Vibrational Spectroscopic Determination of Structure and Ion Pairing in Complexes of Polyethylene oxide) with Lithium Salts

A structural model for crystalline complexes of poly(ethylene oxide) (PEO) with various lithium salts is presented, based on vibrational spectroscopic studies; these complexes are known to exhibit ionic conductivities of > 10−5 (Ω-cm)−1 at 100°C. Cation-dependent vibrational bands observed in the Raman indicate that significant cation-oxygen atom interactions occur and suggest that the polyether chain may wrap around the lithium cations. Spectroscopic studies indicate extensive contact ion pairing occurs in the PEO LiNO3 complex, and this may contribute to the somewhat lower ionic conductivity of this complex as compared to other lithium salt complexes with similar structures but weaker cation-anion interactions.