Strengthened O-H Bonds in an Aqueous Electrolyte for Nonflammable Li-Ion Batteries

Aqueous lithium-ion batteries (ALIBs) have attracted increasing attention for their inherent safety and environmental benefits. However, the narrow electrochemical stability window of water (1.23 V) imposed by hydrogen evolution reaction (HER) and high melting point (0 °C) critically limits the energy density and low-temperature operation. In this work, we report an electrolyte design principle that water activity can be suppressed by strengthening the O-H bonds between water molecules and regulating the pH. A strong polar solvent N,N-dimethylformamide (DMF) interacts with H₂O through intermolecular hydrogen bonds, thereby reinforcing the covalent O-H bonds of water. Meanwhile, KOH renders the electrolyte alkaline, inhibiting water dissociation kinetics and consequently raising the HER overpotential. The designed LD_1.7W_0.6-KOH electrolyte exhibits a freezing point below -82 °C and expanded electrochemical stability window of 4.3 V. The 2.5 V aqueous LiMn₂O₄/Li₄Ti₅O₁₂ full cell delivers 2000 cycles at a rate of 6 C with a Coulombic efficiency of 99% at 30 °C and over 1950 cycles at 0 °C. This work offers atomic-level insights into alkaline HER while providing guidance for advancing low-temperature aqueous batteries by tuning the electrolyte structures.