An investigation on ion solvation and ion association in a gel-type solid state polymer electrolyte

Ion salvation and ion association in polytriethylene glycol dimethacrylate (PTREGD)-LiClO4 gel-type polymer electrolytes were investigated. It was found that the fraction of solute existing as single ions (alpha(i)) decreases and that of triple ions (alpha(i)) increases linearly with increasing LiClO4 concentration, while for ion pairs, as the salt concentration increases, its fraction (alpha(p)) increases first and then falls down. The findings can be rationalized by the fact that the ionic conductance of the polymer electrolyte may be mainly contributed by triple ions and higher ionic aggregates with unequal numbers of positive and negative charges in the salt concentration range of practical significance, i.e. in the range of 0.5-1.5 mol/l. The temperature dependence of these fractions was also examined. In the case of tetraethylene glycol as the solvent, alpha(i) and alpha(p) increase as the temperature is raised, but alpha(t) decreases as the temperature increases from 25 degrees C to 85 degrees C. It seems that the increase of alpha(i) and alpha(p) results from the redissociation of triple ions at higher temperature, The same changing trend of those fractions is also observed when PEG(400) is used as the solvent.