Room Temperature Molten Salts Research Articles

Improved properties of polymer electrolyte by ionic liquid PP1.3TFSI for secondary lithium ion battery

A new kind of polymer electrolyte is prepared from N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP1.3TFSI), polyethylene oxide (PEO), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). IR and X-ray diffraction results demonstrate that the addition of ionic liquid decreases the crystallization of PEO. Thermal and electrochemical properties have been tested for the solid polymer electrolytes, the addition of the room temperature molten salt PP1.3TFSI to the conventional P(EO)20LiTFSI polymer electrolyte leads to the improvement of the thermal stability and the ionic conductivity (x = 1.27, 2.06 × 10−4 S cm−1 at room temperature), and the reasonable lithium transference number is also obtained. The Li/LiFePO4 cell using this polymer electrolyte shows promising reversible capacity, 120 mAh g−1 at room temperature and 164 mAh g−1 at 55 °C.

이온성 액체에 의한 CdSe/ZnS 나노입자의 상과 크기제어 합성

이온성 액체는 일정한 온도 범위에서 액체로 존재하는 이온성 염으로, 유기 양이온과 유기 또는 무기 음이온의 이온결합으로 이루어져 있다. 본 연구에서는 이온성 액체를 CdSe/ZnS 반도체 나노입자 합성의 리간드 및 용매로 사용하여 이들이 나노입자의 형태와 결정 구조에 미치는 영향에 대해서 연구하였다. CdSe/ZnS 나노입자는 용매로 알킬기의 길이가 다른 imidazolium 계열; 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([RMIM][TFSI]), R = ethyl ([EMIM]), butyl ([BMIM]), hexyl ([HMIM]), octyl ([OMIM]), 을 사용하여, 평균 크기는 약 8~9 nm 이고 두 상 zinc-blende 및 wurtzite 혼합물로 합성하는 것을 성공하였다. 또한, CdSe/ZnS 나노입자는 trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([<TEX>$P_{6,6,6,14}$</TEX>][TFSI]) 이온성 액체와 octadecene (ODE)의 혼합 용액을 사용하여 합성하였다. [<TEX>$P_{6,6,6,14}$</TEX>][TFSI]의 부피비가 증가함에 따라 나노입자의 결정 구조가 zinc-blende 구조에서 wurtzite 구조로 조절되었다. 또한 나노입자의 평균 크기는 약 5.5 nm 로써 [RMIM][TFSI] 를 사용했을 때 보다 더 작게 합성되었다. 이처럼 이온성 액체에 의해서 나노입자의 크기뿐 만 아니라 결정 구조도 조절할 수 있음을 처음으로 증명하였다. Ionic liquids are room-temperature molten salts, composed of organic mostly of organic ions that may undergo almost unlimited structural variation. We approach the new aspects of ionic liquids in applications where the semiconductor nanoparticles used as sensitizers of solar cells. We studied the effects of ionic liquids as capping ligand and/or solvent, on the morphology and phase of the CdSe/ZnS nanoparticles. Colloidal CdSe/ZnS nanoparticles were synthesized using a series of imidazolium ionic liquids; 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([RMIM][TFSI]), where R = ethyl ([EMIM]), butyl ([BMIM]), hexyl ([HMIM]), octyl ([OMIM]). The average size of nanoparticles was 8~9 nm, and both zinc-blende and wurtzite phase was produced. We also synthesized the nanoparticles using a mixture of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([<TEX>$P_{6,6,6,14}$</TEX>][TFSI]) and octadecene (ODE). The CdSe/ZnS nanoparticles have a smaller size (5.5 nm) than that synthesized using imidazolium, and with a controlled phase from zinc-blende to wurtzite by increasing the volume ratio of [<TEX>$P_{6,6,6,14}$</TEX>][TFSI]. For the first time, the phase and size control of the CdSe/ZnS nanoparticles was successfully demonstrated using those ionic liquids.

Time‐of‐Flight secondary ion mass spectrometry (TOF‐SIMS) using the metal‐cluster‐complex primary ion of Ir4(CO)7+

AbstractAn orthogonal acceleration Time‐of‐Flight Secondary Ion Mass Spectrometer (TOF‐SIMS) system has been developed with a metal‐cluster‐complex ion source. The ion source can produce ion beams of massive molecules called metal‐cluster‐complexes such as Ir4(CO)12, which has a molecular weight higher than 1000 u. Using the system, TOF‐SIMS of a contaminated silicon substrate and a room temperature molten salt (i.e. an ionic liquid) was performed. The ionic liquid N,N‐diethyl‐N‐methyl‐N‐(2‐methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, which has a molecular weight of 426 u, consists of a polyatomic cation, [C8H20ON]+, and a polyatomic anion, [C2F6NO4S2]−. During SIMS analysis, an analytical sample was bombarded with a continuous primary ion beam of either Ir4(CO)7+ or Ar+ in a beam energy of 10 keV at an incident angle of 45°. It was confirmed that the use of Ir4(CO)7+ ions enhanced secondary ion intensity compared with that of Ar+ ions. Also, experimental results showed that the bombardment of Ir4(CO)7+ caused less fragmentation. In the case of the ionic liquid, cation‐attached ionic‐liquid molecules were observed in addition to the cation of the ionic liquid. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Lithium-ion batteries. A look into the future

A critical overview of the latest developments in the lithium ion batteries technology is reported. We first describe the evolution in the electrolyte area with particular attention to ionic liquids, discussing the expected application of these room temperature molten salts and listing the issues that still prevent their practical implementation. The attention is then focused on the electrode materials presently considered the most promising for enhancing the energy density of the batteries. At the anode side a discussion is provided on the status of development of high capacity tin and silicon lithium alloys. We show that the morphology that is the most likely to ensure commercial exploitation of these alloy electrodes is that involving carbon-based nanocomposites. We finally touch on super-high-capacity batteries, discussing the key cases of lithium-sulfur and lithium-air and attempting to forecast their chances to eventually reach the status of practically appealing energy storage systems. We conclude with a brief reflection on the amount of lithium reserves in view of its large use in the case of global conversion from gasoline-powered cars to hybrid and electric cars.

Characteristics of a charged-droplet beam generated by vacuum electrospray of an ionic liquid

To develop a cluster ion beam source for secondary ion mass spectrometry (SIMS), beam characteristics of charged droplets electrosprayed in a vacuum were investigated using a room-temperature molten salt (i.e., an ionic liquid). A target current exceeding 200nA was produced at a capillary voltage of 1.5kV even with a low flow rate of 0.05μL/min. Efficiency of beam generation varied with increasing capillary voltage and flow rate. Additionally, m/z values of emitted charged particles were investigated by a time-of-flight technique. In addition to masses and charge numbers, radii of the charged droplets were examined.

Pseudolattice theory of charge transport in ionic solutions: Corresponding states law for the electric conductivity

A statistical mechanical framework for charge transport in ionic liquid–solvent mixtures based on the existence of a statistical lattice structure (pseudolattice) throughout the whole range of concentration is reported. The ion distribution is treated in a mean-field Bragg–Williams-like fashion, and the ionic motion is assumed to take place through hops between cells of two different types separated by non-random-energy barriers of different heights depending on the cell type. Assuming non-correlated ion transport, the electrical conductivity is shown to have a maximum, arising from the competition between the concentration of charge carriers in the bulk medium and their mobilities in the pseudolattice. An explicit expression for the concentration at which this maximum occurs is given in terms of microscopic parameters, and the electrical conductivity normalized by its maximum value ( κ/ κ max) is shown to follow rather closely a universal corresponding states law in concentration space when represented against the ionic concentration scaled by its value at the conductivity maximum ( ϕ α/ ϕ max). Ion–ion and ion–solvent interactions are explicitly considered combining the path probability method for charge transport in solid electrolytes and the Bragg–Williams approximation for interparticle interactions, and their impact on the deviations of experimental data from the universal behavior of non-correlated transport analyzed. The theoretical predictions are shown to satisfactorily predict experimental values of electrical conductivity of aqueous solutions of conventional electrolytes and of mixtures of room temperature molten salts with typical solvents.

Performance of NASICON Symmetric Cell with Ionic Liquid Electrolyte

To improve the thermal stability of lithium- and sodium-ion batteries, the room-temperature molten salts /1-ethyl-3-methyl imidazolium tetrafluoroborate and were used as ionic liquid (IL) electrolytes instead of flammable carbonate-type organic electrolyte solvents. To avoid cathodic decomposition of the IL electrolytes, a symmetric cell configuration with Na Superionic CONductor (NASICON)-type (where A is Li or Na) as both cathode and anode was tried in a coin-type cell (type 2320). As a result, both the polyanionic-based (LVP) as well as (NVP) symmetric cells using organic electrolytes were found to operate as secondary batteries and exhibited satisfactory electrochemical performances. The substitution of the organic electrolytes by the appropriate IL electrolytes in both cases resulted in the reduction in the first discharge capacities. However, the IL-based cells revealed better cyclability and a more stable behavior at elevated temperatures. The obtained electrochemical behavior of the symmetric cells was confirmed by the complex impedance measurements at 25 and . In addition, the thermal stability of LVP and NVP with the IL electrolytes was also examined.

A new cluster-ion-beam source for secondary ion mass spectrometry (SIMS) using the electrospray of a pure ionic liquid under high vacuum

Electrospray characteristics were studied using a pure room-temperature molten salt (i.e., an ionic liquid) at pressures around 10 −5 Pa as well as at atmospheric pressure. The ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide was tested, which has negligible vapor pressure and high conductivity. During electrospray, the ionic liquid was introduced at a constant flow rate into a stainless-steel capillary (i.d. 30 μm). It was demonstrated that stable electrosprayed currents exceeding ±1 μΑ were continuously produced in both positive and negative modes. The electrosprayed currents in a high vacuum were twice those at atmospheric pressure. It was found that gas pressure rose slightly with increasing electrosprayed currents. Residual gas analysis revealed that gas component at negative mode was different from that at positive mode. Experimental results indicate that vacuum electrospray of pure ionic liquids is applicable to a massive-cluster beam source for SIMS.

Ion Beam Generation from an Electrolyte Solution Containing Polyatomic Cations and Anions for Secondary Ion Mass Spectrometry

A solution-type ion beam source was fabricated to utilize polyatomic anions as well as polyatomic cations that are stable in solutions. The ion source consists of an electrospray section at atmospheric pressure and a vacuum section with a differential pumping system. To demonstrate the beam generation of cations or anions, ethanol solution containing a room-temperature molten salt (i.e., an ionic liquid) was tested. The ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, consists of a polyatomic cation, [C8H20ON]+, and a polyatomic anion, [C2F6NO4S2]-. Ions produced at atmospheric pressure were passed through an aperture into a vacuum chamber and then transported to a target. The effects of the aperture dimensions were investigated in the range from 50 to 200 µm in diameter and 0.25 to 1 mm in thickness. The ratio of current passing through the aperture into the vacuum chamber to the total electrosprayed current was on the order of 10-3 to 10-5. The ratio increased with increasing aperture diameter. A reduction in the aperture thickness also improved the ratio. Beam current increased with applied voltage in both positive-ion and negative-ion modes. It was demonstrated that stable negative-ion beams as well as positive-ion beams on the order of pA were produced.

A Novel Room Temperature Molten Salt Electrolyte Based on LiBOB and 2-Oxazolidinone for Electrochemical Capacitors

Abstract In this paper, a novel room temperature molten salt electrolyte based on lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB) and 2-Oxazolidinone (C3H5NO2, OZO) has been prepared as the electrolyte of electrochemical capacitors (EDLCs). The conductivity, thermal stability and electrochemical stability of the LiBOB-OZO electrolytes are investigated. It shows excellent thermal stability, high ionic conductivity (up to 10.4mS cm−1) and a wide electrochemical stability window (4.5 V). The temperature dependence of conductivity for the electrolytes follows the VFT equation, which demonstrates a solvent-assisted ionic conductivity mechanism. Based on it, a specific recipe of the LiBOB-OZO electrolytes (with a molar ratio of 1:6) is evaluated by cylic voltammetry, AC impedance spectroscopy, and galvanostatic charging-discharging in a test EDLC capacitor. It is found that the EDLC with the LiBOB-OZO complex electrolyte can be charged up to 2.5 V, the specific capacitance based on an activated carbon electrode can reach 92.5 F g−1 at 50°C, the equivalent series resistance (ESR) decreases sharply from 18.2 Ω at 30 °C to 7.2 Ω at 70 °C. Then, an EDLC of higher energy density and power density can be obtained，especially in the temperatures above 50 °C

Development and characterization of an iodine field emission ion source for focused ion beam applications

Emission of positive and negative ions is possible when a room-temperature molten salt, or ionic liquid, is exposed to a sufficiently high electric field. Ionic liquid ion sources (ILISs) have shown potential to be used in various focused ion beam (FIB) applications, since their operation and characteristics are similar to those of liquid metal ion sources, with the advantage that ILIS work at low temperatures in comparison and a large number of ionic liquids with many different compositions are available. In this article, the authors present results on the emission characteristics of negative ions extracted from an iodine-based ionic liquid using a time-of-flight mass spectrometer and a retarding potential analyzer. The ionic liquid 1-butyl-3-methylimidazolium iodide (BMI-I) is used as source media, producing a droplet free beam with multiple solvated ion species. Attention is given to BMI-I, in particular, due to the potential of creating a beam of pure and clustered I-ions, which are expected to improve the performance in applications based on secondary emission and reactive species. Properties important to the focusing of the ion beam such as mass and energy distributions are obtained. The full width at half maximum of the energy distribution is measured to be on the order of 10eV, with an estimated angular intensity of 0.65×10−6Asr−1. Estimated performance of the ILIS in a hypothetical FIB column gives current densities of 0.15Acm−2.

Ionic-liquid materials for the electrochemical challenges of the future

Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.

Metal cluster complex primary ion beam source for secondary ion mass spectrometry (SIMS)

To develop a solution-type ion beam source utilizing a wide variety of metal cluster complexes that are stable only in organic solvents, we have investigated an electrospray method for transferring ions from solutions to gas phase. As initial experiments, we have studied electrospray characteristics of ethanol solutions containing a room-temperature molten salt (i.e., an ionic liquid) and acetic acid as alternatives to solutions of metal cluster complexes. In electrospray experiments, we used a stainless-steel capillary with an inner diameter of 30 μm. Experimental results showed that electrosprayed currents increased with applied voltage in both positive-ion and negative-ion modes. In addition to positive currents, stable negative currents were also confirmed to be produced. Current exceeding 250 nA was produced at 2 kV with a flow rate of 2 μL/min at a concentration of 1 × 10 −3 mol/L. It was confirmed that several nA out of electrosprayed currents were delivered through an orifice (120 μm internal diameter) into a vacuum chamber. Experimental results indicate that the electrospray method seems to be applicable to an ion beam source for utilizing massive metal cluster complexes in solutions.

Amide-based Room Temperature Molten Salt as Solvent cum Stabilizer for Metallic Nanochains

A simple and efficient method for spontaneous organization of long assemblies of gold nanoparticles is described. This is achieved in a molten solvent containing acetamide, urea and ammonium nitrate that acts as a solvent cum stabilizer. There is no external aggregating agent or stabilizing agent added to the system. Depending on the concentration of the metal salt in the ternary melt, either chain-like assemblies or individual nanoparticles could be obtained. The amine groups present in the components of the melt (acetamide and urea) help in the stabilization of nanoparticles. Ammonium ions present in the eutectic mixture are likely to assist in the organization of the particles. The method is simple, highly reproducible and does not require any templating agent for the formation of chain-like assemblies.

Preparation and electrochemical properties of composite polymer electrolytes containing 1-ethyl-3-methylimidazolium tetrafluoroborate salts

The effects of room-temperature molten salt addition on the micro-structure and electrochemical properties of composite electrolytes (CEs) based on poly(ethylene oxide) (PEO)/ethylene carbonate (EC)/LiBF 4 were studied. Additional salt, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4), was found to influence the crystalline structure and heterogeneous morphology, resulting in changes to the ionic conductivity of the CE. The CE containing 0.2 mol of EMIBF 4 showed a small crystallinity, 27.9%. These CEs showed the highest ion conductivity, 3.1 × 10 −4 S/cm, five times higher than that of the pristine PEO/EC/LiBF 4. This enhanced conductivity originated from the decreased crystallinity and improved ion transference due to a Lewis acid–base interaction. The CE containing 0.3 mol of EMIBF 4 showed decreased conductivity due to the lower mobility, reflecting the high viscosity of the molten salt.

Influence of the Conductivity and Viscosity of Protic Ionic Liquids Electrolytes on the Pseudocapacitance of RuO2 Electrodes

Several new protic ionic liquids (PILs) were prepared by mixing trifluoroacetic acid (TFA) with various heterocyclic amines using different base:acid ratios (1:1 and 1:2). Their specific conductivities have been measured by electrochemical impedance spectroscopy and were found ranging from 0.71 to 9.07 mS·cm−1 at 27.0 °C. In all cases, the conductivity of a given ionic liquid increased with a higher proportion of acid (1:2 ratio) which is explained mainly a smaller viscosity obtained in these conditions. Indeed, in most PILs, the dynamic viscosity (10.3−484 cp at 27.0 °C) is decreased by a higher acid proportion. Both parameters were used to construct a Walden plot in order to evaluate the quality of these protic ionic liquids (PILs) and compare them with common room temperature (RT) molten salts. The physicochemical properties of the PILs were then compared with the specific capacitance values obtained with a thermally prepared RuO2 electrode in these ionic liquid electrolytes. This work brings evidence ...

Electrochemical Behaviors of Polymer Composite Electrolytes Containing Imidazolium-Type Room-Temperature Molten Salts

The effects of room-temperature molten salt addition on electrochemical properties of polymer composite electrolytes (PCE) based on poly(ethylene oxide) (PEO) were studied. Alkyl-imidazolium salt, 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIPF6) could influence ion transference phenomena, resulting the change of ionic conductivity of PCE. The PCE containing 1.2 mole% BMIPF6 showed the slightly lower melting temperature than PEO-LiClO4. The PCE showed the highest ion conductivity of 2.9 * 10(-4) S/cm, which is one-order-of-magnitude higher value than the pristine sample. This is probably originated from the improved ion transference and slightly decreased crystallinity. Li ion transference number was increased to 0.55 and the stable electrochemical voltage limit was upgraded to approximately 4.3 V. Consequently, the ion conducting behaviors and the electrochemical stability had been improved by BMIPF6 addition.

The use of ionic liquid ion sources in focused ion beam applications

A new monoenergetic, high-brightness ion source can be constructed using an arrangement similar to liquid metal ion sources by substituting the liquid metal with an ionic liquid or room-temperature molten salt. Ion beams produced by these ionic liquid ion sources (ILISs) have energy deficits and distributions that closely resemble their metallic counterparts, with the exception that they can be stably operated at current levels as low as a few nanoamperes if needed. ILISs are here presented as having two further key advantages: (1) the ability to obtain both positive and negative ion beams and (2) the ability to produce very diverse molecular ions in terms of their masses, compositions, and properties due to the fact that the number of available ionic liquids is large. In this article an overview of ILISs is presented, as well as preliminary results of their performance in a focused ion beam column.

A Novel Solvent-free Electrolyte Based on LiBOB and Acetamide for Electrochemical Capacitors

Abstract Room temperature molten salts or ionic liquids are promising “solvent-free” electrolytes for high-voltage double layer supercapacitors. In this work, a novel binary room temperature molten salt electrolyte based on LiBOB and acetamide has been prepared. The electrolyte shows excellent thermal stability, high ionic conductivity and a wide electrochemical stability window, especially at higher temperatures. The temperature dependence of conductivity for the electrolytes follows the VFT equation, which demonstrates a solvent-assisted ionic conductivity mechanism. The EDLC with the LiBOB-acetamide complex electrolyte at molar ratio of 1:6 can be charged up to 2.5 V with better rate performance. The specific capacitance based on activated carbon electrodes can reach 103.1 F g−1. It is reasonable to assume that LiBOB-acetamide complex system has advantages as electrolyte for EDLCs with high energy density.

Electronic functions of solid-to-liquid interfaces of organic semiconductor crystals and ionic liquid

The environment of surface electrons at ‘solid-to-liquid’ interfaces is somewhat extreme, subjected to intense local electric fields or harsh chemical pressures that high-density ionic charge or polarization of mobile molecules create. In this proceedings, we argue functions of electronic carriers generated at the surface of organic semiconductor crystals in response to the local electric fields in the very vicinity of the interface to ionic liquid. The ionic liquids (ILs), or room temperature molten salts, are gaining considerable interest in the recent decade at the prospect of nonvolatile ‘green solvents’, with the development of chemically stable and nontoxic compounds. Moreover, such materials are also applied to electrolytes for lithium ion batteries and electric double-layer (EDL) capacitors. Our present solid-to-liquid interfaces of rubrene single crystals and ionic liquids work as fast-switching organic field-effect transistors (OFETs) with the highest transconductance, i.e. the most efficient response of the output current to the input voltage, among the OFETs ever built.