A. Chagnes

Ion transport theory of nonaqueous electrolytes. LiClO4 in γ-butyrolactone: the quasi lattice approach

As a part of a study on the optimisation of the electrolyte for high-density energy lithium batteries, transport properties of concentrated LiClO4 solutions in γ-butyrolactone (BL) have been investigated. The effect of the salt concentration (C) on the viscosity (η) of BL solutions has been discussed in term of the Jones–Dole equation. At concentrations higher than 0.2 M, the molar conductivity (Λ) of LiClO4 solutions follow a C1/3 cube root law which is predicted by the quasi lattice model first introduced by Gosh. In this model, the ions of the strong binary electrolyte are distributed in a lattice-like arrangement (fcc). The experimental value found for the slope of Λ vs. C1/3 relation is in fair agreement with the calculated one. The effect of the temperature on the viscosity and the conductivity of electrolyte solutions have been examined. These two transport processes are well described by Arrhenius type laws from which the activation energies for the viscosity Eaη and conductivity EaΛ are deduced. The variations of Eaη and EaΛ with salt concentration are respectively dependent on C and C4/3 as predicted by the quasi lattice model.

Cycling Ability of γ-Butyrolactone-Ethylene Carbonate Based Electrolytes

The cycling ability of a carbon electrode in γ-butyrolactone (BL)-ethylene carbonate (EC) based mixtures has been investigated in the presence of lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ). lithium bis(trifluoromethylsulfone)imide (LiTFSI), and lithium tetrafluoroborate (LiBF 4 ). LiBF 4 is the only salt, which permits full charge-discharge cycles in BL-EC mixtures. The passivation film formed at the carbon electrode has been studied by microscopy and X-ray photoelectron spectroscopy. The cycling ability of the carbon and Li x CoO 2 electrodes has been evaluated in two BL-EC mixtures (9:1 and 1:1) using LiBF 4 (1 M) as an added salt. The wettability of the Celgard separator used in the full-cell configuration has been enhanced by the addition of a surfactant: tetraethylammonium perfluorooctanesulfonate (TEAFOS). This additive does not perturb the quality of the passivative film and increases the wettability by lowering the surface tension of the electrolyte. The electrolyte BL-EC (9:1) + LiBF 4 (I M) has been selected for full-cell cycling experiments at different temperatures (-15 to 25°C) in the presence of TEAFOS (0.014 M).

X-ray powder diffraction structure determination of γ-butyrolactone at 180 K: phase-problem solution from the lattice energy minimization with two independent molecules

The crystal structure of the solid phase of the dipolar aprotic solvent gamma-butyrolactone (BL1), C(4)H(6)O(2), has been solved using the atom-atom potential method and Rietveld-refined against powder diffraction data collected at T = 180 K with a curved position-sensitive detector (INEL CPS120) using Debye-Scherrer diffraction geometry with monochromatic X-rays. It was first deduced from the X-ray experiment that the lattice parameters are a = 10.1282 (4), b = 10.2303 (5), c = 8.3133 (4) A, beta = 93.291 (2) degrees and that the space group is P2(1)/a, with Z = 8 and two independent molecules in the asymmetric unit. The structure was then solved by global energy minimization of the crystal-lattice atom-atom potentials. The subsequent GSAS-based Rietveld refinement converged to the final crystal-structure model indicator R(F(2)) = 0.0684, profile factors R(p) = 0.0517 and R(wp) = 0.0694, and a reduced chi(2) = 1.671. After further cycles of heating and cooling, a powder diffraction pattern markedly different from the first pattern was obtained, again at T = 180 K, which we tentatively assign to a second polymorph (BL2). All the observed diffraction peaks are well indexed by a triclinic unit cell essentially featuring a doubling of the a axis. An excellent Le Bail fit is obtained, for which R(p) = 0.0312 and R(wp) = 0.0511.