Tailoring Energy Landscapes for Vehicular Transport in Single-Ion Conducting Organo-Ionic Solids

Single-ion conducting organo-ionic (ORION) solids with concomitantly high carrier concentration and cation mobility are highly sought after as electrolytes for batteries, yet largely out of reach due to the abundance and static character of contact ion pairs, which inhibit long-range cation transport. Here, we show how glyme-based organic ligands reduce the prevalence of contact ion pairs in sodium-ion conducting ORION solids created from tetrameric bis(sulfonylimides), opening the door to vehicular transport with tunable energy landscapes. Activation barriers to Na+ transport were reduced by >50%─from 117.2 to 52.2 kJ·mol-1─when the stoichiometric number of L-type ether ligands relative to Na+ ions was increased, up to four. Within this preferred regime, 1,2-dimethoxyethane delivered the highest ionic conductivity─0.28 mS·cm-1 at 60 °C─due to the lower effective mass for the mobile charge carrier. Molecular dynamics simulations and 23Na-NMR experiments showed contact ion pairs are effectively converted into vehicular Na+ species through the addition of glyme ligands, improving sodium conduction. Electrophoretic NMR measurements show mobility of the anionic tetramer under high field strength (9.1 × 10-11 m2 V-1 s-1) is remarkably low, providing a high cationic transference number of t+ = 0.84.