Conductivities of a number of uni-univalent salts, including tetrabutylammonium and lithium nitrophenolates, were measured at 25.0 °C in low-permittivity solvents such as tetrahydrofuran (THF, er = 7.58), 1,2-dimethoxyethane (DME, 7.2), chloroform (4.8), and ethyl acetate (6.0). Minima in the conductometric curves (Λ−C1/2) were observed for concentrations which were dependent upon both the salt and the solvent, Cmin = 1.73 × 10-4 mol dm-3 for 2,4-(NO2)2C10H5OLi (lithium 2,4-dinitro-1-naphtholate) in THF and 2.56 × 10-2 mol dm-3 for LiPic (lithium picrate) in DME. The observed molar conductivities including Cmin could be completely explained by the formation of ion pairs (M+ + X- ⇌ MX, K1), “symmetrical” triple ions (2M+ + X- ⇌ M2X-, K2; M+ + 2X- ⇌ MX2-, K3; K2 = K3), and (in some cases) additional formation of quadrupoles (2MX ⇌ M2X2, K41). A linear relationship (the slope of −1) between the triple ion formation constants (log(K2/K1)) and the salt concentrations at the minimum (log Cmin) was given for all...

Relationship between Triple Ion Formation Constants and the Salt Concentration of the Minimum in the Conductometric Curves in Low-Permittivity Solvents

In aprotic electrolytes and, in particular, in most polyether−salt systems the molar conductivity increases dramatically with increase in salt concentration from a minimum at low concentrations to an unexpected high maximum. Such increases in conductivity are larger than would be accounted for by Fuoss−Onsager type transport theories in which complete dissociation is assumed. Examples can be found in poly(propylene glycol) (PPG) complexed with triflate salts. The series MCF3SO3/PPG4000 (M = Li, Na, NH4, ND4) has been studied and illustrates the effect of cation on the value of the maximum molar conductivity and the rate of increase of molar conductivity with increase in concentration. Particular attention has been paid to the previously reported enhancement of the ionic conductivity for ND4CF3SO3/PPG4000 electrolytes over that of NH4CF3SO3/PPG4000. Detailed infrared and Raman studies of the polyether C−O−C vibrations and of the salt vibrations have been carried out as a function of temperature (FT-IR) and...

Studies of ionic interactions in Poly(propylene glycol) 4000 complexed with triflate salts.

Six lithium salts of tris- and tetrakis(polyfluoroalkoxy)aluminate superweak anions have been studied for their potential use as battery electrolytes. Four of the six are based on the formula LiAl(OCR(CF 3 ) 2 ) 4 (R = H, Me, CF 3 , Ph); the other two are LiAl(OCH 2 CF 3 ) 4 and LiAIF(OCPh(CF 3 ) 2 ) 3 . The thermally stable electrolytes LiAk(OCH(CF 3 ) 2 ) 4 and LiAl(OCPh(CF 3 ) 2 ) 4 were not oxidized at potentials less than or equal to 5.0 V vs. Li +/0 in dimethoxyethane (DME) or in 50:50% ethylene carbonate:dimethylcarbonate (EC:DMC). The LiAl(OCH(CF 3 ) 2 ) 4 electrolyte was not reduced at 0 V vs. Li +/0 in DME. Neither LiAl(OCH(CF 3 ) 2 ) 4 nor LiAl(OCPh(CF 3 ) 2 ) 4 promoted the corrosion of aluminum at 5.0 V vs. Li +/0 . The electrolyte LiAl(OCH(CF 3 ) 2 ) 4 underwent efficient, reversible reductive intercalation of Li + with MCMB carbon or LiCoO 2 electrodes over the potential ranges 0-2 and 2.4-4.8 V, respectively, vs. Li +/0 , but did not react in any other way with these electrode materials. The conductivities of some of the LiAl(OR F ) 4 electrolytes in DME or in EC:DMC were high enough for them to be considered as potential replacements for LiPF 6 in primary and secondary lithium batteries.

Conductivities and Electrochemical Stabilities of Lithium Salts of Polyfluoroalkoxyaluminate Superweak Anions

We investigate the ion–ion pair association equilibrium in the hard sphere ionic fluid as predicted by several Debye–Huckel-based theories. The degree of dissociation is examined in a pairing theory based on Ebeling’s definition of the association constant, and in extensions of this theory for ion pair–free ion interactions by Fisher and Levin, and ion pair–ion pair interactions by Weiss and Schroer. The effect of an increase of the dielectric constant on the degree of dissociation is studied. In all cases, minima of the density-dependent degree of dissociation along isotherms are found at low ionic density, at least over part of the temperature range. The loci of these minima in the temperature-density plane are calculated. The results are compared with conductivity data. We discuss a possible resemblance of the system’s behavior in a region in which the degree of association changes rapidly with a tricritical scenario, in which a line of second-order insulator–conductor phase transitions intersects the coexistence curve.

Ion association and electrical conductance minimum in Debye–Hückel-based theories of the hard sphere ionic fluid

The role of ion-aggregate formation in the calculation of physical properties of electrolyte solutions

Investigations in the temperature range −45 ≤ θ/°C ≤ + 25 on LiBF4 solutions in dimethoxyethane from infinite dilution to saturation permit to exemplify the features of conductance in solvents of low permittivity. Conductance measurements on thoroughly purified materials with the help of a measuring equipment known to produce precise data yield a complete set of conductance curves from infinite dilution to saturation at all temperatures of the program. The conductance curves show a minimum and a maximum of equivalent conductance and the change from positive to negative and once more to positive temperature coefficients of conductance. Various methods both for the evaluation of the limiting conductances, Λ∞, and the formation constants of ion pairs, KA, triple ions, KT, are critically discussed and reliable data for the LiBF4 solutions in dimethoxyethane at all temperatures of the program are communicated.

The Temperature Dependence of the Properties of Electrolyte Solutions. VI. Triple Ion Formation in Solvents of Low Permittivity Exemplified by LiBF4 Solutions in Dimethoxyethane

R. Gerber

Papers

The Temperature Dependence of the Properties of Electrolyte Solutions. VI. Triple Ion Formation in Solvents of Low Permittivity Exemplified by LiBF4 Solutions in Dimethoxyethane