Hybrid Sodium–Air Cell with Na[FSA–C₂C₁im][FSA] Ionic Liquid Electrolyte

Na[FSA–C₂C₁im][FSA] (C₂C₁im⁺:1-ethyl-3-methylimidazolium and FSA⁻:bis(fluorosulfony)amide) ionic liquid was utilized as the aprotic electrolyte in hybrid sodium–air cells for the first time. The sodium–air cells were operated at relatively high temperatures up to 70 °C to prove their excellent thermal stability. A large output power density was obtained by increasing the operation temperature because of the high Na⁺ diffusivity and high ionic conductivity of the ionic liquid. The cells exhibited an extremely large specific capacity of 835 mAh g⁻¹ at 50 °C; this capacity corresponds to 99% of the theoretical capacity. In addition, maximum areal output power density of 27.6 mW cm⁻² was obtained at 50 °C. The Na[FSA–C₂C₁im][FSA] ionic liquid was proved to be a promising aprotic electrolyte to enhance the electrochemical performance of hybrid sodium–air cells.