Characteristics of an ionic liquid electrolyte for sodium-ion batteries

• Pyr14TFSI-NaTFSI IL-electrolyte is characterized for sodium-ion battery.
• The IL-electrolyte has high sodium conductivity and thermal stability.
• The suitability of the IL-electrolyte is verified in sodium half cells.
• The cells employ P2-Na0.6Ni0.22Fe0.11Mn0.66O2 cathode and nanostructured Sb–C anode.
• A full sodium-ion cell combining the two electrodes is studied.

We study the liquid mixture of sodium bis(trifluoromethanesulfonyl)imide in N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI-NaTFSI) for application in sodium-ion batteries. The ionic liquid-based electrolyte is characterized in terms of electrochemical and thermal properties. Ionic conductivity and electrochemical stability windows are evaluated through electrochemical impedance spectroscopy (EIS) measurements and voltammetry tests, respectively. The thermal stability is evaluated by differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA). Moreover, the suitability of the IL-electrolyte is preliminary verified in half and in full-cells at room temperature, using P2-Na0.6Ni0.22Fe0.11Mn0.66O2 layered oxide cathode and nanostructured Sb–C composite anode. The cell shows promising characteristics with a working voltage of about 2.7 V and a delivered capacity of about 100 mAh g−1. Despite requiring further optimization in terms of cycle life and energy density, the data here reported suggest the suitability of the ionic liquid electrolyte for application in sodium-ion battery.