FAST-ION TRANSPORT IN NEW LITHIUM ELECTROLYTES GELLED WITH PMMA .2. INFLUENCE OF LITHIUM SALT CONCENTRATION

Gel electrolytes made of poly(methyl methacrylate) dissolved in a liquid electrolyte, i.e. LiClO4-propylene carbonate, provide a convenient medium with high ionic conductivity and high viscosity. In a previous paper we have shown that a change in the conduction paths of the material occurs around 30-35% of weight (w/o) of PMMA in the gels. To understand this phenomenon we studied the influence of lithium salt concentration in two particular gels, i.e. 20 w/o and 45 w/o of PMMA gels, each of them being in both sides of the abovementioned limit. A model which emphasizes the importance of PC and/or PMMA lithium solvation, the effects of ion pairing and the crosslinking action of cations at high PMMA concentration, accounts satisfactorily for the electrical and mechanical properties of these gelatinized materials. The 20 w/o of PMMA gels can be viewed as a liquid electrolyte encaged in an inert polymer matrix. On the other hand in the 45 w/o of PMMA gels the presence of very strong interactions between the polymeric chains and the ionic species is consistent with the observed decrease of conductivity and the variation of viscosity with lithium salt concentration.