Solid state NMR study on the structures of PEO/LiClO₄ polymer electrolyte system

Lithium perchlorate/poly (ethylene oxide) complex, as potential polymer electrolytes, has attracted much research interests in the past decades, due to its great applicational significance. However, despite of great efforts, the mechanism of ion conducting of the system is still a topic with debates. In this work, the ¹³C CP/MAS spectra of a series of PEO/LiClO₄ complexes were measured with different compositions. It is found that for the extensively dried samples, the ¹³C CP/MAS spectrum can exhibit up to 11 narrow peaks and the characteristics of the spectrum varies greatly with the composition. The ¹³C spin-lattice relaxation time (T₁) of these narrow peaks are found to be comparable to that of the neat PEO crystalline region, indicating these narrow peaks are corresponding to the complexed crystalline structures. On the other hand, the ¹H T _1ρ of the narrow peaks are much longer than that of the neat PEO crystalline region, suggesting that the chain motion of PEO in the complex is greatly restricted due to the interaction between the oxygen of PEO and Li ⁺. The aforementioned 11 peaks are assigned to three complexed crystalline structures. The conductivity of the complex sample decreases greatly when [O] : [Li] molar ratio decreases to 4:1, while half of the ¹³C peaks that are attributed to one crystalline structure varnish, indicating that there should exist certain kind of correlation between the complexed crystalline structure and the conductivity.