Development of New Plastic‐Crystal Based Electrolytes using Pyrrolidinium‐ Bis(fluorosulfonyl)imide Dicationic Salts

Abstract

AbstractDicationic organic salts are an interesting class of solid‐state electrolyte materials due to their unique structure. Here we present, for the first time, the synthesis and characterization of three dicationic‐FSI salts, 1,2‐bis(N‐methylpyrrolidinium)ethane bi(bis(fluorosulfonyl)imide) ([C2‐Pyrr1][FSI]2), 1,2‐bis(N‐ethylpyrrolidinium)ethane bi(bis(fluorosulfonyl)imide) ([C2‐Pyrr2][FSI]2) and 1,2‐bis(N‐n‐propylpyrrolidinium)ethane bi(bis(fluorosulfonyl)imide) ([C2‐Pyrr3][FSI]2). The structure and dynamics of the organic salts were probed using variable temperature solid‐state NMR and were compared with the thermal and transport properties. The investigation revealed that [C2‐Pyrr1][FSI]2, with shorter alkyl‐side chains on the dication, displayed increased transport properties compared to [C2‐Pyrr2][FSI]2 and [C2‐Pyrr3][FSI]2. To determine the proficiency of these dicationic‐FSI salts as electrolyte materials for battery applications, 10 mol% and 50 mol% lithium bis(fluorosulfonyl)imide (LiFSI) was mixed with [C2‐Pyrr1][FSI]2 and [C2‐Pyrr2][FSI]2. Increased transport properties were observed for [C2‐Pyrr1][FSI]2/10 mol % LiFSI in comparison to [C2‐Pyrr2][FSI]2/10 % LiFSI, while pulse field gradient NMR analysis revealed the highest Li+ self‐diffusion ratio for [C2‐Pyrr1][FSI]2/50 % LiFSI out of the four Li‐salt‐containing mixtures.