Single Cationic Conduction Under Anion-Blocking Conditions in Sodium Ionic Liquids: Na[((FSO₂)₂N)x((CF₃SO₂)(FSO₂)N)1−x]

There is a demand for low-melting-point molten-salt electrolytes with high thermal and electrochemical stability for the development of high-performance sodium-ion batteries. Mixing sodium bis(fluorosulfonyl)amide (NaFSA) and sodium (fluorosulfonyl)(trifluoromethylsulfonyl)amide (NaFTA) results in a large depression in their melting points. In this study, the phase behavior and Na + transport properties of binary mixtures of NaFSA and NaFTA were investigated. The mixture of NaFSA and NaFTA with a molar ratio of 8:2 has a melting temperature ( T m ) of 363 K, successfully achieving an ionic liquid consisting of single cationic (Na + ) salts. This mixture easily forms a super-cooled liquid. The ionic conductivity ( σ ) of Na[(FSA) 0.8 (FTA) 0.2 ] continuously varied from above T m to below T m , obeying the Vogel–Tamman–Fulcher equation, which coincides with its super-cooling nature. The ionic conductivity and apparent Na + transference number ( t Na+ ) under anion-blocking conditions at T m approached 10 −3 S cm −1 and 0.92, respectively.