The electrochemical performance of Na0.45Ni0.22Co0.11Mn0.66O2 in an ionic liquid-based electrolytic solutions is reported and compared with that obtained in a conventional, carbonate-based electrolyte. Even at ambient temperature, the Na-ion intercalation material reveals a much better electrochemical performance in 10 mol% NaTFSI (or 0.45 M) in PYR14FSI electrolyte than 0.5 M NaPF6 in PC electrolyte in terms of specific capacity and cycling stability. In particular, the electrodes cycled in the IL-based electrolyte combine a capacity retention of about 80% after 100 cycles with high specific capacities (about 200 mAh g−1) and high average voltage (2.7 V vs. Na/Na+), demonstrating that Na0.45Ni0.22Co0.11Mn0.66O2 is a promising cathode material for sodium-ion batteries.