The effect of ageing on the multiphase Pb(CF3SO3)(2)PEO(n) system has been studied with NMR, DSC and X-ray diffraction. At room temperature, fresh samples with n>11 contain crystalline PEO and an amorphous salt-polymer complex. The relative amount of the crystalline phase increases with decreasing salt concentration and the actual salt concentration in the amorphous phase shows an approximately linear dependence on the nominal salt concentration in the samples. After ageing, the initially amorphous salt complex is transformed to a crystalline complex for samples with n>9. In addition to the complex, the samples contain crystalline PEG. The stoichiometry of this complex is different from the previously known crystalline complexes in this system with n=5 and 7.