Lean‐Water Gel Electrolyte Enables Zinc Ion Battery at −70 °C

Aqueous zinc ion batteries are attracting growing interest in electrochemical energy storage due to safety, reliability, and affordability. However, water brings drawbacks including parasitic reactions, narrow electrochemical window, and cathode degradation. The freezing nature of water also challenges the zinc ion transport and storage at sub-zero temperatures, especially below -40 °C. Here, we design a water-in-polymer electrolyte to confine water using a weak-solvation monomer-directed polymerization technique initiated by protons. This electrolyte strategy significantly suppresses the water-induced parasitic reactions and widens the electrochemical window to 2.59 V. Besides, a high ionic conductivity of 0.36 mS cm^-1 is achieved at -70 °C benefiting from unique fast ion transport channel and favorable desolvation process at the interface. Symmetric Zn cells exhibit excellent cycle stability over 10 000 h (437 days) at room temperature (1 mA cm^-2@1 mAh cm^-2) and 700 h at -40 °C (5.25 mA cm^-2@5.25 mAh cm^-2). Zn||Zn_0.58V₂O₅ full cells show impressive performance under high mass loading and low temperatures originating from the suppression of H⁺ insertion. The electrolyte strategy in this work will inspire more efforts for water confinement in aqueous batteries.