Single-Ion-Conducting Polyether Electrolytes via Orthogonal Postpolymerization Modification

Solid polymer electrolytes are considered promising alternatives for overcoming the safety issues of conventional liquid electrolytes. In particular, poly­(ethylene oxide)-based polymer electrolytes are widely studied because of their high flexibility and ion-solvating capability but suffer from low ionic conductivity at room temperature due to high crystallinity of poly­(ethylene oxide) restricting segmental motion. To address this challenge, we present a new type of polyether-based single-ion-conducting solid polymer electrolyte whose constituent functional groups can be tailored in an orthogonal manner. The electrolyte structure was designed to possess weakly binding anionic and flexible lithium-cation-solvating pendants along the polyether backbone. Specifically, bulk polymerization between allylamine and diepoxide was employed to synthesize the polyether backbone with functional allyl and hydroxyl groups. The resulting polymer was subsequently further functionalized with lithium bis­(trifluoromethanesulfonyl)­imide and tri­(ethylene glycol) groups to create a single-ion conductor. Tri­(ethylene glycol) promoted segmental α and ion-rearranging α2 relaxations (arising from a lowered glass transition temperature and increased ion mobility, μ) as well as increased the dielectric constant (leading to a large number density of conducting ions, p), resulting in a significant increase in the ionic conductivity (σ ∼ μp), e.g., a 250-fold increase at 60 °C. Furthermore, addition of succinonitrile (a plasticizer) increased the ionic conductivity of the single-ion-conducting solid polymer electrolyte to 1.8 × 10–5 S cm–1 at 60 °C because of a weakened ion–ion correlation as revealed by wide-angle X-ray scattering analyses. These results demonstrate the potential of tailoring properties of solid polymer electrolytes by introducing various functional moieties.