In the market of medium- and large- scale energy supplies, sodium (Na⁺) ion batteries are considered a possible alternative to current technologies. This is because sodium is naturally more abundant and cheaper than the ubiquitous lithium. Room temperature Na⁺ batteries typically employ organic solvents such as propylene carbonate. However, room temperature ionic liquids – while more viscous – are safer, and because of this attention is being paid towards their partial or complete replacement of organic solvents. Towards this endeavor, we investigated ions dynamics in mixtures of varying concentrations of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) or sodium bis(fluorosulfonyl)imide (NaFSI) salts, combined with the 1-butyl-1-methylpyrrolidinium (PYR_1,4) FSI and PYR_1,4 TFSI ionic liquids. We used variable-temperature ¹H and ²³Na Nuclear Magnetic Resonance (NMR) spin-lattice relaxation times (T₁) and self-diffusion coefficients (D) measurements to investigate the short- and long- range ions dynamics and a preview of or results are shown in Figure 1. Both T₁ (¹H and ²³Na) and ¹H D data show greater short- and long- range dynamics for mixtures containing the FSI salt or ionic liquid. A more comprehensive discussion will be presented.

Figure 1. Variable-temperature Na⁺ spin-lattice relaxation times (left) and ¹H self-diffusion coefficients (right) for mixtures of various mol% of NaFSI or NaTFSI salt with PYR_1,4 based ILs.