POTENTIOMETRIC STUDY OF COMPLEXATION AND SOLVATION OF LITHIUM IONS INSOME 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 w as assumed to be solvated by four PC molecules. For monoglyme (DME), e ach of the two-step complexing was considered to be the replacement of two solvating PC molecules by one DME molecule. Complexing of up to t wo 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 wer e obtained. The values of beta(1) were 1.5, 15, 46 and 68 mol(-1) L fo r mono-, di-, tri-and tetraglymes, respectively. The lithium ion activ ity in mixtures of PC-DME, PC-dimethyl carbonate (DMC), PC-diethyl car bonate (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 ex plained considering the complexing of the lithium ion with DME and the effects of dielectric constant to the lithium ion solvation and ion a ssociation. In the mixtures of PC with DMC, DEC and EMC, the variation in the lithium ion activity was explained only by the effects of diel ectric constant to the lithium ion solvation and ion association. Copy right (C) 1996 Elsevier Science Ltd.