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

Rechargeable aqueous batteries based on the chloride/chlorine (Cl^-/Cl₂) 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^-/Cl₂ 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 (TAACl₃ and TAACl₅) with electrochemically generated Cl₂, effectively suppressing chlorine volatilization, diffusion, and disproportionation. Paired with a MoO₃ anode that reversibly stores protons via intercalation, the MoO₃-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 H₃PO₄ further improves cycle life by enhancing redox kinetics and suppressing side reactions.