Potentiometric study of complexation and solvation of lithium ions in some solvents related to lithium batteries

The complexing of lithium ion in propylene carbonate (PC) with glymes (H3CO(CH2CH2O)(n)CH3) of n=1 to 4 was studied potentiometrically using a univalent cation-sensitive glass electrode. The lithium ion in PC was assumed to be solvated by four PC molecules. For monoglyme (DME), each of the two-step complexing was considered to be the replacement of two solvating PC molecules by one DME molecule. Complexing of up to two molecules was assumed for diglyme but of one molecule for tri- and tetraglymes. Equations were derived to relate the glyme concentration and the potential of the glass electrode, taking the effect of solvent dielectric constant into account, and complex formation constants were obtained. The values of beta(1) were 1.5, 15, 46 and 68 mol(-1) L for mono-, di-, tri-and tetraglymes, respectively. The lithium ion activity in mixtures of PC-DME, PC-dimethyl carbonate (DMC), PC-diethyl carbonate (DEC) and PC-ethylmethyl carbonate (EMC) was also studied with the same electrode. In PC-DME, the lithium ion activity was lowest at around 60 (v/v)% DME. The variation in the lithium ion activity was explained considering the complexing of the lithium ion with DME and the effects of dielectric constant to the lithium ion solvation and ion association. In the mixtures of PC with DMC, DEC and EMC, the variation in the lithium ion activity was explained only by the effects of dielectric constant to the lithium ion solvation and ion association. Copyright (C) 1996 Elsevier Science Ltd.