Study of DSC, Ionic Conductivity, and 7Li NMR Spectral Changes Associated with Cation Complexation in an Epoxide-Cross-Linked Polysiloxane/Polyether Electrolyte

Abstract

Solid polymer electrolytes based on epoxide-cross-linked polysiloxane/polyether hybrid (SE55) were characterized by DSC, impedance measurements, and 7Li MAS NMR spectra. The DSC results indicate that initially a cation complexation dominated by the cross-link site of SE55 is present, and subsequently the formation of transient cross-links between Li+ ions and the ether oxygens of polyether segment results in an increase in Tg of the polyether segment (Tg1). However, the Tg1 remains almost invariant at the highest salt concentration of O/Li+ = 4. A VTF-like temperature dependence of ionic conductivity is observed in all of the investigated salt concentrations, implying that the diffusion of charge carrier is assisted by the segmental motions of the polymer chains, and furthermore, a maximum conductivity value is observed at O/Li+ = 20 in the analyzed temperature range. Significantly, the 7Li MAS NMR spectra provide high spectral resolution to demonstrate the presence of at least two distinct Li+ local environments in SE55-based electrolytes. Detailed analyses of DSC and 7Li MAS NMR spectra results are achieved and discussed in terms of ion−polymer and ion−ion interactions and further correlated with ion transport behavior.