New solid ionic conductor based on poly(ethylene oxide) and sodium trifluoroacetate

Solid polymer electrolytes consisting of poly(ethylene oxide) (PEO) and sodium trifluoroacetate (CF3COONa) with various salt mass fractions (x less than or equal to 0.435) have been prepared by the solvent casting method. Temperature and concentration dependent impedance studies of the cells M \ electrolyte \ M (M stands for stainless steel electrodes), as well as the conductivity behavior of the electrolyte suggest the existence of a complex in the blend. This is confirmed by differential scanning calorimetry (DSC) that shows a high melting (400 K) phase with a EO/Na ratio corresponding roughly to a 4:1 (x = 0.435) complex. The DSC measurements also indicate that the blends are thermally stable up to approximately 480 K. The conductivity (sigma) of the electrolyte is very sensitive to temperature (T) and salt mass fraction (s) in the blend: samples with low salt concentration show a linear dependence of ln sigma with (1/T) below 333 K (the euthetic melting temperature of PEO + complex), with an activation energy of 0.1 +/- 0.05 eV, and an almost flat variation above this temperature. The sample with concentration x = 0.306 shows only one activated process in the whole temperature range (T < 400 K). Typically, blends with the highest salt concentrations exhibit an anhydrous conductivity of 10(-4.5) S cm(-1) at 303 K and 10(-3.5) S cm(-1) at 313 K. The conductivity results are discussed in terms of the high mobility of the Na+ ions in the amorphous phase of the complex. <(c)> 2001 Elsevier Science Ltd. All rights reserved.