Poly(ethylene oxide) electrolytes containing mixed-alkali metal perchlorates

Impedance spectroscopy and differential scanning calorimetry studies have been performed for mixed-alkali systems of [(1-x)LiClO4 + xMClO4](PEO)16 complexes (M = K, NH4) with varying concentrations of x. At high temperatures above the melting temperature (Tm of poly(ethylene oxide) (PEO), 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 conductivity has been observed. However, the properties related to the phase formation exhibit the mixed-salt effect, showing a negative deviation of Tm from additivity, the appearance of low-melting crystalline complexes and an increase in crystallinity. Hence, the conductivity below Tm, which is directly related to the phase formation at ambient temperature, shows a small negative deviation from additivity, especially for Li+ /NH4+ systems. The conductivity changes due to mixing salts are discussed by two terms, i.e., changes in the crystallinity and in the polymer segmental motion.