Water/Ionic Liquid Hybrid Electrolyte for High Cycling Stability and Low-Temperature Adaptability in Aqueous Lithium-Ion Battery.

Aqueous lithium-ion batteries (ALIBs) often suffer from water crystallization and suppressed ionic transport under subzero conditions as well as narrow electrochemical stability windows. Here, we report a hybrid electrolyte based on 1 M LiNO3 in [EMIM][DEP]0.1-(H2O)0.9 that combines the non-flammability of ionic liquids with the high ionic conductivity of water. Strong [DEP]-(H2O) hydrogen bonding disrupts the water network, lowering the freezing point from -24°C to -56°C while maintaining an ionic conductivity of 1.295 × 10-3 S cm-1 at -35°C. Meanwhile, ionic-liquid enrichment at the anode forms a water-restricted interphase that widens the apparent electrochemical stability window from 1.4 to 2.15 V, as supported by experimental characterization and molecular dynamic simulations. In a LiMn2O4/LiTi2(PO4)3 full cell, this hybrid electrolyte delivers 90 mAh g-1 at -35°C and 0.2 C and retains 90% of its initial capacity after 700 cycles at -35°C and 0.5 C, with an average Coulombic efficiency of 99.86%. Adding 0.05 M ZnSO4 further stabilizes the electrode/electrolyte interface, enabling 80% retention after 1400 cycles at 4 C. These results demonstrate a practical route to safe aqueous batteries with low-temperature adaptability and long cycle life.