POLY(ETHYLENE OXIDE) ELECTROLYTES CONTAINING MIXED-ALKALI METAL PERCHLORATES

Impedance spectroscopy and differential scanning calorimetry studies h ave been performed for mixed-alkali systems of [(1 - x)LiClO4 + xMClO( 4)](PEO)(16) complexes (M = K, NH4) with varying concentrations of x. At high temperatures above the melting temperature (T-m) of poly(ethyl ene oxide) (PEG), the ionic conductivity exhibits no mixed-salt effect , revealing that there are no cation-cation interference effects as in the mixed-alkali glasses, in which a great reduction of the conductiv ity has been observed. However, the properties related to the phase fo rmation exhibit the mixed-salt effect, showing a negative deviation of T-m from additivity, the appearance of low-melting crystalline comple xes and an increase in crystallinity. Hence, the conductivity below T- m, which is directly related to the phase formation at ambient tempera ture, shows a small negative deviation from additivity, especially for Li+/NH4+ systems. The conductivity changes due to mixing salts are di scussed by two terms, i.e., changes in the crystallinity and in the po lymer segmental motion. (C) 1997 Elsevier Science S.A.