Structures of crystalline and amorphous phases of the poly(ethylene oxide)/lithium trifluoromethanesulfonate complexes as studied by solid-state high-resolution ¹³C nuclear magnetic resonance

Solid-state high-resolution ¹³C NMR studies are carried out on a series of PEO/LiCF₃SO₃ complexes with different EO/Li molar ratios at room temperature. The obtained spectra clearly show that there are four phases, namely the crystalline PEO, the amorphous PEO, the PEO ₃:LiCF₃SO₃ crystalline complex and the PEO ₃:LiCF₃SO₃ amorphous complex, coexisting in the samples with EO/Li molar ratios larger than 3. The solid-state ¹³C NMR spectrum of the PEO₃:LiCF₃SO₃ crystalline complex exhibits six peaks with high resolution at room temperature, while the previously reported ¹³C NMR spectra showed only one peak. These six peaks are assigned with the combination of the ¹³C dipolar-INADEQUATE and the two-dimensional exchange spectra. Moreover, remarkable helical jumps of PEO segments are demonstrated to exist in the crystalline complex. Our study paves the way towards a better understanding of the phase structures and subsequently the conduction mechanism of PEO-based solid polymer electrolytes.