Conversion‐Type Organic‐Inorganic Tin‐Based Perovskite Cathodes for Durable Aqueous Zinc‐Iodine Batteries

Abstract Aqueous metal‐iodine batteries have recently attracted widespread attention, but their intrinsic issues such as the undesired shuttle effect and volatility of iodine hinder their reliable long‐term performance. Herein, organic–inorganic MXDA₂SnI₆ (MXDA²⁺ denotes protonated m‐xylylenediamine cation) perovskite microcrystals with a zero‐dimensional arrangement of octahedral perovskite units offering high content of elemental iodine (46 wt% in the whole cathode) are proposed as conversion‐type cathode materials for aqueous ZnI₂ batteries. Iodide anions deliver reliable electrochemical activity and are effectively immobilized on the cathode to relieve the shuttle process by both physical steric hindrance and chemical adsorption offered by long‐chain organic matrix and the presence of B‐site Sn(II) cations in the MXDA₂SnI₆ perovskite, respectively. Moreover, the formation of triiodide anions is alleviated in favor of a significant proportion of pentaiodide ions during the end of the charging process, enabled by increased formation energy of I₃⁻ and effective confinement via SnI…I halogen bonds and NH…I hydrogen bonds, as revealed by density functional theory calculations. As a result, rechargeable aqueous ZnI₂ batteries are realized that achieve a champion capacity of over 206 mAh g⁻¹_I at 0.5 A g⁻¹ (close to the theoretical limit), and outstanding rate capability with a capacity retention of 87% at 3 A g⁻¹. Suppressed shuttle of polyiodide anions endows aqueous ZnI₂ batteries with prolonged cyclic stability, namely high capacity retention of 95% after 5700 cycles at 1 A g⁻¹. This study promotes the development of high‐performance cathode materials for metal‐I₂ batteries by revealing the feasibility of using ionic perovskites as conversion‐type cathodes.