Imidazolium, pyrrolidinium and piperidinium room temperature ionic liquids (RTILs) are characterized to evaluate their thermal stability, ionic conductivity, viscosity, potential window and lithium solvation, which are key parameters for lithium–oxygen (Li–O₂) battery electrolytes. The electrochemical tests of these RTILs are also carried out in Li–O₂ cells and show reasonable values of specific capacity, up to 1659 mA h per gram of carbon in the case of 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (PMI TFSI) with a molar fraction of 0.2 of LiTFSI. RTILs are compared with conventional organic electrolytes like ethylene carbonate (EC)/diethyl carbonate (DEC) solution or tetraethylene glycol dimethyl ether (TEGDME), which enables us to provide a further insight into ways of improving the electrolyte properties of Li–O₂ batteries. In particular, a viscosity lower than 100 cP combined with a lithium coordination number lower than 1.5 tends to enhance the battery performance.