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

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.