FTIR spectra of P(EO)_nLiX [X＝N(SO₂CF₃)₂, SCN, ClO₄] polymer electrolytes have been obtained for ethylene oxide/Li ratios from 60∶1 to 4∶1. It was shown that ion association in the PEO-LiSCN system is more serious than in the other two systems. At a high LiSCN concentration, contact ion pairs, triple ions and dimers are main ion species in the polymer electrolytes. However, free ions are main ion species in PEO-LiTFSI and PEO-LiClO₄ systems. When Li salt was added into PEO, a plastizing role of Li salt anions can lead to transformation of a crystalline phase of PEO into an amorphous phase. When Li salt content exceeds a certain value, some kinds of crystalline complexes will be formed in PEO-LiX systems.

Key words: polymer electrolyte, ion association, crystal, FTIR