Ionic liquid/water bilayer electrolyte was developed as a new electrolyte of aqueous rechargeable lithium batteries (ARLBs) that compatible with spinel lithium titanium oxide (Li4Ti5O12). Butyltrimethylammonium bis(trifluoromethanesulfonyl) amide containing 1 mol kg(-1) of lithium bis(trifluoromethanesulfonyl) amide and aqueous LiNO3 were used as hydrophobic ionic liquid and water media, respectively. A clear ionic liquid/water interface was successfully generated within the bilayer electrolyte. The lithium-ion insertion/extraction mechanism of the LTO thin-film electrode was investigated in the bilayer electrolyte. Cyclic voltammetry confirmed that this lithium ion insertion/extraction of Li4Ti5O12 thin-film electrode was successfully performed within the bilayer electrolyte. (C) 2016 The Electrochemical Society. All rights reserved.