LiAsF6 Solutions Research Articles

LiAsF6 SOLUTIONS IN THE MIXED SOLVENTS OF PROPYLENE CARBONATE – DIMETHYL SULFOXIDE: ELECTRIC CONDUCTIVITY AND ELECTROCHEMICAL STABILITY

The specific conductivities of LiAsF6 solutions in a mixed solvent of propylene carbonate (PC) –dimethyl sulfoxide (DMSO) were measured at temperatures of 253.15, 263.15, 273.15, 283.15, 293.15, 303.15, 313.15, 323.15 and 333.15 K being a ionophore concentration of 0.2 to 1.4 mol / kg. The portion of DMSO in the mixed solvent was varied in the range of (0.2 - 0.75) mole fractions. The specific conductivities of LiAsF6 in DMSO were studied in the temperature range of (293.15 – 333.15) K. Concentration dependences of specific conductivity of the system can be described by the Casteel-Amis equation. The contributions of the solvent and ionophore to the activation energy of the ionic conduction process are determined on the base of the transition state theory. It has been found that the LiAsF6 solutions in a mixed PC – DMSO solvent have a narrower electrochemical window compared to the solutions of this ionophore in pure PC and DMSO solvents.

LiAsF6 Solutions in the Propylene Carbonate–Dimethylsulfoxide Mixed Solvent: The Conductivity and Electrochemical Stability

LiAsF6 Solutions in the Propylene Carbonate–Dimethylsulfoxide Mixed Solvent: The Conductivity and Electrochemical Stability

Electrical Conductivity and Decomposition Potentials of the LiAsF6 Solutions in the Propylene Carbonate–N,N-Dimethylformamide Mixed Solvent

Electrical Conductivity and Decomposition Potentials of the LiAsF6 Solutions in the Propylene Carbonate–N,N-Dimethylformamide Mixed Solvent

Electrochemical Properties of LiAsF6 Solutions in Propylene Carbonate—Acetonitrile Binary Mixtures

Conductivity of LiAsF6 solutions in propylene carbonate—acetonitrile binary mixtures containing 0.2 to 1.4 mol/kg of ionophore is measured at temperatures of 283.15, 293.15, 303.15, and 313.15 K throughout the mixed solvent entire composition range. Concentration dependences of the system’s conductivity can be described by the Casteel—Amis equation, except the lithium hexafluoroarsenate solution in acetonitrile. The activation energy of the charge transfer process in the studied solutions is determined; the LiAsF6 solution in acetonitrile has the lowest activation energy. From conductometry measurements in dilute solutions, the electrolyte limiting molar conductivity is calculated using the Lee—Wheaton equation. The LiAsF6 ionic association in the propylene carbonate—acetonitrile mixtures with the acetonitrile mole fraction from 0.2093 to 0.9006 is not observed; the salt is fully dissociated over this concentration range. The electrochemical stability range for 0.5 mol/kg LiAsF6 in the propylene carbonate—acetonitrile mixture was determined by means of voltammetry at 298.15 K. The decomposition potentials in the cathodic region are due to lithium electro-deposition; they depend on ion—molecule and intermolecular interactions in the system; the anodic decomposition potentials are associated with the solvent oxidation.

An ion-selective potentiometric sensor for hexafluoroarsenate

Ion-selective potentiometric sensors (ion selective electrodes, ISEs) based on tetradecylphosphonium hexafluoroarsenate are developed for the determination of AsF6− ions. Their main parameters, such as selectivity, linearity range of response, detection limit, and also the effect of pH on the readings of electrodes are evaluated. The developed electrode demonstrated high selectivity to the AsF6− acido-complex in the presence of various anions. The detection limit goes up with increasing concentration of HF; for fluoridefree neat solutions of LiAsF6, it is 3 × 10−7, pAsF6 = 6.52; at the concentrations of HF 0.1 and 4 M, it is 1.5 × 10−6 M, pAsF6 = 5.82, and 7 × 10−6 M, pAsF6 = 5.15, respectively.

Electrochemical properties of LiAsF6 solutions in low-polar aprotic solvents

The electrochemical behavior of the concentrated solutions of lithium hexafluoroarsenate in tetrahydrofuran and methyl acetate, having low dielectric constants, was studied. Their high specific conductivity compared with solutions of this ionophore in highly polar solvents (propylene carbonate, γ-butyrolactone) may be due to the additional contribution from the charge transfer by the ionotropic mechanism. Voltammetric curves were obtained on a platinum electrode for LiAsF6 solutions in tetrahydrofuran and methyl acetate. The efficiency of lithium cycling in the systems was evaluated.

Effect of ultrasound on transport properties of nonaqueous solutions of lithium hexafluoroarsenate

The speed of ultrasound in solutions of LiAsF6 in propylenecarbonate and γ-butyrolactone was measured with an ultrasonic laser interferometer over a concentration range from 0.076 to 1.2 mol/kg at 273, 288, 298, 308, and 313 K. The solvation number h and molar adiabatic compressibility of the solvation complexes (βS,hVh) of LiAsF6 in propylenecarbonate and γ-butyrolactone were determined at concentrations typical of lithium batteries. Linear correlations between the molar physicochemical parameters of liquid-phase systems (time of propagation of ultrasound, fluidity, and electric conductivity) were established.

Temperature dependence of transport properties and ion-molecular forms of LiAsF6 in γ-butyrolactone

The solvation and association electrolyte interactions are analyzed in the concentration range of 0–2 m at temperatures of 253.15–313.15 K using measurements of the conductivity and viscosity of LiAsF6 solutions in γ-butyrolactone (γ-BL). Concentrated LiAsF6 solutions in γ-BL are considered as molten electrolytic solvates, whose transport processes are considerably influenced by a cooperative restructuring of the system. The concentration dependence of the molar conductivity is linear in the λ vs. c 1/3 coordinates, which agrees with a theory of quasi-crystalline electrolyte lattice in solution. The Lee–Wheaton model is used to determine the limiting molar conductivities, distance parameters, and association constants and their temperature dependences. The size of solvate spheres increases with decreasing temperature and their overlapping occurs at lower concentrations.

X-ray Photoelectron Spectroscopy Study of Surface Films Formed on Li Electrodes Freshly Prepared in Alkyl Carbonate Solutions

Li samples were freshly prepared (shearing) and stored (2 days) in dimethyl carbonate (DMC), and ethyl carbonate−diethyl carbonate (EC−DEC), and dry (20 ppm of H2O) and wet (500 ppm of H2O) EC−DMC solutions of LiAsF6 (1 M), and were then studied by X-ray photoelectron spectroscopy (XPS). The XPS analysis, including depth profiling of these surface films, appears to be reliable on the qualitative level only, because both the X-ray beam and sputtering should be suspected as being partially destructive to the surface films on lithium. These studies basically confirm previous conclusions obtained by Fourier transform infrared spectroscopy spectroscopic studies of Li surfaces. Surface films formed on Li in alkyl carbonate solutions of LiAsF6 are comprised of ROCO2Li, Li2CO3, LiF, LixAsFy, and Li oxides. XPS could also detect surface species with Li−C bonds (e.g., LiCH2CH2OCO2Li). When EC is present, its reduction dominates the surface film formation. The presence of water suppresses both solvent and salt anion reduction and enriches the surface films with Li2CO3 (because of secondary reactions of water with surface species), LiOH, and Li2O. These studies also confirm that the surface films formed on Li have a multilayer structure.

Speed of Sound, Densities, and Viscosities for Solutions of Lithium Hexafluoroarsenate in Tetrahydrofuran at 283.15, 298.15, and 313.15 K

Speed of sound, viscosity, and density have been measured for solutions of LiAsF6 in tetrahydrofuran over a wide range of concentrations at temperatures from 283.15 K to 313.15 K.

The application of EQCM to the study of the electrochemical behavior of propylene carbonate solutions

The electrochemical behavior of gold electrodes in propylene carbonate (PC) solutions was investigated using an electrochemical quartz crystal microbalance (EQCM). The solutions studied included uncontaminated LiAsF6 and LiPF6 solutions, and CO2 and H2O-containing LiAsF6 solutions. Surface film formation on the electrodes in these solutions was investigated during a potential scan from the open-circuit potential (OCV) to 0.5 V vs. LiLi+ and during potential steps from the OCV to various lower potentials. The data obtained from the EQCM experiments were analyzed with the help of the results of previous spectroelectrochemical studies of several surface species formed on noble metal electrodes in these solutions. Analysis of the EQCM data enabled the definition of potential domains in which salt anion, solvent or contaminant reduction are dominant. Using this technique it was also possible to follow the dissolution processes of surface species and hydration of hygroscopic surface film compounds in water-contaminated solutions. The results obtained are in good agreement with previous spectroelectrochemical studies of these systems.

The Use of EQCM for the Study of Nonactive Metal Electrodes in Propylene Carbonate ‐ LiAsF6 Solutions: Significance of the Data Obtained

The electrochemical behavior of gold electrodes in propylene carbonate solutions was studied using an electrochemical quartz crystal microbalance (EQCM). When polarized to low potentials, these electrodes develop surface films containing species similar to those formed on lithium in these solutions. Such surface films were precipitated on the electrodes in two different experiments using linear sweep voltammetry and potential steps. EQCM is discussed as a tool for determining the molecular weight of the species precipitated on the electrode surface. In parallel, the same electrodes were explored using impedance spectroscopy. It was found that the frequency changes due to the mass accumulation on the electrodes during the electrochemical processes could be correlated with the surface film thickness calculated from impedance spectroscopy. Several different surface film formation processes could be identified. The EQCM data could be nicely correlated to previous spectroscopic studies.

The electrical double layer at the interface between mercury and a polyether electrolyte Part 2. The effect of varying the relative molar mass of the solvent

Differential capacitance measurements made at a hanging mercury drop electrode using highly purified solvents are compared for a series of LiAsF6 solutions in CH3O(CH2CH2O)nCH3 for n = 1, 2, 4, 8 and 10. Measured values of the capacitance were essentially independent of the relative molar mass of the solvent except for n = 1 where the values in the cathodic region were lower and close to those reported for tetrahydrofuran. The inner-layer capacitance was determined as a function of charge density for n = 10 and, using Parsons' four-state model, was shown to behave similarly to “group 1group 2” solvents. By subtracting the contribution of the metal to the inner-layer capacitance, it is shown that there is no significant preferential orientation of the dipoles at the potential of zero charge at the mercury surface for LiAsF6 solutions for n = 10.

Conductivities of 1?1 salts in 2-cyanopyridine

Electrolytic conductivities of eight simple 1∶1 electrolytes have been measured in dilute solutions of 2-cyanopyridine (2CNP) at 30°. Infinite dilution mobilities and association constants were calculated using the Fuoss-Hsia equation. With the exception of LiCF3SO3 all salts show very little association, consistent with the very high dielectric constant of 2CNP. The weak association which does occur is attributed to weak ion-solvent interactions. No evidence was found for triple ion formation. Conductivities of concentrated solutions of LiAsF6 in 2CNP increase slowly with concentration reaching a maximum at a concentration of around 0.65 mol-dm−3. These conductances are slightly lower than those in propylene carbonate which has a lower dielectric constant and a higher viscosity. Conductivities of concentrated LiAsF6 solutions in 2CNP mixtures with acetonitrile vary monotonically, consistent with solution viscosities, and show no sign of the maximum commonly observed in mixed organic solvents.

Surface-Enhanced Raman Scattering from Silver Electrode Surfaces in Contact with Solutions of LiAsF6 + Tetramethylammonium Bromide/Methyl Acetate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface-Enhanced Raman Scattering from Silver Electrode Surfaces in Contact with Solutions of LiAsF6 + Tetramethylammonium Bromide/Methyl AcetateZhongyi Deng and Donald E. IrishCite this: Langmuir 1994, 10, 2, 586–591Publication Date (Print):February 1, 1994Publication History Published online1 May 2002Published inissue 1 February 1994https://doi.org/10.1021/la00014a041RIGHTS & PERMISSIONSArticle Views110Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Study of Lithium Salts in Solvents with Low Dielectric Constant by Means of Ultrasonic Velocity and Absorption

Abstract Ultrasonic velocity at 1.92 MHz has been measured precisely in 1,2-dimethoxyethane (DME), acetonitrile (AN), and propylene carbonate (PC) solutions of lithium tetrafluoroborate (LiBF4) and in DME solution of lithium hexafluoroarsenate (LiAsF6) at 25 °C. The molar relative sound velocity for the LiBF4 solution has been found to show a clear inflection in the DME solution at 0.01 mol dm−3 and in the AN one at 0.02 mol dm−3 concentration though such an inflection has not been found in PC solution. The inflection for DME solution of LiAsF6 is found near 0.0013 mol dm−3. These sound velocity inflection points are believed to be due to formation of triple ions or dimers (quadrupoles) in solvents of low dielectric constants. Ultrasonic absorption coefficients in DME solutions of LiAsF6 and LiBF4 have been measured in the frequency range from 8.5 to 220 MHz by a pulse method as a function of their concentration. A single relaxational absorption has been observed in both solutions. In DME solution of LiBF4, the observed relaxational absorption mechanism has been attributed to the dimerization reaction, as reported by Maaser et al. (J. Phys. Chem., 88, 5100 (1984)). Our determination of the rate and thermodynamic constants, however, has taken into account the presence of triple ions. The results in LiAsF6 solutions are compared to those reported by Farber et al. (J. Phys. Chem., 87, 3515 (1983)) in the concentration range higher than 0.1 mol dm−3. At concentrations lower than that, however, a phenomenon with a concentration dependent relaxation frequency has been found. From a consideration of various reaction models, it has been concluded that the relaxation is associated with formation of triple ions in solution. The rate and thermodynamic parameters have been determined from the concentration dependence of the relaxation frequency and the maximum absorption per wavelength.

Lithium Cycling in Polymethoxymethane Solvents

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