Wide‐Temperature Operation of High‐Capacity Aqueous Chlorine Batteries Enabled by Complexation Chemistry

Rechargeable aqueous batteries based on the chloride/chlorine (Cl − /Cl 2 ) redox couple offer high theoretical energy density but have been limited by the volatility/disproportionation of chlorine gas and its inherently poor electrochemical reversibility. Previous approaches have relied on operational constraints to achieve desirable efficiency—such as low temperatures (<−40 °C) and/or high charge/discharge rates (>5C)—to mitigate chlorine evolution, but these strategies restrict areal capacity to <1 mAh cm −2 and compromise practical viability. Here, we report a molecularly engineered Cl − /Cl 2 redox system stabilized by quaternary ammonium complexation in an acidic chloride electrolyte, enabling both high areal capacity (7 mAh cm −2 ) and long charge/discharge durations (∼7 h) with >98% coulombic efficiency. The optimized tetraamylammonium chloride (TAACl) forms phase‐separated ionic liquid complexes (TAACl 3 and TAACl 5 ) with electrochemically generated Cl 2 , effectively suppressing chlorine volatilization, diffusion, and disproportionation. Paired with a MoO 3 anode that reversibly stores protons via intercalation, the MoO 3 ‐TAACl full battery demonstrates robust performance across a wide temperature range (−45 to 40 °C). At 25 °C, the battery retains >99% coulombic efficiency over 3000 cycles and maintains excellent cycling stability (>1000 cycles) even at 40 °C. Electrolyte optimization with high‐concentration tetramethylammonium chloride (TMACl) and H 3 PO 4 further improves cycle life by enhancing redox kinetics and suppressing side reactions.