Poly(ethylene oxide)/lithium triflate phase diagram

The complete phase diagram of the poly(ethylene oxide)/lithium trifluoromet hane sulfonate polymer electrolyte was determined by combined X-ray diffrac tion and differential scanning calorimetry. The sample preparation has dram atic effects on morphology and consequently on the phase diagram. The exist ence of three different molecular adducts involving the polymer and the sal t was deduced from the phase diagram. These adducts transform into each oth er by peritectic reactions. Moreover, two different forms of pure lithium t rifluoromethane sulfonate were observed. This polymorphism was studied by X -ray diffraction and differential scanning calorimetry. It was demonstrated that this salt undergoes a transition to a phase of higher symmetry at 179 degrees C. An orthorhombic unit cell (a = 1.496 nm, b = 1.475 nm, c = 1.42 5 nm) was proposed for the high temperature form of the salt. (C) 1999 Else vier Science Ltd. All rights reserved.