Cation Engineering Perovskite Cathodes for Fast and Stable Anion Redox Chemistry in Zinc‐Iodine Batteries

Abstract Zinc‐halogen batteries are promising for sustainable energy storage, offering high redox capacities at economical price points. However, they are hindered by issues such as the irreversibility caused by the dissolution of intermediates and the sluggish charge transfer, which limit their widespread adoption. Addressing these issues, bismuth‐iodide perovskite cathodes are employed as a halogen element enriched model system. These perovskite cathodes demonstrate considerable anion redox capacities. In a combined simulation and experimental study, it is uncovered that the (BAD)BiI 4 (BAD + denotes benzamidinium) cathode, greatly improves interactions with iodine species and boosts charge transfer capability compared to its (BA)BiI 4 (BA + denotes benzylaminium) counterpart. These enhancements can be attributed to the synergistic effects arising from stronger Bi−I···I halogen bonds and C═N─H···I hydrogen bonds. The (BAD)BiI 4 cathode attains a reversible I − /I 0 redox chemistry with 92% capacity retention after 30 000 cycles at a current density of 10 A g −1 I , outperforming previously reported anion redox batteries. Additionally, the defect‐tolerant property and the I − /I 0 /I + conversion of the (BAD)BiI 4 are elucidated. The I 5 − forms a notably stronger bond with (BAD)BiI 4 in comparison to I 3 − , which effectively mitigates polyiodide shuttling. These advantageous characteristics highlight the promise and adaptability of the developed perovskite cathodes for high‐performance anion redox chemistry.