A Solvate Ionic Liquid as the Anolyte for Aqueous Rechargeable Li–O₂ Batteries

A reversible high‐areal‐capacity metallic lithium anode is pivotal to develop high specific‐energy‐density lithium‐metal‐based batteries. A novel solvate ionic liquid has been prepared by mixing tetraethylene glycol dimethyl ether (G4) and lithium bis(fluorosulfonyl)imide (LiFSI). Raman measurements revealed that the solvent was completely complexed by lithium cations to form a solvate ionic liquid (SIL) when the molar ratio of solvent to lithium cations was lower than 2. A symmetrical Li/LiFSI‐2G4/Li cell showed no short circuit for 41.2 h, until the capacity of the loaded lithium anode at 1 mA cm −2 and 60 °C was reached. A metallic lithium anode could deliver a high areal capacity of 12 mAh cm −2 for 40 cycles in the SIL of LiFSI‐2G4 with a current density as high as 6 mA cm −2 at 60 °C. This novel SIL of LiFSI‐2G4 as an anolyte coupled with lithium metal allows favorable cyclability for a high specific‐energy‐density aqueous lithium–O 2 cell.