An overview of the field of low-melting ionic liquids is given from its inception in 1886 through to the present time. The subject is divided into an introductory section that summarizes the early history of the field, and differentiates its subsections, before addressing matters judged of some interest in "pre-surge" and "post-surge" stages of its development, focusing on physicochemical as opposed to the prolific synthetic and industrial aspects in which the author has no competence. We give a final section specifically to protic ionic liquids, which we consider to have particular scientific potential.

Bulk and surface properties of the ionic liquids 1-alkyl-3-methyl-imidazolium iodides ([C(n)mim]I) were simulated by classical molecular dynamics using all atom non-polarizable force field (n = 4, butyl; 6, hexyl; 8, octyl). The structure of ionic liquids were initially optimized by density functional theory and atomic charges obtained by CHELPG method. Reduction of partial atomic charges (by 20% for simulation of density and surface tension, and by 10% for viscosity) found to improve the accuracy, while a non-polarizable force field was applied. Additionally, the simulation ensembles approach the equilibrium faster when the charge reduction is applied. By these refined force field parameters, simulated surface tensions in the range of 323-393 k are quite in agreement with the experiments. Simulation of temperature dependent surface tension of [C(4)mim]I well beyond room temperature (up to 700 K) permits prediction of the critical temperature in agreement with that predicted from experimental surface tension data. Simulated densities in the range of 298-450 K for the three ionic liquids are within 0.8% of the experimental data. Structural properties for [C(4)mim]I were found to be in agreement with the results of Car-Parrinello molecular dynamics simulation we performed, which indicates a rather well-structured cation-anion interaction and occurs essentially through the imidazolium ring cation. Diffusion coefficient changes with alkyl chain length in the order of [C(8)mim]I > [C(6)mim]I > [C(4)mim]I for the cation and the anion. Formation of a dense domain in subsurface region is quite evident, and progressively becomes denser as the alkyl chain length increases. Bivariate orientational analysis was used to determine the average orientation of molecule in ionic liquids surface, subsurface, and bulk regions. Dynamic bisector-wise and side-wise movement of the imodazolium ring cation in the surface region can be deduced from the bivariate maps. Atom-atom density profile and bivariate analysis indicate that the imidazolium cation takes a spoon like configuration in the surface region and the tilt of alkyl group is a function length of alkyl chain exposing as linear as possible to the vapor phase.

with the state-of-the-art high voltage cathode batteries with theoretical specific energy of ≈600 Wh kg −1 . In addition, elemental sulfur is environmentally friendly, inexpensive, and abundant.The Li-S battery poses some challenges that need to be overcome. One of the major challenges of the Li-S battery is that it generally suffers from the shuttling of soluble polysulfide species (Li 2 S x , x = 4-8) during cycling, which results in a low Coulombic efficiency and reduces its cycle life, typically to less than 100 cycles. In addition, since sulfur [1] and lithium sulfide are electronic insulators, the electronic conductivity of the cathode typically has to be augmented by addition of a significant amount of conductive carbon. To overcome these issues, most efforts have been directed to prevent soluble polysulfides from shuttling, by encapsulation of sulfur with conducting membranes or porous structures, most recently through designing 3D cathode architechtures [30][31][32][33][34] or other sulfur hosts [35,36] which allow improved stability as well as fast kinetics. Among conductive polymers, polypyrrole has been widely investigated [20,26,28,37] owing to its high electronic conductivity, low cost of precursors, and ease of synthesis. However, studies of polypyrrole encapsulated sulfur composites have shown no major successes perhaps due to the presence of large pores (≈5 nm, Figure S1, Supporting Information) in the encapsulating polymer. In addition, encapsulated sulfur nanocomposites require dissolution of a certain amount of sulfur by organic solvents to provide a void space in order to accommodate the large volumetric expansion of sulfur upon lithiation. [26] Here, for the first time, we demonstrate a strategy to improve the stability of Li-S battery using a multilayer encapsulation of sulfur nanoparticles. To ensure an effective encapsulation of sulfur, the following coating layers are selected. We coat the sulfur nanoparticles with MnO 2 particles as the interior shell since it was demonstrated that soluble lithium polysulfide species can be easily oxidized to thiosulfate groups by MnO 2 particles. The thiosulfate groups formed on the surface of the MnO 2 are proposed to anchor long-chain polysulfides by catenating them to form polythionates and therefore catalyze their conversion to insoluble short-chain polysulfides which significantly minimizes the shuttle effect. [29] We use polypyrrole as the exterior shell since (a) its porous structure allows electrolyte uptake, (b) its flexible network supports and contains the inner MnO 2 shell during discharging where the volumetric expansion of sulfur occurs, and (c) its remarkable electronic conductivity Advancements in portable electronic devices and electric powered transportation has drawn more attention to high energy density batteries, especially lithium-sulfur batteries due to the low cost of sulfur and its high energy density. However, the lithium-sulfur battery is still quite far from commercialization mostly because of incompatibility between all ma...

Ab initio Car-Parinnello molecular dynamics is used to simulate the structure and the dynamics of 1-butyl-3-methylimidazolium iodide ([bmim]I) ionic liquid at 300 K. Site-site pair correlation functions reveal that the anion has a strong interaction with any three C-H's of the imidazolium ring. The ring bends over and wraps around the anion such that the two nitrogen atoms take a distance to the anion. Electron donating butyl group contributes the electronic polarization in addition to geometrical (out-of-plane) polarization of the ring due to the liquid environment. This facilitates bending of the ring along the axis passing through nitrogen atoms. The average bending angle depends largely on the alkyl chain length and slightly on the anion type. Redistribution of electron density over the ring caused by the electron donating alkyl group provides additional independent evidence to the instability of lattice structure, hence the low melting point of the ionic liquid. Simulated viscosity and diffusion coefficients of [bmim]I are in quite agreement with the experiments.

We describe here preparation and performance of an ultra-flexible and low-cost Sb 2 O 3 /polymer composite membrane separator for Na-ion or Li-ion batteries operating with metallic Na or Li anodes. The separator has a large electrolyte window, excellent thermal and mechanical stabilities when infused with EC/DEC/AClO 4 (1M) electrolyte (A = Li or Na), excellent wettability and acceptable ionic conductivity to 1C rate. The ability of the separator to block anode dendrites from crossing it is demonstrated in symmetric alkali-metal cells and in the performances of Na-ion and Li-ion cells with/without loading with Sb 2 O 3 .

The search for fuel cell membranes has focused on carbon backbone polymers, among which Nafion seems to best survive the most severe of the degradation mechanismsattack by peroxide radicals. Less attention has been given to inorganic membranes because of their generally inflexible nature and lower conductivity, though some SiO 2-Nafion composites have shown improved properties. Nafion dominates, despite needing hydration, which then restricts operation to below 100ºC (so CO poisoning problems persist). Described herein is a low cost, flexible, and all-inorganic fiberglass reinforced gel membrane with conductivity exceeding that of Nafion at any temperature above 60ºC. Using Teflon fuel cells, maximum currents >1 Acm-2 and OCV of 1.03 V at 150ºC are demonstrated. No detectable loss of cell potential was observed over 24 hours during 50 mAcm-2 constant current operation at 120ºC while, at 150ºC and maximum power, the degradation rate is intermediate among other high conductivity H 3 PO 4-PBI type membranes. The structure of the membrane is deduced, mainly from 29 Si solid state-NMR. The-115 ppm resonance, which is extreme for Q 4 Si(O) structures, identifies a zeolite-like

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Superacids have been the source of much spectacular chemistry but very little interesting physics despite the fact that the states of cations formed by transfer of the superacid proton to molecular bases can approach that of the cations in free space. Indeed, some of the very strongest acids, such as HPF 6 and HAlCl 4 , have no independent existence due to lack of screening of the bare proton self-energy: their acidities can only be assessed by study of the conjugate bases.Here we show that, by allowing the protons of transient HAlCl 4 and HAlBr 4 to relocate on pentafluoropyridine, PFP (a very weak base that is stable to superacids), we can create glass forming protic ionic liquids (PILs) that are themselves superacids but, being free of superacid vapors, are of benign character. At T g , conductivities exceed "good" ionic liquid values by 9 decades, so must be superprotonic. Anomalous Walden plots confirm superprotonicity.