POLY(ETHYLENE OXIDE) ELECTROLYTES CONTAINING MIXED SALTS

An unusual conductivity enhancement occurs in PEO-based ZnBr2/LiBr electrolytes of composition, [ xZnBr2 + (1 - x) LiBr] (PEO) 16 with x = 0.00, 0.05, 0.50, 0.75, 1.00. The conductivity of the mixed-salt electrolytes is higher than that of either pure salt electrolyte. The highest conductivity, observed for x = 0.5, is two orders of magnitude higher than that of pure LiBr(PEO)16 and one order higher than ZnBr2 (PEO)16. In contrast, the conductivity of mixed Mg(ClO4)2/LiClO4 electrolytes, [XMg(ClO4)2 + (1 - x)LiClO4] (PEO)16 where x = 0.00, 0.20, 0.50, 0.80, 1.00, increases monotonically with the mole fraction of the higher conductivity component, LiClO4 (PEO)16. The conductivity and differential scanning calorimetry (DSC) results suggest that the conductivity enhancement in the ZnBr2/LiBr electrolytes results from a change in charge carrier type and concentration, whereas the conductivity change in the Mg(ClO4)2/LiClO4 electrolytes arises from a change in the microscopic viscosity of the electrolytes.