(469c) Superionicity in Structurally Inhomogeneous, Solvent-Free Polymeric Zwitterionic Liquids Doped with Lithium Salts

Increasing the capacity of electrochemical cells is a critical scientific challenge that has been hindered in part due to instabilities at the electrolyte-anode interface, leading to poor cycling stability and safety hazards associated with the use of alkali-metal anodes. Solid polymeric electrolytes (SPEs) can address these challenges, however, ion transport in SPEs is conventionally coupled to polymer segmental dynamics, resulting in a compromise between mechanical robustness and conduction. Zwitterionic SPEs with bulky ionic groups represent an alternate design paradigm whereby high ion mobility can be imparted into rigid electrolytes. These materials exhibit competitive Lithium salt conductivities (up to 2 mS/cm) and cation transport numbers (t₊=0.67). Remarkably, modest ion conductivity (~10^-5 S/cm) is maintained even as the electrolyte is cooled below the glass transition temperature of the material. Scaling analysis of conduction versus structural relaxation demonstrates a breakdown of diffusive dynamics, suggesting a ballistic mode of ion transport. This behavior is attributed to crystalline regions, which are shown to selectively transport Li⁺ via solid state NMR lineshape, relaxometry, and diffusion measurements.