We introduce here a novel in situmeasurement method for solubility of solids in various liquids. Without any calibration the saturation point can be obtained in a relative manner. We exemplified the new method at four systems including water, organic carbonates and an ionic liquid as the solvents and various salts as dissolved solids.

The salt lithium difluoromono(oxalato)borate (LiDFOB) showed some promising results for lithium-ion-cells. It was synthesized via a new synthetic route that avoids chloride impurities. Here we report the properties of its solutions (solvent blend ethylene carbonate/diethyl carbonate (3:7, mass ratio), including its conductivity, cationic transference number, hydrolysis, Al-current collector corrosion-protection ability and its cycling performance with some electrode materials. Some Al-corrosion studies were also performed with the help of our recently developed computer controlled impedance scanning electrochemical quartz crystal microbalance (EQCM) that proofed to be a useful tool for battery material investigations.

We add a new method to previously used approaches in corrosion research of copper by applying a direct measurement method for adsorption kinetics which is able to directly monitor in-situ adsorption. For our study we selected a well known system for that: copper surfaces and benzotriazole (BTA) dissolved in methanol. Measurements were performed with our recently developed impedance scanning quartz crystal microbalance (QCM). Time dependence of its serial resonance frequency can be used to study the kinetics of adsorption by fitting the measured adsorption curve to the Langmuir adsorption isotherm. The free adsorption energy ΔGads determined by this approach is in accordance with results from literature determined by other electrochemical methods showing that our approach yields reliable results.Research Highlights► Adsorption is a well known measure to prevent metals from corroding. ► We examined adsorption of benzotriazole at copper surfaces. ► A new impedance scanning quartz crystal microbalance was used for these studies. ► Obtained thermodynamic results are in accordance with results from literature. ► Kinetics of adsorption can also be studied via this novel method.

We report here on comparative measurements of cationic transference numbers of some lithium battery related electrolytes including lithium tetrafluoroborate in propylene carbonate, lithium hexafluorophosphate in blends of ethylene carbonate/diethyl carbonate and ethylene carbonate/propylene carbonate/dimethyl carbonate, as well as lithium difluoromono (oxalate) borate in an ethylene carbonate/diethyl carbonate blend via four different methods. Whereas three electrochemical methods yield transference numbers decreasing with concentration in accordance with electrostatic theories, valid for low to intermediate concentrations of the electrolyte, nuclear magnetic resonance spectroscopy measurements show increasing transference numbers with increasing concentration. The discrepancy is attributed to effects of ion–ion and ion–solvent interaction.Research highlights► Lithium ion transference numbers (t+) of lithium battery related electrolytes are studied. ► Four recently used methods for measuring t+ are compared. ► Electrochemical methods yield Li+ transference numbers decreasing with concentration and are in agreement with electrostatic theories. ► In contrast, NMR measurements show increasing Li+ transference numbers with increasing concentration. ► The discrepancy is attributed to effects of ion–ion and ion–solvent interaction.

Several properties of the electrolyte solution lithium difluoromono(oxalato)borate (LiDFOB) in ethylene carbonate diethylcarbonate (EC/DEC (3:7 mass ratio)) are given, including transference numbers, diffusion coefficients, concentration dependence of cell potentials, and the Haven ratio. The concentration range of the salt covers 0.1 mol·kg–1 to 1.0 mol·kg–1. In comparison to the standard salt LiPF6 currently in use in lithium ion cells LiDFOB has higher transference numbers. However, the Haven ratio related to ion pair formation in an electrolyte indicates a high amount of aggregates in concentrated LiDFOB/EC/DEC (3:7) electrolytes.

Thermometers with temperature resolutions of equal or better than 1 mK typically make use of platinum wire temperature sensors such as the PT100. Alternating current techniques to read out these fairly low dynamic temperature sensors are complex and expensive and act slowly. This work shows that it is possible to build up a thermometer with even higher resolution up to 75 μK, capable of delivering a data-rate of up to ten readouts per second by means of negative temperature coefficient sensors. We selected the measurement of two binary solid–liquid phase diagrams (biphenyl/naphthalene and biphenyl/benzophenone) to check the presented equipment.

Triiodide diffusion coefficients were determined in two ionic liquid based electrolyte systems for dye-sensitized solar cells. The electrolytes comprised iodine, 1-methyl-3-propylimidazolium iodide ([MPIM][I]), and either 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Determination of triiodide diffusion coefficients was performed by two independent methods, steady-state cyclic voltammetry at ultramicroelectrodes and polarization measurements at thin layer cells, both temperature-dependent and over a broad mixing range with varying ionic liquid molar ratios. The triiodide diffusion coefficients strongly increase with increasing temperature and therefore decreasing electrolyte viscosity. However, the triiodide diffusion coefficients stay almost constant with decreasing [MPIM][I] mole fraction or they even have a maximum at high [MPIM][I] mole fractions and therefore high viscosities. The Einstein–Stokes ratios for both systems strongly increase with increasing [MPIM][I] mole fraction. So as the Einstein–Stokes equation is not obeyed, a strong non-Stokesian charge transport can be assumed to occur in both electrolyte systems.

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.

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 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.

A comprehensive characterization of an ionic liquid based electrolyte for dye-sensitized solar cells (DSSC) was performed by determination of triiodide diffusion coefficients, viscosities, specific conductivities, and densities. The observed non-Stokesian transport behavior was ensured by determination of triiodide diffusion coefficients with two independent methods, steady-state cyclic voltammetry at ultramicroelectrodes, and polarization measurements at thin layer cells. The electrolyte, consisting of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-methyl-3-propylimidazolium iodide ([MPIM][I]), and iodine, was examined at fixed iodine concentration over a broad mixing range with varying ionic liquid molar ratio and over a broad temperature range as well. The triiodide diffusion coefficients and the specific conductivity increase with decreasing [MPIM][I] mole fraction or increasing temperature, caused by decreasing electrolyte viscosity. The Einstein−Stokes ratios strongly increase with increasing [MPIM][I] mole fraction and viscosity and thus do not obey the Einstein−Stokes equation. The magnitude of this strong non-Stokesian behavior decreases with increasing temperature. Additional non-Stokesian behavior was found for [MPIM][I]-rich blends since for these blends the Einstein−Stokes ratios strongly decrease at increasing temperatures and simultaneously decreasing viscosity.

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 record simultaneously 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 the value of the transition temperature of some other materials differed from published results. It is shown that both the viscosity of the material and carbon fibres as crystallisation aids have an effect on supercooling. The value given for the equilibrium point of the ionic liquid trioctylmethylammonium trifluorocetate Ttr = (285.62 ± 0.1) K is new.

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.Substitution of the [BF4]− anion by [BF2Ox]− in [NEt4]+ salts leads to a significant decrease of the melting point proving that ionic liquids can be also based on reduced symmetry of the anion even if the cation is highly symmetrical.

Results of diffusion coefficient measurements of triiodide in a mixture of two ionic liquids (1-methyl-3-propylimidazolium iodide and 1-butyl-3-methylimidazolium tetrafluoroborate) at 25 °C are described in this paper. Four electrochemical methods for measuring diffusion coefficients 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 investigate the transport behaviour of triiodide ions used in Grätzel-type dye-sensitized solar cells.

We introduce here a novel in situmeasurement method for solubility of solids in various liquids. Without any calibration the saturation point can be obtained in a relative manner. We exemplified the new method at four systems including water, organic carbonates and an ionic liquid as the solvents and various salts as dissolved solids.