Pyrrolidium‐ and Imidazolium‐Based Ionic Liquids and Electrolytes with Flexible Oligoether Anions

Abstract

A new class of fluorine‐free ionic liquids (ILs) and electrolytes based on aliphatic flexible oligoether anions, 2‐(2‐methoxyethoxy)acetate (MEA) and 2‐[2‐(2‐methoxyethoxy)ethoxy]acetate (MEEA), coupled with pyrrolidinium and imidazolium cations is introduced. For the ILs with MEEA anions, Li+ conducting electrolytes are created by doping the ILs with 30 mol% of LiMEEA. The structural flexibility of the oligoether functionality in the anion results in glass transition temperatures (Tg) as low as ‐60 ºC for the neat ILs and the electrolytes. The imidazolium‐based ILs and electrolytes reveal better thermal stabilities but higher Tg and lower electrochemical stabilities than the corresponding pyrrolidinium‐based analogues. All neat ILs show comparable transport properties for the cations and these decrease by the addition of lithium salt ‐ the pyrrolidinium‐based electrolyte being affected the most.

Mini-Review on Organic Electrode Materials: Recent Breakthroughs and Advancement in Metal Ion Batteries

“…Ahmed et al recently developed a fluorine-free aliphatic flexible oligoether anion, namely, 2-(2-methoxyethoxy)­acetate (MEA) and 2-[2-(2-methoxyethoxy)­ethoxy]­acetate (MEEA), coupled with pyrrolidinium and imidazolium cations. The synthesized [(MBPyrr)­(MEEA)] 0.7 [Li­(MEEA)] 0.3 and [(MMBIm)­(MEEA)] 0.7 [Li­(MEEA)] 0.3 exhibited an ionic conductivity of 7.5 × 10 –5 and 8.4 × 10 –5 S cm –1 . Wu et al developed a new class of quasi ionic-liquid electrolyte PQILE, Li­(DME) 0.7 FSI-PEO 0.6 , which exhibited excellent interfacial stability by forming stable interfacial layers on both sides of the NMC cathode and the Li metal anode, because of the reduction of electron density in ethereal oxygens in PEO and ether solvent molecules However, these electrolytes still undergo physical damages, such as cracking due to lithium dendrite growth.…”