium deposition and morphology of the deposit in FSI anion-based RTIL media does not result in lithium penetration of the separator. Therefore, FSI-based electrolytes can play a key role in the development of a viable lithium-metal battery technology.

Improving electrochemical properties of room temperature ionic liquid (RTIL) based electrolyte for Li-ion batteries

Abstract Room temperature ionic liquids (RTILs) with high safety characteristic usually have high viscosity and melting point, which is adverse for the application of RTIL-based electrolytes in Li-ion batteries. In this investigation, a promising RTIL, i.e. PP13TFSI consisting of N-methyl-N-propylpiperidinium (PP13) cation and bis(trifluoromethanesulfonyl)imide (TFSI) anion is synthesized. The effect of the content of Li salt in the electrolytes containing PP13TFSI and LiTFSI on the ionic conductivity and cell performance is investigated. The electrolyte of 0.3 mol kg −1 LiTFSI/PP13TFSI is recommended for its higher lithium transference number and discharge capacity in the LiCoO 2 /Li cell than other electrolytes. In addition, it is found that, by introducing 20% diethyl carbonate (DEC) as a co-solvent into pure RTIL electrolyte, the rate capability and low-temperature performance of the LiCoO 2 /Li cells are improved obviously, without sacrificing its safety characteristics. It suggests that a component with low viscosity and melting point, i.e. DEC, is necessary to effectively overcome the shortcomings of RTIL for the application in Li-ion batteries.

Mg2+ Ion Behavior in Ionic Liquids

The behavior of the Mg ion in ionic liquids is characterized in this paper. High ionic conductivity and electrochemical stability is observed for ionic liquids composed of a 1,2-dimethyl-3-n-R-imidazolium cation (R = propyl (MMPI) and butyl (MMBI)) and a bis(trifluoromethanesulfonyl)-imide (TFSI) anion containing Mg(TFSI)2. The ionic liquids containing the Mg ion are also used to create solid polymer gel electrolytes using PVdF-HFP. The ionic conductivity of the TFSI-based ionic liquids, in both liquid form and solid gel, ranges from 1-3 mS/cm at room temperature. Electrochemical measurements indicate that the Mg ion is readily intercalated and de-intercalated from graphite, with charge/discharge efficiencies typically above 80%. X-ray diffraction analysis indicates a difference of only 1 Aå in the c-axis expansion of the graphite when intercalated with the imidazolium cation or the Mg ion and the imidazolium cations. This indicates that co-intercalation of the Mg ion and the imidazolium cation is occurring.

Nafion-Doped Polypyrrole as a Supercapacitor Electrode in Ionic Liquid

The supercapacitive properties of flexible Nafion-doped polypyrrole(PPy/Nafion) electrodes prepared using a flexible gold coated porous PVDF substrate were investigated in the presence of an ionic liquid, N-methyl-N-propylpyridinium trifluoromethanesulfonyl imide(P1,3TFSI), by means of cyclic voltammetry for supercapacitors. The PPy/Nafion showed capacitance values in the range of 350–450 F/g at the scan rates of 50–300 mV/s, indicating the ionic liquid is suitable for the electrolyte in supercapacitor.

Electrochemical investigations of ionic liquids with vinylene carbonate for applications in rechargeable lithium ion batteries

Abstract Ionic liquids based on methylpropylpyrrolidinium (MPPY) and methylpropylpiperidinium (MPPI) cations and bis(trifluoromethanesulfonyl)imide (TFSI) anion have been synthesized and characterized by thermal analysis, cyclic voltammetry, impedance spectroscopy as well as galvanostatic charge/discharge tests. 10 wt% of vinylene carbonate (VC) was added to the electrolytes of 0.5 M LiTFSI/MPPY.TFSI and 0.5 M LiTFSI/MPPI.TFSI, which were evaluated in Li || natural graphite (NG) half cells at 25 °C and 50 °C under different current densities. At 25 °C, due to their intrinsic high viscosities, the charge/discharge capacities under the current density of 80 μA cm−2 were much lower than those under the current density of 40 μA cm−2. At 50 °C, with reduced viscosities, the charge/discharge capacities under both current densities were almost indistinguishable, which were also close to the typical values obtained using conventional carbonate electrolytes. In addition, the discharge capacities of the half cells were very stable with cycling, due to the effective formation of solid electrolyte interphase (SEI) on the graphite electrode. On the contrary, the charge/discharge capacities of the Li || LiCoO2 cells using both ionic liquid electrolytes under the current density of 40 μA cm−2 decreased continually with cycling, which were primarily due to the low oxidative stability of VC on the surface of LiCoO2.

Application of bis(fluorosulfonyl)imide-based ionic liquid electrolyte to silicon–nickel–carbon composite anode for lithium-ion batteries

An ionic liquid electrolyte containing bis(fluorosulfonyl)imide (FSI) anion without any solvent is applied to a silicon–nickel–carbon (Si–Ni–carbon) composite anode for rechargeable lithium (Li)-ion batteries. The FSI-based ionic liquid electrolyte successfully provides a stable, reversible capacity for the Si–Ni–carbon anode, which is comparable to the performance observed in a typical commercialized solvent-based electrolyte, while a common ionic liquid electrolyte containing bis(trifluoromethanesulfonyl)imide (TFSI) anion without FSI presents no reversible capacity to the anode at all. Ac impedance analysis reveals that the FSI-based electrolyte provides very low interfacial and charge-transfer resistances at the Si-based composite anode, even when compared to the corresponding resistances observed in a typical solvent-based electrolyte. Galvanostatic cycling of the Si-based composite anode in the FSI-based electrolyte with a charge limitation of 800 mAh g −1 is stable and provides a discharge capacity of 790 mAh g −1 at the 50th cycle, corresponding to a cycle efficiency of 98.8%.

Physicochemical Properties of New Dicationic Ether-Functionalized Low Melting Point Ammonium Salts

Eleven new and one previously known but insufficiently characterized dicationic quaternary ammonium (QA) salts were synthesized and characterized. They contain an ethoxy ethyl group either in a side chain and/or as spacer of the diammonium cation and have bromide, hexafluorophosphate (PF6–), bis(trifluoromethanesulfonyl)imide (TFSI), or trifluoromethanesulfonate (TFMS) as an anion. 1H and 13C techniques, mass spectrometry, and elemental analysis together with X-ray diffraction and thermoanalytical methods were used for their characterization both in the liquid and solid state. In addition, residual water content and viscosity measurements were made for the two room temperature ionic liquids (RTILs). Capillary electrophoresis was used to measure the conductivity of the RTILs. Crystal structures of four compounds were determined by X-ray single crystal diffraction, and powder diffraction was used to study the crystallinity of the solid salts and to compare the structural similarities between the single crystals and the microcrystalline bulk form. Two of the TFSI salts were liquids below room temperature, having liquid ranges of ~380 and 350°C, respectively, and seven out of 12 salts melted below 100°C. In addition, both the TFSI and PF6 salts exhibited high thermal stabilities decomposing at about, or above 300°C. Both RTILs presented moderate viscosities at elevated temperatures. The determined physicochemical properties of the reported ILs suggest their applicability for various applications such as heat transfer fluids, high temperature synthesis, and lubricants.

Phenyleneethynylene- and Thienyleneethynylene-Based π-Conjugated Polymers with Imidazolium Units in the Main Chain

Phenyleneethynylene-based and thienyleneethynylene-based π-conjugated polymers with imidazolium cationic units in the main chain and their model compounds were synthesized and characterized. The imidazolium-containing cationic polymers were transferred to an ionic liquid by the spontaneous anion-exchange from iodide to bis(trifluoromethanesulfonyl)imide (TFSI). The fluorescence quantum yield of phenyleneethynylene-based π-conjugated polymer in the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (emimTFSI), was higher than that of polymer based on iodide anion in pyridine because of a low degree of aggregation of the main chain and/or the absence of an external heavy-atom effect of the iodide counteranion. UV−vis and fluorescence spectra of N-methylated polymer and model compound with TFSI counteranion exhibited a significant blue shift with respect to the parent neutral molecules. Density functional theory (DFT) calculations for the model compounds showed a decrease in π-conju...

Phase Behavior and Ionic Conductivity in Lithium Bis(trifluoromethanesulfonyl)imide-Doped Ionic Liquids of the Pyrrolidinium Cation and Bis(trifluoromethanesulfonyl)imide Anion

The phase behavior and the ionic conductivity of ionic liquids (ILs) of the N-alkyl-N-alkylpyrrolidinium (PYR(xy)) cation and the bis(trifluoromethanesulfonyl)imide (TFSI) anion are investigated upon addition of LiTFSI salt. We compare the case of two new ILs of the PYR(2y) cation (where 2 is ethyl and y is butyl or propyl) with that of the PYR(14) (where 1 is methyl and 4 is butyl). We find that the addition of LiTFSI increases the glass transition temperature, decreases the melting temperature and the heat of fusion and, in the ILs of the PYR(2y) family, suppresses crystallization. In the solid state, significant ionic conductivities are found, being as high as 10(-5) S cm(-1), strongly increasing with Li(+) concentration. The opposite trend is found in the liquid state, where the conductivity is on the order of 10(-3)-10(-2) S cm(-1) at room temperature. A T(g)-scaled Arrhenius plot shows that the liquid-state ionic conductivity in these systems is mainly governed by viscosity and that the fragility of the liquids is slightly influenced by the structural modifications on the cation.

Polymerized Ionic Liquids: The Effect of Random Copolymer Composition on Ion Conduction

Ionic conductivity in new polymerized ionic liquids is of great interest as it applies to solid-state electrolytes for electrochemical and electromechanical applications. In this study, an ionic liquid monomer was synthesized and polymerized into random copolymers and their ionic conductivity and structure were investigated as a function of copolymer composition. Both nonionic−ionic and ionic−ionic copolymers were synthesized, where the nonionic and ionic monomers were hexyl methacrylate (HMA) and a methacrylate-based imidizolium neutralized with tetrafluoroborate (BF4) or bis(trifluoromethane sulfonyl)imide (TFSI). In the nonionic−ionic copolymer, the ionic conductivity increased by over an order of magnitude with increasing HMA composition, even though the overall charge content decreased, because the addition of HMA significantly lowered the glass transition temperature. The ionic conductivity also increased by more than an order of magnitude in the ionic−ionic copolymer with increasing TFSI content, even though there was no change in the overall charge content, because substituting the larger anion TFSI for BF4 resulted in weaker ionic interactions and also significantly lowered the glass transition temperature. In both types of copolymers, the temperature dependence of the ionic conductivity was well described by both Arrhenius and Vogel−Tamman−Fulcher models. An important difference between the two classes of random copolymers was that the nonionic−ionic copolymer exhibited microphase separation in X-ray scattering that correlated with a discontinuity in the increasing ionic conductivity with increasing HMA content suggesting that structure can also play a significant role in ion transport in polymerized ionic liquids.

Application of hybrid materials in solid-state electrochromic devices

Sol–gel derived cross-linked PEO/siloxane xerogels (designated as di-ureasils) were prepared using lithium trifluoromethanesulfonyl imide (LiTFSI) as a guest salt. In this paper we describe the assembly of a prototype solid-state electrochromic device (ECD) based on a four-layer sandwich structure, with the following configuration: glass/IZO/WO 3/polymer electrolyte/IZO/glass. The electrochromic switching performance of these devices was characterized as a function of salt concentration. The average transmittance in the visible region of the spectrum was above 69% for all the bleached samples characterized. After coloration the structures assembled with d-U(900) n LiTFSI presented an average transmittance in the visible wavelength region above 22% and an optical density above 0.49.

Pyrrolidinium-based polymeric ionic liquids as mechanically and electrochemically stable polymer electrolytes

A new family of polymeric ionic liquids having pyrrolidinium cation pendant units was synthesized from commercially available poly(diallyldimethylammonium) chloride. A simple anion exchange procedure was applied to the poly(diallyldimethylammonium) chloride using different salts such as LiTFSI, KPF 6, LiBF 4 and NaDBSA. The anion exchange reaction was quantitative as confirmed by NMR, FT-IR and titration experiments. Among these polymers, poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (TFSI) showed excellent performance as polymer matrix for polymer electrolyte compositions together with pyrrolidinium ionic liquid and lithium salt having a similar TFSI counter-anion. In this sense, free standing mechanically stable transparent polymer films showing an ionic conductivity higher than 10 −4 S cm −1 at room temperature were prepared and characterized. Furthermore, the polymer electrolytes presented a wide electrochemical stability window (7.0 V) which makes them interesting candidates for solid-state lithium batteries.

Ionic liquid‐based luminescent composite materials

AbstractLuminescent composite materials based on semiconductor nanocrystals (NCs) with ionic liquid and subsequently with an ionic liquid‐based polymer have been prepared. Cationic CdTe NCs passivated with thiocholine bromide (TCB) were prepared in an aqueous phase and easily transferred to hydrophobic ionic liquids by means of a simple biphasic extraction process without using any surfactant. TCB‐capped CdTe NCs were stably dispersed in hydrophobic ionic liquids and their absorption spectra and optical density (extinction coefficient) were maintained even after the extraction. While the emission peak position was also identical with the original one, its intensity increased almost twice. The efficient extraction and photoluminescence enhancement of CdTe NCs were generally observed for the hydrophobic ionic liquids based on both bis(trifluoromethanesulfonyl)imide (TFSI) and hexafluorophosphate (PF6) anions. However, the generation of a trace of hydrofluoric acid gradually collapsed the CdTe NCs in a PF6‐based ionic liquid. A polymerizable ionic liquid which possesses an acrylate group could also extract the CdTe NCs from water and gave a CdTe NC‐polymer composite with strong luminescence by the polymerization of ionic liquid. Copyright © 2008 John Wiley & Sons, Ltd.

Electrostatic Layer-by-Layer Deposition and Electrochemical Characterization of Thin Films Composed of MnO2 Nanoparticles in a Room-Temperature Ionic Liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly(diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.

Solid Polymer Electrolytes from Crosslinked PEG and Dilithium N,N'-Bis(trifluoromethanesulfonyl)perfluoroalkane-1,ω-disulfonamide and Lithium Bis(trifluoromethanesulfonyl)imide Salts

The present work consists of a series of studies with regard to the structure and charge transport in solid polymer electrolytes (SPE) prepared using various new bis(trifluoromethanesulfonyl)imide (TFSI)-based dianionic dilithium salts in crosslinked low-molecular-weight poly(ethylene glycol). Some of the thermal properties (glass transition temperature, differential molar heat capacity) and ionic conductivities were determined for both diluted (EO/Li = 30:1) and concentrated (EO/Li = 10:1) SPEs. Trends in ionic conductivity of the new SPEs with respect to anion structure revealed that while for the dilute electrolytes ionic conductivity is generally rising with increased length of the perfluoroalkylene linking group in the dianions, for the concentrated electrolytes the trend is reversed with respect to dianion length. This behavior could be the result of a combination of two factors: on one hand a decrease in dianion basicity that results in diminished ion pairing and an enhancement in the number of charge carriers with increasing fluorine anion content, thereby increasing ionic conductivity while on the other hand the increasing anion size and concentration produce an increase in the friction/entanglements of the polymeric segments which lowers even more the reduced segmental motion of the crosslinked polymer and decrease the dianion contribution to the overall ionic conductivity. DFT modeling of the same TFSI-based dianionic dilithium salts reveals that the reason for the trend observed is due to the variation in ion dissociation enthalpy, derived from minimum-energy structures, with respect to perfluoroalkylene chain length.

Synthesis and Properties of Pyrrolidinium and Piperidinium Bis(trifluoromethanesulfonyl)imide Ionic Liquids with Allyl Substituents

New pyrrolidinium and piperidinium bis(trifluoromethanesulfonyl)imide (TFSI) ionic liquids (ILs) having allyl substituents were synthesized and characterized. All of them are liquid at room temperature and stable up to 300 oC. The pyrrolidinium-based ILs showed better conductivities and lower viscosities than the corresponding piperidinium-based ILs. Among them, 1-allyl-1-methylpyrrolidinium TFSI showed the lowest viscosity of 52 cP, the highest conductivity of 5.7 mS cm?1, and the most negative cathodic voltage window of ?3.2 V (vs. Fc/Fc+) on a platinum electrode, which are the improved results compared to the corresponding analogue having a saturated substituent, 1-methyl-1-propylpyrrolidinium TFSI.

The Electrochemical Behavior of Trialkylimidazolium Imide Based Ionic Liquids and Their Polymer Gel Electrolytes

The physical and electrochemical properties of 1,2-dimethyl-3-n--imidazolium ionic liquids [ (MMPI) and butyl (MMBI)] were investigated. The anions studied were bis(trifluoromethanesulfonyl)imide (TFSI) or bis(perfluoroethanesulfonyl)imide (PFESI). In addition, polymer gel electrolytes were prepared using polyethylene oxide of poly(vinylidenefluoride-co-hexafluoropropene) (PVDF-HFP) and these ionic liquids with and without . Electrochemical measurements showed similar behavior for the TFSI based ionic liquids, although MMBITFSI exhibited lower ionic conductivity than MMPITFSI. The MMPIPFESI is an extremely viscous liquid, which solidifies if cooled slightly below room temperature. MMBIPFESI is a wax at room temperature. For both MMPIPFESI and MMBIPFESI, addition of lithium (as LiPFESI) resulted in crystallization of the pure ionic liquid at room temperature. Electrochemical studies indicated that in all cases, the PVDF-HFP polymer gel systems exhibited higher charge/discharge efficiencies and higher ionic conductivity than the PEO based polymer gel systems.

Infinite Dilution Activity Coefficients for Trihexyltetradecyl Phosphonium Ionic Liquids: Measurements and COSMO-RS Prediction

Separation of aliphatic and aromatic compounds was studied using the high molecular weight trihexyl-tetradecyl-phosphonium cation (thtd-Ph) based ionic liquids (ILs) with the anions chloride [Cl], tetrafluoroborate [BF4], and bis(trifluoromethane sulfonylimide)[(Tf)2N]. Infinite dilution activity coefficients (γ∞) for these novel solvents have been measured at T = (308.15, 318.15, and 328.15) K, using gas−liquid chromatography. The aliphatic solutes studied were normal alkanes (pentane, hexane, heptane, octane), alkenes (hexene, heptene, octene), alkynes (hexyne, heptyne, octyne), cycloalkanes (cyclopentane, cylcohexane, cycloheptane), and alcohols (methanol, ethanol). The aromatic solute studied was benzene. The molar excess enthalpy at infinite dilution (HE,∞) was calculated using the temperature dependency of γ∞ data. The selectivity values for the phosphonium-based ILs indicate a poorer separation capability than imidazolium- or pyridinium-based ILs. The values of γ∞ have been found to be in the follo...

Characterization of Solvent-Free Polymer Electrolytes Consisting of Ternary PEO – LiTFSI – PYR14 TFSI

The physical properties and electrochemical performance of solvent-free polymer electrolytes, consisting of poly(ethylene oxide) [P(EO)] with and -butyl--methylpyrrolidinium salts of bis(trifluoromethanesulfonyl)imide (TFSI), are reported. The addition of the room-temperature molten salt to the conventional polymer electrolyte results in a significant enhancement of the ionic conductivity (to at ). batteries making use of this new family of solid polymer electrolytes have shown a very promising low-temperature cycle life. It was found that a cell at can deliver during the first discharge, corresponding to 90% of the nominal specific capacity , and a promisingly low capacity fading of about 0.2%/cycle over 500 cycles.

Additive-containing ionic liquid electrolytes for secondary lithium battery

Room temperature ionic liquid (RTIL) consisting of N-methyl- N-propylpiperidinium (PP13) cation and bis(trifluoromethanesulfonyl)imide (TFSI) anion was synthesized and its electrochemical stability was investigated in comparison with 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF 4) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF 6). The electrochemical window of PP13-TFSI (5.8 V versus Li/Li +) is wider than that of BMIBF 4 (4.7 V) and BMIPF 6 (4.5 V). The cathodic limit of the PP13-TFSI is about −0.3 V versus Li/Li +, against 0.7 V for BMIPF 6 and BMIBF 4, so it may be used as the electrolyte for second lithium batteries based on lithium anode. In this work, charge efficiency of lithium plating/striping on nickel substrate and the cycle life have been measured using 0.4 M LiTFSI/PP13-TFSI electrolyte both without and with additives such as vinyl acetate (VA), ethylene sulfite (ES), and ethylene carbonate (EC). Remarkable improvement in cycling efficiency and cycle life was found for EC as additive.