There is growing interest in ionic liquid based electrolytes for Na metal and Na-ion batteries. Here we compare three quite distinct bis(fluorosulfonyl) imide (FSI) anion based ionic liquids with small alkyl phosphonium (trimethyl isobutyl phosphonium, methyl tri-isobutyl:P-111i4, P-1i4i4i4) or alkoxy ammonium counter cations (N-ethyl-2-(2-methoxyethoxy)-N, N-bis(2-(2-methoxyethoxy) ethyl) ethan-1-ammonium bis(fluorosulfonyl) imide:N-2(2O2O1)3) mixed at near 1:1 mol ratio with NaFSI. The conductivities of these electrolytes range from 4.4 mScm(-1) for the smallest P111i4FSI:NaFSI system to 0.3 mScm(-1) for the N2(2O2O1)3FSI:NaFSI mixture at 50 degrees C. This difference in conductivity is interestingly not reflected in the cyclic voltammetry for Na/Na+ where the maximum peak current density of 10 mAcm(-2) is surprisingly high for the poorly conductive N2(20201)3FSI:NaFSI solution (e.g. 17 mAcm(-2) for P111i4FSI:NaFSI). The overpotentials observed for Na symmetric cell cycling show very little differences after initial stabilising/conditioning for the three electrolytes being 50 mV for P111i4FSI:NaFSI and 100 mV for the others (at 0.1 mA cm(-2)). Also the Na+ transport number is similar for the three electrolytes ranging from 0.33 to 0.37. Full cells were prepared with layered transition metal oxide cathodes:O3-Na-2/3(Fe2/3Mn1/3)O-2), P2-Na-2/3(Fe2/3Mn1/3)O-2 and P2-Na-2/3(Mn0.8Fe0.1Ti0.1)O-2. While for the O3/P2-Na-2/3(Fe2/3Mn1/3)O-2 structures the device performance is consistent with the electrolyte properties, with the P2-Na-2/3(Mn0.8Fe0.1Ti0.1)O-2 cathode the N2(2O2O1)3FSI:NaFSI electrolyte cycling extremely well. The P111i4FSI and N2(2O2O1)3FSI yield almost equivalent specific capacities of approximately 180 and 160 mAhg(-1) respectively at C/10 rate. (c) 2018 Elsevier Ltd. All rights reserved.