Polycationic Scaffolds for Li-ion Anion Exchange Transport in Ion Gel Polyelectrolytes

Ion gel polyelectrolytes (IGP) were prepared by photopolymerization of the synthetic cationic monomers: 1-(2-Methacryloyloxy)ethyl-3-butylimidazolium Bis(trifluoromethane sulfonyl)imide) (IMMATFSI)/ Bisfluorosulfonylimide (IMMAFSI) or 1-(2-Methacryloyloxy)ethyl-1-methylpyrrolidinium Bisfluorosulfonylimide (PYRMAFSI) /Bis(trifluoromethane sulfonyl)imide (PYRMATFSI) in the presence of bis(trifluoromethane)sulfonamide (LiTFSI) solutions at different concentrations in either 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), 1-ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide (EMITFSI) or N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PMPFSI). The resulting IGPs are thermally stable, easy to handle solids where overall ionic conductivity ranges from about 1 to about 10 mS·cm^-1 at 25ºC. The diffusivity of the ions Li, FSI and TFSI was studied at 25ºC by PGSE-NMR. In IGPs containing imidazolium groups both in the polycationic scaffold and the ionic liquid phase, large Li ion diffusivities (up to 40×10^-12 m²·s^-1, well above that of the anions) suggest the existence of an important contribution of anion exchange Li transport. To a lesser extent anion exchange can be also suspected in IGPs containing pyrrolidinium groups in the polycationic scaffold and imidazolium groups in the ionic liquid phase, and to an even lesser extent in those IGPs with pyrrolidinium in both the polyelectrolyte and the ionic liquid phase. Because of the dimensional and thermal stability of the IGPs, safety of their components, and large Li-ion diffusivity, this type of electrolytes appear as excellent candidates for Li and Li-ion batteries.