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

Abstract

Solid polymer electrolytes consisting of poly(ethylene oxide) (PEO) and sodium trifluoroacetate (CF 3COONa) with various salt mass fractions ( x≤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 ( σ) of the electrolyte is very sensitive to temperature ( T) and salt mass fraction ( x) in the blend: samples with low salt concentration show a linear dependence of ln σ 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.