Iodide Perovskites Leveraging Ionic Liquid Electrolytes Activate I + /I 0 /I − Four‐Electron Redox for Long‐Life and High‐Voltage Aluminum/Iodine Batteries

ABSTRACT The multi‐electron transfer capability of iodine renders it a promising conversion‐type cathode for aluminum‐ion batteries. However, conventional aluminum/iodine (Al/I 2 ) batteries typically operate via the I 0 (or I 3 − )/I − redox couple at low voltages, leaving the high‐potential I + /I 0 redox largely unexplored and limiting both capacity and energy density. Herein, we develop high‐performance Al/I 2 batteries by employing iodine‐rich 1D perovskite cathodes that leverage the thermodynamically favorable ionic liquid electrolyte environment to achieve a four‐electron I + /I 0 /I − redox process. These perovskite cathodes lower the reaction barrier for I + /I 0 conversion and suppress the shuttle effect of iodine species through hydrogen bonding and halogen bonding interactions, ensuring cycling stability and a stable environment for four‐electron transfer reaction. The I + formed can be effectively stabilized by AlCl 4 − , further accelerating the reaction kinetics. Through organic and metal cation engineering to modulate bonding interactions and electronic properties, the benzamidinium and Bi 3+ ‐based perovskite (PFABiI 4 ) cathode achieves a high specific capacity of 311.2 mAh g −1 I at 0.2 A g −1 and exceptional cycling stability, with a capacity decay rate of only 0.0056% per cycle over 8000 cycles at 2 A g −1 . This work opens an avenue for designing high‐voltage, high‐energy‐density, and long‐cycle‐life Al/I 2 batteries.