Publikationen

The determination of phase transition points of nine different ionic liquids (ILs) was performed by thermal
analysis with simultaneous recording of conductivity. Conductivity of electrolyte solutions and ILs
drastically changes during phase transitions and thus is an additional and very sensitive indicator for
measuring phase transition points. Evaluation of temperature–time functions and conductivity–time
functions with our computer-coupled automated equipment enabled the determination of melting temperatures
with high accuracy and reliability. This claim is based on large samples, low temperature
change rates and by regularly repeated measurements, i.e. at least seven measurements per IL. The melting
temperatures of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium
tris(penta-fluoroethyl)trifluorophosphate, and 1-methyl-3-propylimidazolium iodide were, to
our knowledge, determined for the first time. The melting temperatures of the other 1-butyl-1-methylpyrrolidinium-,
1-ethyl-3-methylimidazolium-, 1-hexyl-3-methylimidazolium-, and trimethylsulfonium-
based ILs showed either a very good accordance with values published in literature or were
distinctly higher.

Temperature-dependent conductivity, viscosity, and density of four ionic liquids (ILs), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][NTf2]), and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]), were measured with high precision from +80 °C down to −35 °C, if possible. Fitting parameters for the Vogel−Fulcher−Tammann (VFT) equation were obtained for conductivity and viscosity data, and obtained data were analyzed with the help of the fractional Walden rule and the Walden plot. Excellent linear behavior is observed for all ILs; however, the average slope is not unity as expected for the ideal Walden rule, but 0.92 ± 0.02. The so-called ideal KCl line that is used to compare ILs within the Walden plot is discussed, as literature data for aqueous KCl solutions show that its assumed ideality has to be modified.

Knowledge of the (specific) conductivities (κ) of nonaqueous electrolytes and their liquid range are key issues for the development and optimization of lithium ion batteries. Solidification and melting points of ionic liquids (ILs) cannot be determined easily, as ILs show a tendency toward supercooling, especially when high cooling rates are needed to get useful signals. Therefore, we have developed an integrated computer-controlled measurement apparatus that allows the determination of conductivity and solidification or fusion points as functions of temperature simultaneously for up to 30 samples and at very small cooling rates (as low as 1 K·h−1). The accuracy of the conductivity measurement equipment was analyzed by the error propagation law and by experiments as well. Over the range 5 μS·cm−1 to 5 mS·cm−1, relative uncertainties of better than 2 % of the measured values were achieved. The relative resolution of the conductivity measurements is better than 0.001 times the measured value. A detailed description of our system, including circuitries and error calculations, is given along with some examples of its application in studying liquid electrolyte solutions and ILs.

We investigated the influence that eight ionic liquids (ILs) as additives have on the conductivity and electrochemical stability of lithium salt-based electrolytes. The investigated salts were the well-known lithium hexafluorophosphate (LiPF6), which is the preferred salt for lithium ion batteries (LIBs), and the new salt lithium difluoro(oxalato)borate (LiDFOB). Conductivity studies performed over the temperature range (238.15 to 333.15) K showed a temperature-dependent increase in conductivity caused by several IL additives. The electrochemical stabilities of the solutions were determined at platinum and aluminum electrodes. At the Pt electrode, LiPF6 is the more stable salt, whereas at the aluminum electrode, LiDFOB exhibits a 0.5 V higher potential window in comparison with LiPF6-based solutions. An investigation of the influence of added ILs on the corrosion of aluminum, the current collector material for cathodes of LIBs, did not reveal any adverse effects.

The determination of phase transition points of nine different ionic liquids (ILs) was performed by thermal
analysis with simultaneous recording of conductivity. Conductivity of electrolyte solutions and ILs
drastically changes during phase transitions and thus is an additional and very sensitive indicator for
measuring phase transition points. Evaluation of temperature–time functions and conductivity–time
functions with our computer-coupled automated equipment enabled the determination of melting temperatures
with high accuracy and reliability. This claim is based on large samples, low temperature
change rates and by regularly repeated measurements, i.e. at least seven measurements per IL. The melting
temperatures of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium
tris(penta-fluoroethyl)trifluorophosphate, and 1-methyl-3-propylimidazolium iodide were, to
our knowledge, determined for the first time. The melting temperatures of the other 1-butyl-1-methylpyrrolidinium-,
1-ethyl-3-methylimidazolium-, 1-hexyl-3-methylimidazolium-, and trimethylsulfonium-
based ILs showed either a very good accordance with values published in literature or were
distinctly higher.

Plating-stripping and corrosion tests have been carried out at electrolyte soln. contg. lithium difluoro(oxalato)borate (LiDFOB) as a lithium salt. For comparison, also electrolytes contg. other common borate salts have been investigated. After these tests, the same electrolyte solns. have been used in combination with lithium iron phosphate base electrodes at RT. The results of these studies are reported in this paper.

Temperature-dependent conductivity and viscosity data of over ten new fluoroborate-based ionic liquids (ILs) were measured in a temperature range spanning about 100 K. Data are presented and evaluated according to the fractional Walden rule and Angell’s fragility concept. All ILs show excellent linear relationships for their Walden plots with similar slopes in the range from about 0.90 to about 0.94. It was found empirically that the slopes of the Walden plots reflect the ratio of the corresponding Arrhenius activation energies for the ILs’ temperature-dependent viscosities and molar conductivities. Further analysis of viscosity data of ILs leads to the conclusion that all investigated ILs, including some more common ones, can be classified as highly fragile, very weak liquids, reaching even the limiting value estimated by Vilgis.

The hydrolysis of lithium bis[1,2-oxalato(2-)-O,O] borate (LiBOB) was investigated in pure water and in solutions of acetonitrile at low water content. The reaction in pure water can easily be observed by time-dependent conductivity measurements as protons are generated in the first step of hydrolysis. The results of these measurements can be evaluated according to a reaction of pseudo first order. Hydrolysis of other lithium borates in water was also studied for comparison. In acetonitrile as solvent, hydrolysis is much more complicated. NMR studies show a very slow reaction of LiBOB with water resulting in equilibria, depending on the water content of acetonitrile. Temperatures of 60 °C and water contents of several percent are necessary to achieve observable effects.

In this work the conductivities of LiAlCl4 in dilute sulfur dioxide solutions were measured in the temperature range 238.15 K to 288.15 K. The major challenge of these measurements was the handling of the very water sensitive salt LiAlCl4 and the formulation of sulfur dioxide solutions at low salt concentrations. These low concentration solutions are needed to obtain association constants of the salt and thermodynamic parameters using the low concentration chemical model developed by J. Barthel. The viscosities of liquid sulfur dioxide were also measured in the temperature range 231.46 K to 257.98 K. Unexpectedly, the determined association constants of LiAlCl4 in liquid sulfur dioxide are very small ranging from 42 at 238.15 K to 354 dm3 mol1 at 288.15 K. This result shows that the lithium-ion solvent interaction is much stronger when compared with the interaction of the lithium-ion with the weakly coordinating anion tetrachloroaluminate, in contrast to lithium halides in liquid sulfur dioxide where association constants up to 96000 dm3 mol1 are observed.

Keywords: Non aqueous solutions, electric conductivity, lithium tetrachloroaluminate, ion association, sulfur dioxide

In this work we synthesized two novel salts for electrochemical double layer capacitors, i.e. N,N-dimethylpyrrolidinium tetrakis(trifluoroacetato)borate (DMPBTFAc) and N-ethyl-N-methyl-pyrrolidinium bis[1,2-oxalato(2-O,O)]borate (EMPBOX), and determined the electrochemical window of their solutions in acetonitrile (AN) by using stepwise cyclic voltammetry. The electrochemical window plays an important role in electrochemical double layer capacitors (EDLCs) as the energy density of such devices depends on the square of the operating voltage. Because anodic and cathodic decomposition voltages may be shifted with respect to the open circuit voltage (OCV), the OCV is another important characteristic of such an electrolyte. Both DMPBTFAc and EMPBOX solutions show wide electrochemical windows of about 4 V with nearly equal voltage gaps for the anodic and cathodic decomposition at activated carbon electrodes.

Keywords: Double layer capacitor, EDLC, DLC, electrochemical window, cyclic voltammetry, Faradaic Fraction

Chloride avoided! A new chloride-free method to synthesise ionic liquids (ILs) with mixed borate anions, starting from tetrafluoroborate compounds, has been developed and a number of examples including some new ILs are presented (see scheme; [CAT] =cation). It is widely applicable and allows access to mixed borates with various types of ligands in a straightforward manner.

Poly(aniline) was synthesized by electrochemical oxidation from phosphoric acid at concentrations from 0.1 mol/L up to 7 mol/L in an electrochemical quartz crystal microbalance (EQCM) equipped cell in a three-electrode configuration. Deposition processes were monitored by a recently introduced fast impedance-scanning quartz crystal microbalance to determine the optimal concentration for most effective electropolymerization parameters.

Keywords: impedance scanning quartz crystal microbalance, EQCM, polyaniline, electrodeposition, H3PO4

We studied melting and solidification points of 14 pure solvents and two ionic liquids with a recently constructed automatic computer-controlled equipment, which is able to simultaneously record temperature time functions of up to 30 samples at very low heating and cooling rates down to 1.5 K h-1. The effects of viscosity of the studied samples and of carbon fibres as an added crystallisation aid were also investigated. Equilibrium temperatures for the solid-liquid phase transition are in accordance with literature for materials that were often checked - such as acetonitrile - showing the quality of our new equipment, whereas values of some other materials differ from published results. It is shown that both, the viscosity o the material and carbon fibres as crystallisation aids have an effect on supercooling. The given value for the equilibrium point of the ionic liquid trioctylmethylammonium trifluoracetate (285.62 ? 0.1) K is new.

Keywords: Phase transition points; Organic solvents; Ionic liquids; Crystallisation aids; Fast computer-controlled equipm

A comprehensive characterisation of an ionic liquid based electrolyte for dye-sensitised solar cells (DSSC) was performed by determination of triiodide diffusion coefficients, viscosities and photovoltaic performances. The electrolyte, consisting of 1-ethyl-3-methylimidazolium dicyanamide, 1-methyl-3-propylimidazolium iodide (MPII), and iodine, was examined at varying ionic liquid molar ratio and fixed iodine concentration, as well as at fixed ionic liquid molar ratio and varying iodine concentration. All measurements were conducted at controlled temperature over a broad temperature range to analyse the electrolyte properties in view of thermal stress of the DSSC during later practical application. The triiodide diffusion coefficient increases with decreasing MPII concentration or increasing temperature, caused by decreasing electrolyte viscosity. Additionally, strong non-Stokesian behaviour over the whole ionic liquid mixing range was found, decreasing at higher temperatures. Photovoltaic measurements showed that the DSSC efficiency is limited by triiodide diffusion at low temperatures and low iodine concentrations whereas at high temperatures it is limited by recombination processes, leading to a maximum for DSSC efficiency at a certain temperature. The exchange between diffusion limitation of DSSC efficiency and limitation by recombination and therefore the maximum for DSSC efficiency is shifted to lower temperatures by increasing iodine concentration.

Keywords: Ionic liquid electrolyte, Dye-sensitised solar cell, Diffusion coefficients, Photovoltaic performance

In this paper, we report on the outcome of a German network project conducted with 12 partners from universities and research institutes on the material development of dye solar cells (DSC). We give an overview in the field and evaluate the concept of monolithic DSC further with respect to upscaling and producibility on glass substrates. We have developed a manufacturing process for monolithic DSC modules which is entirely based on screen printing. Similar to our previous experience gained in the sealing of standard DSC, the encapsulation of the modules is achieved in a fusing step by soldering of glass frit layers. For use in monolithic DSC, a platinum free, conductive counter electrode layer, showing a charge transfer resistance of RCT < 1?5 Omega cm2, has been realized by firing a graphite/carbon black composite under an inert atmosphere. Glass frit sealed monolithic test cells have been prepared using this platinum-free material. A solar efficiency of 6% on a 2?0 cm2 active cell area has been achieved in this case. Various types of non-volatile imidazolium-based binary ionic liquid electrolytes have been synthesized and optimized with respect to diffusion-limited currents and charge transfer resistances in DSC. In addition, quasi-solid-state electrolytes have been successfully tested by applying inorganic (SiO2) physical gelators. For the use in semi-transparent DSC modules, a polyol process has been developed which resulted in the preparation of screen printed, transparent catalytic platinum layers showing an extremely low charge transfer resistance (0?25 Omega cm2). Copyright ¦ 2008 John Wiley & Sons, Ltd.

The diffusion coefficients of triiodide in binary mixtures of ionic liquids at 25 °C were determined via steady-state cyclic voltammetry at platinum disk microelectrodes in five different electrolyte systems, all representing potential ionic liquid based electrolytes for dye-sensitised solar cells. These electrolytes were composed of iodine, 1-methyl-3-propylimidazolium iodide (acting as iodide source) and a second lower viscous ionic liquid, namely 1-ethyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and were investigated either at fixed ionic liquid composition and varying iodine concentration or at fixed iodine concentration and varying 1-methyl-3-propylimidazolium iodide content. To check and optimise our measurement set-up, four Pt disk microelectrodes with four different electrode radii (0.3?5?m) were tested at a well known system (ferrocene/tetraethylammonium tetrafluoroborate/acetonitrile solutions). The radius of each electrode was controlled by scanning electron microscopy at the beginning and during the work.

Data on temperature and concentration dependence of conductivities of some new ionic liquids based on the reduced symmetry of the semichelato-borate anion are presented and compared to data for the corresponding symmetrical chelato-borate and tetrafluoroborate salts. The compounds under investigation are the semichelato-borates tetraethylammonium difluoromono[1,2-oxalato(2-)-O,O?]borate, ([TEA][BF2OX]) and the new 1-ethyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O?]borate, ([EMIM][BF2OX]), the chelato-borates tetraethylammonium bis[1,2-oxalato(2-)-O,O]-borate, ([TEA][B(OX)2]) and the new 1-ethyl-3-methylimidazolium bis[1,2-oxalato(2-)-O,O]borate, ([EMIM][B(OX)2]) and the well known tetrafluoroborates, tetraethylammonium tetrafluoroborate, ([TEA][BF4]), and the 1-ethyl-3-methylimidazolium tetrafluoroborate, ([EMIM][BF4]). The concentration dependence of conductivities of [TEA][BF2OX], [EMIM][BF2OX], [TEA][B(OX)2], [EMIM][B(OX)2], [TEA][BF4] and [EMIM][BF4] in pure acetonitrile were measured at 25 °C, 5 °C, -15 °C, and -35 °C, and fitted to the Casteel-Amis equation. Data presented in this work should clarify the influence of reduced symmetry caused by the substitution of two fluorine atoms by the oxalate moiety in the borate anion on its conductivity behavior, especially at low temperatures.

According to literature, binary mixtures of ionic liquids (ILs) such as 1-methyl-3-propylimidazolium iodide (MPII) as an iodide source and another IL of low viscosity such as 1-ethyl-3-methylimidazolium thiocyanate (EMISCN) may be used to increase the diffusion coefficients of redox-active species (I-/I3 -). As dye-sensitized solar cells (DSCs) are diffusion limited a better performance may result with blends when compared to cells based on MPII alone. In order to learn more about EMISCN and its blends with MPII, we electrochemically characterized this IL and measured diffusion coefficients of triiodide in binary mixtures containing EMISCN by polarization and impedance studies at thin layer cells with a distance between Pt-electrodes of about 30 to 40 m. The electrochemical windows of the used ILs were measured by cyclic voltammetry (CV) and compared to those of other ILs, recently investigated by us.

Keywords: dye-sensitized solar cell, ionic liquids, electrochemical stability, diffusion measurement, cyclic voltammetry

An impedance system for QCM measurements is described which produces a much higher information content than existing oscillator methods. The new system is favourably priced, and fits on a small single printed circuit board. The use of a personal computer with a dedicated software algorithm enables fast fitting of the collected data and allows high flexibility without the need of a change in hardware. It was shown that this QCM device is able to collect stable and high-quality data with the ? in electrochemistry not very commonly used ? small and very inexpensive 0.55 inch diameter quartz devices, even under heavy load. A full spectrum containing serial and parallel resonance frequencies, with a band width of 20 kHz can be scanned within 200 ms at a resolution of 0.2 Hz. Lowering requirements, e.g. by scanning series resonance frequency only, the acquisition time can be reduced drastically. The EQCM so developed was checked using known electrochemical tasks such as copper deposition, dissolution and the electropolymerization of aniline.

Keywords: Impedance, Quartz microbalance, Linear data fit algorithm, Copper electrodeposition and dissolution, Electropolymerization of aniline

We investigated 13 additives well known from literature and studied their effect on the performance of lithium ion cells comprised of electrolytes based on lithium bis[1,2-oxalato(2-)-O,O] borate. The additives can be attributed to three classes including chemically modified solvents, metal salts, and oligoethers. In contrast to similar studies in literature, where often only a single additive was investigated, the effect of 13 additives was studied under the same conditions at cells cycled up to 500 times at 60°C in a thermostat. The internal resistance of the cells and the charge capacity of cells are reported. Whereas tetra ethylene glycol dimethyl ether showed the best performance, increasing the lifetime of cells by a factor of five and doubling the cell capacity after 500 cycles other additives did show no effect or even deteriorated the cell performance.

Keywords: Lithium-ion battery, cycling, additive, lithium bis[1,2-oxalato(2-)-O,O] borate

A new, extremely simple concept for the use of energy transfer as a means to the enhancement of light absorption and current generation in the dye solar cell (DSC) is presented. This model study is based upon a carboxy-functionalized 4-aminonaphthalimide dye (carboxy-fluorol) as donor, and (NBu4)2[Ru(dcbpy)2(NCS)2] (N719) as acceptor chromophores. A set of three different devices is assembled containing either exclusively carboxy-fluorol or N719, or a mixture of both. This set of transparent devices is characterized via IV-measurements under AM1.5G and monochromatic illumination and their light-harvesting and external quantum efficiencies (LHE and EQE, respectively) are determined as well. It is shown that the device containing only the donor chromophore has a marginal power conversion efficiency, thus indicating that carboxy-fluorol is a poor sensitizer for the DSC. Cyclovoltametric measurements show that the poor sensitization ability arises from the kinetic inhibition of electron injection into the TiO2 conduction band. Comparing the spectral properties of the DSCs assembled presently, however, demonstrates that light absorbed by carboxy-fluorol is almost quantitatively contributing to the photocurrent if N719 is present as an additional sensitizer. In this case, N719 acts as a catalyst for the sensitization of TiO2 by carboxy-fluorol in addition to being a photosensitizer. Evaluation of the maximum output power under blue illumination shows that the introduction of an energy-donor moiety via coadsorption, leads to a significant increase in the monochromatic maximum output power. This result demonstrates that energy transfer between coadsorbed chromophores could be useful for the generation of current in dye-sensitized solar cells.

This paper describes a fast multichannel precision thermometer working in a temperature range from -50 °C to 40 °C. Thermistors are used as temperature sensing elements. A detailed discussion of the choice of thermistor and design of the circuitry is given. It is shown that accuracy similar to that of calibrated platinum thermometers can be achieved by calibration of thermistors. During our tests, the accuracy of the thermometer was both mathematically and experimentally analyzed in detail. The stability of 30 thermistors after six months of laboratory use was analyzed. Deviations smaller than 30 mK in the range from -50 °C to 10 °C were observed.

Keywords: NTC, precision thermometry, resistance thermometer,
temperature measurement, temperature sensor, thermistor, thermometer

Three ionic liquids with borate anions of low symmetry, tetraethylammonium difluoromono[1,2-oxalato(2-)-O,O']borate, 1-ethyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O']borate, and 1-butyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O']borate were synthesised and characterised by physicochemical and electrochemical measurements including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), cyclic voltammetry (CV), viscosity and conductivity measurements.

Keywords: Ionic liquids, Difluoroborates, Low symmetry, Bidentate ligands, Synthesis, Melting point, Thermal analysis, Viscosity, Electrochemical window, Conductivity

The conductivity of ion conductors in cells is the best studied key property for the performance of lithium ion cells. It determines voltage drop, power density as well as heat evolution. The best choice for a method useful for optimizing the conductivity would be a theoretical approach. However, no such method is available. According to Tarascon and Armand Guided by general concepts of viscosity and dielectric constants, optimizing the ionic conductivity of a liquid electrolyte becomes a field trial approach with the hope of finding the key ingredients. As a consequence, numerous scientists performed experimental studies based on some empirical rules. We hope that we have shown the benefits of a more efficient method.

At platinum electrodes kinetics of the I-/I-3(-) electrode reaction were studied at two potential electrolyte systems for dye-sensitized solar cells (DSSCs) based on binary ionic liquid (IL) blends, i.e., 1-ethyl-3-methylimidazolium dicyanamide ([EMIM] [N(CN)(2)])/1-methyl-3-propylimidazolium iodide ([PMIM]I) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM] [BF4])/[PMIM]I, respectively. The charge transfer resistances of the electrode reaction were determined via impedance spectroscopy for electrolyte blends at a mixing ratio of ILs of 9 mol % [PMIM]I (for [EMIM][N(CN)(2)]/[PMIM]I) and 10 mol % [PMIM]I (for[EMIM][BF4]/[PMIM]I) up to 100 mol % [PMIM]I. In addition, the influence of iodine concentration on the electrode reaction was investigated for both electrolyte systems. The measurements were taken in a temperature range of 25 to 60 degrees C to analyze the electrolyte properties in view of thermal stress of the DSSC for later practical application. Furthermore, exchange current densities were determined: the expected Arrhenius behavior was observed. Activation energies were obtained by fitting linearized Arrhenius plots.

Keywords: electrolytes; solar cells; electrochemical electrodes; charge exchange; electrochemical impedance spectroscopy; thermal stresses; current density

In this article details of the synthesis, anal., purifn., and electrochem. properties of 1-ethyl-3-methylimidazolium bis[1,2-oxalato(2-)-O,O']borate (EMIBOX) are reported. The concn. dependence of conductivities of EMIBOX in non-aq. pure solvents and blends of solvents were measured at 25 Deg C, 5 Deg, 15 DegC, and 35 Deg C, and fitted to the Casteel-Amis equation. Cyclic voltammetry showed a high anodic voltage limit of more than 4.9V vs. Li/Li sufficient for charging/discharging double-layer capacitor modules over the potential range 0 V to 2.5V. Capacitors employing cloth-type carbon electrodes, filled with solns. of EMIBOX based on pure solvents and solvent blends were submitted to cycling up to 100,000 cycles, and measurements of impedance spectroscopy, open-circuit voltage and voltage decay were made. The salt may be a useful substitute for fluorine-contg. salts such as tetraethylammonium tetrafluoroborate, at least at ambient and higher temps.

Electroplating of Dy from several nonaq. solns. and from an ionic liq. was studied. Dy metal was used as the anode material, and several metals and a Si wafer with a vacuum-deposited Au layer were used as cathode materials. Dy was successfully electroplated from DMF-based solns. with high coulombic efficiency. The resulting Dy layer was effectively protected vs. reactions with H2O and oxygen from air by electroplating an Al layer onto Dy from a nonaq. electrolyte. All processes were studied by electrochem. methods including cyclic voltammetry, chronoamperometry, chronopotentiometry, and with the help of an electrochem. quartz microbalance coupled to an Autolab PGSTAT30 controlled by the GPES software. A nonaq. ref. electrode developed by Izutsu was applied; the diffusion potential was kept low by a slight modification of his original proposal. X-ray fluorescence spectroscopy was used to verify electroplating of Dy. The presence of metallic Dy was also confirmed by superconducting quantum interference device magnetometry which showed a ferromagnetic moment at 5 K.

Keywords: electroplating dysprosium magnetic property

Results of diffusion coeff. measurements of triiodide in a mixt. of 2 ionic liqs. (1-methyl-3-propylimidazolium iodide and 1-butyl-3-methylimidazolium tetrafluoroborate) at 25 Deg are described. Four electrochem. methods for measuring diffusion coeffs. of triiodide were evaluated for their reliability and performance, including impedance spectroscopy and polarization measurements at thin layer cells as well as cyclic voltammetry and chronoamperometry at microelectrodes of different radii. Viscosities of the blends were measured to study the transport behavior of triiodide ions used in Graetzel-type dye-sensitized solar cells.

Keywords: electrochem detn triiodide diffusion binary ionic liq

Trialkylsulfonium dicyanamides show surprisingly low viscosities down to -20 degrees C and are therefore highly interesting liquid materials for separation processes and electrolyte applications at low temperatures.

Keywords: Trialkylsulfonium dicyanamides

Cond. optima of battery electrolytes can be detd. with the help of cond. measurements guided by a program based on a simplex algorithm. The method was successfully checked by one with data from literature. Cond. measurements at -25 DegC for lithium bis[1,2-oxalato(2-)-O,O']borate (LiBOB) in various solvent blends were performed, where suggestions from this program for the compn. of solvent and salt concn. were applied. Data for cond. measurements at 25 and at -25 DegC for several blends of LiBOB in ethylene carbonate (EC)/propylene carbonate (PC)/dimethyl carbonate (DMC), in EC/PC/DMC/ethyl Me carbonate (EMC), EC/PC/DMC/ethyl acetate (EA), and EC/PC/DMC/EMC/EA are given.

Keywords: cond battery electrolyte simplex optimization algorithm

Karl Fischer titrn. is the std. method for the detn. of the H2O content in many materials. However, in some cases unwanted side reactions occur which leads to unacceptably large errors. A NMR-based method for the detn. of trace amts. of H2O in a salt was developed for Li-ion batteries contg. lithium bis(oxalato)borate (LiBOB). This method may be applied to many Li salts used in batteries and it can det. traces of H2O in a salt down to .apprx.6 ppm. Errors depend on the salt studied. Deviations from expected values obtained by std. addn. were 28% for LiBOB, 4% for LiPF6, and 6% for LiClO4. Using the error propagation law, the overall error is .apprx.10%.

Keywords: water lithium salt electrolyte proton NMR lithium battery

Two new Li chelatophosphates were synthesized, purified, and characterized, Li tris[3,4,5,6-tetrafluor-1,2-benzenediolato(2-)-O,O']-phosphate(1-) and Li tris[3-fluoro-1,2-benzenediolato(2-)-O,O']-phosphate(1-). A precursor, the corresponding acid of Li tris[3,4,5,6-tetrafluor-1,2-benzenediolato(2-)-O,O']-phosphate(1-), H [P(C6F4O2)3]-, presumably a super acid, shows a hexacoordinated phosphorous in x-ray anal., when solvated by two Et2O mols. The anodic oxidn. limits of benzenechelatoborates and -phosphates are closely related to the energy of the HOMO from semiempirical quantum-mech. calcns. with the help of QuantumCache and MOPAC 2002, yielding EHOMO = -(3.70 - 0.26)*EOX( 8.4 - 1.0).

Keywords: lithium chelatophosphate prepn structure cyclic voltammetry; crystal structure hydrogen fluorobenzenediolato phosphate super acid; anodic oxidn lithium fluorobenzenediolato phosphate; elec cond lithium tetrafluorbenzenediolato phosphate