Quantum-Chemical Study of Ion Association in Electrolyte Systems Containing LiAsF₆

Abstract

The possibility that ion clusters of different species are formed during dissolution of LiAsF6 in a low- or high-molecular-weight solvent has been studied. The Hessian matrix of clusters has been calculated by the numerical and analytical differentiation of their full energy in the MO LCAO approximation using the Roothaan−Hartree−Fock method and the PC GAMESS software package. It was found that stable ion clusters are represented by ion pairs Li+[AsF6]- with the bi- or tridentate coordination of the cation relative to the octahedral anion, triple ions [AsF6]-Li+[AsF6]- and Li+[AsF6]-Li+ with the bi- or tridentate coordination, ion dimers {Li+[AsF6]-}2 with the bidentate coordination, and also ion trimers {Li+[AsF6]-}3 and ion tetramers {Li+[AsF6]-}4 shaped as symmetric ring structures with the unidentate coordination. The frequencies and intensities of IR absorption bands of different species of ion clusters in the gaseous phase and nonaqueous solutions (acetone, ethanol, nitromethane, and tetrahydrofurane) have been calculated. This presents a basis for identification of ion particles during IR spectroscopic measurements in electrolyte solutions containing LiAsF6.

Ionic Transport in Dilute Solid Polymer Electrolytes with Amorphous Structure

“…4b. Figure 5 presents concentration dependences of parameters K σ , T 0 , and A, which were obtained from the temperature dependences of the SPE conductivity with the aid of the VTF equation, and values of parameters B and T 0 for the saltless polymer, which were obtained with formula (9). As seen, A is directly proportional to c, which well conforms to the above models.…”

“…The emergence in the IR spectra (Fig. 2) of a high-frequency component at ~718 cm -1 and a low-frequency shoulder near 680 cm -1 in the absorption band for a free anioñ 700 cm -1 as well as the fresh bands at about 380 and 550 cm -1 may be attributed, on the basis of data [9], to the formation of contact ionic pairs Li + ··· . The lithium cation in these species is linked to three fluorine atoms simultaneously (tridentate coordination).…”

“…The vibrational spectrum of octahedral anion , which is highly symmetrical, is very sensitive to its coordination with cations [8,9]. As shown by quantum-chemical calculations in [9], each type of ionic associates has a specific IR spectrum at 200-850 cm -1 . The emergence in the IR spectra (Fig.…”

“…If the ion transport in SPE is defined by the polymer matrix properties, parameter K σ must be the same for all SPE and equal parameter B for a saltless polymer. Parameter B may be determined from the equation (9) which describes the temperature dependence of the reciprocal relaxation time 1/τ 0 . The latter was obtained from impedance measurements, which were performed at 313-373 K, on the copolymer of acrylonitrile and butadiene (40 : 60) containing no salt.…”

Spectroscopic Measurements of Ionic Association in Solutions of LiPF6

“…Vibrational spectroscopic techniques are extremely useful for probing ionic associations in many electrolytes. − Early work focused on solutions of LiClO 4 , or LiCF 3 SO 3 13,15 and utilized frequency shifts of nondegenerate modes in the Raman spectrum. Later work also examined frequency shifts of nondegenerate modes in the infrared spectrum. , Several researchers have demonstrated that LiXF 6 salts (X = P, As, or Sb) form ion pairs in aprotic solvents by investigating the infrared-active modes of the XF 6 - anion. − Most of these studies have focused on the ν 3 (F 1u ) and ν 4 (F 1u ) vibrations. The symmetry labels designate the point group irreducible representations of ν 3 and ν 4 in the isolated anion.…”