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 LiNO 3 in [EMIM][DEP] 0.1 ‐(H 2 O) 0.9 that combines the non‐flammability of ionic liquids with the high ionic conductivity of water. Strong [DEP]‐(H 2 O) 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 LiMn 2 O 4 /LiTi 2 (PO 4 ) 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 ZnSO 4 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. A dilute hybrid electrolyte containing only 10 mol% [EMIM][DEP] simultaneously reorganizes the water hydrogen‐bond network and creates an ionic‐liquid‐rich region at the anode. This coupled bulk and interfacial regulation suppresses freezing and hydrogen evolution, broadens the electrochemical stability window, and enables an aqueous LMO/LTP full cell to retain 90% capacity after 700 cycles at −35°C.