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

Solid polymer electrolytes consisting of poly(ethylene oxide) (PEO) and sod ium trifluoroacetate (CF3COONa) with various salt mass fractions (x less th an or equal to 0.435) have been prepared by the solvent casting method. Tem perature and concentration dependent impedance studies of the cells M \ ele ctrolyte \ M (M stands for stainless steel electrodes), as well as the cond uctivity behavior of the electrolyte suggest the existence of a complex in the blend. This is confirmed by differential scanning calorimetry (DSC) tha t shows a high melting (400 K) phase with a EO/Na ratio corresponding rough ly to a 4:1 (x = 0.435) complex. The DSC measurements also indicate that th e blends are thermally stable up to approximately 480 K. The conductivity ( sigma) of the electrolyte is very sensitive to temperature (T) and salt mas s fraction (s) in the blend: samples with low salt concentration show a lin ear dependence of ln sigma with (1/T) below 333 K (the euthetic melting tem perature of PEO + complex), with an activation energy of 0.1 +/- 0.05 eV, a nd an almost flat variation above this temperature. The sample with concent ration x = 0.306 shows only one activated process in the whole temperature range (T < 400 K). Typically, blends with the highest salt concentrations e xhibit 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.